Current landscape of Oculocutaneous Albinism in Japan

Unusual Autosomal Dominant Inheritance of Oculocutaneous Albinism Type 4 (OCA-4): Clinical and Functional Features From A Chinese Family

Oculocutaneous albinism (OCA) is a complex genetic disorder characterized by reduced or absent pigmentation in the skin, hair, and eyes. Among the eight known subtypes, OCA-4 is caused by a mutation in SLC45A2, which plays a crucial role in melanin biosynthesis. While autosomal recessive inheritance is the most common pattern for all OCA subtypes, autosomal dominant cases are extremely rare. We report three patients from a Chinese family exhibiting autosomal dominant OCA-4. Clinical assessments evaluated pigmentation and ocular features in affected family members. Next-generation sequencing was performed to identify pathogenic variants, and functional studies in MNT-1 cells were performed to explore the variant's biological effects. Patients exhibited mild hypopigmentation and foveal hypoplasia, consistent with the OCA-4 phenotype. Genetic analysis identified a heterozygous c.208T>C (p.Tyr70His) variant in SLC45A2, the same variant that has been previously reported in association with autosomal dominant OCA-4. Functional studies demonstrated that this variant caused protein retention in the endoplasmic reticulum, resulting in reduced melanin production. This family represents the first documented cases of autosomal dominant OCA-4 in the Chinese population and only the second reported worldwide. Our findings confirm that the p.Tyr70His variant causes autosomal dominant OCA-4. This study deepens our understanding of OCA-4's genetic mechanisms and increases the complexity of its inheritance patterns in genetic counseling.

Recent Advances in Clinical Research on Rare Intractable Hereditary Skin Diseases in Japan

Our Research Group for Rare and Intractable Skin Diseases operates within the Project for Research on Intractable Diseases of the Ministry of Health, Labour, and Welfare of Japan and is conducting research on eight rare intractable skin diseases. Five of these are monogenic disorders (epidermolysis bullosa, congenital ichthyoses, oculocutaneous albinism, pseudoxanthoma elasticum, and hereditary angioedema), and for a sixth [generalized pustular psoriasis (GPP)], genetic predisposing factors are important. This review introduces our activities for raising public awareness of these six intractable hereditary skin diseases and summarizes our recent achievements in clarifying the situation of medical treatments for these diseases in Japan. We note our current progress in elucidating the pathogeneses of these diseases and in developing new treatment methods, and we discuss our progress in establishing clinical practice guidelines. A nationwide survey on epidermolysis bullosa and a clinical survey on congenital ichthyoses are progressing. The Angioedema Activity Score and the Angioedema Quality-of-Life Questionnaire, the latter of which is a quality-of-life evaluation tool, have been established for hereditary angioedema. Registries of patients with oculocutaneous albinism and pseudoxanthoma elasticum have been created, and the registry for the latter has achieved its target of 170 cases. For GPP, the results of our survey on clinical practice were published in 2021. Information regarding all six of these hereditary skin diseases has been disseminated to academic societies, medical professionals, patients, and the general public.

Synonymous but Significant: New Findings of Pathological Variants in Hermansky-Pudlak Syndrome

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder characterized by oculocutaneous albinism and systemic complications, including bleeding tendencies. While 11 genes associated with HPS have been identified, cases of HPS5 remain exceedingly rare, particularly in Japan. Here, we report two Japanese patients with novel pathological HPS5 variants, expanding the genetic spectrum of this disorder. Both patients exhibited typical features of mild skin and hair hypopigmentation, and significant ocular involvement. Genetic analysis revealed a heterozygous nonsense variant, NG_008877.1 (NM_181507.2): c.2275G>T, in both patients, inherited from their fathers. Additionally, maternal variants NG_008877.1 (NM_181507.2): c.2952-13G>A and NG_008877.1 (NM_181507.2): c.1128A>G were identified in patient 1 and patient 2, respectively. These variants, initially presumed non-pathogenic, were found to induce alternative splicing, leading to truncated protein production. Our findings highlight the functional importance of synonymous variants and their potential role in HPS. This report represents the first documented case of a synonymous pathogenic variant associated with HPS and underscores the need for comprehensive genetic and transcriptomic analyses in rare genetic disorders.

Di-Genic Inheritance in Genodermatoses: Insights from Two Consanguineous Cases in a Reference Lebanese Center within the Middle East and North Africa (MENA) Region

INTRODUCTION

Genodermatoses refer to a group of heterogenous rare genetic diseases with cutaneous expression. Several genodermatoses present with multisystem involvement that can range from mild to life-threatening conditions leading to increased morbidity and mortality.

OBJECTIVE

Given the paucity in the literature in the field of genodermatoses, especially in the Middle East and North Africa (MENA) region, and building upon the first established genodermatoses database based in Lebanon, this study aimed to decipher the genetic basis of two different types of skin-inherited diseases (androgenic alopecia and vitiligo).

METHODS

We conducted a pilot study on two subjects with androgenic alopecia and vitiligo to investigate the possibility of a digenic inheritance model as a potential underlying mechanism for these conditions. Whole exome sequencing (WES) and Gene Expression Omnibus (GEO) DataSets were employed to validate the methodology and provide a foundation for future, larger-scale studies.

RESULTS

We identified two gene variants FOXC1(p.His484Tyr) and SMARCD1 (p.Arg351Cys) responsible for androgenic alopecia and HPS1(p.Ser566Ter) and ITK (p.Pro521Leu) responsible for vitiligo. Further analysis using GEO DataSets confirmed the association between the genes involved in each each disease.

CONCLUSION

This study identified novel candidate disease genes and inheritance model that could explain the underlying phenotypes that could open the door for a better-guided genomic approach for personalized treatment and early diagnosis.

Oncogenic genodermatoses in paediatric patients with skin of colour: a review

Cutaneous neoplasms are relatively rare in children. Most commonly, skin cancers arise through environmental factors, particularly ultraviolet radiation; thus, age is the most predictive factor in developing cutaneous carcinomas. However, children born with certain genodermatoses are significantly more likely to develop malignancies and must be carefully monitored and treated. Most published data are based mainly on signs and symptoms present in White patients. Therefore, we aim to highlight the cutaneous presentations and relative differences of these genodermatoses among patients with skin of colour, who are underrepresented in medicine. We conducted a literature review of 504 patients presented in 236 published articles. Manuscripts with accessible case reports for children aged ≤ 17 years were included. Patients with skin of colour often present with fewer classical findings and have higher incidences of scarring and dyspigmentation. There is also a higher incidence of consanguinity in affected patients. Providers who are able to recognize nonclassical signs can provide proper management and treatment regimens, potentially bringing outcomes for patients with skin of colour more in line with those of White children.

The molecular landscape of oculocutaneous albinism in India and its therapeutic implications

Oculocutaneous albinism is an inherited disorder of melanin biosynthesis, characterized by absent or reduced pigmentation of the skin, hair, and eyes. Molecular alterations of genes that cause non-syndromic albinism in Asian Indians are poorly characterized. This information would be useful for developing therapies for this disorder. We analyzed 164 persons with non-syndromic albinism, belonging to unrelated families from all parts of India, for molecular changes in the causative genes. Subjects with white hair, white skin, and red iris had their tyrosinase gene sequenced and were also tested by MLPA for deletions/duplications. Subjects with negative results or with darker skin, golden/brown or darker hair had sequencing of TYR, P, TYRP1, SLC45A2 and GPR143 genes. Pathogenic variants in TYR (OCA1) were observed in 139 (84.7%) patients, in the P gene (OCA2) in 20 (12.2%), in TYRP1 (OCA3) in two (1.2%), in SLC45A2 (OCA 4) in one (0.61%), and in GPR143 (X-linked ocular albinism) in two (1.2%) patients. Of 278 alleles with variants in TYR, 179 (64.3%) alleles had (p.R278*) alteration, suggesting the possibility of therapy with a stop codon readthrough molecule. We report 20 patients with 13 disease associated variants in the P gene and 18 novel pathogenic variants in TYR, P, TYRP1, SLC45A2 and GPR143 genes. The data are compared with those reported from India, Pakistan and rest of the world. The therapeutic options in albinism are briefly described, opening this field for future therapies.

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.

Ataxia Telangiectasia Mutated Signaling Delays Skin Pigmentation upon UV Exposure by Mediating MITF Function toward DNA Repair Mode

Skin pigmentation is paused after sun exposure; however, the mechanism behind this pausing is unknown. In this study, we found that the UVB-induced DNA repair system, led by the ataxia telangiectasia mutated (ATM) protein kinase, represses MITF transcriptional activity of pigmentation genes while placing MITF in DNA repair mode, thus directly inhibiting pigment production. Phosphoproteomics analysis revealed ATM to be the most significantly enriched pathway among all UVB-induced DNA repair systems. ATM inhibition in mouse or human skin, either genetically or chemically, induces pigmentation. Upon UVB exposure, MITF transcriptional activation is blocked owing to ATM-dependent phosphorylation of MITF on S414, which modifies MITF activity and interactome toward DNA repair, including binding to TRIM28 and RBBP4. Accordingly, MITF genome occupancy is enriched in sites of high DNA damage that are likely repaired. This suggests that ATM harnesses the pigmentation key activator for the necessary rapid, efficient DNA repair, thus optimizing the chances of the cell surviving. Data are available from ProteomeXchange with the identifier PXD041121.

Development and usability evaluation of a mHealth application for albinism self-management

BACKGROUND

Reduced or absence of melanin poses physical, social, and psychological challenges to individuals with albinism. Mobile health (mHealth) applications have the potential to improve the accessibility of information and services while reducing time and costs. This study aimed to develop and evaluate a mHealth application for self-management of albinism.

METHODS

This applied study was conducted in two stages (development and evaluation) in 2022. Initially, the functional requirements were determined, and the conceptual model of the application was then developed using Microsoft Visio 2021. In the second phase, the application was evaluated using the Mobile Application Usability Questionnaire (MAUQ) involving patients with albinism to reflect their views on the usability of the application.

RESULTS

The key capabilities of the application included: reminders, alerts, educational content, useful links, storage and exchange of images of skin lesions, specialist finder, and notifications for albinism-relevant events. Twenty-one users with albinism participated in the usability testing of the application. The users were predominantly satisfied with the application (5.53 ± 1.10; Max: 7.00).

CONCLUSIONS

The findings of this study suggest that the developed mobile application could assist individuals with albinism to effectively manage their condition by considering the users' requirements and services that the application should deliver.

Clinical and Mutation Spectrum of Autosomal Recessive Non-Syndromic Oculocutaneous Albinism (nsOCA) in Pakistan: A Review

Oculocutaneous albinism (OCA) is an autosomal recessive syndromic and non-syndromic defect with deficient or a complete lack of the melanin pigment. The characteristics of OCA appears in skin, hair, and eyes with variable degree of pigmentation. Clinical manifestations of OCA include nystagmus, photophobia, reduced visual acuity, hypo-plastic macula, and iris trans-illumination. There are eight OCA types (OCA1–8) documented with non-syndromic characteristics. Molecular studies identified seven genes linked to the OCA phenotype (TYR, OCA2, TYRP1, SLC45A2, SLC24A5, C10orf11, and DCT) and one locus (OCA5) in consanguineous and sporadic albinism. The complications of OCA result in skin cancer and variable syndromes such as Hermansky–Pudlak syndrome (HPS) Chediak–Higashi syndrome (CHS). In the Pakistani population, autosomal recessive non-syndromic OCA is common and is associated with a large number of consanguineous families, and mutations in genes of non-syndromic types are reported. This review highlights the updates on the genetic mutation of OCA genes reported from Pakistani families. Several studies reported the genetic mutations in OCA1, OCA2, OCA3, OCA4, and OCA6 albinism in Pakistani families. A locus, OCA5, was also reported from the Pakistani population, but the gene has not been identified. A new type of OCA8 was identified due to the DCT gene mutation, and it is also reviewed here.

Ophthalmological Manifestations of Oculocutaneous and Ocular Albinism: Current Perspectives

Albinism describes a heterogeneous group of genetically determined disorders characterized by disrupted synthesis of melanin and a range of developmental ocular abnormalities. The main ocular features common to both oculocutaneous albinism (OCA), and ocular albinism (OA) include reduced visual acuity, refractive errors, foveal hypoplasia, congenital nystagmus, iris and fundus hypopigmentation and visual pathway misrouting, but clinical signs vary and there is phenotypic overlap with other pathologies. This study reviews the prevalence, genetics and ocular manifestations of OCA and OA, including abnormal development of the optic chiasm. The role of visual electrophysiology in the detection of chiasmal dysfunction and visual pathway misrouting is emphasized, highlighting how age-associated changes in visual evoked potential (VEP) test results must be considered to enable accurate diagnosis, and illustrated further by the inclusion of novel VEP data in genetically confirmed cases. Differential diagnosis is considered in the context of suspected retinal and other disorders, including rare syndromes that may masquerade as albinism.

Two Novel Homozygous HPS6 Mutations (Double Mutant) Identified by Whole-Exome Sequencing in a Saudi Consanguineous Family Suspected for Oculocutaneous Albinism

Background: Oculocutaneous albinism (OCA) is an autosomal recessive disorder of low or missing pigmentation in the eyes, hair, and skin. Multiple types of OCA, including Hermansky-Pudlak syndrome 6 (HPS6), are distinguished by their genetic cause and pigmentation pattern. HPS6 is characterized by OCA, nose bleeding due to platelet dysfunction, and lysosome storage defect. To date, 25 disease-associated mutations have been reported in the HPS6 gene. Methods: DNA was extracted from proband, and whole-exome sequencing (WES) was performed using the Illumina NovaSeq platform. Bioinformatic analysis was done with a custom-designed filter pipeline to detect the causative variant. We did Sanger sequencing to confirm the candidate variant and segregation analysis, and protein-based structural analysis to evaluate the functional impact of variants. Result: Proband-based WES identified two novel homozygous mutations in HPS6 (double mutation, c.1136C>A and c.1789delG) in an OCA suspect. Sanger sequencing confirmed the WES results. Although no platelet and/or lysosome storage defect was detected in the patient or family, an oculocutaneous albinism diagnosis was established based on the HPS6 mutations. Structural analysis revealed the transformation of abnormalities at protein level for both nonsense and frameshift mutations in HPS6. Conclusion: To the best of our knowledge, the double mutation in HPS6 (p.Ser379Ter and p.Ala597GlnfsTer16) represents novel pathogenic variants, not described previously, which we report for the first time in the Saudi family. In silico analyses showed a significant impact on protein structure. WES should be used to identify HPS6 and/or other disease-associated genetic variants in Saudi Arabia, particularly in consanguineous families.

Impact of a SLC24A5 variant on the retinal pigment epithelium of a Japanese patient with oculocutaneous albinism type 6

Oculocutaneous albinism (OCA) 6 is a non-syndromic type of OCA that has distinct ocular symptoms and variable cutaneous hypopigmentation. The causative gene of OCA6 is SLC24A5, which encodes NCKX5, a K⁺ -dependent Na⁺ /Ca²⁺ exchanger 5. NCKX5 is involved in the maturation of melanosomes, but its function is still unclear. In this study, we characterized a Japanese patient with OCA6. Genetic analysis revealed compound heterozygous variants in SLC24A5, c.590 + 1dupG, and c.598G>A (p.G200R). To clarify the functional significance of the missense variant, we generated a knock-in (KI) mouse model carrying the mouse homolog of the G200R variant using the CRISPR/Cas9 system. Chemical analysis showed decreased amounts of eumelanin in the hair and skin of KI mice, while levels of benzothiazine units in pheomelanin were significantly increased in their hair. Retinal pigment was also decreased in KI mice. Notably, a histopathologic study revealed a significant pigment loss in the retinal pigment epithelium (RPE) but not in the choroid. Immunohistochemically, the expression of NCKX5 in the RPE was decreased but was maintained in the choroid of KI mice. These findings could explain the difference in phenotypic severity between eye symptoms and hypopigmentation in the skin/hair.

Role of Amine Neurotransmitters and Their Receptors in Skin Pigmentation: Therapeutic Implication

Skin pigmentation can occur due to increased melanin, including melanocyte proliferation, melanin biosynthesis, or melanocyte migration. There are many factors that influence the melanin production process, but the role of neurotransmitters in this process is still unclear. We found that histamine and serotonin influence the different stages of melanogenesis and melanogenesis, which increase melanogenesis. Since then, several related papers have been published, and from these papers, it has been recognised that the role of neurotransmitters in skin-pigment-related diseases needs to be summarised. By introducing the role of neurotransmitters in the regulation of various pigment disorders, including vitiligo and melasma, through this review, many researchers can be expected to try to apply neurotransmitter-related agonists and antagonists as treatments for skin pigment disorders.

A custom capture sequence approach for oculocutaneous albinism identifies structural variant alleles at the OCA2 locus

Oculocutaneous albinism (OCA) is a heritable disorder of pigment production that manifests as hypopigmentation and altered eye development. Exon sequencing of known OCA genes is unsuccessful in producing a complete molecular diagnosis for a significant number of affected individuals. We sequenced the DNA of individuals with OCA using short-read custom capture sequencing that targeted coding, intronic, and noncoding regulatory regions of known OCA genes, and genome-wide association study-associated pigmentation loci. We identified an OCA2 complex structural variant (CxSV), defined by a 143 kb inverted segment reintroduced in intron 1, upstream of the native location. The corresponding CxSV junctions were observed in 11/390 probands screened. The 143 kb CxSV presents in one family as a copy number variant duplication for the 143 kb region. In the remaining 10/11 families, the 143 kb CxSV acquired an additional 184 kb deletion across the same region, restoring exons 3-19 of OCA2 to a copy-number neutral state. Allele-associated haplotype analysis found rare SNVs rs374519281 and rs139696407 are linked with the 143 kb CxSV in both OCA2 alleles. For individuals in which customary molecular evaluation does not reveal a biallelic OCA diagnosis, we recommend preliminary screening for these haplotype-associated rare variants, followed by junction-specific validation for the OCA2 143 kb CxSV.

Genetics of non-syndromic and syndromic oculocutaneous albinism in human and mouse

Oculocutaneous albinism (OCA) is the most frequent presentation of albinism, a heterogeneous rare genetic condition generally associated with variable alterations in pigmentation and with a profound visual impairment. There are non-syndromic and syndromic types of OCA, depending on whether the gene product affected impairs essentially the function of melanosomes or, in addition, that of other lysosome-related organelles (LROs), respectively. Syndromic OCA can be more severe and associated with additional systemic consequences, beyond pigmentation and vision alterations. In addition to OCA, albinism can also be presented without obvious skin and hair pigmentation alterations, in ocular albinism (OA), and a related genetic condition known as foveal hypoplasia, optic nerve decussation defects, and anterior segment dysgenesis (FHONDA). In this review, we will focus only in the genetics of skin pigmentation in OCA, both in human and mouse, updating our current knowledge on this subject.