Disruption of Normal Refractive Development in Individuals with Ocular and Oculocutaneous Albinism

PurposeAlbinism is known to disrupt emmetropisation in animal models. However, it is not clear if the same effect is seen in humans. This study aimed to investigate the refractive profile in individual diagnosed with ocular albinism (OA) and oculocutaneous albinism (OCA) based on a large dataset.MethodsRequired data from 618 individuals (61% males and 39% females) diagnosed with albinism were exported from the eyeSmart electronic medical records of L V Prasad Eye Institute. Overall, there were 112 (18%) individuals diagnosed with OA and 506 (82%) with OCA. Based on the spherical equivalent refraction (SER), individuals were classified as emmetropes, myopes, and hyperopes.ResultsThe overall spherical equivalent refraction of the individuals ranged from -25.00D to +12.00D with median 0.25 (-2.00 to 2.25). The proportion of individuals with albinism (combined OA, OCA) having hyperopia and myopia (overall: N=282;46% vs. N=245;40%) were similar (p = 0.18), and the least were with emmetropia (overall: N=91;14%). Across all the age groups (0-10, 11-20, 21-30, > 30 years) the frequency of hyperopes and myopes were significantly higher (p<0.05) compared to emmetropes. Both high degrees of hyperopia and myopia were found in individual diagnosed with OA and OCA. Irrespective of the albinism type, with-the-rule (70%) astigmatism was the most prevalent compared to other types of astigmatism. The frequency of with-the-rule astigmatism was significantly high in the presence of nystagmus compared to individuals with no nystagmus in both OA (75 % vs 25%, p = 0.01) and OCA (77% vs 23 %, p = 0.014) group. Conclusion The presence of both high hyperopia and high myopia and very less numbers with emmetropia across all age groups indicates disrupted normal refractive development in individuals with albinism. With-the-rule astigmatism and nystagmus may result in meridional degradation of retinal image leading to impairment of normal emmetropisation process in individuals with albinism.

Neurodevelopmental Profile in Children Affected by Ocular Albinism

Aim The aim of this study was to detail the neurodevelopmental profile of subjects affected by ocular albinism (OA) and to collect data on GPR143 gene analysis. Design The design of the study involves a retrospective longitudinal observational case series. Methods We collected data on the neurodevelopmental profile of 13 children affected by OA from clinical annual assessments conducted for a period of 6 years after the first evaluation. We described visual profile, neuromotor development and neurological examination, cognitive profile, communication and language skills and behavioral characteristics. The GPR143 gene analysis was performed as well. Results Children presented a variable combination of ocular and oculomotor disorders unchanged during the follow-up, a deficit in visual acuity and in contrast sensitivity that progressively improved. Abnormalities in pattern visual evoked potential were found. No deficits were detected at neurological examination and neuromotor development except for a mild impairment in hand-eye coordination observed in five cases. A language delay was observed in five cases, two of whom had also a developmental quotient delay at 2 years evolving to a borderline/deficit cognitive level at preschool age, difficulties in adaptive behavior and autistic-like features were found. Mutations in the GPR143 gene were identified in the two patients who presented the most severe clinical phenotype. Conclusion Children with OA may share, in addition to a variable combination of ocular signs and symptoms, a neurodevelopment impairment regarding mostly the cognitive, communicative, and social area, especially those with GPR143 mutation.

Ocular Albinism

Ocular albinism is an X-linked melanosome biogenesis disorder, leading to mild cutaneous symptoms and persistent visual impairment in affected males. As a result of mutations in the GPR143 gene, a defect occurs in the transformation of melanosomes into macromelanosomes with loss of function at the GPBR143 receptor. Clinically, manifests with nystagmus, which typically occurs in infants until the sixth month from birth. Optic nerve misdirection which can be detected by VEP is important in the differential diagnosis of another infantile nystagmus. Foveal hypoplasia is the most responsible finding for poor vision. Today, functional losses are tried to be minimized by differential diagnosis and early treatment. It is predicted that more effective treatment can be provided with gene therapy in the future.

Prospective Study of the Phenotypic and Mutational Spectrum of Ocular Albinism and Oculocutaneous Albinism

Albinism encompasses a group of hereditary disorders characterized by reduced or absent ocular pigment and variable skin and/or hair involvement, with syndromic forms such as Hermansky–Pudlak syndrome and Chédiak–Higashi syndrome. Autosomal recessive oculocutaneous albinism (OCA) is phenotypically and genetically heterogenous (associated with seven genes). X-linked ocular albinism (OA) is associated with only one gene, GPR143. We report the clinical and genetic outcomes of 44 patients, from 40 unrelated families of diverse ethnicities, with query albinism presenting to the ocular genetics service at Moorfields Eye Hospital NHS Foundation Trust between November 2017 and October 2019. Thirty-six were children (≤ 16 years) with a median age of 31 months (range 2–186), and eight adults with a median age of 33 years (range 17–39); 52.3% (n = 23) were male. Genetic testing using whole genome sequencing (WGS, n = 9) or a targeted gene panel (n = 31) gave an overall diagnostic rate of 42.5% (44.4% (4/9) with WGS and 41.9% (13/31) with panel testing). Seventeen families had confirmed mutations in TYR (n = 9), OCA2, (n = 4), HPS1 (n = 1), HPS3 (n = 1), HPS6 (n = 1), and GPR143 (n = 1). Molecular diagnosis of albinism remains challenging due to factors such as missing heritability. Differential diagnoses must include SLC38A8-associated foveal hypoplasia and syndromic forms of albinism.

Identification of a novel GPR143 mutation in a large Chinese family with isolated foveal hypoplasia

Background Pathogenic variants of G-protein coupled receptor 143 (GPR143) gene often leads to ocular albinism type I (OA1) characterized by nystagmus, iris and fundus hypopigmentation, and foveal hypoplasia. In this study, we identified a novel hemizygous nonsense mutation in GPR143 that caused an atypical manifestation of OA1. Case presentation We reported a large Chinese family in which all affected individuals are afflicted with poor visual acuity and foveal hypoplasia without signs of nystagmus. Fundus examination of patients showed an absent foveal reflex and mild hypopigmentation. The fourth grade of foveal hypoplasia and the reduced area of blocked fluorescence at foveal region was detected in OCT. OCTA imaging showed the absence of foveal avascular zone. In addition, the amplitude of multifocal ERG was reduced in the central ring. Gene sequencing results revealed a novel hemizygous mutation (c.939G > A) in GPR143 gene, which triggered p.W313X. However, no iris depigmentation and nystagmus were observed among both patients and carriers. Conclusions In this study, we reported a novel nonsense mutation of GPR143 in a large family with poor visual acuity and isolated foveal hypoplasia without nystagmus, which further expanded the genetic mutation spectrum of GPR143.

Novel Biallelic Variants and Phenotypic Features in Patients with SLC38A8-Related Foveal Hypoplasia

Biallelic pathogenic variants in solute carrier family 38 member 8, SLC38A8, cause a pan-ocular autosomal recessive condition known as foveal hypoplasia 2, FVH2, characterised by foveal hypoplasia, nystagmus and optic nerve chiasmal misrouting. Patients are often clinically diagnosed with ocular albinism, but foveal hypoplasia can occur in several other ocular disorders. Here we describe nine patients from seven families who had molecularly confirmed biallelic recessive variants in SLC38A8 identified through whole genome sequencing or targeted gene panel testing. We identified four novel sequence variants (p.(Tyr88*), p.(Trp145*), p.(Glu233Gly) and c.632+1G>A). All patients presented with foveal hypoplasia, nystagmus and reduced visual acuity; however, one patient did not exhibit any signs of chiasmal misrouting, and three patients had features of anterior segment dysgenesis. We highlight these findings in the context of 30 other families reported to date. This study reinforces the importance of obtaining a molecular diagnosis in patients whose phenotype overlap with other inherited ocular conditions, in order to support genetic counselling, clinical prognosis and family planning. We expand the spectrum of SLC38A8 mutations which will be relevant for treatment through future genetic-based therapies.