Albinism is caused by the loss of melanin pigment in areas of normal pigmentation such as the skin, eyes, and hair. Aside from the hypopigmentation that these patients suffer, melanin pigment is needed for normal vision. The lack of melanin pigment in the skin predisposes these patients to many types of skin cancers. Broadly speaking, albinism is divided into two main types: ocular and oculocutaneous, with oculocutaneous type more common than ocular types.
Epidemiology Disease Associations Pathogenesis Laboratory/Radiologic/Other Diagnostic Testing Gross Appearance and Clinical Variants Histopathological Features and Variants Special Stains/
Differential Diagnosis Prognosis Treatment Commonly Used Terms Internet Links
EPIDEMIOLOGY CHARACTERIZATION INCIDENCE About 18,000 affected in United States GEOGRAPHY
Hermansky-Pudlak syndrome (HPS). An epidemiologic study.
Witkop CJ, Almadovar C, Pineiro B, Nunez Babcock M.
Department of Oral Sciences, University of Minnesota, Minneapolis 55455.
Ophthalmic Paediatr Genet 1990 Sep;11(3):245-50 Abstract quote
A study of albinism in Puerto Rico identified 693 persons with albinism. Among these, the type of albinism was determined in 595, Hermansky-Pudlak syndrome (HPS) was found in 495. Approximately five of every six Puerto Rican albinos had HPS.
The highest prevalence of HPS yet reported was in the northwestern quarter of the island where at least 1 in 1,800 persons had HPS, and approximately 1 in 21 were carriers. The HPS albino pigment phenotype was variable, and HPS albinos phenotypically resembled other types of oculocutaneous and ocular albinos. Ceroid storage was also variable.
The consistent finding in HPS was storage pool deficient platelets. HPS is best diagnosed by lack of platelet dense bodies seen by electron microscopy. Evidence from family studies indicates that HPS is a distinct disorder due to the pleiotropic effects of a single gene mutation or a small deletion.
Diverse prevalence of large deletions within the OA1 gene in ocular albinism type 1 patients from Europe and North America.
Bassi MT, Bergen AA, Bitoun P, Charles SJ, Clementi M, Gosselin R, Hurst J, Lewis RA, Lorenz B, Meitinger T, Messiaen L, Ramesar RS, Ballabio A, Schiaffino MV.
Telethon Institute of Genetics and Medicine, Milan, Italy.
Hum Genet 2001 Jan;108(1):51-4 Abstract quote
Ocular albinism type 1 (OA1) is an X-linked disorder mainly characterized by congenital nystagmus and photodysphoria, moderate to severe reduction of visual acuity, hypopigmentation of the retina, and the presence of macromelanosomes in the skin and eyes. We have previously isolated the gene for OA1 and characterized its protein product as melanosomal membrane glycoprotein displaying structural and functional features of G protein-coupled receptors. We and others have identified mutations of various types within the OA1 gene in patients with this disorder, including deletions and splice site, frameshift, nonsense, and missense mutations. However, different prevalences of large intragenic deletions have been reported, ranging from 10% to 50% in independent studies.
To determine whether these differences might be related to the geographic origin of the OA1 families tested, we performed a further extensive mutation analysis study leading to the identification of pathogenic mutations in 30 unrelated OA1 patients mainly from Europe and North America. These results, together with our earlier mutation reports on OA1, allow us to resolve the apparent discrepancies between previous studies and point to a substantial difference in the frequency of large intragenic deletions in European (<10%) compared with North American (>50%) OA1 families.
These observations and our overall refinement of point mutation distribution within the OA1 gene have important implications for the molecular diagnosis of OA1 and for the establishment of any mutation detection program for this disorder.
Attitudes and beliefs of an albino population toward sun avoidance: advice and services provided by an outreach albino clinic in Tanzania.
McBride SR, Leppard BJ.
Department of Dermatology, Royal Free Hospital, Pond Street, London NW3 2QG, England.
Arch Dermatol 2002 May;138(5):629-32 Abstract quote
OBJECTIVE: To determine an albino population's expectations from an outreach albino clinic, understanding of skin cancer risk, and attitudes toward sun protection behavior.
DESIGN: Survey, June 1, 1997, to September 30, 1997.
SETTING: Outreach albino clinics in Tanzania.
PARTICIPANTS: All albinos 13 years and older and accompanying adults of younger children attending clinics. Unaccompanied children younger than 13 years and those too sick to answer questions were excluded. Ninety-four questionnaires were completed in 5 villages, with a 100% response rate.
INTERVENTIONS: Interview-based questionnaire with scoring system for pictures depicting poorly sun-protected albinos.
RESULTS: The most common reasons for attending the clinic were health education and skin examination. Thirteen respondents (14%) believed albinism was inherited; it was more common to believe in superstitious causes of albinism than inheritance. Seventy-three respondents (78%) believed skin cancer was preventable, and 60 (63%) believed skin cancer was related to the sun. Seventy-two subjects (77%) thought sunscreen provided protection from the sun; 9 (10%) also applied it at night. Reasons for not wearing sun-protective clothing included fashion, culture, and heat. The hats provided were thought to have too soft a brim, to shrink, and to be ridiculed. Suggestions for additional clinic services centered on education and employment. Albinos who had read the educational booklet had no better understanding of sun avoidance than those who had not (P =.49).
CONCLUSIONS: There was a reasonable understanding of risks of skin cancer and sun-avoidance methods. Clinical advice was often not followed for cultural reasons. The hats provided were unsuitable, and there was some confusion about the use of sunscreen. A lack of understanding of the cause of albinism led to many superstitions.
DISEASE ASSOCIATIONS CHARACTERIZATION ANGLEMAN SYNDROME
Hypopigmentation in Angelman syndrome.
King RA, Wiesner GL, Townsend D, White JG.
Department of Medicine, University of Minnesota, Minneapolis 55455.
Am J Med Genet 1993 Apr 1;46(1):40-4 Abstract quote
Chromosome region 15q is thought to contain one or more genes that are important for melanin pigment synthesis in the hair, skin, and eyes. Hypopigmentation has been identified in the Prader-Willi (PWS) and Angelman (AS) syndromes.
We have examined 6 individuals with AS to further characterize the pigment pattern in this condition. The age of the 5 girls and one boy ranged from 2.4 to 7.0 years. None had obvious albinism. Hair color ranged from light blond to brown. Skin was type I in 3 and type II in 3. Eye changes included nystagmus in 2, strabismus in 4, and reduced retinal pigment in 5. The mean hairbulb tyrosinase activity was 0.37 +/- 0.44 pmol/hb/120 min for the individuals with AS, with a range of 0.00 to 1.13 (normal brown control 1.49 +/- 0.79, normal blond control 1.50 +/- 0.85). Electron microscopic examination of hairbulb melanocytes showed normal melanosome and melanocyte architecture and number, but reduced melanin formation, with many stage II and III premelanosomes but few stage IV fully melanized melanosomes.
Hypopigmentation characterized by light skin, reduced retinal pigment, low hairbulb tyrosinase activity, and incomplete melanization of melanosomes is part of the phenotype of AS, and is similar to that found in PWS.
Phenotypic differences in Angelman syndrome patients: imprinting mutations show less frequently microcephaly and hypopigmentation than deletions.
Burger J, Kunze J, Sperling K, Reis A.
Institute of Human Genetics, Virchow-Klinikum, Humboldt University, Berlin, Germany.
Am J Med Genet 1996 Dec 11;66(2):221-6 Abstract quote
Angelman syndrome (AS) is a relatively frequent disorder of psychomotor development caused by loss of function of a gene from chromosome 15q11-q13, a region subject to genomic imprinting. The AS gene(s) is exclusively expressed from the maternal chromosome. Several kinds of mutations have been found to cause AS. More than half of the cases exhibit a deletion of the maternal 15q11-q13 region. Recently, we and others described a new mutation type, the imprinting mutation, characterised by normal, biparental inheritance but aberrant methylation patterns of the entire chromosomal region. In AS, a paternal imprint is found on the maternal chromosome probably leading to functional inactivation of the AS gene(s).
We have now compared the phenotype of 9 AS patients with imprinting mutation to that of nine age-matched ones with a maternally derived deletion. Both groups were evaluated for 19 common AS symptoms. All patients, independently of their molecular findings, showed classical AS symptoms such s mental retardation, delayed motor development, and absent speech. In contrast, for two signs, hypopigmentation and microcephaly, a different distribution among both groups was observed. Only one of nine AS patients with an imprinting mutation, but seven of nine in the deletion control group showed either symptom. Our results suggest that imprinting mutations, in contrast to deletions, cause only incomplete loss of gene function or that maternally derived deletions affect also genes not subject to genomic imprinting.
We conclude that AS is caused by loss of function of a major gene that is imprinted but that there are also other genes that contribute to the phenotype when in hemizygous condition.
Distinct phenotypes distinguish the molecular classes of Angelman syndrome.
Lossie AC, Whitney MM, Amidon D, Dong HJ, Chen P, Theriaque D, Hutson A, Nicholls RD, Zori RT, Williams CA, Driscoll DJ.
R C Philips Unit and Division of Genetics, Department of Pediatrics, University of Florida, Gainesville, FL, USA.
J Med Genet 2001 Dec;38(12):834-845 Abstract quote
BACKGROUND: Angelman syndrome (AS) is a severe neurobehavioural disorder caused by defects in the maternally derived imprinted domain located on 15q11-q13. Most patients acquire AS by one of five mechanisms: (1) a large interstitial deletion of 15q11-q13; (2) paternal uniparental disomy (UPD) of chromosome 15; (3) an imprinting defect (ID); (4) a mutation in the E3 ubiquitin protein ligase gene (UBE3A); or (5) unidentified mechanism(s). All classical patients from these classes exhibit four cardinal features, including severe developmental delay and/or mental retardation, profound speech impairment, a movement and balance disorder, and AS specific behaviour typified by an easily excitable personality with an inappropriately happy affect. In addition, patients can display other characteristics, including microcephaly, hypopigmentation, and seizures.
METHODS: We restricted the present study to 104 patients (93 families) with a classical AS phenotype. All of our patients were evaluated for 22 clinical variables including growth parameters, acquisition of motor skills, and history of seizures. In addition, molecular and cytogenetic analyses were used to assign a molecular class (I-V) to each patient for genotype-phenotype correlations.
RESULTS: In our patient repository, 22% of our families had normal DNA methylation analyses along 15q11-q13. Of these, 44% of sporadic patients had mutations within UBE3A, the largest percentage found to date. Our data indicate that the five molecular classes can be divided into four phenotypic groups: deletions, UPD and ID patients, UBE3A mutation patients, and subjects with unknown aetiology. Deletion patients are the most severely affected, while UPD and ID patients are the least. Differences in body mass index, head circumference, and seizure activity are the most pronounced among the classes.
CONCLUSIONS: Clinically, we were unable to distinguish between UPD and ID patients, suggesting that 15q11-q13 contains the only significant maternally expressed imprinted genes on chromosome 15.
Chediak-Higashi syndrome: presentation of seven cases.
Carnide EM, Jacob CM, Pastorino AC, Bellinati-Pires R, Costa MB, Grumach AS.
Department of Pediatrics, Faculdade de Medicina, Universidade de Sao Paulo, Brazil.
Rev Paul Med 1998 Nov-Dec;116(6):1873-8 Abstract quote
CONTEXT: Chediak-Higashi Syndrome (CHS) is a rare autosomal recessive disease characterized by recurrent infections, giant cytoplasmic granules, and oculocutaneous albinism.
OBJECTIVE: To describe clinical and laboratory findings from CHS patients.
DESIGN: Case report.
SETTING: The patients were admitted into the Allergy and Immunology Unit of the Instituto da Crianca, a tertiary public care institution.
CASES REPORT: Seven patients had oculocutaneous albinism, recurrent infections and giant cytoplasmic granules in the leukocytes. One patient had low IgG levels and three showed impaired bactericidal activity of neutrophils. Six patients died of infectious complications during the accelerated phase. Therapy included ascorbic acid and antibiotics. Chemotherapy was used for the accelerated phase in two patients. Bone marrow transplantation (BMT) was proposed for one patient.
DISCUSSION: The authors emphasize the need for early diagnosis and therapy of CHS. BMT should be indicated before the accelerated phase of the disease has developed.
Dermatologic manifestations of Hermansky-Pudlak syndrome in patients with and without a 16-base pair duplication in the HPS1 gene.
Toro J, Turner M, Gahl WA.
Dermatology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1908, USA.
Arch Dermatol 1999 Jul;135(7):774-80 Abstract quote
BACKGROUND: Hermansky-Pudlak syndrome (HPS) consists of oculocutaneous albinism, a platelet storage pool deficiency, and lysosomal accumulation of ceroid lipofuscin. Patients with HPS from northwest Puerto Rico are homozygous for a 16-base pair (bp) duplication in exon 15 of HPS1, a gene on chromosome 10q23 known to cause the disorder.
OBJECTIVE: To determine the dermatologic findings of patients with HPS.
DESIGN: Survey of inpatients with HPS by physical examination.
SETTING: National Institutes of Health Clinical Center, Bethesda, Md (a tertiary referral hospital).
PATIENTS: Sixty-five patients aged 3 to 54 years were diagnosed on the basis of the absence of platelet dense bodies in individuals with albinism and a bleeding diathesis. The presence of a 16-bp duplication in HPS1 was determined by polymerase chain reaction amplification; 40 patients were homozygous for the duplication and 25 lacked the duplication. All patients with the duplication were from northwest Puerto Rico; all patients without the duplication were non-Puerto Rican except 4 from central Puerto Rico.
RESULTS: Both patients homozygous for the 16-bp duplication and patients without the duplication displayed skin color ranging from white to light brown. Patients with the duplication, as well as those lacking the duplication, had hair color ranging from white to brown and eye color ranging from blue to brown. New findings in both groups of patients with HPS were melanocytic nevi with dysplastic features, acanthosis nigricans-like lesions in the axilla and neck, and trichomegaly. Eighty percent of patients with the duplication exhibited features of solar damage, including multiple freckles, stellate lentigines, actinic keratoses, and, occasionally, basal cell or squamous cell carcinomas. Only 8% of patients lacking the 16-bp duplication displayed these findings. As a group, the patients with the duplication lived closer to the equator than those without the duplication.
CONCLUSION: Patients with HPS exhibit wide variation in pigmentation and dermatologic findings.
The Hermansky-Pudlak syndrome (HPS) protein is part of a high molecular weight complex involved in biogenesis of early melanosomes.
Oh J, Liu ZX, Feng GH, Raposo G, Spritz RA.
Human Medical Genetics Program, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, B-161, Denver, CO 80262, USA.
Hum Mol Genet 2000 Feb 12;9(3):375-85 Abstract quote
Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder in which oculocutaneous albinism, bleeding tendency and a ceroid-lipofuscin lysosomal storage disease result from defects of multiple cytoplasmic organelles: melanosomes, platelet dense granules and lysosomes. The HPS polypeptide, a 700 amino acid protein which is unrelated to any known proteins, is likely to be involved in the biogenesis of these different organelles.
Here, we show that HPS is a non-glycosylated, non-membrane protein which is a component of two distinct high molecular weight complexes. In non-melanotic cells the HPS protein is contained almost entirely in an approximately 200 kDa complex that is widely distributed throughout the cytosol. In melanotic cells the HPS protein is partitioned between this cytosolic complex and a >500 kDa complex that appears to consist of the approximately 200 kDa complex in association with membranous components. Subcellular fractionation, immunofluorescence and immunoelectron microscopy studies indicate that the membrane-associated HPS complex of melanotic cells is associated with tubulovesicular structures, small non-coated vesicles, and nascent and early-stage melanosomes.
These findings suggest that the HPS complex is involved in the biogenesis of early melanosomes.
Abnormal translocation of tyrosinase and tyrosinase-related protein 1 in cutaneous melanocytes of Hermansky-Pudlak Syndrome and in melanoma cells transfected with anti-sense HPS1 cDNA.
Sarangarajan R, Budev A, Zhao Y, Gahl WA, Boissy RE.
Department of Dermatology, University of Cincinnati, Cincinnati, Ohio 45267, USA.
J Invest Dermatol 2001 Sep;117(3):641-6 Abstract quote
Hermansky-Pudlak syndrome is an autosomal recessive disorder characterized by oculocutaneous albinism, a bleeding disorder, and, in some patients, ceroid storage and progressive lung disease. Although Hermansky-Pudlak syndrome exhibits locus heterogeneity, most patients have mutations in the HPS1 gene. Melanocytes in the basal epithelial layer of skin from patients with different mutations in the HPS1 gene exhibited occasional large complexes containing dihydroxyphenylalanine-positive cisterna and 50 nm vesicles. To characterize the role of the HPS1 protein in cells, human HPS1 cDNA was transfected into pigmented SK-MEL-188 melanoma cells (M-188) in either the sense (S-188) or the antisense (A-188) orientation. Expression of the 79 kDa HPS1 protein (in M-188 and S-188 cells) or lack of expression (in A-188 cells) was confirmed by Western blotting using two HPS1-protein-specific polyclonal antibodies. Significant reduction in expression of HPS1 protein in A-188 cells resulted in a significant decrease in tyrosinase activity and melanin content compared with M-188 and S-188 cells using an intact cell assay for tyrosinase. In contrast, tyrosinase activities in cell lysates of M-188, S-188, and A-188 cells were not significantly different. Knockout of HPS1 protein expression in A-188 cells caused both tyrosinase and tyrosinase-related protein 1 to be localized to large granular complexes in the cell cytosol and dendrites. Electron microscope analysis of the A-188 cells revealed that absence of HPS1 protein resulted in the deposition of dihydroxyphenylalanine reaction products (i.e., tyrosinase) confined to large membrane-bound structures with limiting membranes. We conclude that lack of HPS1 protein expression results in mistranslocation of tyrosinase and tyrosinase-related protein 1 to large granular complexes rather than melanosomes, compromising melanin synthesis.
Hermansky-pudlak syndrome type 3 in ashkenazi jews and other non-puerto rican patients with hypopigmentation and platelet storage-pool deficiency.
Huizing M, Anikster Y, Fitzpatrick DL, Jeong AB, D'Souza M, Rausche M, Toro JR, Kaiser-Kupfer MI, White JG, Gahl WA.
Section on Human Biochemical Genetics, Heritable Disorders Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA.
Am J Hum Genet 2001 Nov;69(5):1022-32 Abstract quote
Hermansky-Pudlak syndrome (HPS), consisting of oculocutaneous albinism and a bleeding diathesis due to the absence of platelet dense granules, displays extensive locus heterogeneity. HPS1 mutations cause HPS-1 disease, and ADTB3A mutations cause HPS-2 disease, which is known to involve abnormal intracellular vesicle formation. A third HPS-causing gene, HPS3, was recently identified on the basis of homozygosity mapping of a genetic isolate of HPS in central Puerto Rico.
We now describe the clinical and molecular characteristics of eight patients with HPS-3 who are of non-Puerto Rican heritage. Five are Ashkenazi Jews; three of these are homozygous for a 1303+1G-->A splice-site mutation that causes skipping of exon 5, deleting an RsaI restriction site and decreasing the amounts of mRNA found on northern blotting. The other two are heterozygous for the 1303+1G-->A mutation and for either an 1831+2T-->G or a 2621-2A-->G splicing mutation. Of 235 anonymous Ashkenazi Jewish DNA samples, one was heterozygous for the 1303+1G-->A mutation. One seven-year-old boy of German/Swiss extraction was compound heterozygous for a 2729+1G-->C mutation, causing skipping of exon 14, and resulting in a C1329T missense (R396W), with decreased mRNA production. A 15-year-old Irish/English boy was heterozygous for an 89-bp insertion between exons 16 and 17 resulting from abnormal splicing; his fibroblast HPS3 mRNA is normal in amount but is increased in size. A 12-year-old girl of Puerto Rican and Italian background has the 3,904-bp founder deletion from central Puerto Rico on one allele. All eight patients have mild symptoms of HPS; two Jewish patients had received the diagnosis of ocular, rather than oculocutaneous, albinism.
These findings expand the molecular diagnosis of HPS, provide a screening method for a mutation common among Jews, and suggest that other patients with mild hypopigmentation and decreased vision should be examined for HPS.
Mutation of a new gene causes a unique form of Hermansky-Pudlak syndrome in a genetic isolate of central Puerto Rico.
Anikster Y, Huizing M, White J, Shevchenko YO, Fitzpatrick DL, Touchman JW, Compton JG, Bale SJ, Swank RT, Gahl WA, Toro JR.
Section on Human Biochemical Genetics, Heritable Disorders Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Nat Genet 2001 Aug;28(4):376-80 Abstract quote
Oculocutaneous albinism and a storage pool deficiency due to an absence of platelet dense bodies. Lysosomal ceroid lipofuscinosis, pulmonary fibrosis and granulomatous colitis are occasional manifestations of the disease. HPS occurs with a frequency of one in 1800 in north-west Puerto Rico due to a founder effect. Several non-Puerto Rican patients also have mutations in HPS1, which produces a protein of unknown function. Another gene, ADTB3A, causes HPS in the pearl mouse and in two brothers with HPS-2 (refs. 11,12). ADTB3A encodes a coat protein involved in vesicle formation, implicating HPS as a disorder of membrane trafficking.
We sought to identify other HPS-causing genes. Using homozygosity mapping on pooled DNA of 6 families from central Puerto Rico, we localized a new HPS susceptibility gene to a 1.6-cM interval on chromosome 3q24. The gene, HPS3, has 17 exons, and a putative 113.7-kD product expected to reveal how new vesicles form in specialized cells.
The homozygous, disease-causing mutation is a large deletion and represents the second example of a founder mutation causing HPS on the small island of Puerto Rico. We also present an allele-specific assay for diagnosing individuals heterozygous or homozygous for this mutation.
Oculocutaneous albinism types 1 and 3 are ER retention diseases: mutation of tyrosinase or Tyrp1 can affect the processing of both mutant and wild-type proteins.
Toyofuku K, Wada I, Valencia JC, Kushimoto T, Ferrans VJ, Hearing VJ.
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
FASEB J 2001 Oct;15(12):2149-61 Abstract quote
Various types of oculocutaneous albinism (OCA) are associated with reduced pigmentation in the skin, hair, and eyes that results from mutations in genes involved in melanin synthesis. Immortal mouse melanocyte lines (melan-a, melan-b, and melan-c) provide opportune models with which to investigate the etiology of two different types of OCA (types I and III), which arise from mutations in Tyr and Tyrp1, respectively. We compared intracellular processing, sorting, and degradation of tyrosinase and Tyrp1, and the effects on their catalytic function and melanin synthesis, in these wild-type and mutant melanocytes. A mutation in either Tyr or Tyrp1 increased the time of association of tyrosinase and Tyrp1 with calnexin and Bip, which in turn resulted in the retention of these mutant products in the ER. A mutation in either gene selectively enhanced the duration and efficiency of chaperone interactions (even with the wild-type protein in the mutant melanocytes) and markedly slowed their transport to melanosomes.
These results show that OCA1 and OCA3 are (in some cases, at least) ER retention diseases wherein a mutation in one melanogenic protein affects the maturation and stability of the other in the melanogenic pathway.
Oculocutaneous albinoidism as a manifestation of reduced neural crest derivatives in the Prader-Willi syndrome.
Hittner HM, King RA, Riccardi VM, Ledbetter DH, Borda RP, Ferrell RE, Kretzer FL.
Am J Ophthalmol 1982 Sep;94(3):328-37 Abstract quote
Nine patients with Prader-Willi syndrome (five female and four male; one Oriental and eight white), all of whom had interstitial deletions of the proximal long arm of one chromosome 15 (q11-q13) were found to have decreased tyrosinase activity in isolated hair bulbs.
As infants, all patients had light hair and skin coloring, both of which darkened with age. Light and electron microscopic analysis of skin and hair bulbs disclosed a reduced number of melanocytes in the basal epidermis and hair bulbs. Each patient demonstrated decreased pigmentation of the iris stroma, which was accentuated peripherally and manifested clinically as iris translucency. There was no foveal hypoplasia, nystagmus, or photophobia, and ocular function was normal.
Oculocutaneous albinoidism is thus a component of del(15q) Prader-Willi syndrome with reduction of melanocytes of neural crest origin (skin, hair, and iris stroma) and retention of normal retinal and iris pigment epithelia of neuroectodermal origin.
Hypopigmentation in the Prader-Willi syndrome.
Wiesner GL, Bendel CM, Olds DP, White JG, Arthur DC, Ball DW, King RA.
Am J Hum Genet 1987 May;40(5):431-42 Abstract quote
Cutaneous and ocular pigmentation were evaluated in 29 individuals with the Prader-Willi syndrome (PWS). Criteria for hypopigmentation included the presence of type I or II skin, the lightest skin type in the family by history, and iris translucency on globe transillumination.
On the basis of these criteria, 48% of the PWS individuals were hypopigmented. The presence of hypopigmentation correlated with a small interstitial deletion on the proximal long arm of chromosome 15; however, this deletion was also found in individuals who did not meet the full criteria for hypopigmentation. Hairbulb tyrosinase activity and glutathione content, as well as urine cysteinyldopa excretion, were low in PWS individuals with and without hypopigmentation and did not separate these two groups.
We conclude that hypopigmentation is found in a significant proportion of individuals with PWS and that the hypopigmentation may be associated with a deletion of the long arm of chromosome 15. The mechanism for the hypopigmentation is unknown.
Hypopigmentation in the Prader-Willi syndrome correlates with P gene deletion but not with haplotype of the hemizygous P allele.
Spritz RA, Bailin T, Nicholls RD, Lee ST, Park SK, Mascari MJ, Butler MG.
Department of Medical Genetics, University of Wisconsin School of Medicine, Madison 53706, USA.
Am J Med Genet 1997 Jul 11;71(1):57-62 Abstract quote
The Prader-Willi syndrome (PWS) usually results from a paternal deletion of 15q11-q13 or maternal disomy for chromosome 15. Reduced pigmentation of skin, hair, and eyes is common in PWS and was suggested previously to be associated with the 15q11-q13 deletion. The P gene, located in this same region, is associated with OCA2, an autosomal recessive disorder that is the most frequent form of tyrosinase-positive oculocutaneous albinism.
We studied 28 individuals with PWS and found that hemizygosity for the P gene was significantly correlated with the occurrence of hypopigmentation among PWS patients. However, we found little or no relationship between the occurrence of hypopigmentation and the polymorphism haplotype of the intact P allele.
Thus, our results indicate that hypopigmentation is likely the result of deletion of the P gene in the context of PWS but do not support the linked hypothesis that hypopigmentation results from hemizygosity for variant P alleles with reduced function.
TUBEROUS SCLEROSIS WAARDENBERG SYNDROME
Heterogeneity in Waardenburg's syndrome. Report of a family with ocular albinism
Arch Ophthalmol 1978 Jul;96(7):1193-8 Abstract quote
A family had the following manifestations of Waardenburg's syndrome (WS): prominent nasal root, white forelock, premature graying of the hair, freckled pigmentation of pale skin, hypoplastic heterochromia irides, heterochromia of the ocular fundi, congenital sensorineural hearing loss, and autosomal dominant heredity.
This family differs from those previously reported in that none of its members showed dystopia of the inner canthi or lower puncta. In addition, four siblings had the combination of hyperopia-estropia-amblyopia, as well as ocular albinism, manifested by foveal hypoplasia and transilluminable irides. Observations on this family support prior suggestions of heterogeneity in WS.
PATHOGENESIS CHARACTERIZATION ABNORMAL MELANOSOME GROWTH
Oa1 knock-out: new insights on the pathogenesis of ocular albinism type 1.
Incerti B, Cortese K, Pizzigoni A, Surace EM, Varani S, Coppola M, Jeffery G, Seeliger M, Jaissle G, Bennett DC, Marigo V, Schiaffino MV, Tacchetti C, Ballabio A.
Telethon Institute of Genetics and Medicine, San Raffaele Biomedical Science Park, Via Olgettina 58, I-20132 Milan, Italy.
Hum Mol Genet 2000 Nov 22;9(19):2781-8 Abstract quote
Ocular albinism type I (OA1) is an X-linked disorder characterized by severe reduction of visual acuity, strabismus, photophobia and nystagmus. Ophthalmologic examination reveals hypopigmentation of the retina, foveal hypoplasia and iris translucency. Microscopic examination of both retinal pigment epithelium (RPE) and skin melanocytes shows the presence of large pigment granules called giant melanosomes or macromelanosomes.
In this study, we have generated and characterized Oa1-deficient mice by gene targeting (KO). The KO males are viable, fertile and phenotypically indistinguishable from the wild-type littermates. Ophthalmologic examination shows hypopigmentation of the ocular fundus in mutant animals compared with wild-type. Analysis of the retinofugal pathway reveals a reduction in the size of the uncrossed pathway, demonstrating a misrouting of the optic fibres at the chiasm, as observed in OA1 patients. Microscopic examination of the RPE shows the presence of giant melanosomes comparable with those described in OA1 patients.
Ultrastructural analysis of the RPE cells, suggests that the giant melanosomes may form by abnormal growth of single melanosomes, rather than the fusion of several, shedding light on the pathogenesis of ocular albinism.
In Southern Africa, brown oculocutaneous albinism (BOCA) maps to the OCA2 locus on chromosome 15q: P-gene mutations identified.
Manga P, Kromberg J, Turner A, Jenkins T, Ramsay M.
Department of Human Genetics, School of Pathology, The South African Institute for Medical Research and University of the Witwatersrand, Johannesburg, 2000, South Africa.
Am J Hum Genet 2001 Mar;68(3):782-7 Abstract quote
In southern Africa, brown oculocutaneous albinism (BOCA) is a distinct pigmentation phenotype. In at least two cases, it has occurred in the same families as tyrosinase-positive oculocutaneous albinism (OCA2), suggesting that it may be allelic, despite the fact that this phenotype was attributed to mutations in the TYRP1 gene in an American individual of mixed ancestry.
Linkage analysis in five families mapped the BOCA locus to the same region as the OCA2 locus (maximum LOD 3.07; theta=0 using a six-marker haplotype). Mutation analysis of the human homologue of the mouse pink-eyed dilution gene (P), in 10 unrelated individuals with BOCA revealed that 9 had one copy of the 2.7-kb deletion. No other mutations were identified. Additional haplotype studies, based on closely linked markers (telomere to centromere: D15S1048, D15S1019, D15S1533, P-gene 2.7-kb deletion, D15S219, and D15S156) revealed several BOCA-associated P haplotypes.
These could be divided into two core haplotypes, suggesting that a limited number of P-gene mutations give rise to this phenotype.
DISORDER OF LYSOSOMAL VESICLE FORMATION AND TRAFFICKING
Altered trafficking of lysosomal proteins in Hermansky-Pudlak syndrome due to mutations in the beta 3A subunit of the AP-3 adaptor.
Dell'Angelica EC, Shotelersuk V, Aguilar RC, Gahl WA, Bonifacino JS.
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Mol Cell 1999 Jan;3(1):11-21 Abstract quote
Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by defective lysosome-related organelles.
Here, we report the identification of two HPS patients with mutations in the beta 3A subunit of the heterotetrameric AP-3 complex. The patients' fibroblasts exhibit drastically reduced levels of AP-3 due to enhanced degradation of mutant beta 3A. The AP-3 deficiency results in increased surface expression of the lysosomal membrane proteins CD63, lamp-1, and lamp-2, but not of nonlysosomal proteins. These differential effects are consistent with the preferential interaction of the AP-3 mu 3A subunit with tyrosine-based signals involved in lysosomal targeting.
Our results suggest that AP-3 functions in protein sorting to lysosomes and provide an example of a human disease in which altered trafficking of integral membrane proteins is due to mutations in a component of the sorting machinery.
Endoplasmic reticulum retention is a common defect associated with tyrosinase-negative albinism.
Halaban R, Svedine S, Cheng E, Smicun Y, Aron R, Hebert DN.
Department of Dermatology, Yale University School of Medicine, New Haven, CT 06520, USA.
Proc Natl Acad Sci U S A 2000 May 23;97(11):5889-94 Abstract quote
Tyrosinase is a melanocyte-specific enzyme critical for the synthesis of melanin, a process normally restricted to a post-Golgi compartment termed the melanosome. Loss-of-function mutations in tyrosinase are the cause of oculocutaneous albinism, demonstrating the importance of the enzyme in pigmentation.
In the present study, we explored the possibility that trafficking of albino tyrosinase from the endoplasmic reticulum (ER) to the Golgi apparatus and beyond is disrupted. Toward this end, we analyzed the common albino mouse mutation Tyr(C85S), the frequent human albino substitution TYR(T373K), and the temperature-sensitive tyrosinase TYR(R402Q)/Tyr(H402A) found in humans and mice, respectively. Intracellular localization was monitored in albino melanocytes carrying the native mutation, as well as in melanocytes ectopically expressing green fluorescent protein-tagged tyrosinase. Enzymatic characterization of complex glycans and immunofluorescence colocalization with organelle-specific resident proteins established that all four mutations produced defective proteins that were retained in the ER. TYR(R402Q)/Tyr(H402A) Golgi processing and transport to melanosomes were promoted at the permissive temperature of 32 degrees C, but not at the nonpermissive 37 degrees C temperature. Furthermore, evidence of protein misfolding was demonstrated by the prolonged association of tyrosinase mutants with calnexin and calreticulin, known ER chaperones that play a key role in the quality-control processes of the secretory pathway.
From these results we concluded that albinism, at least in part, is an ER retention disease.
Intracellular distribution and late endosomal effects of the ocular albinism type 1 gene product: consequences of disease-causing mutations and implications for melanosome biogenesis.
Shen B, Rosenberg B, Orlow SJ.
The Ronald O. Perelman Department of Dermatology and the Department of Cell Biology, NYU School of Medicine, New York, NY 10016, USA.
Traffic 2001 Mar;2(3):202-11 Abstract quote
To investigate the function of ocular albinism type 1 (OA1), the gene responsible for X-linked ocular albinism, we employed a construct containing murine Oa1 fused to green fluorescent protein (GFP) in a heterologous COS cell expression system. The cellular distribution of wild-type (WT) Oa1 protein and Oa1 proteins reflecting mutations causing X-linked ocular albinism were examined.
Comparison with different organelle markers revealed that Oa1-GFP localized to the late endolysosomal compartments. Some Oa1 mutant proteins failed to exit the endoplasmic reticulum (ER) (Class I mutants), while other mutants partially (Class II mutants) or fully (Class III mutants) exited the ER and trafficked to endolysosomal compartments. We observed that expression of WT Oa1-GFP in COS cells caused an apparent enlargement of late endosomes and a redistribution of the mannose-6-phosphate receptor (M6PR). None of the mutants displayed the full range of effects on the redistribution of M6PR exhibited by WT Oa1. The effects of Oa1 on late endosome structure and content are thus likely to reflect an important biological property of Oa1.
We propose that OA1 is involved in reorganizing the endolysosomal compartment as a necessary step in ocular melanosome biogenesis.
Hermansky-Pudlak syndrome and Chediak-Higashi syndrome: disorders of vesicle formation and trafficking.
Huizing M, Anikster Y, Gahl WA.
Section on Human Biochemical Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-1830, USA.
Thromb Haemost 2001 Jul;86(1):233-45 Abstract quote
The rare autosomal recessive metabolic disorders Hermanky-Pudlak syndrome (HPS) and Chediak-Higashi syndrome (CHS)share the clinical findings of oculocutaneous albinism and a platelet storage pool deficiency. In addition, HPS exhibits ceroid lipofuscinosis and CHS is characterized by infections and an accelerated phase.
The two disorders result from defects in vesicles of lysosomal lineage. Of the two known HPS-causing genes, HPS1 has no recognizable function, while ADTB3A codes for a subunit of an adaptor complex responsible for new vesicle formation from the trans-Golgi network. Other HPS-causing genes are likely to exist. The only known CHS-causing gene, LYST, codes for a large protein of unknown function.
In general, HPS appears to be a disorder of vesicle formation and CHS a defect in vesicle trafficking. These diseases and their variants mirror a group of mouse hypopigmentation mutants. The gene productsinvolved will reveal how the melanosome, platelet dense body, and lysosome are formed and trafficked within cells.
DEGRADATION OF MUTANT TYROSINASES
- Molecular basis of oculocutaneous albinism type 1 in Lebanese patients.
Zahed L, Zahreddine H, Noureddine B, Rebeiz N, Shakar N, Zalloua P, Haddad F.
Department of Pathology and Laboratory Medicine, American University of Beirut Medical Center, Beirut, Lebanon,
J Hum Genet. 2005 Jun 4; [Epub ahead of print] Abstract quote
Oculocutaneous albinism type 1 (OCA1) results from mutations in the tyrosinase gene, which lead to partial or complete loss of activity of the corresponding enzyme. A large number of mutations have been identified worldwide, providing insight into the pathogenesis of the disorder.
We performed ophthalmic and dermatological exams on 30 Lebanese subjects with oculocutaneous albinism, then screened for mutations in the tyrosinase gene in an effort to establish the molecular basis of the disorder in our population and correlate it with phenotypic findings. The five exons of the gene together with the exon-intron boundaries and part of the promoter region were sequenced. Mutations were found in a total of 14 patients (47%) while no mutation was identified in the sequenced regions in 53% of patients. Fourteen different mutations were identified of which eight were novel while six had been previously reported.
Mutations were mainly seen in patients with clinical findings, suggestive of OCA1A (64% of patients with OCA1A versus 25% of patients with OCA1B); therefore, the absence of mutations in some of the other patients may indicate the involvement of other genes.
The molecular basis of oculocutaneous albinism type 1 (OCA1): sorting failure and degradation of mutant tyrosinases results in a lack of pigmentation.
Toyofuku K, Wada I, Spritz RA, Hearing VJ.
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Building 37, Room 1B25, Bethesda, MD 20892, USA.
Biochem J 2001 Apr 15;355(Pt 2):259-69 Abstract quote
Oculocutaneous albinism type 1 (OCA1) is an autosomal recessive disease resulting from mutations of the tyrosinase gene (TYR).
To elucidate the molecular basis of OCA1 phenotypes, we analysed the early processing and maturation of several different types of mutant tyrosinase with various degrees of structural abnormalities (i.e. two large deletion mutants, two missense mutants that completely destroy catalytic function and three missense mutants that have a temperature-sensitive phenotype).
When expressed in COS7 cells, all mutant tyrosinases were sensitive to endoglycosidase H digestion, and immunostaining showed their localization in the endoplasmic reticulum (ER) and their failure to be sorted further to their target organelles. Pulse-chase experiments showed that all mutant tyrosinases were retained by calnexin in the ER and that they were degraded at similarly rapid rates, which coincided with their dissociation from calnexin. Temperature-sensitive mutant enzymes were sorted more efficiently at 31 degrees C than at 37 degrees C, and their degradation was accelerated at 37 degrees C compared with 31 degrees C. Thus in contrast to the current concept that mutant tyrosinases are transported to melanosomes but are functionally inactive there, our results suggest that mutant tyrosinases may not be transported to melanosomes in the first place.
We conclude that a significant component of mutant tyrosinase malfunction in OCA1 results from their retention and degradation in the ER compartment. This quality-control process is highly sensitive to minimal changes in protein folding, and so even relatively minor mutations in peripheral sequences of the enzyme not involved with catalytic activity may result in a significant reduction of functional enzyme in melanosomes.
CHARACTERIZATION RADIOLOGIC LABORATORY MARKERS
X-linked ocular albinism (Nettleship-Falls): a novel 29-bp deletion in exon 1. Carrier detection by ophthalmic examination and DNA analysis.
Rudolph G, Meindl A, Bechmann M, Schworm HD, Achatz H, Boergen KP, Kampik A, Berninger T, Meitinger T.
Augenklinik der Universitat Munchen, Mathildenstrasse 8, 80336 Munich, Germany.
Graefes Arch Clin Exp Ophthalmol 2001 Mar;239(3):167-72 Abstract quote
BACKGROUND: Mutations in the OA1 gene on the short arm of the X chromosome are known to cause X-linked ocular albinism (x1OA) in males. A four-generation family with this disorder, including asymptomatic carrier females, was investigated by molecular analysis of the OA1 gene.
METHODS: DNA samples were available from 22 individuals of this family, including 6 affected males and 6 obligate carriers. The nine exons of the OA1 gene were amplified and further analyzed by SSCP and sequencing.
RESULTS: A detailed clinical examination of the index patient and two female carriers showed the typical signs of ocular albinism. Visual evoked potential responses showed markedly asymmetrical responses from the two hemispheres in the affected person as well as in the carriers, as a result of misrouting and decussation of optic nerve fibers. Molecular genetic analysis demonstrated a previously undescribed 29-bp deletion at position 225-253 in exon 1 of the OA1 gene, which segregated in the family.
CONCLUSION: Clinical examination combined with molecular genetic analysis enhances the potential for a precise diagnosis for persons at risk of x1OA and provide an accurate basis for genetic counseling.
DNA diagnosis and management of Hermansky-Pudlak syndrome in pregnancy.
Wax JR, Rosengren S, Spector E, Gainey AJ, Ingardia CJ.
Department of Obstetrics and Gynecology, Hartford Hospital, Connecticut, USA.
Am J Perinatol 2001 May;18(3):159-61 Abstract quote
Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by oculocutaneous albinism (OCA), platelet storage pool deficiency, and ceroid lipofuscin deposition. Sequelae including pulmonary fibrosis, colitis, and hemorrhagic diathesis can impact obstetric management.
An 18-year-old primigravida with OCA was diagnosed during pregnancy with Hermansky-Pudlak syndrome by DNA analysis. Uneventful vaginal delivery occurred at term following prophylactic platelet transfusion.
Women of northwestern Puerto Rican descent with OCA should be offered testing for HPS. Identification of affected individuals may permit optimal obstetric management.
CHARACTERIZATION GENERAL OCULOCUTANEOUS ALBINISM (OCA) OCA1-Tyrosinase Related Oculocutaneous Albinism. OCA1B OCA2 P-Gene Related Oculocutaneous Albinism Brown OCA OCA3 TRP1-Related OCA OCULAR ALBINISM (OA) OA1 X-Linked Ocular Albinism (Nettleship-Falls) Autosomal recessive ocular albinism VARIANTS
Albinism and agenesis of the corpus callosum with profound developmental delay: Vici syndrome, evidence for autosomal recessive inheritance.
del Campo M, Hall BD, Aeby A, Nassogne MC, Verloes A, Roche C, Gonzalez C, Sanchez H, Garcia-Alix A, Cabanas F, Escudero RM, Hernandez R, Quero J.
Division of Dysmorphology, Department of Pediatrics, University of California, San Diego, California 92103-8446, USA.
Am J Med Genet 1999 Aug 27;85(5):479-85 Abstract quote
We report on two sibs and two other unrelated patients with agenesis of corpus callosum, oculocutaneous albinism, repeated infections, and cardiomyopathy.
All manifested postnatal growth retardation, microcephaly, and profound developmental delay. Additional central nervous system anomalies present in at least one patient included hypoplasia of the cerebellar vermis, white matter neuronal heterotopia, or bilateral schizencephaly. Repeated viral, bacterial, and fungal infections were consistent with a primary immunodeficiency. However, immunological studies showed variable, nonspecific findings. Cardiomyopathy with progressive heart failure or infection led to death before age 2 years in three of the patients.
This syndrome was first described by Vici et al. [1988: Am. J. Med. Genet. 29:1-8]. The four patients reported herein confirm this unique disorder. Affected sibs of both sexes born to unaffected parents provide evidence for autosomal recessive inheritance.
HISTOLOGICAL TYPES CHARACTERIZATION GENERAL VARIANTS
The melanin pigmentary disorder in a family with Hermansky-Pudlak syndrome.
Frenk E, Lattion F.
J Invest Dermatol 1982 Feb;78(2):141-3 Abstract quote
The albinotic skin and hair of 2 patients with Hermansky-Pudlak syndrome were investigated by light and electron microscopy. Incubation of hairbulbs and epidermis in 1-dopa revealed a weak tyrosinase activity. The epidermal melanocyte population was of normal density.
The most striking feature was the presence of numerous giant melanosomes resembling those mainly reported in various hyperpigmented skin lesions. The association of this melanosomal disorder with the platelet dysfunction and ceroid storage typical of the autosomal recessive Hermansky-Pudlak syndrome might provide new insights into the mechanism leading to formation of giant melanosomes.
Hermansky-Pudlak syndrome: report of a case with histological, immunohistochemical and ultrastructural findings.
Husain S, Marsh E, Saenz-Santamaria MC, McNutt NS.
Department of Pathology, New York Hospital-Cornell University Medical Centre, New York 10021, USA
J Cutan Pathol 1998 Aug;25(7):380-5 Abstract quote
We report a 38-year-old female of Puerto Rican descent with Hermansky-Pudlak syndrome and decreased levels of von Willebrand factor. Histologic and ultrastructural findings of non-sunexposed skin showed melanocytes with short dendritic processes and decreased numbers of melanosomes. Ultrastructural examination of platelets revealed greatly reduced numbers of delta granules.
Recognition of this syndrome is important because skin neoplasms, ceroid deposition and hemorrhagic manifestations can be causes of morbidity and of potential death in patients affected with this syndrome.
CHARACTERIZATION SPECIAL STAINS
Electron microscopic DOPA reaction test for oculocutaneous albinism.
Takizawa Y, Kato S, Matsunaga J, Aozaki R, Tomita Y, Nishikawa T, Shimizu H.
Department of Dermatology, Keio University School of Medicine, Tokyo, Japan.
Arch Dermatol Res 2000 Jun;292(6):301-5 Abstract quote
Oculocutaneous albinism (OCA) is an autosomal recessive disorder in which the biosynthesis of melanin is reduced or absent in skin, hair and eyes. Tyrosinase-related OCA (OCA1) is caused by mutations in the tyrosinase gene. Tyrosinase-negative OCA (OCA1A) is the most severe phenotype in which tyrosinase catalytic activity is completely lost, resulting in no mature melanin pigment. Yellow OCA (OCA1B) varies from very little pigment associated with whitish-blond hair to nearly normal pigment with dark-blond hair and skin.
We determined the tyrosinase activity in melanocytes by the electron microscopic dihydroxyphenylalanine (EM-DOPA) reaction test using skin samples and analyzed tyrosinase gene mutations in nine Japanese patients with OCA. In 18 alleles of nine patients, the OCA1A-associated mutations, P310insC, R77Q and R278X, were found in seven, three and one alleles, respectively. Five patients who had these mutations in both alleles showed white hair, blue eyes and white skin and demonstrated no tyrosinase activity by the EM-DOPA reaction test. Three patients who had no tyrosinase gene mutation showed tyrosinase activity and heterogeneous clinical features. One patient in whom only an R77Q OCA1A mutation was found in one allele demonstrated a reduced tyrosinase activity, indicating OCA1B. This patient had white hair at birth, but it had turned blond by the age of 1 year.
These results indicate that the EM-DOPA reaction test provides clear information on the status of tyrosinase activity which is essential for the identification of the disease subtype which in turn is important for the prognosis of patients with OCA.
IMMUNOPEROXIDASE ELECTRON MICROSCOPY
Macromelanosomes in X-linked ocular albinism.
Garner A, Jay BS.
Histopathology 1980 May;4(3):243-54 Abstract quote
Examination of clinically normal skin from four patients with X-linked ocular albinism of the Nettleship-Falls type by light and electron microscopy revealed the presence of macromelanosomes in some melanocytes and keratinocytes. Measuring up to 5 micron many of the abnormal melanosomes showed a concentrically laminated structure suggestive of a phasic growth pattern. Epidermis from three female carriers contained similar but fewer macromelanosomes.
These findings indicate that skin biopsy could be of value not only in confirming the diagnosis of ocular albinism in affected males, but also to establish carrier status in asymptomatic females.
DIFFERENTIAL DIAGNOSIS KEY DIFFERENTIATING FEATURES Hypopigmented lesions of the skin
PROGNOSIS AND TREATMENT CHARACTERIZATION PROGNOSTIC FACTORS MELANOMA
Malignant melanoma in a patient with oculocutaneous albinism.
Streutker CJ, McCready D, Jimbow K, From L.
Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada.
J Cutan Med Surg 2000 Jul;4(3):149-52 Abstract quote
BACKGROUND: Sun-induced malignancies (basal cell and squamous cell carcinomas) are common in oculocutaneous albinism, however, the incidence of malignant melanoma is a topic of controversy.
OBJECTIVE: We have reviewed the literature and report a case of a woman with oculocutaneous albinism with an amelanotic melanoma of the anterior chest wall.
RESULTS: There are only 26 previously reported cases (both case reports and African albino population studies) in 25 patients in the literature. A 27th case with immunohistochemical and ultrastructural evaluation is presented.
CONCLUSIONS: It appears that melanoma, a malignancy for which sun exposure and light colouration are felt to be major risk factors, has a low incidence among a population that is both hypopigmented and often exposed to high levels of ultraviolet light. This low incidence is poorly understood and frequently disputed.
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