Expanding the Spectrum of Oculocutaneous Albinism: Does Isolated Foveal Hypoplasia Really Exist?
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SUBMITTER: Rocca C
PROVIDER: S-EPMC9317384 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Background/aimsTo investigate the foveal morphology in carriers of oculocutaneous albinism (OCA) using spectral domain optical coherence tomography (SD-OCT). A cross-sectional, observational study.MethodsHandheld SD-OCT (Envisu C2300) was used to acquire horizontal scans through the centre of the fovea in biological parents of patients with OCA (n=28; mean age±SD=40.43±8.07 years) and age-matched and ethnicity-matched controls (n=28; mean age±SD=38.04±10.27 years). Sequence analysis was performed for variants in known genes associated with OCA. Best-corrected visual acuity (BCVA), presence of foveal hypoplasia and grade, foveal, parafoveal and perifoveal thickness measurements of total retinal layers (TRL), inner retinal layers (IRL) and outer retinal layers (ORL) thickness were measured.ResultsFoveal hypoplasia was identified in 32.14% of OCA carriers; grade 1 in all cases. OCA carriers demonstrated significant thicker TRL thickness (median difference: 13.46 µm, p=0.009) and IRL thickness (mean difference: 8.98 µm, p<0.001) at the central fovea compared with controls. BCVA of carriers was between -0.16 and 0.18 logMAR (mean: 0.0 logMAR). No significant differences in BCVA was noted between OCA carriers or controls (p=0.83). In the OCA carriers, we identified previously reported pathogenic variants in TYR, OCA2 and SLC45A2, novel OCA2 variants (n=3) and heterozygosity of the pathogenic TYR haplotype.ConclusionWe have, for the first time, identified foveal abnormalities in OCA carriers. This provides clinical value, particularly in cases where limited phenotype data are available. Our findings raise the possibility that previously reported mild cases of foveal hypoplasia or isolated foveal hypoplasia could correspond to OCA carrier status.
| S-EPMC10359511 | biostudies-literature
Project description:Oculocutaneous albinism (OCA) is a group of inherited disorders of melanin biosynthesis characterized by a generalized reduction in pigmentation of hair, skin and eyes. The prevalence of all forms of albinism varies considerably worldwide and has been estimated at approximately 1/17,000, suggesting that about 1 in 70 people carry a gene for OCA. The clinical spectrum of OCA ranges, with OCA1A being the most severe type with a complete lack of melanin production throughout life, while the milder forms OCA1B, OCA2, OCA3 and OCA4 show some pigment accumulation over time. Clinical manifestations include various degrees of congenital nystagmus, iris hypopigmentation and translucency, reduced pigmentation of the retinal pigment epithelium, foveal hypoplasia, reduced visual acuity usually (20/60 to 20/400) and refractive errors, color vision impairment and prominent photophobia. Misrouting of the optic nerves is a characteristic finding, resulting in strabismus and reduced stereoscopic vision. The degree of skin and hair hypopigmentation varies with the type of OCA. The incidence of skin cancer may be increased. All four types of OCA are inherited as autosomal recessive disorders. At least four genes are responsible for the different types of the disease (TYR, OCA2, TYRP1 and MATP). Diagnosis is based on clinical findings of hypopigmentation of the skin and hair, in addition to the characteristic ocular symptoms. Due to the clinical overlap between the OCA forms, molecular diagnosis is necessary to establish the gene defect and OCA subtype. Molecular genetic testing of TYR and OCA2 is available on a clinical basis, while, at present, analysis of TYRP1 and MATP is on research basis only. Differential diagnosis includes ocular albinism, Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, Griscelli syndrome, and Waardenburg syndrome type II. Carrier detection and prenatal diagnosis are possible when the disease causing mutations have been identified in the family. Glasses (possibly bifocals) and dark glasses or photocromic lenses may offer sufficient help for reduced visual activity and photophobia. Correction of strabismus and nystagmus is necessary and sunscreens are recommended. Regular skin checks for early detection of skin cancer should be offered. Persons with OCA have normal lifespan, development, intelligence and fertility.
| S-EPMC2211462 | biostudies-literature
Project description:Foveal hypoplasia and optic nerve misrouting are developmental defects of the visual pathway and only co-occur in connection with albinism; to date, they have only been associated with defects in the melanin-biosynthesis pathway. Here, we report that these defects can occur independently of albinism in people with recessive mutations in the putative glutamine transporter gene SLC38A8. Nine different mutations were identified in seven Asian and European families. Using morpholino-mediated ablation of Slc38a8 in medaka fish, we confirmed that pigmentation is unaffected by loss of SLC38A8. Furthermore, by undertaking an association study with SNPs at the SLC38A8 locus, we showed that common variants within this gene modestly affect foveal thickness in the general population. This study reveals a melanin-independent component underpinning the development of the visual pathway that requires a functional role for SLC38A8.
| S-EPMC3853409 | biostudies-literature
Project description: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.
| S-EPMC8065601 | biostudies-literature
Project description:PurposeAlbinism is a group of genetic disorders, showing a broad spectrum of different phenotypes. The purpose of this study was to screen known candidate genes for oculocutaneous albinism (OCA) and ocular albinism (OA) mutations in Indian patients.MethodsBlood samples were collected from 23 probands and 13 affected family members from 23 genetically unrelated Indian families (22 diagnosed as OCA and 1 diagnosed as OA) and analyzed by bidirectional DNA sequencing of the classic OCA genes--tyrosinase (TYR, or oculocutaneous albinism IA), pink eyed dilution (P; or oculocutaneous albinism II (OCA2]), tyrosinase-related protein 1 (TYRP1), solute carrier family 45, member 2 (SLC45A2; or membrane-associated transporter protein [MATP])--and the OA1 gene, G protein-coupled receptor 143 (GPR143).ResultsThree missense mutations, c. 715 C>T (R239W), c. 896 G>A (R299H), c.1255 G>A (G419R), and one termination c. 832 C>T (R278X), were identified in TYR, as well as one novel mutation, c.1453 G>A (G485R) in P. One novel single nucleotide polymorphism (SNP) was identified in both TYR and P; few reported SNPs were identified. The G>A base substitution caused relatively conservative amino acid changes, which altered glycine to arginine residues within the topological domain. The novel OCA2 mutation was not present in 100 control samples. This study identified two probands carrying mutations alone, 16 probands carrying SNPs alone, 4 probands carrying both mutations and SNPs and only one proband carrying neither mutations nor SNPs.ConclusionsAlthough sequence analysis was performed with all five candidate genes, only four (17.39%) of the 23 probands showed mutations in TYR and 2 probands (8.69%) showed an unreported novel mutation in P. Genetic counseling for phenotypical diagnosis and genetic mutation screening of these genes will help to minimize the incidence of OCA and OA in future generations.
| S-EPMC2925902 | biostudies-literature
Project description:Background/aimsTo analyse the distribution of macular ganglion cell layer thickness (GCLT) in patients with foveal hypoplasia (FH) with or without albinism to obtain new insights into visual pathway anomalies in albinos.MethodsPatients with FH who presented at our institution between 2013 and 2018 were retrospectively drawn for analysis. Mean GCLT was calculated after automated segmentation of spectral domain-optical coherence tomography (SD-OCT) scans. Patients with FH due to albinism (n = 13, termed 'albinism FH') or other kinds (n = 10, termed 'non-albinism FH') were compared with control subjects (n = 15). The areas: fovea (central), parafovea (nasal I, temporal I) and perifovea (nasal II, temporal II) along the horizontal meridian were of particular interest. Primary endpoints of this study were the ratios (GCLT-I- and GCLT-II-Quotient) between the GCLT measured in the temporal I or II and nasal I or II areas.ResultsThere was a significant difference between the GCLT-I-Quotient of healthy controls and albinism FH (p<0.001), as well as between non-albinism FH and albinism FH (p = 0.004). GCLT-II-Quotient showed significant differences between healthy controls and albinism FH (p<0.001) and between non-albinism FH and albinism FH (p = 0.006). The best measure for distinguishing between non-albinism FH and albinism FH was the calculation of GCLT-II-Quotient (area temporal II divided by area nasal II), indicating albinism at a cut-off of <0.7169. The estimated specificity and sensitivity for this cut-off were 84.6% and 100.0%, respectively. The estimated area under the curve (AUC) was 0.892 [95%CI: 0.743-1.000, p = 0.002].ConclusionMacular GCLT-distribution showed a characteristic temporal to central shift in patients with FH due to albinism. Calculation of the GCLT-II-Quotient at a cut-off of <0.7169 presents a new diagnostic criterion for identification of ocular albinism.
| S-EPMC6860421 | biostudies-literature
Project description:PurposeThe purpose of this study was to further expand the mutational spectrum of the Foveal Hypoplasia, Optic Nerve Decussation defect, and Anterior segment abnormalities (FHONDA syndrome), to describe the phenotypic spectrum, and to compare it to albinism.Subjects and methodsWe retrospectively collected molecular, ophthalmic, and electrophysiological data of 28 patients molecularly confirmed with FHONDA from the Netherlands (9), Israel (13), France (2), and the United States of America (4). We compared the data to that of 133 Dutch patients with the 3 most common types of albinism in the Netherlands: oculocutaneous albinism type 1 (49), type 2 (41), and ocular albinism (43).ResultsPatients with FHONDA had a total of 15 different mutations in SLC38A8, of which 6 were novel. Excluding missing data, all patients had moderate to severe visual impairment (median visual acuity [VA] = 0.7 logMAR, interquartile range [IQR] = 0.6-0.8), nystagmus (28/28), and grade 4 foveal hypoplasia (17/17). Misrouting was present in all nine tested patients. None of the patients had any signs of hypopigmentation of skin and hair. VA in albinism was better (median = 0.5 logMAR, IQR = 0.3-0.7, P 0.006) and the phenotypes were more variable: 14 of 132 without nystagmus, foveal hypoplasia grades 1 to 4, and misrouting absent in 16 of 74.ConclusionsCompared to albinism, the FHONDA syndrome appears to have a more narrow phenotypic spectrum, consisting of nonprogressive moderately to severely reduced VA, nystagmus, severe foveal hypoplasia, and misrouting. The co-occurrence of nystagmus, foveal hypoplasia, and misrouting in the absence of hypopigmentation implies that these abnormalities are not caused by lack of melanin, which has important implications for understanding the pathogenesis of these features.
| S-EPMC8762694 | biostudies-literature
Project description: Not available
| S-EPMC10570940 | biostudies-literature
Project description: Not available
| S-EPMC4350605 | biostudies-literature
Project description:The human fovea is a specialized pit structure in the central retina. Foveal hypoplasia is a condition where the foveal pit does not fully develop, and it is associated with poor vision. Autosomal dominant isolated foveal hypoplasia (FVH1) is a rare condition of foveal hypoplasia (FH) that lacks any other ocular manifestations. FVH1 is associated with hypomorphic mutations in the PAX6 gene that encodes a sequence-specific DNA-binding transcription factor for morphogenesis and evolution of the eye. We report our findings in 17 patients with PAX6 mutations associated with FVH1 or FH with aniridia and corneal opacities. Patients with three mutations, p.V78E, p.V83F and p.R128H, in the C-terminal subdomain of the paired domain (CTS) consistently have severe FH. Luciferase assays for a single reporter containing a representative PAX6 binding site indicated that the transcriptional activities of these mutations were significantly reduced, comparable to that of the truncation mutation of p.G65Rfs*5. Patients with p.P20S in the N-terminal subdomain of the paired domain, and a patient with p.N365K in the proline-serine-threonine-rich domain (PSTD) had mild FH. A patient with p.Q255L in the homeodomain had severe FH. The P20S and Q255L mutants did not affect the transcriptional activity. Mutant N365K has a retained DNA-binding activity but a reduced transcriptional activity, due to a low PSTD transactivation. These findings demonstrated that mutations associated with FVH1 underlie a functional divergence between DNA-binding ability and transcriptional activity. We conclude that a wide range of mutations in the PAX6 gene is not limited to the CST region and are responsible for FVH1.
| S-EPMC10379490 | biostudies-literature