Mapping the TYR gene reveals novel and previously reported variants in Eastern Indian patients highlighting preponderance of the same changes in multiple unrelated ethnicities.

Oculocutaneous albinism (OCA) is a group of congenital autosomal recessive disorders with seven known subtypes (OCA1-OCA7) characterized by loss or absence of pigmentation in the skin, hair, and eyes. OCA1, caused by pathogenic variations in the tyrosinase (TYR) gene, has been documented to be the most prevalent subtype across the world including India. In the present study, we recruited 53 OCA-affected individuals from 45 unrelated families belonging to 20 different marriage groups/ethnicities of 15 different districts of West Bengal. We took a targeted sequencing-based approach to find the causal variations in the TYR gene. We report here identification of two novel potentially pathogenic variations [NM_000372.4:c.614C>T, NP_000363.1:p.(Pro205Leu), and NM_000372.4:c.1036+1=/G>T], one novel synonymous TYR variant [NM_000372.4:c.204=/A>G, NP_000363.1:p.(Gln68=)], two pathogenic variations documented for the first time in Indian OCA cases [NM_000372.4:c.1147G>A, NP_000363.1:p.(Asp383Asn), and NM_000372.4:c.585G>A, NP_000363.1:p.(Trp195*)], along with nine previously reported pathogenic variants in 36 out of 53 (∼68%) patients recruited. We report common haplotype backgrounds for the two most prevalent variations [NM_000372.4:c.124G>A, NM_000372.4:c.832C>T] in cases belonging to different marriage/ethnic groups, suggesting a possible founder effect. To our knowledge, this is the most comprehensive genetic study on OCA1 from India, firmly establishing OCA1 as the commonest form of albinism in this part of the world.

Genetic analyses of oculocutaneous albinism types 1 and 2 with four novel mutations.

BACKGROUND: Oculocutaneous albinism (OCA) is a human autosomal-recessive hypopigmentation disorder with hypopigmentation in the skin, hair, and eyes. OCA1 and OCA2 are caused by mutations of the TYR and OCA2 genes, respectively, which are responsible for most oculocutaneous albinism. However, the incidence of oculocutaneous albinism patients in Guangxi remains unclear. METHODS: To evaluate the molecular basis of oculocutaneous albinism in thirty-six patients in Guangxi, China. Peripheral venous blood samples were collected from these unrelated patients. The TYR and OCA2 genes of all individuals were analyzed by direct DNA sequencing and the sequences compared with are reference database and bioinformatics analysis. RESULTS: Among the 36 OCA patients, 8(22.2%) were found mutations on TYR gene, 28 (77.8%) on OCA2. And we identified Twenty-seven different TYR and OCA2 mutations in these patients, including one novel TYR framshift mutation c.561_562insTTATTATGTGTCAAATTATCCCCCA, three novel OCA2 mutations: one nonsense mutation c.2195C > G(p.S732X), one deletation mutation(c.1139-1141delTGG), one missense mutations c.2495A > C(p.H832P). The population screening and the bioinformatic analysis to determined the effects of the mutations, which revealed these four novel mutations were pathogenic. CONCLUSIONS: This study expands the mutation spectrum of oculocutaneous albinism. Four novel mutational alleles c.1139-1141delTGG, c.1832 T > C and c.2195C > G and of the OCA2 gene and c.561_562insTTATTATGTGTCAAATTATCCCCCA of TYR were associated with OCA. The genotype-phenotype correlations suggest that molecular diagnosis is more accurate and important in OCA.

Oculocutaneous albinism and consanguineous marriage among Spanish Gitanos or Calé--a study of 83 cases.

This paper studies 83 cases of oculocutaneous albinism (OCA) in family networks of Gitanos in southeastern Spain, and analyzes their sustained inbreeding patterns and complex genealogical relationships. It is based in the family and genealogy reconstitution of the Gitano population of 22 contiguous localities using ethnographic and historical demography methods. The study found a prevalence of OCA among Gitanos in the area of about 1: 1,200. Most of the cases belong to three extended kin networks in which consanguineous marriages have been common for generations. In these networks there are other cases of visual and auditive congenital anomalies, and other birth defects such as brachydactily, polydactily, neurological defects, Potter Sequence, etc. In 61 OCA cases it was possible to trace inbreeding links with a depth of three to nine generations. For these cases the estimated alpha (average of the inbreeding coefficient, F) is 0.0222. Relationships between the parents of people affected are of three types: close, as between first or second cousins; distant, as between third or fourth cousins, and non-existent, as in mixed marriages. In most cases, however, persons with albinism are linked by multiple consanguineous links. Albinism seems to be a visible example of a high prevalence of birth defects in this minority, associated with founder effects, sustained inbreeding and high fertility rates. These conditions derive from Gitano's marriage preferences and pronatalist strategies. In turn, these strategies have to be related to the exclusion, persecution and segregation that Spanish Gypsies have suffered for centuries.

TYPES OF ALBINISM IN THE BLACK SOUTHERN AFRICA POPULATION.

BACKGROUND: Oculocutaneous albinism (OCA) is the most common inherited disorder in Southern African blacks and several types have been described. Molecular techniques, where available, can be used to confirm a clinical diagnosis and the type of OCA, if necessary, and for prenatal diagnosis. OBJECTIVES: To investigate and classify the different types of albinism commonly found and to determine the clinical implications for each type. DESIGN: A descriptive survey. SETTING: Gauteng province, South Africa, and Lesotho. SUBJECTS: Three groups of subjects with OCA (96 from a genetics clinic, 62 from a dermatology clinic, and 31 from community surveys) from the black African population participated. MAIN OUTCOME MEASURES: Subjects underwent clinical and/or dermatological examinations and were then classified according to type of OCA. RESULTS: Four forms of OCA were identified: most (82%) subjects had OCA2 (a tyrosinase- positive type) with three sub-types: those without large freckles (ephelides) on exposed areas (named OCA 2a in this study), those with such freckles (named OCA 2b), and those with brown albinism (BOCA); the remainder had red/rufous albinism, ROCA (OCA 3). The four forms could be distinguished from each other clinically without using molecular genetic testing. CONCLUSION: The most common types of albinism found in the black population of Southern Africa are OCA2 and OCA3. Given the high prevalence of the disorder, together with the high risk of skin cancer, and the recent persecution of affected individuals in certain East African countries, these findings and their clinical implications have significance in terms of both education and awareness for health professionals and lay people caring for those with albinism.

High resolution mapping of OCA2 intragenic rearrangements and identification of a founder effect associated with a deletion in Polish albino patients.

Oculocutaneous albinism type 2 (OCA2) represents about 30% of OCA worldwide. Using quantitative multiplex fluorescent PCR and very high-resolution array-CGH focussed on the OCA2 gene and surrounding regions in 15q12, we identified new rearrangements. Deletion 1, encompassing exons 3-20, was present in three patients (including one in the homozygous state), and Deletion 2 (exons 1-20) was found in one patient (heterozygous state). The duplication (exons 3-20) was found in one patient in the homozygous state. Using 14 microsatellite markers we determined haplotypes associated with these rearrangements. Deletion 1 was associated with the same haplotype in three patients who were all of Polish origin, which is strongly in favour of a founder effect. Deletion 2 was associated with a distinct haplotype. The homozygous duplication was inherited from the two unrelated parents of the patients on two different haplotypes. Analysis of the sequences around the breakpoints of these rearrangements showed that all occurred within complex arrays of repetitive sequences. The combined use of very high-resolution array-CGH and of microsatellites (including new intragenic ones described here) constitutes a powerful approach for the precise characterization of OCA2 rearrangements, which have been found in more than 20% of OCA2 patients.

Squamous-cell carcinoma in situ in a patient with oculocutaneous albinism.

A 36-year-old African man from Guinea with a history of albinism presented with a many-year history of scaling and erythema of the face, neck, and arms. The patient had light eyes, hair, and skin. Physical examination showed extensive photodamage. A skin biopsy specimen from the posterior aspect of the lower leg showed a squamous-cell carcinoma in situ. The most common types of oculocutaneous albinism (OCA), OCA 1 and OCA 2, are autosomal recessive disorders of pigmentation that commonly affect the skin, hair, eyes, and ears. Photodamage and skin cancers plague patients with albinism. In Africa, where albinism is prevalent, albinos face a myriad of social and medical issues. Skin cancer surveillance is an important consideration for albinos, and sun protection is paramount.

Comprehensive analysis of the molecular basis of oculocutaneous albinism in Indian patients lacking a mutation in the tyrosinase gene.

BACKGROUND: Oculocutaneous albinism (OCA) refers to a group of inherited disorders where the patients have little or no pigment in the eyes, skin and hair. Mutations in genes regulating multi-step melanin biosynthesis are the basis of four 'classical' OCA types with overlapping clinical features. There are a few reports on defects in TYR and a single report on SLC45A2 in Indians affected with OCA but no report on OCA2 (a major locus related to the disease) and TYRP1. OBJECTIVES: To assess and describe a comprehensive picture of the molecular genetic basis of OCA among Indians with no apparent mutations in TYR. METHODS: Twenty-four affected pedigrees from 14 different ethnicities were analysed for mutations in OCA2, TYRP1, SLC45A2 and SLC24A5 using the polymerase chain reaction-sequencing approach. RESULTS: Two splice-site and four missense mutations were detected in OCA2 in seven unrelated pedigrees, including four novel mutations. Haplotype analysis revealed a founder mutation (Ala787Thr) in two unrelated families of the same ethnicity. A patient homozygous for a novel SLC45A2 mutation also harboured a novel OCA2 defect. No mutation was detected in TYRP1 or SLC24A5. CONCLUSIONS: Our results suggest that an OCA2 gene defect is the second most prevalent type of OCA in India after TYR. The presence of homozygous mutations in the affected pedigrees underscores the lack of intermixing between the affected ethnicities. Direct detection of the genetic lesions prevalent in specific ethnic groups could be used for carrier detection and genetic counselling to contain the disease.

Identification of two Chinese oculocutaneous albinism type 6 patients and mutation updates of the SLC24A5 gene.

Oculocutaneous albinism (OCA) is a rare and heterogeneous disorder characterized by hypopigmentation of the skin, hair and eyes. Thirty OCA type 6 (OCA6) patients with 24 mutations in SLC24A5 have been reported across various populations; however, only one patient has been identified in a Chinese population. This study identifies two novel SLC24A5 frame-shift variants in two unrelated Chinese patients and both are predicted to be pathogenic by American College of Medical Genetics guidelines. The genotypes and phenotypes of all three Chinese OCA6 patients are unique compared with those identified in other populations. All of the mutations identified to date in Chinese OCA6 patients are predicted to be non-functional, a finding that is useful in guiding genetic diagnosis and counseling for OCA6 in China.

Tyrosinase (TYR) gene sequencing and literature review reveals recurrent mutations and multiple population founder gene mutations as causative of oculocutaneous albinism (OCA) in Pakistani families.

PURPOSE: To investigate eight previously unreported Pakistani families with genetically undefined OCA for mutations in TYR. METHODS: Sanger sequencing of TYR has been performed in eight families with OCA phenotype. Mutation analysis was performed to establish the pathogenic role of novel mutation. Bioinformatics analysis was performed to predict the structural and functional impacts on protein due to the mutation. RESULTS: In this study, we identified six likely pathogenic variants of TYR (c.272 G>A, c.308 G>A, c.346C>T, c.715 C>T, c.832 C>T and c.1255 G>A), including one novel variant (c.308 G>A; p.Cys103Tyr), segregating as appropriate in each family. Cys103 lies in the highly conserved region of the tyrosinase enzyme, and p.Cys103Tyr is predicted to disturb enzymatic function via alteration of the configurational orientation of TYR leading to a more rigid polypeptide structure. We have also reviewed the mutation spectrum of TYR in Pakistani ethnicity. Published data on OCA families proposed that ~40% have been associated with genetic variations in the TYR gene. The mutations reported in this study have now been described with varying frequencies in Pakistani families, including very rare/unique mutations. CONCLUSION: A literature review of TYR gene mutations in Pakistani populations, combined with our genetic data, identified a number of gene mutations likely to represent regional ancestral founder mutations of relevance to Pakistani populations, in addition to sporadic and recurrent 'hotspot' mutations present repeatedly in other regions worldwide.

Identification of Five Novel Variants in Chinese Oculocutaneous Albinism by Targeted Next-Generation Sequencing.

BACKGROUND: The diagnosis of oculocutaneous albinism (OCA) is established using clinical signs and symptoms. OCA is, however, a highly genetically heterogeneous disease with mutations identified in at least nineteen unique genes, many of which produce overlapping phenotypic traits. Thus, differentiating genetic OCA subtypes for diagnoses and genetic counseling is challenging, based on clinical presentation alone, and would benefit from a comprehensive molecular diagnostic. AIM: To develop and validate a more comprehensive, targeted, next-generation-sequencing-based diagnostic for the identification of OCA-causing variants. MATERIALS AND METHODS: The genomic DNA samples from 28 OCA probands were analyzed by targeted next-generation sequencing (NGS), and the candidate variants were confirmed through Sanger sequencing. RESULTS: We observed mutations in the TYR, OCA2, and SLC45A2 genes in 25/28 (89%) patients with OCA. We identified 38 pathogenic variants among these three genes, including 5 novel variants: c.1970G>T (p.Gly657Val), c.1669A>C (p.Thr557Pro), c.2339-2A>C, and c.1349C>G (p.Thr450Arg) in OCA2; c.459_470delTTTTGCTGCCGA (p.Ala155_Phe158del) in SLC45A2. CONCLUSION: Our findings expand the mutational spectrum of OCA in the Chinese population, and the assay we developed should be broadly useful as a molecular diagnostic, and as an aid for genetic counseling for OCA patients.

Albinism in Africa as a public health issue.

BACKGROUND: Oculocutaneous albinism (OCA) is a genetically inherited autosomal recessive condition and OCA2, tyrosine-positive albinism, is the most prevalent type found throughout Africa. Due to the lack of melanin, people with albinism are more susceptible to the harmful effects of ultraviolet radiation exposure. This population must deal with issues such as photophobia, decreased visual acuity, extreme sun sensitivity and skin cancer. People with albinism also face social discrimination as a result of their difference in appearance. The World Health Organization is currently investigating the issues concerning this vulnerable population. METHODS: Systematic electronic search of articles in PubMed concerning albinism in Africa. Furthermore, a World Health Organization (WHO) pilot survey of albinism was drafted in English, French and Portuguese, and distributed to African countries through WHO African Regional Offices (AFRO) in an attempt to gather further information on albinism. RESULTS: Epidemiologic data on albinism, such as prevalence, were available for South Africa, Zimbabwe, Tanzania and Nigeria. Prevalences as high as 1 in 1,000 were reported for selected populations in Zimbabwe and other specific ethnic groups in Southern Africa. An overall estimate of albinism prevalences ranges from 1/5,000-1/15,000. In addition, both the literature review and the survey underscored the medical and social issues facing people with albinism. CONCLUSION: The estimated prevalence of albinism suggests the existence of tens of thousands of people living with albinism in Africa. This finding reiterates the need for increased awareness of and public health interventions for albinism in order to better address the medical, psychological and social needs of this vulnerable population.

[A novel P gene mutation in a Chinese family with oculocutaneous albinism].

OBJECTIVE: To investigate gene mutations of a consanguineous family with two oculocutaneous albinism (OCA) patients. METHODS: Genomic DNA was prepared from peripheral leukocytes. All of the exons and flanking introns of P gene and TYR gene were PCR-direct-sequenced. Hha I restriction fragment length polymorphism in codon 787 of the P gene was studied in the family and 102 unrelated normal Chinese individuals. RESULTS: Although no mutations were found in TYR gene, a missense mutation A787T was found in P gene. Two patients of the family were both homozygous for A787T. Their parents and brother were heterozygous for the mutation. The mutation was not observed among 102 normally pigmented subjects. CONCLUSION: The A787T mutation is not a common polymorphism among normal Chinese and it seems most likely to be a pathological OCA2 mutation. This is the first report on the study of gene diagnosis in Chinese OCA2 patients.

P gene mutations associated with oculocutaneous albinism type II (OCA2).

Oculocutaneous albinism type II (OCA2) is the most common form of albinism in humans. OCA2 has been previously associated with mutations of the P gene, the human homologue to the murine pink-eyed dilution gene. The P gene encodes a 110 kDa protein containing 12 potential membrane spanning domains and is associated with melanosomal membranes. The specific function of the P protein is currently unknown but is thought to be involved in tyrosinase processing and transport. We report nine novel mutations in the P gene associated with OCA2. These include two missense mutations, c.1938A>C (p.Ile646Val) and c.1556T>C (p.Val519Ala); one nonsense mutation c.612G>A (p.Trp204X); five frameshift mutations: c.2372_2373delTC, c.1555delG, c.1938_1939insC, c.2050delT, and c.1045_1046delAT; and a splice site mutation c.1951+1G>A. We also report 12 novel polymorphisms including one amino acid substitution, c.2365_2366GC>CA (p.Ala789Glu). At present, there is no functional assay to determine if a mutation is truly pathogenic. The presence of numerous polymorphisms of the P gene in the coding region, several of which result in amino acid substitutions, makes molecular diagnosis problematic. To ensure accurate molecular diagnosis, further mutational analysis will be necessary to produce a comprehensive list of mutations associated with OCA2. This information will also help define the critical functional domains of the P protein. Mutations associated with OCA2 can be found in the Albinism Database (http://albinismdb.med.umn.edu).

Oculocutaneous albinism type 3: a Japanese girl with novel mutations in TYRP1 gene.

BACKGROUND: Oculocutaneous albinism (OCA) type 3 caused by mutations of the TYRP1 gene is an autosomal recessive disorder of pigmentation characterized by reduced biosynthesis of melanin pigment in the skin, hair, and eye. The clinical phenotype has been reported as mild in Caucasian OCA3 patients. OBJECTIVE: We had the opportunity to examine a Japanese girl with OCA3 and investigated activity of TYRP1 protein derived from the mutant allele detected in the patient. METHODS: Mutation search for OCA responsible genes was done. A mutant allele with a missense mutation was analyzed using melanocyte cultures (b cells) established from a mouse model of OCA3. RESULTS: Compound heterozygous mutations, p.C30R and p.367fsX384, were detected in the Japanese girl. Then we revealed that the missense mutation, p.C30R, was functionally incapable of melanin synthesis with in vitro experiments. CONCLUSION: This is the first report of the occurrence of OCA3 in Japanese population.

A comprehensive analysis reveals mutational spectra and common alleles in Chinese patients with oculocutaneous albinism.

Oculocutaneous albinism (OCA) is a heterogeneous recessive disorder with hypopigmentation in the skin, hair, and eyes. At least 16 genes have been identified as causative genes for human OCA. No comprehensive analysis has been conducted to study the spectral distribution of OCA in Chinese patients. We screened 127 unrelated and unselected Chinese OCA patients for mutations in the TYR, OCA2, TYRP1, SLC45A2, and HPS1 genes. We found that the spectrum of mutational genes and alleles of OCA is population specific. OCA1 is the most common (70.1% of cases) form of Chinese OCA, whereas OCA2, OCA4, and HPS1 account for 10.2%, 12.6%, and 1.6%, respectively. No apparent pathological mutation of TYRP1 has been found. Thirty-eight previously unreported mutational alleles were identified from these OCA patients and were not found in 100 nonalbinism subjects. Of the TYR mutational alleles, 81.1% were clustered on exons 1 and 2. Ten common alleles account for 74.6% of the mutational TYR alleles in Chinese OCA1 patients. The p.D160H allele accounts for 55.6% of the mutational SLC45A2 alleles in Chinese OCA4 patients. These results provide useful information for the establishment of an optimized strategy of gene diagnosis and genetic counseling of Chinese OCA patients.