Haplotype-based analysis resolves missing heritability in oculocutaneous albinism type 1B.

Oculocutaneous albinism (OCA) is a rare disorder of pigment production. Affected individuals have variably decreased global pigmentation and visual-developmental changes that lead to low vision. OCA is notable for significant missing heritability, particularly among individuals with residual pigmentation. Tyrosinase (TYR) is the rate-limiting enzyme in melanin pigment biosynthesis and mutations that decrease enzyme function are one of the most common causes of OCA. We present the analysis of high-depth short-read TYR sequencing data for a cohort of 352 OCA probands, ∼50% of whom were previously sequenced without yielding a definitive diagnostic result. Our analysis identified 66 TYR single-nucleotide variants (SNVs) and small insertion/deletions (indels), 3 structural variants, and a rare haplotype comprised of two common frequency variants (p.Ser192Tyr and p.Arg402Gln) in cis-orientation, present in 149/352 OCA probands. We further describe a detailed analysis of the disease-causing haplotype, p.[Ser192Tyr; Arg402Gln] ("cis-YQ"). Haplotype analysis suggests that the cis-YQ allele arose by recombination and that multiple cis-YQ haplotypes are segregating in OCA-affected individuals and control populations. The cis-YQ allele is the most common disease-causing allele in our cohort, representing 19.1% (57/298) of TYR pathogenic alleles in individuals with type 1 (TYR-associated) OCA. Finally, among the 66 TYR variants, we found several additional alleles defined by a cis-oriented combination of minor, potentially hypomorph-producing alleles at common variant sites plus a second, rare pathogenic variant. Together, these results suggest that identification of phased variants for the full TYR locus are required for an exhaustive assessment for potentially disease-causing alleles.

Biallelic TYR and TKFC variants in Egyptian patients with OCA1 and new expanded TKFC features.

BACKGROUND: Oculocutaneous albinism type1 (OCA1) is caused by the TYR gene's homozygous and compound heterozygous variants. TKFC gene variants cause triokinase & FMN cyclase deficiency syndrome with variable multisystemic disorders. OBJECTIVES: To determine the potential disease-causing variants in two deceased patients presenting atypical OCA1 features by demonstrating three generations for a single family. The two deceased neonates had severe skeletal abnormalities and fatal hypertrophic cardiomyopathy. We also explored the potential mechanisms for the causative relationship between TKFC and multisystem disorders. PATIENTS AND METHODS: Due to the new emerging symptoms that weren't reported before with the TYR gene, the following methods were performed: Sanger sequencing for the TYR gene, followed by whole exome sequencing, co-segregation, and computational analyses. RESULTS: Extensive parental consanguinity was found, and consequently an autosomal recessive mode of inheritance was prioritized. Upon performing sequencing and segregation data, the following has been confirmed: positive co-segregation of nonsense homozygous NM_000372.5:c.346C > T p.(Arg116*) variant in TYR gene and multisystem disease-missense homozygous NM_015533.4:c.598G > A p.(Val200Ile) variant in TKFC gene in the two affected index patients who deceased due to hypertrophic cardiomyopathy. Using computational analysis, we found that c.598G > A p.(Val200Ile) pathogenicity has led to the failure of L2-K1 active site closure due to the potential differential fluctuation between valine and isoleucine residues. Subsequently, disruption of endogenous DHA phosphorylation was found. Two potential mechanisms exploring the causative relationship between TKFC gene and multisystem disorders have been suggested. CONCLUSIONS: This study presented a first family with the co-existence of biallelic variants in TYR and TKFC genes associating severe skeletal abnormalities and lethal hypertrophic cardiomyopathy. Neither of these genes would have been pursued in the standard genetic counseling. Such discovery is paving the way for more efficient genetic counseling. Comparing TKFC results with literature data showed that our relevant expanded TKFC variant is the 3rd worldwide.

A novel deletion in the BLOC1S6 Gene Associated with Hermansky-Pudlak syndrome type 9 (HPS-9).

BACKGROUND: Hermansky-Pudlak Syndrome (HPS), a rare autosomal recessive disorder, is characterized by oculocutaneous albinism, bleeding diathesis, and sometimes severe lung problems and inflammatory bowel disease. Symptoms include skin and hair pigmentation variations, along with visual impairments. Variants in eleven genes encoding protein complexes essential for membrane trafficking and intracellular endosomal transport pathways underlie various recognized HPS subtypes. This study focuses on HPS-9, a subtype of Hermansky-Pudlak Syndrome caused by a variant in the BLOC1S6 gene, which is a subunit of the BLOC1 complex. In this study, a novel Copy Number Variation (CNV) in the aforementioned gene in an Iranian family is reported. The study aims to better understand the etiology of HPS-9 symptoms by identifying and confirming the variant and determining whether the gene is expressed despite the deletion. There have only been five reports of this syndrome in the literature thus far. Our novel CNV represents a significant contribution to understanding the genetic basis of HPS-9. RESULTS: This study investigates a male patient presenting with albinism. Whole Exome Sequencing (WES) identified a homozygous deletion of approximately 350 bp using CNV analysis. The deletion affects the intronic region of the BLOC1S6 gene, causing uncertainties in defining the exact boundaries due to WES limitations. Primer walking and GAP-PCR techniques were used to define the deletion boundaries. Subsequent assessments of this variant across other family members helped identify homozygous affected members and heterozygous carriers. The absence of BLOC1S6 expression in the affected individual was confirmed through Real-time PCR experiments. These findings underscore the importance of understanding the implications for the patient's healthcare and potential therapeutic approaches. CONCLUSION: This study introduces a case of Hermansky-Pudlak Syndrome Type 9 (HPS-9) caused by a homozygous deletion in the BLOC1S6 gene. We identified an approximately 7-kb deletion encompassing exon 1 and the intronic region of the gene. The absence of BLOC1S6 expression, confirmed via Real-time PCR, highlights the importance of studying the pathogenicity of the deletion and its impact on the patient's health. Our findings contribute to the sparse knowledge on HPS-9 and underscore the need for further exploration into the genetic causes of this rare disorder.

The experience of albinism in France: a qualitative study on dyads of parents and their adult child with albinism.

BACKGROUND: To date, almost no research on the psychosocial implications of albinism has been conducted in France and an exploration of albinism-related experiences could be beneficial, in order to better understand this condition. The aim of this study was to examine how French people with albinism and their parents live with and adapt to this condition in all the areas of their lives. METHODS: Semi-structured phone interviews were conducted with 9 parent-child dyads, each participating separately. Participants were recruited by convenience sampling, thanks to the combined efforts of a patient association (Genespoir) and professionals from the partner medical referral centers involved in the project. Dyads in which the individual with albinism had any comorbidity were excluded. The interviews were then transcribed and subjected to in-depth thematic analysis. Two codebooks were constructed in a mirrored process: one for people with albinism; the other for their parents. They were finally merged at the end of the coding step. RESULTS: Four main categories were identified: personal perceptions and social representations of albinism, difficulties and obstacles encountered by people with albinism, resources and facilitators, and the importance of parent-child functioning. The results indicated that experiences of stigmatization during childhood and adolescence are common and that people with albinism face challenges in adapting to certain obstacles related to their visual impairments (VI) (e.g., inability to drive a car; eye strain...). Parents emerged as one, if not as the main, source of support for people with albinism throughout their development. Although external support systems exist to assist them in various aspects of their lives, some of them primarily rely on their own personal resources to cope. CONCLUSIONS: This research highlights the importance of a systemic and transdisciplinary approach to make sure families receive the support that best meets their needs.

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.

Mapping a research-advocacy-policy agenda on human rights and albinism: a mixed methods project.

BACKGROUND: Persons with albinism face challenges to their wellbeing, safety, and security, ranging from vision impairment and skin cancer to stigma and discrimination. In some regions, they also face human rights atrocities including mutilation and murder. Research on human rights and albinism is a relatively new field that has gained momentum since the United Nations appointment of an Independent Expert on the enjoyment of human rights by persons with albinism. In this paper, we present the results of a mixed methods study undertaken to identify priorities for research, advocacy, and policy on albinism and human rights. METHODS: The first component was a synthesis of peer-reviewed and grey literatures at the nexus of albinism, spiritual/cultural beliefs and practices, and human rights. We then conducted a priority-setting survey, informed by Delphi methods, on extant knowledge-practice gaps and research, advocacy, and policy priorities. Inclusion criteria included demonstrated expertise in the field (e.g., peer-reviewed publications, funded research), membership on national or international associations, or advocacy (civil society organizations) of more than 2 years in albinism and human rights. Thereafter, we gathered leading researchers, policy-makers, and civil society stakeholders for a Roundtable to gain consensus on these priorities. RESULTS: Access to skin and vision care, and education were not deemed high priority for research, likely because the evidence supporting the need for these is well established. However, they were priorities for advocacy and policy: what is needed is mobilization of this evidence through advocacy and implementation of such services (policy). Other social determinants of health (rurality, poverty, and gender equality) are present as subtext in the findings, more so than priorities for research, advocacy, or policy, despite their preponderance in the lives of persons with albinism. Research was prioritized on stigma and discrimination; advocacy; and witchcraft, but with some differentiation between Global North and Global South priorities. Priorities for research, advocacy, and policy vary in keeping with the explanatory frameworks at play, including how harmful practices and witchcraft are viewed. CONCLUSIONS: The lived experience of albinism is profoundly shaped by the social determinants of health (SDOH). Threats to the security and well-being of persons with albinism should be viewed through a human rights lens that encompasses the explanatory frameworks at play.

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.

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.

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.

Novel Variants of HPS6 Cause Suspected Ocular Albinism: A Report of 2 Cases and the Profile of HPS6 Variants.

INTRODUCTION: Hermansky-Pudlak syndrome (HPS) is a rare autosomal-recessive disease characterized by ocular albinism (OA) or oculocutaneous albinism (OCA), platelet dysfunction, and other symptoms. This study aimed to analyze the molecular defect in two Chinese families with suspected OA, as well as to investigate the profile of HPS6 variants and their genotype-phenotype correlations. METHODS: Seven members from two families were recruited and underwent clinical ophthalmologic examinations. The genomic DNA was extracted from peripheral blood leukocytes. Whole-exome sequencing was performed on the proband of family JX. The single coding exon of HPS6 was directly Sanger sequenced based on PCR amplification in all available family members. An additional 46 probands from families or sporadic cases with the pathogenic variants of HPS6 reported in the literature were reviewed. RESULTS: We identified two different compound heterozygous truncating variants of HPS6 in probands with suspected OA from two independent families. The proband of family JX had c.1674dup and c.503-504del variants, and the other proband from family CZ had a nonsense variant of c.1114C>T and a frameshift variant of c.1556del. Among them, c.1674dup and c.1556del variants in HPS6 have not been reported previously. Therefore, our patients were diagnosed as HPS6 disease by molecular diagnostics. In the retrospective cohort of HPS6 patients, we delineated the profile of HPS6 variants and revealed a significant overlap between CpG islands and the variants of HPS6, suggesting a potential link between DNA methylation and HPS6 variants. We also observed a spatial aggregation of the variants in 3D structure of HPS6 protein, implying the possible functional significance of these structural regions. In addition, we did not find any significant genotype-phenotype correlation of HPS6, and neither did we observe a correlation between the truncation length of the HPS6 protein and the phenotype of HPS6 disease. CONCLUSION: Our research expands the spectrum of HPS6 variants, providing a comprehensive delineation of their profile and systematically investigating genotype-phenotype correlations in HPS6. These findings could offer potentially valuable clues for investigating the molecular mechanism underlying HPS6 pathogenesis, as well as aiding the clinical diagnosis of HPS6 patients and improving disease prognosis.

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.

Identification of Candidate Genes for Red-Eyed (Albinism) Domestic Guppies Using Genomic and Transcriptomic Analyses.

Guppies are small tropical fish with brightly colored bodies and variable tail shapes. There are two phenotypes of domestic guppy eye color: red and black. The wild type is black-eyed. The main object of this study was to identify candidate genes for the red-eyed phenotype in domestic guppies. We hope to provide molecular genetic information for the development of new domestic guppy strains. Additionally, the results also contribute to basic research concerning guppies. In this study, 121 domestic guppies were used for genomic analysis (GWAS), and 44 genes were identified. Furthermore, 21 domestic guppies were used for transcriptomic analysis, and 874 differentially expressed genes (DEGs) were identified, including 357 upregulated and 517 downregulated genes. Through GO and KEGG enrichment, we identified some important terms or pathways mainly related to melanin biosynthesis and ion transport. qRT-PCR was also performed to verify the differential expression levels of four important candidate genes (TYR, OCA2, SLC45A2, and SLC24A5) between red-eyed and black-eyed guppies. Based on the results of genomic and transcriptomic analyses, we propose that OCA2 is the most important candidate gene for the red-eyed phenotype in guppies.

Missing Heritability in Albinism: Deep Characterization of a Hungarian Albinism Cohort Raises the Possibility of the Digenic Genetic Background of the Disease.

Albinism is characterized by a variable degree of hypopigmentation affecting the skin and the hair, and causing ophthalmologic abnormalities. Its oculocutaneous, ocular and syndromic forms follow an autosomal or X-linked recessive mode of inheritance, and 22 disease-causing genes are implicated in their development. Our aim was to clarify the genetic background of a Hungarian albinism cohort. Using a 22-gene albinism panel, the genetic background of 11 of the 17 Hungarian patients was elucidated. In patients with unidentified genetic backgrounds (n = 6), whole exome sequencing was performed. Our investigations revealed a novel, previously unreported rare variant (N687S) of the two-pore channel two gene (TPCN2). The N687S variant of the encoded TPC2 protein is carried by a 15-year-old Hungarian male albinism patient and his clinically unaffected mother. Our segregational analysis and in vitro functional experiments suggest that the detected novel rare TPCN2 variant alone is not a disease-causing variant in albinism. Deep genetic analyses of the family revealed that the patient also carries a phenotype-modifying R305W variant of the OCA2 protein, and he is the only family member harboring this genotype. Our results raise the possibility that this digenic combination might contribute to the observed differences between the patient and the mother, and found the genetic background of the disease in his case.

Molecular Modeling of the Multiple-Substrate Activity of the Human Recombinant Intra-Melanosomal Domain of Tyrosinase and Its OCA1B-Related Mutant Variant P406L.

Tyrosinase serves as the key enzyme in melanin biosynthesis, catalyzing the initial steps of the pathway, the hydroxylation of the amino acid L-tyrosine into L-3,4-dihydroxyphenylalanine (L-DOPA), followed by the subsequent oxidation of L-DOPA into dopaquinone (DQ), and it facilitates the conversion of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) into 5,6-indolequinone-2-carboxylic acid (IQCA) and 5,6-dihydroxy indole (DHI) into indolequinone (IQ). Despite its versatile substrate capabilities, the precise mechanism underlying tyrosinase's multi-substrate activity remains unclear. Previously, we expressed, purified, and characterized the recombinant intra-melanosomal domain of human tyrosinase (rTyr). Here, we demonstrate that rTyr mimics native human tyrosinase's catalytic activities in vitro and in silico. Molecular docking and molecular dynamics (MD) simulations, based on rTyr's homology model, reveal variable durability and binding preferences among tyrosinase substrates and products. Analysis of root mean square deviation (RMSD) highlights the significance of conserved residues (E203, K334, F347, and V377), which exhibit flexibility during the ligands' binding. Additionally, in silico analysis demonstrated that the OCA1B-related P406L mutation in tyrosinase substantially influences substrate binding, as evidenced by the decreased number of stable ligand conformations. This correlation underscores the mutation's impact on substrate docking, which aligns with the observed reduction in rTyr activity. Our study highlights how rTyr dynamically adjusts its structure to accommodate diverse substrates and suggests a way to modulate rTyr ligand plasticity.

Functional Characterization of Splice Variants in the Diagnosis of Albinism.

Albinism is a genetically heterogeneous disease in which 21 genes are known so far. Its inheritance mode is autosomal recessive except for one X-linked form. The molecular analysis of exonic sequences of these genes allows for about a 70% diagnostic rate. About half (15%) of the unsolved cases are heterozygous for one pathogenic or probably pathogenic variant. Assuming that the missing variant may be located in non-coding regions, we performed sequencing for 122 such heterozygous patients of either the whole genome (27 patients) or our NGS panel (95 patients) that includes, in addition to all exons of the 21 genes, the introns and flanking sequences of five genes, TYR, OCA2, SLC45A2, GPR143 and HPS1. Rare variants (MAF < 0.01) in trans to the first variant were tested by RT-PCR and/or minigene assay. Of the 14 variants tested, nine caused either exon skipping or the inclusion of a pseudoexon, allowing for the diagnosis of 11 patients. This represents 9.8% (12/122) supplementary diagnosis for formerly unsolved patients and 75% (12/16) of those in whom the candidate variant was in trans to the first variant. Of note, one missense variant was demonstrated to cause skipping of the exon in which it is located, thus shedding new light on its pathogenic mechanism. Searching for non-coding variants and testing them for an effect on RNA splicing is warranted in order to increase the diagnostic rate.

Identification and characterization of two novel noncoding tyrosinase (TYR) gene variants leading to oculocutaneous albinism type 1.

Oculocutaneous albinism type 1 (OCA1), resulting from pathogenic variants in the tyrosinase (TYR) gene, refers to a group of phenotypically heterogeneous autosomal recessive disorders characterized by a partial or a complete absence of pigment in the skin/hair and is also associated with common developmental eye defects. In this study, we identified two novel compound heterozygous TYR variants from a Chinese hypopigmentary patient by whole-exome sequencing. Specifically, the two variants were c.-89T>G, located at the core of the initiator E-box (Inr E-box) of the TYR promoter, and p.S16Y (c.47C>A), located within the signal sequence. We performed both in silico analysis and experimental validation and verified these mutations as OCA1 variants that caused either impaired or complete loss of function of TYR. Mechanistically, the Inr E-box variant dampened TYR binding to microphthalmia-associated transcription factor, a master transcriptional regulator of the melanocyte development, whereas the S16Y variant contributed to endoplasmic reticulum retention, a common and principal cause of impaired TYR activity. Interestingly, we found that the Inr E-box variant creates novel protospacer adjacent motif sites, recognized by nucleases SpCas9 and SaCas9-KKH, respectively, without compromising the functional TYR coding sequence. We further used allele-specific genomic editing by CRISPR activation to specifically target the variant promoter and successfully activated its downstream gene expression, which could lead to potential therapeutic benefits. In conclusion, this study expands the spectrum of TYR variants, especially those within the promoter and noncoding regions, which can facilitate genetic counseling and clinical diagnosis of OCA1.

OCA7 is a melanosome membrane protein that defines pigmentation by regulating early stages of melanosome biogenesis.

Mutations in C10orf11 (oculocutaneous albinism type 7 [OCA7]) cause OCA, a disorder that presents with hypopigmentation in skin, eyes, and hair. The OCA7 pathophysiology is unknown, and there is virtually no information on the OCA7 protein and its cellular function. Here, we discover that OCA7 localizes to the limiting membrane of melanosomes, the specialized pigment cell organelles where melanin is synthesized. We demonstrate that OCA7 is recruited through interaction with a canonical effector-binding surface of melanosome proteins Rab32 and Rab38. Using newly generated OCA7-KO MNT1 cells, we show OCA7 regulates overall melanin levels in a melanocyte autonomous manner by controlling melanosome maturation. Importantly, we found that OCA7 regulates premelanosome protein (PMEL) processing, impacting fibrillation and the striations that define transition from melanosome stage I to stage II. Furthermore, the melanosome lumen of OCA7-KO cells displays lower pH than control cells. Together, our results reveal that OCA7 regulates pigmentation through two well-established determinants of melanosome biogenesis and function, PMEL processing, and organelle pH.

MIR204 n.37C>T variant as a cause of chorioretinal dystrophy variably associated with iris coloboma, early-onset cataracts and congenital glaucoma.

Four members of a three-generation Czech family with early-onset chorioretinal dystrophy were shown to be heterozygous carriers of the n.37C>T in MIR204. The identification of this previously reported pathogenic variant confirms the existence of a distinct clinical entity caused by a sequence change in MIR204. Chorioretinal dystrophy was variably associated with iris coloboma, congenital glaucoma, and premature cataracts extending the phenotypic range of the condition. In silico analysis of the n.37C>T variant revealed 713 novel targets. Additionally, four family members were shown to be affected by albinism resulting from biallelic pathogenic OCA2 variants. Haplotype analysis excluded relatedness with the original family reported to harbour the n.37C>T variant in MIR204. Identification of a second independent family confirms the existence of a distinct MIR204-associated clinical entity and suggests that the phenotype may also involve congenital glaucoma.

Analysis of morphological traits and regulatory mechanism of a semi-dwarf, albino, and blue grain wheat line.

The plant height and leaf color are important traits in crops since they contribute to the production of grains and biomass. Progress has been made in mapping the genes that regulate plant height and leaf color in wheat (Triticum aestivum L.) and other crops. Wheat line DW-B (dwarfing, white leaves, and blue grains) with semi-dwarfing and albinism at the tillering stage and re-greening at the jointing stage was created using Lango and Indian Blue Grain. Transcriptomic analyses of the three wheat lines at the early jointing stages indicated that the genes of gibberellin (GA) signaling pathway and chlorophyll (Chl) biosynthesis were expressed differently in DW-B and its parents. Furthermore, the response to GA and Chl contents differed between DW-B and its parents. The dwarfing and albinism in DW-B were owing to defects in the GA signaling pathway and abnormal chloroplast development. This study can improve understanding of the regulation of plant height and leaf color. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01379-z.

Oculocutaneous albinism: the neurological, behavioral, and neuro-ophthalmological perspective.

Oculocutaneous albinism (OCA) is a group of rare, genetic disorders caused by absent/reduced melanin biosynthesis. The aim of this study was to explore the neurovisual, cognitive, adaptive, and behavioral profile of children affected by OCA, also evaluating any possible effect of the visual acuity deficit on the clinical profile and genotype-phenotype correlations. Eighteen children (9 males, mean age 84 months ± 41; range 18-181 months) with a molecular confirmed diagnosis of OCA were enrolled in the study. We collected data on clinical history, neurodevelopmental profile, neurological and neurovisual examination, and cognitive, adaptive, and emotional/behavioral functioning. A global neurodevelopmental impairment was detected in 56% of the children, without evolving into an intellectual disability. All the patients showed signs and symptoms of visual impairment. Low adaptive functioning was observed in 3 cases (17%). A risk for internalizing behavioral problems was documented in 6 cases (33%), for externalizing problems in 2 (11%), and for both in 5 (28%). Twelve children (67%) showed one or more autistic-like features. Correlation analyses revealed significant associations between the visual acuity level and performance intelligence quotient (p = 0.001), processing speed index (p = 0.021), Vineland total score (p = 0.020), Vineland communication (p = 0.020), and socialization (p = 0.037) domains. No significant correlations were found between genotype and phenotype. CONCLUSION: Children with OCA may present a global neurodevelopmental delay that seems to improve with age and emotional/behavioral difficulties, along with the well-known visual impairment. An early neuropsychiatric evaluation and habilitative training are recommended to improve vision-related performance, neurodevelopment, and any psychological difficulties. WHAT IS KNOWN: • Children with oculocutaneous albinism show dermatological and ophthalmological problems. • An early visual impairment may have negative implications on motor, emotional, and cognitive processes that would allow the child to organize his or her experiences. WHAT IS NEW: • In addition to a variable combination of ocular signs and symptoms, children with oculocutaneous albinism may present an early neurodevelopmental delay and emotional/behavioral difficulties. • An early visual treatment is recommended to improve vision-related performance, neurodevelopment, and any psychological difficulties.