Overlapping retinal phenotypes in a consanguineous family harboring mutations in CRB1 and RS1

Genotypic and phenotypic diversity in X-linked retinoschisis: Findings from a South Indian patient cohort

PURPOSE

Retinoschisis is a distinctive condition characterized by intraretinal layer clefts, primarily associated with X-linked recessive inheritance due to RS1 gene mutations. This study aims to uncover the RS1 mutation spectrum in a cohort of 22 X-linked retinoschisis cases from South India and emphasizes the genotypic and phenotypic associations within patients harboring only RS1 mutations.

METHODS

A total of 22 probands were suspected of having X-linked retinoschisis. All study subjects underwent ophthalmic investigations, including assessments of visual acuity, fundus examination, optical coherence tomography (OCT), and electroretinogram (ERG). RS1 gene screening was conducted using Sanger sequencing, and the pathogenicity of the variants was assessed through Sorting Intolerant from Tolerant (SIFT) and PolyPhen-2 in silico tools.

RESULTS

The study found that the probands had an average visual acuity of 0.79 ± 0.39 log of minimum angle of resolution (logMAR), ranging from 0.17 to 1.77. During fundus examination, the probands exhibited a characteristic spoke wheel-like pattern in the macular region. Furthermore, OCT analysis revealed distinct alterations in the inner retinal microstructure, and ERG results consistently showed a reduction in b-wave amplitude. Eventually, Sanger sequencing results showed hemizygous mutations in the RS1 gene in only 12 probands, including a novel missense mutation in the RS1 gene's signal sequence.

CONCLUSION

This study provides valuable insights into the spectrum of RS1 mutations in X-linked retinoschisis probands from South India. It reveals distinct genotypic-phenotypic associations and highlights the clinical manifestations associated with the disease pathogenesis.

A Carrier Female Manifesting an Unusual X-Linked Retinoschisis Phenotype Associated with the Pathogenic Variant c.266delA, p.(Tyr89LeufsTer37) in RS1, and Skewed X-Inactivation

X-linked retinoschisis (XLRS) is the most common juvenile macular degeneration in males. Unlike most other X-linked retinal dystrophies, carrier heterozygous females are very rarely reported to show clinical features of the disease. Herein, we describe unusual retinal features in a 2-year-old female infant with family history and genetic testing consistent with XLRS.

PHENOTYPE-GUIDED GENETIC TESTING OF PEDIATRIC INHERITED RETINAL DISEASE IN THE UNITED ARAB EMIRATES

PURPOSE

Inherited retinal disease is relatively common in the Arabian Gulf, but details regarding pediatric inherited retinal disease in the region are lacking. The purpose of this study is to report the experience of a regional Ocular Genetics Service with childhood-onset inherited retinal disease in the United Arab Emirates.

METHODS

Retrospective series of consecutive Emirati patients referred to the Ocular Genetics Service of Cleveland Clinic Abu Dhabi over a 3-year period (2016-2018) who were diagnosed with childhood-onset inherited retinal disease (onset before 16 years old) and underwent diagnostic genetic testing guided by clinical phenotype (single gene, next-generation panel, or exome sequencing).

RESULTS

Seventy-one probands were identified (38 male and 33 females), the majority of whom were symptomatic with visual problems within the first 5 years of life. All patients had disease causing mutations in 1 of 26 retinal disease genes. Recessive disease was frequently due to homozygous mutations. The most frequently mutated genes (and number of probands) were ABCA4 (14), KCNV2 (8), CRB1 (6), and CNGA3 (5). Recurrent specific gene mutations included ABCA4 p.Gly1961Glu/p.Leu857Pro, KCNV2 p.Glu143*, MERTK p.Cys738Trpfs*32, and RS1 c.52+3A>G. Some probands had mutations in syndromic genes and were confirmed to have extraocular findings.

CONCLUSION

Phenotype-guided genetic testing had a remarkable yield for this patient population. Recessive disease is often from homozygous mutations. Cone-dominated phenotypes are common. There are apparent founder mutations for several genes that could be used in a targeted genetic testing strategy. Molecular diagnosis is particularly important in affected children when inherited retinal dystrophy could be a sign of syndromic disease as proper earlier diagnosis minimizes potential extraocular morbidity.

Electronegative Electroretinograms in the United Arab Emirates

PURPOSE

An electronegative electroretinogram (ERG), defined as having a b:a wave ratio ≤1 in the scotopic flash ERG response, indicates relative inner retinal dysfunction. Causes vary depending upon the study population. In the Arabian Gulf, where inherited retinal disease is relatively prevalent, common diagnoses associated with electronegative ERGs have not been described. In this study, we report the frequency and causes of electronegative ERGs in a cohort of Emirati patients with inherited retinal disease.

METHODS

A retrospective review was performed of all full-field ERGs done for Emirati patients in the Ocular Genetics Service of Cleveland Clinic Abu Dhabi from January 2017 to December 2019. Those who had an electronegative ERG in at least one eye were included in the study.

RESULTS

Out of 137 patients, 9 probands (6.6%) had an electronegative ERG. The mean age at presentation was 24 years (range 5-48 years), and five patients (55.6%) were male. The final clinical diagnoses were congenital stationary night blindness (CSNB) (two TRPM1-related and one Oguchi disease), X-linked retinoschisis (XLRS) (one genetically confirmed and two not genetically tested), cone-rod dystrophy (one CRX-related and one not genetically tested), and enhanced S-cone syndrome (ESCS) (one NRL-related). The one patient who did not have bilateral electronegative ERGs was a male with XLRS whose fellow eye had an unrecordable ERG.

CONCLUSIONS

In this series of Emirati patients, an electronegative ERG was most commonly associated with the inherited retinal diseases recessive CSNB and XLRS. An electronegative ERG was noted in a case of NRL-related ESCS.