The degradation of TYR variants derived from Chinese OCA families is mediated by the ERAD and ERLAD pathway.

Oculocutaneous albinism (OCA) is a genetically heterogeneous group of autosomal recessive disorders, which presents with decreased or absent pigmentation in the hair, skin, and eyes. OCA1, as a subtype of OCA, is caused by mutations in the tyrosinase gene (TYR). In this study, we performed in vitro functional analysis of eight TYR variants (one frameshift variant: c.929dupC (p.Arg311Lysfs*7); seven missense variants: c.896G>A (p.Arg299His), c.1234C>A (p.Pro412Thr), c.1169A>G (p.His390Arg), c.937C>A (p.Pro313Thr), c.636A>T (p.Arg212Ser), c.623 T>G (p.Leu208Arg), c.1325C>A (p.Ser442Tyr)) identified in Chinese OCA families. TYR plasmids were transfected into HEK 293 T cells to explore the effects of TYR variants on their processing, protein expression, activity, and degradation. The results showed that all eight variants caused TYR to be retained in the endoplasmic reticulum (ER), processing was blocked, and TYR activity almost disappeared; the frameshift variant caused the size of the TYR protein to be reduced by about 30KD, and the protein expression of the remaining seven missense variants was reduced; the ER-associated degradation (ERAD) pathway mediates the degradation of TYR variants that occur on the Tyrosinase copper-binding domain, while the degradation of TYR variants that are not located on that domain may be mediated by a new degradation pathway--ER-to-lysosome-associated degradation (ERLAD). In summary, TYR variants affected their protein processing and activity, and may also induce ER stress and trigger degradation through the ERLAD pathway in addition to the ERAD degradation pathway, providing new insights into the potential pathogenic mechanism for OCA1 caused by TYR variants.

Modulating OCA2 Expression as a Promising Approach to Enhance Skin Brightness and Reduce Dark Spots.

The oculocutaneous albinism II (OCA2) gene encodes a melanosomal transmembrane protein involved in melanogenesis. Recent genome-wide association studies have identified several single nucleotide polymorphisms within OCA2 genes that are involved in skin pigmentation. Nevertheless, there have been no attempts to modulate this gene to improve skin discoloration. Accordingly, our aim was to identify compounds that can reduce OCA2 expression and to develop a formula that can improve skin brightness and reduce hyperpigmented spots. In this study, we investigated the effects of OCA2 expression reduction on melanin levels, melanosome pH, and autophagy induction through siRNA knockdown. Additionally, we identified several bioactives that effectively reduce OCA2 expression. Ultimately, in a clinical trial, we demonstrated that topical application of those compounds significantly improved skin tone and dark spots compared to vitamin C, a typical brightening agent. These findings demonstrate that OCA2 is a promising target for the development of efficacious cosmetics and therapeutics designed to treat hyperpigmentation.

Mutational spectrum associated with oculocutaneous albinism and Hermansky-Pudlak syndrome in nine Pakistani families.

BACKGROUND: Oculocutaneous albinism (OCA) is a genetically heterogeneous condition that is associated with reduced or absent melanin pigment in the skin, hair, and eyes, resulting in reduced vision, high sensitivity to light, and rapid and uncontrolled eye movements. To date, seventeen genes have been associated with OCA including syndromic and non-syndromic forms of the condition. METHODS: Whole exome sequencing (WES) was performed to identify pathogenic variants in nine Pakistani families with OCA, with validation and segregation of candidate variants performed using Sanger sequencing. Furthermore, the pathogenicity of the identified variants was assessed using various in-silico tools and 3D protein structural analysis software. RESULTS: WES identified biallelic variants in three genes explaining the OCA in these families, including four variants in TYR, three in OCA2, and two in HPS1, including two novel variants c.667C > T: p.(Gln223*) in TYR, and c.2009 T > C: p.(Leu670Pro) in HPS1. CONCLUSIONS: Overall, this study adds further knowledge of the genetic basis of OCA in Pakistani communities and facilitates improved management and counselling services for families suffering from severe genetic diseases in Pakistan.

Altered Functional Responses of the Retina in B6 Albino Tyrc/c Mice.

Purpose: Mammals with albinism present low visual discrimination ability and different proportions of certain retinal cell subtypes. As the spatial resolution of the retina depends on the visual field sampling by retinal ganglion cells (RGCs) based on the convergence of upstream cell inputs, it could be affected in albinism and thus modify the RGC function. Methods: We used the Tyrc/c line, a mouse model of oculocutaneous albinism type 1 (OCA1), carrying a tyrosinase mutation, and previously characterized by a total absence of pigment and severe visual deficits. To assess their retinal function, we recorded the light responses of hundreds of RGCs ex vivo using multi-electrode array (MEA). We estimated the receptive field (RF)-center diameter of Tyr+/c and Tyrc/c RGCs using a checkerboard stimulation before simultaneously stimulating the center and surround of RGC RFs with full-field flashes. Results: Following checkerboard stimulation, the RF-center diameters of RGCs were indistinguishable between Tyrc/c and Tyr+/c retinas. Nevertheless, RGCs from Tyrc/c retinas presented more OFF responses to full-field flashes than RGCs from Tyr+/c retinas. Unlike Tyr+/c retinas, very few OFF-center RGCs switched polarity to ON or ON-OFF responses after full-field flashes in Tyrc/c retinas, suggesting a different surround suppression in these retinas. Conclusions: The retinal output signal is affected in Tyrc/c retinas, despite intact RF-center diameters of their RGCs. Adaptive mechanisms during development are probably responsible for this change in RGC responses, related to the absence of ocular pigments.

After an initial Hermansky-Pudlak syndrome clinical diagnosis, molecular testing reveals variants for oculocutaneous albinism type 1B: A case report.

BACKGROUND: Albinism is a heterogeneous condition in which patients present complete absence, reduction, or normal pigmentation in skin, hair and eyes in addition to ocular defects. One of the heterogeneous forms of albinism is observed in Hermansky-Pudlak syndrome (HPS) patients. HPS is characterized by albinism and hemorrhagic diathesis due to the absence of dense bodies in platelets. METHODS: In this report, we describe a case of a pair of Puerto Rican siblings with albinism that were clinically diagnosed with HPS during childhood. Since they did not harbor the founder changes in the HPS1 and HPS3 genes common in Puerto Ricans, as adults they wanted to know the type of albinism they had. We performed exome sequencing, validation by PCR, and cloning of PCR products followed by Sanger sequencing in the family members. RESULTS: We discovered no mutations that could explain an HPS diagnosis. Instead, we found the siblings were compound heterozygotes for 4 variants in the Tyrosinase gene: c.-301C>T, c.140G>A (rs61753180; p.G47D), c.575C>A (rs1042602; p.S192Y), and c.1205G>A (rs1126809; p.R402Q). Our results show that the correct diagnosis for the siblings is OCA1B. CONCLUSION: Our study shows the importance of molecular testing when diagnosing a rare genetic disorder, especially in populations were the disease prevalence is higher.

Identifying genetic defects in oculocutaneous albinism patients of West Bengal, Eastern India.

BACKGROUND: Oculocutaneous albinism (OCA) is a congenital heterogeneous group of autosomal recessive disorders characterized by the absence or loss of melanin in the skin, eyes and hair of the affected individuals. Based on the mutated gene, OCA has been classified into eight sub-types (OCA1-8) with overlapping clinical phenotypes. Mutations in the TYR gene cause OCA1, the most prevalent OCA worldwide including India. Mutations in OCA2 and SLC45A2, both of which regulate melanosomal pH that is critical to TYR activity, cause OCA2 and OCA4 respectively, the other common OCA subtypes in India. METHODS: In the present study, we have included 54 OCA-affected cases from 41 unrelated families representing 16 different marriage/ethnic groups from 17 districts of West Bengal, India. We pursued a PCR-sequencing based approach followed by bioinformatic analysis to identify mutations in TYR, OCA2 and SLC45A2 genes. RESULTS: Mutations were detected in 27 of the 54 (50%) OCA patients from 18 unrelated families, representing 9 different marriage/ethnic groups from 11 districts of West Bengal. Three TYR variants: NM_000372.4: c.391 A > G, NP_000363.1: p. Lys131Glu; NM_000372.4: c.1037G > T; NP_000363.1: p. Gly346Val, NM_000372.4: c.715 C > T; NP_000363.1:p.Arg239Trp was identified for the first time in Eastern Indian OCA cases. A novel nonsense variant: NM_016180.5: c.389 T > A, NP_057264.4: p. Leu130* and a novel synonymous variation NM_016180.5: c.1092 A > G; NP_057264.4: p.364E = were identified in SLC45A2. Additionally, NM_016180.5: c.904A > T; NP_057264.4: p. Thre302Ser was identified for the first time in any Eastern Indian OCA case. We identified 2 previously reported mutations in OCA2. In concordance with previous reports, NM_000372.4: c.832C > T, NP_000363.1: p. (Arg278*) was the commonest TYR mutation. CONCLUSION: The results of our study enrich the mutational spectrum of the known OCA causing genes in Eastern India, which would facilitate accurate diagnosis, familial screening, carrier detection and containment of the disease load.

Functional analysis of two mutation sites in the OCA2 gene.

To analyse the genetic aetiology of a child with oculocutaneous albinism and to explore the effects of two mutation sites on the function of the OCA2 protein at the mRNA and protein levels via the use of recombinant carriers in vitro. Whole-exome sequencing (WES) and Sanger sequencing were used to analyse the pathogenic genes of the child and validate the mutations in the parents. pEGFP and phage vectors carrying wild-type and mutant OCA2 were constructed using the coding DNA sequence (CDS) of the whole gene-synthesized OCA2 as a template and transfected into HEK293T cells, after which expression analysis was performed. The child in this study was born with white skin, hair, eyelashes, and eyebrows and exhibited nystagmus. Genetic analysis indicated that the child carried two heterozygous mutations: c.1079C > T (p.Ser360Phe) of maternal origin and c.1095_1103delAGCACTGGC (p.Ala366_Ala368del) of paternal origin, conforming to an autosomal recessive inheritance pattern. In vitro analysis showed that the expression of the c.1079C > T (p.Ser360Phe) mutant did not significantly change at the mRNA level but did increase at the protein level, suggesting that the mutation may lead to enhanced protein stability, and the c.1095_1103delAGCACTGGC (p.Ala366_Ala368del) mutation resulted in the loss of three amino acids in exon 10, producing a truncated protein. In vitro expression analysis also revealed that the expression of the mutant gene was significantly downregulated at both the mRNA and protein levels, suggesting that the mutation can simultaneously produce truncated proteins and lead to protein degradation. This case study enriches the phenotypic spectrum of OCA2 gene disease. In vitro expression analysis confirmed that both mutations affect protein expression, providing a theoretical basis for analysing the pathogenicity of these two mutations.

Genetic Linkage between CAPN5 and TYR Variants in the Context of Albinism and Autosomal Dominant Neovascular Inflammatory Vitreoretinopathy Absence: A Case Report.

We present a case involving a patient whose clinical phenotype aligns with oculocutaneous albinism (OCA), yet exhibits a complex genotype primarily characterized by variants of unknown significance (VUS). An 11-year-old boy manifested iris hypopigmentation and translucency, pronounced photophobia, diminished visual acuity and stereopsis, nystagmus, reduced pigmentation of the retina, and foveal hypoplasia. Genetic testing was performed. A heterozygous missense VUS CAPN5 c.230A>G, p.(Gln77Arg), a heterozygous missense VUS TYR c.1307G>C, p.(Gly436Ala), and a heterozygous missense variant TYR c.1205G>A, p.(Arg402Gln) which was classified as a risk factor, were identified. We hypothesized that the TYR c.1307G>C, p.(Gly436Ala) variant is in genetic disequilibrium with the TYR c.1205G>A, p.(Arg402Gln) variant leading to deficient expression of melanogenic enzymes in retinal cells, resulting in the manifestation of mild OCA. Additionally, this study represents the case where we did not detect chiasmal misrouting in visual evoked potentials, nor did we observe a shift in the distribution of ganglion cell thickness from a temporal to a central position. Moreover, our patient's case supports the probable benign nature of the CAPN5 c.230A>G, p.(Gln77Arg) variant.

Successful treatment of retinopathy of prematurity in oculocutaneous albinism with OCA2 variants: a case report and review of literature.

BACKGROUND: Oculocutaneous albinism (OCA) is a group of autosomal recessive hereditary disorders that affect melanin biosynthesis, resulting in abnormalities in hair, skin, and eyes. Retinopathy of prematurity (ROP) is a proliferative retinopathy mainly observed in premature infants with low birth weight and early gestational age, but it can also affect full-term infants or children with normal weight, particularly in developing countries. The coexistence of ROP and OCA is rare. There is limited documentation regarding treatment approaches, with few studies reporting positive outcomes with laser treatment due to the absence of melanin pigment. This study discusses the treatment challenges in a female infant diagnosed with ROP and OCA, and underscores the importance of genetic analysis in guiding therapeutic decisions for this rare comorbid condition. CASE PRESENTATION: The study presents a case of ROP occurring concurrently with OCA. Genetic testing revealed two variants, c.727C > T (p.R243C) and c.1832 T > C (p.L611P), in the OCA2 gene, inherited from the patient's mother and father, respectively. The identified mutations were consistent with a diagnosis of OCA2, classified as a subtype of OCA. The patient initially received intravitreal anti-vascular endothelial growth factor (anti-VEGF) injection, followed by laser photocoagulation therapy for a recurrent event. A favorable outcome was observed during the 2-month follow-up period. CONCLUSIONS: The co-occurrence of ROP and OCA is a rare phenomenon, and this is the first recorded case in the Chinese population. The current case supports the use of laser as the primary treatment modality for ROP in OCA2 patients with partial pigmentation impairment. Furthermore, genetic analysis can aid in predicting the effectiveness of laser photocoagulation in this patient population.

Nystagmus and Foveal Hypoplasia in a Carrier of Oculocutaneous Albinism.

We report a 23-year-old female patient with ophthalmic features of albinism, including refractive errors, nystagmus, depigmented fundus, and foveal hypoplasia. She presented for a rhegmatogenous retinal detachment, which was surgically reattached with no complications. Further genetic testing revealed the presence of a heterozygous pathogenic oculocutaneous albinism OCA2 gene mutation, conferring carrier status. To the best of our knowledge, this is the first reported case of typical ocular phenotype of albinism, specifically nystagmus, in a patient who is carrier for oculo-cutaneous albinism. Further research is required to expand the genotype-phenotype relationship in carriers of oculocutaneous albinism. [Ophthalmic Surg Lasers Imaging Retina 2024;55:349-353.].

Genotypic spectrum of albinism in Mali.

Albinism is a phenotypically and genetically heterogeneous condition characterized by a variable degree of hypopigmentation and by ocular features leading to reduced visual acuity. Whereas numerous genotypic studies have been conducted throughout the world, very little is known about the genotypic spectrum of albinism in Africa and especially in sub-Saharan Western Africa. Here we report the analysis of all known albinism genes in a series a 23 patients originating from Mali. Four were diagnosed with OCA 1 (oculocutaneous albinism type 1), 17 with OCA 2, and two with OCA 4. OCA2 variant NM_000275.3:c.819_822delinsGGTC was most frequently encountered. Four novel variants were identified (two in TYR, two in OCA2). A deep intronic variant was found to alter splicing of the OCA2 RNA by inclusion of a pseudo exon. Of note, the OCA2 exon 7 deletion commonly found in eastern, central, and southern Africa was absent from this series. African patients with OCA 1 and OCA 4 had only been reported twice and once, respectively, in previous publications. This study constitutes the first report of the genotypic spectrum of albinism in a western sub-Saharan country.

Clinical and mutational characteristics of oculocutaneous albinism type 7.

The purpose of this paper is to expand on the phenotype of oculocutaneous albinism type 7 (OCA7). We described three patients with OCA7: two from a consanguineous family of Kurdish origin and one patient of Dutch origin. We compared them with all patients described to date in the literature. All newly described patients had severely reduced visual acuity (VA), nystagmus, hypopigmentation of the fundus, severe foveal hypoplasia, and chiasmal misrouting. None had iris translucency. All patients had normal pigmentation of skin and hair. We found one novel mutation in the Dutch patient: c.565G > A; p.(Gly189Ser). We compared our patients to the 15 described in the literature to date. All 18 patients had substantially pigmented skin and hair, very poor VA (0.4-1.3 logMAR), nystagmus, (mild) ocular hypopigmentation, foveal hypoplasia, and misrouting. Although pigmentation levels were mildly affected in OCA7, patients had a severe ocular phenotype with VA at the poorer end of the albinism spectrum, severe foveal hypoplasia, and chiasmal misrouting. OCA7 patients had a phenotype restricted to the eyes, and similar to that of X-linked ocular albinism. We therefore propose to rename the disorder in ocular albinism type 2. Unfolding the role of LRMDA in OCA7, may bring us a step closer in identifying the responsible factors for the co-occurrence of foveal hypoplasia and misrouting.

Genetic analysis of albinism caused by compound heterozygous mutations of the OCA2 gene in a Chinese family.

BACKGROUND: Oculocutaneous albinism (OCA) is a group of rare genetic disorders characterized by a reduced or complete lack of melanin in the skin, hair, and eyes. Patients present with colorless retina, pale pink iris, and pupil, and fear of light. The skin, eyebrows, hair, and other body hair are white or yellowish-white. These conditions are caused by mutations in specific genes necessary for the production of melanin. OCA is divided into eight clinical types (OCA1-8), each with different clinical phenotypes and potential genetic factors. This study aimed to identify the genetic causes of non-syndromic OCA in a Chinese Han family. METHODS: We performed a comprehensive clinical examination of family members, screened for mutation loci using whole exome sequencing (WES) technology, and predicted mutations using In silico tools. RESULTS: The patient's clinical manifestations were white skin, yellow hair, a few freckles on the cheeks and bridge of the nose, decreased vision, blue iris, poorly defined optic disk borders, pigmentation of the fundus being insufficient, and significant vascular exposure. The WES test results indicate that the patient has compound heterozygous mutations in the OCA2 gene (c.1258G > A (p.G420R), c.1441G > A (p.A481T), and c.2267-2 A > C), respectively, originating from her parents. Among them, c.1258G > A (p.G420R) is a de novo mutation with pathogenic. Our analysis suggests that compound heterozygous mutations in the OCA2 gene are the primary cause of the disease in this patient. CONCLUSIONS: The widespread application of next-generation sequencing technologies such as WES in clinical practice can effectively replace conventional detection methods and assist in the diagnosis of clinical diseases more quickly and accurately. The newly discovered c.1258G > A (p.G420R) mutation can update and expand the gene mutation spectrum of OCA2-type albinism.

Oculocutaneous albinism type 4: Novel compound heterozygous mutations in the SLC45A2 gene in a Chinese case.

BACKGROUND: Oculocutaneous albinism type 4 (OCA4) is a rare autosomal recessive disorder characterized by a reduction of pigmentation in skin, hair, and eyes, and OCA4 is mainly seen in the SLC45A2 gene variants. OBJECTIVE: To report a Chinese patient suspected of oculocutaneous albinism and identify the causing mutation. METHODS: Genomic DNA was extracted from the peripheral blood samples of the patient, his parents, and elder brother. Whole exome sequencing was performed in the family, and Sanger sequencing was then used to verify the mutations. RESULTS: Compound heterozygous variants, c.1304C>A (p.S435Y) and c.301C>G (p.R101G) in SLC45A2 gene, were detected in the proband, which were inherited from his father and mother respectively. Based on the ACMG guidelines, we can interpret the c.1304C>A (p.S435Y) variant as a suspected pathogenic variant and the c.301C>G (p.R101G) variant as a clinically significant unspecified variant. The diagnosis of OCA4 is confirmed. CONCLUSION: We firstly reported this case of OCA4 with the compound heterozygous variants in the SLC45A2 gene. Our findings further enrich the reservoir of SLC45A2 mutations in OCA4.

Visual acuity improvement in children with albinism beyond the first decade of life.

PURPOSE: To determine if visual maturation continues beyond the first decade of life in children with albinism and whether this is related to albinism type, presence of nystagmus, eye muscle surgery or refractive errors. DESIGN: Case series based on retrospective study of children with confirmed genetic diagnosis of albinism. METHODS: Clinical data were obtained from medical files of children examined during school years, including albinism type, visual acuity, eye muscle surgery, nystagmus, and others on different visits (Visit 1: ages 7-9; Visit 2: ages: 10-12; Visit 3: ages 13-16; Visit 4: ages >16). RESULTS: Seventy-five children with albinism were included in the study. Patients were divided into different groups according to the albinism type including OCA1A: 17; OCA1B: 28; OCA2: 26; HPS: 3; OCA4: 1. Follow-up ranged from 3-13 years. Progressive visual acuity improvement was seen in all three main groups. T-test paired samples showed a statistically significant improvement when comparing vision from Visit 1 and Visit 3 in both OCA1A and OCA2 groups, with a mean vision improvement of 2 lines. There was no correlation between visual improvement and refractive error, eye muscle surgery or nystagmus. CONCLUSION: An improved visual performance was seen in a large percentage of children with albinism during the second decade of life. The reason for this late improvement in vision is not clear but may be related to late foveal maturation or improvement in nystagmus with time. This information is useful for clinicians of these patients and when counseling parents.

Generation and characterization of retinal pigment epithelium from patient iPSC line to model oculocutaneous albinism (OCA)1A disease.

Oculocutaneous albinism (OCA) is characterized by reduced melanin biosynthesis affecting the retina, thus impairing visual function. The disease pathology of OCA is poorly understood at the cellular level due to unavailability of suitable biological model systems. This study aimed to develop a disease-specific in vitro model for OCA type 1A, the most severe form caused by TYR (tyrosinase) gene mutations, using retinal pigment epithelium (RPE) differentiated from patient-derived human-induced pluripotent stem cells (hiPSCs). A comparative study between healthy and OCA1A RPE cells revealed that while healthy RPE cells exhibited timely onest of pigmentation during differentiation, OCA1A RPE cells failed to pigment even after an extended culture period. This observation was validated by ultrastructural studies using electron microscopy, hinting at melanosome-specific defects. Immunocytochemistry demonstrated abnormal expression patterns of melanogenesis-specific protein markers in OCA1A RPE cells, indicating reduced or absence of melanin synthesis. Next, a quantitative assay was performed to confirm the absence of melanin production in OCA1A RPE cells. Tyrosinase assay showed no activity in OCA1A compared with healthy RPE, suggesting non-functionality of TYR, further corroborated by western blot analysis showing complete absence of the protein. Gene expression by RNA sequencing of healthy and OCA1A RPE cells uncovered differential gene expression associated with lens development, visual perception, transmembrane transporter activity, and key signaling pathways. This disease-in-a-dish model of OCA1A provides an excellent platform to understand disease mechanism, identify potential therapeutic targets, and facilitate gene therapy or gene correction.

Unveiling genetics of non-syndromic albinism using whole exome sequencing: A comprehensive study of TYR, TYRP1, OCA2 and MC1R genes in 17 families.

BACKGROUND: Oculocutaneous albinism (OCA) is a group of skin depigmentation disorders. Clinical presentation of OCA includes defects in melanocyte differentiation, melanin biosynthesis, and melanosome maturation and transport. OBJECTIVES: A molecular diagnostics study of families presenting oculocutaneous albinism. METHODS: In this study, 17 consanguineous OCA families consisting of 93 patients were investigated. Whole Exome Sequencing (WES) of the index patient in each family were performed. Short listed variants of WES were Sanger validated for Mendelian segregation in obligate carriers and other available family members. Variant prioritization and pathogenicity were classified as per the criteria of American College Medical Genetics and Genomics (ACMG). Comparative computational modelling was performed to predict the potential damaging effect of the altered proteins. RESULTS: 15 pathogenic variations: c.132 T > A, c.346C > T, c.488C > G, c.1037G > A in TYR, c.1211C > T, c.1441G > A, c.1706_1707insT, c.2020C > G, c.2402G > C, c.2430del, in OCA2, c.1067G > A in TYRP1 and c.451C > T, c.515G > T, c.766C > T, c.917G > A in MC1R genes were identified. Three variants in OCA2 gene were characterized: c.1706_1707insT, c.2430del, and c.2402G > C, all of which were not reported before in OCA families. CONCLUSION: A few studies focusing on mutation screening of OCA patients have been reported before; however, this study has uniquely presents the Pakhtun ethnic population residing on the North-Western boarder. It explains that TYR, OCA2, TYRP1, and MC1R variations lead to non-syndromic OCA phenotype The overlapping phenotypes of OCA can precisely be diagnosed for its molecular pathogenicity using WES. This study recommends WES as a first-line molecular diagnostic tool, and provides a basis for developing customized genetic tests i.e. pre-marital screening to reduce the disease burden in the future generations.

Novel compound heterozygous mutations in OCA2 gene were identified in a Chinese family with oculocutaneous albinism.

BACKGROUND: Oculocutaneous albinism (OCA) is a group of rare autosomal recessive disorders characterized by clinical genetic heterogeneity. OCA type II (OMIM: 203200) is the most common subtype among African and African Americans, primarily caused by pathogenic variants in the OCA2 (HGNC ID: 8101) gene. In this study, we presented a Chinese family with OCA and reported two novel variants in the OCA2 gene. METHODS: Whole-exome sequencing (WES) was performed to identify pathogenic variants in the proband. The candidate variants were subsequently validated using Sanger sequencing and QPCR assay. Additionally, bioinformatics analyses were employed to predict the deleteriousness and conservation of the identified mutations. RESULTS: In the 16-year-old male proband, two novel compound heterozygous OCA2 variants, NM_000275.3: c.1640T>G (NP_000266.2: p.L547R) and an exons 10-19 deletion variant, were identified. Meanwhile, a reported heterozygous variant c.1441G>A/p.A481T (NM_000275.3, NP_000266.2) in the OCA2 gene was also found in the proband. Sanger sequencing confirmed that the two variants c.1441G>A/p.A481T and c.1640T>G/p.L547R were inherited from his father. Moreover, qPCR assay revealed that the exons 10-19 deletion was inherited from the mother, his sister also carried this variant. Fortunately, the variant was not detected in the amniotic fluid of the proband's sister. Multiple online bioinformatics tools predicted the variant c.1640T>G to be damaging, leading to the replacement of a highly conserved leucine with an arginine. The gross exon 10-19 deletion in the OCA2 gene resulted in a truncated, non-functional protein losing the 3-9 transmembrane α-helices domains. According to the American College of Medical Genetics and Genomics classification, these three variants in the OCA2 gene were evaluated as likely pathogenic. CONCLUSION: This study has identified two novel compound variants in the OCA2 gene and a previously reported variant in a Chinese family with OCA. By expanding the mutation spectrum of the OCA2 gene, our findings contribute to a better understanding of the genetic basis of OCA.

TYR mutation in a Chinese population with oculocutaneous albinism: Molecular characteristics and ophthalmic manifestations.

Oculocutaneous albinism (OCA) is a rare inherited disorder characterized by a partial or complete reduction of melanin biosynthesis that leads to hypopigmentation in the skin, hair and eyes. The OCA1 subtype is caused by mutations in TYR. The purpose of this study was to investigate the genetic and clinical ophthalmic characteristics of TYR mutations in patients with OCA. Herein, 51 probands with a clinical diagnosis of OCA were enrolled. Whole-exome sequencing and comprehensive ophthalmic examinations were performed. Overall, TYR mutations were detected in 37.3% (19/51) in the patients with OCA. Fifteen patients had compound heterozygous variants, and four cases had homozygous variants. Eleven different pathogenic variants in TYR were detected in these 19 patients, with missense, insertion, delins and nonsense in 71.1% (27/38), 15.8% (6/38), 2.6% (1/38), and 10.5% (4/38), respectively. Clinical examinations revealed that 84.2% (16/19) of patients were OCA1A, and 15.8% (3/19) were OCA1B. Most TYR probands (52.6%, 10/19) had moderate vision impairment, 15.8% (3/19) had severe visual impairment, 10.5% (2/19) exhibited blindness, only 5.3% (1/19) had mild visual impairment and 15.8% (3/19) were not available. Photophobia and nystagmus were found in 100% (19/19) of the patients. In addition, grade 4 foveal hypoplasia was detected in 100% (12/12) of the patients. In conclusion: The TYR patients exhibited severe ocular phenotypes: the majority (93.8%, 15/16) of them had a moderate vision impairment or worse, and 100% (12/12) had severe grade 4 foveal hypoplasia. These novel findings could provide insight into the understanding of OCA.