Predominant Founder Effect among Recurrent Pathogenic Variants for an X-Linked Disorder

Biallelic Loss-of-Function Variants in UBAP1L and Nonsyndromic Retinal Dystrophies

Importance

Inherited retinal dystrophies (IRDs) present a challenge in clinical diagnostics due to their pronounced genetic heterogeneity. Despite advances in next-generation sequencing (NGS) technologies, a substantial portion of the genetic basis underlying IRDs remains elusive. Addressing this gap seems important for gaining insights into the genetic landscape of IRDs, which may help improve diagnosis and prognosis and develop targeted therapies in the future.

Objective

To provide a clinical and molecular characterization of 6 patients with IRDs with biallelic disease-causing variants in a novel candidate IRD disease gene.

Design, Setting, and Participants

This multicenter case series study included 6 patients with IRDs from 4 tertiary hospitals (in the US: National Eye Institute, National Institutes of Health Clinical Center; in the UK: Moorfields Eye Hospital, Royal Liverpool University Hospital, Birmingham Women's and Children's).

Exposures

Biallelic disease-causing variants in the novel candidate IRD disease gene, UBAP1L.

Main Outcome and Measures

Participants underwent comprehensive clinical ophthalmic assessments to characterize the features of retinal dystrophy. Exome and genome sequencing revealed candidate variants in the UBAP1L gene; no other plausible disease variants in known IRD genes were identified. A minigene assay provided functional insights for a noncanonical splice variant, and a knockout mouse model was used for in vivo functional elucidation.

Results

Four homozygous UBAP1L variants were identified in the affected individuals from 6 families, including 2 frameshift variants (c.710del and c.634_644del), 1 canonical splice variant (c.121-2A>C), and 1 noncanonical splice variant (c.910-7G>A), which was shown to cause aberrant splicing and frameshift in a minigene assay. Participants presented with retinal dystrophy including maculopathy, cone dystrophy, and cone-rod dystrophy. Single-cell RNA sequencing of the retina showed that human UBAP1L is highly expressed in both cones and retinal pigment epithelium, whereas mouse Ubap1l is highly expressed in cone cells only. Mice with truncation of the C-terminal SOUBA domain did not manifest retinal degeneration up to 15 months of age.

Conclusions and Relevance

Study results reveal clinical and genetic evidence that loss of UBAP1L function was associated with inherited retinopathy in humans. These findings hold promise for improved clinical diagnostics, prognosis, and the potential development of targeted therapies for individuals affected by IRDs.

Genotype-Phenotype Correlations in 83 Korean X-linked Retinoschisis Patients: Impact of RS1 Secretion Profiles on Clinical Phenotypes

PURPOSE

To assess the correlation between genotype and phenotype severity in X-linked juvenile retinoschisis (XLRS) by examining clinical and genetic features of a cohort of Korean XLRS patients.

DESIGN

Retrospective, observational study.

PARTICIPANTS

Data from 83 consecutive male patients with molecularly confirmed XLRS were collected retrospectively.

METHODS

Clinical evaluation included best-corrected visual acuity (BCVA), fundus photography, spectral-domain optical coherence tomography (SD-OCT), and full-field electroretinography (ERG).

MAIN OUTCOME MEASURES

The phenotypic characteristics of a cohort of pediatric Korean XLRS patients, based on mutation types (truncating versus missense) and secretory profile (secretion versus non-secretion), were assessed.

RESULTS

One hundred sixty-six eyes of 83 patients were included. The mean age at diagnosis was 6.1 ± 8.8 years (range, 0.5-20.7 years), with a mean follow-up time of 9.2 ± 7.0 years (range, 0.6-24.3 years). The BCVA at first and last examination ranged from light perception to 0.1 logarithm of the minimum angle of resolution (mean ± SD, 0.75 ± 0.59 and 0.82 ± 0.65, respectively). There were no significant differences in the first and last BCVA measurements between the truncating (0.71 ± 0.51 and 0.75 ± 0.44) and missense (0.77 ± 0.59 and 0.84 ± 0.66) variants (P = 0.678 and 0.551, respectively). Additionally, there were no differences in clinical parameters from fundus photography, SD-OCT, and full-field ERG. However, the BCVA at the first and last measurement were better for patients in the secretion group (0.51 ± 0.24 and 0.61 ± 0.30) compared to patients in the non-secretion group (0.65 ± 0.71 and 0.87 ± 0.81). The last BCVA showed a statistically significant difference between the two groups (P = 0.021). In OCT findings, the frequency of ellipsoid zone disruption was higher in patients with non-secretion variants than those with secretion variants (P = 0.030), with no significant differences in other parameters.

CONCLUSIONS

The secretion profile of RS1 could influence the severity of XLRS phenotypes. Patients with RS1-secreted mutants, particularly with intact octamerization, exhibit more homogeneous phenotypes and better visual acuity than the RS1-non-secreted group. This data provides insights for studying genotype and phenotype correlations in both clinical and research fields.

A paradigm shift in the treatment of refractory angle closure glaucoma in a patient with X-linked juvenile retinoschisis

BACKGROUND

X-linked retinoschisis (XLRS) is a rare inherited bilateral retinal degeneration caused by mutations in RS1 gene, occurring exclusively in men. Various ocular complications associated with XLRS are reported, and angle closure glaucoma in these eyes is one such complication that is refractory and needs surgery for intraocular pressure control. Glaucoma surgery in these eyes often results in refractory malignant glaucoma with its serious sequelae. Several surgical modifications to prevent this complication have been tried with no or limited success.

METHODOLOGY

In this report, we present a case of XLRS in a young male with a 22-year follow-up. We have described the natural history and progression of retinal disease and glaucoma.

RESULTS

Refractory angle closure glaucoma in our patient was treated with core vitrectomy, phacoemulsification with intraocular lens implantation, and irido-zonulo-hyaloido-vitrectomy. This helped in successful deepening of anterior chamber, good IOP control, and preventing malignant glaucoma.

CONCLUSION

Our case highlights the role of vitrectomy in managing the secondary angle closure glaucoma in eyes with X-LRS.

The qMini assay identifies an overlooked class of splice variants

Splice variants are known to cause diseases by utilizing alternative splice sites, potentially resulting in protein truncation or mRNA degradation by nonsense-mediated decay. Splice variants are verified when altered mature mRNA sequences are identified in RNA analyses or minigene assays. Using a quantitative minigene assay, qMini, we uncovered a previously overlooked class of disease-associated splice variants that did not alter mRNA sequence but decreased mature mRNA level, suggesting a potentially new pathogenic mechanism.