Whole-exome sequencing identifies novel mutations in genes responsible for retinitis pigmentosa in 2 nonconsanguineous Chinese families

Biallelic occult macular dystrophy

PURPOSE

Occult macular dystrophy (OMD) is a cause of visual loss in young adults with a grossly normal fundus appearance. It is considered an autosomal dominant disorder, related to heterozygous pathogenic variants in the gene RP1L1. The purpose of this study is to report a biallelic form of the disease.

RESULTS

A 29-year-old female had undergone neurological workup and ophthalmic examinations for transient visual loss in her left eye over the past two years but there was no definitive diagnosis. The best-corrected visual acuity was 20/30, 20/20. Indirect ophthalmoscopy with a 78D lens revealed subtle central retinal pigment epithelium mottling and optical coherence tomography confirmed subtle central thickening of the ellipsoid zone. Full-field electroretinography was normal, but pattern electroretinography showed decreased p50 responses. OMD was suspected. Retinal gene panel testing was significant only for a homozygous variant in RP1L1 (NM_178857.6: c.3571 G>T; p.Glu1191*). The parents and older brother were unavailable for segregation analysis. By history they did not have visual complaints other than a need for glasses.

CONCLUSIONS

This report presents the clinical and genetic findings of a biallelic form of OMD associated with a novel pathogenic variant in RP1L1. It would be of interest to carefully assess macular function in heterozygotes with this variant.

Morphological and Functional Comparison of Mice Models for Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the predominant form of inherited retinal degenerations (IRDs) caused by abnormalities and loss of photoreceptor cells ensuing diminishment of vision. RP is a heterogenous genetic disorder associated with mutations in over 80 genes, showing various inheritance patterns. Laboratory mouse models are important for our understanding of disease mechanisms, modifier effects, and development of therapeutic modalities. In this review, we have summarized a comprehensive comparison of our previously reported Fam161a knockout (KO) mouse model with other well-studied RP mouse models, Fam161aGT/GT, Pde6brd1, Nr2e3rd7, Rpgrrd9, and Pde6brd10 using structural and functional analysis of the retina. Fam161atm1b/tm1b mouse models are important for developing novel therapies and mainly AAV-based gene therapy and translational read-through-inducing drugs.

Interactions between C8orf37 and FAM161A, Two Ciliary Proteins Essential for Photoreceptor Survival

Mutations in C8orf37 cause Bardet-Biedl syndrome (BBS), retinitis pigmentosa (RP), and cone-rod dystrophy (CRD), all manifest in photoreceptor degeneration. Little is known about which proteins C8orf37 interacts with to contribute to photoreceptor survival. To determine the proteins that potentially interact with C8orf37, we carried out a yeast two-hybrid (Y2H) screen using C8orf37 as a bait. FAM161A, a microtubule-binding protein localized at the photoreceptor cilium required for photoreceptor survival, was identified as one of the preys. Double immunofluorescence staining and proximity ligation assay (PLA) of marmoset retinal sections showed that C8orf37 was enriched and was co-localized with FAM161A at the ciliary base of photoreceptors. Epitope-tagged C8orf37 and FAM161A, expressed in HEK293 cells, were also found to be co-localized by double immunofluorescence staining and PLA. Furthermore, interaction domain mapping assays identified that the N-terminal region of C8orf37 and amino acid residues 341-517 within the PFAM UPF0564 domain of FAM161A were critical for C8orf37-FAM161A interaction. These data suggest that the two photoreceptor survival proteins, C8orf37 and FAM161A, interact with each other which may contribute to photoreceptor health.

Prognosis and treatment of 46 Chinese pediatric cystic fibrosis patients

BACKGROUND

Since public awareness of cystic fibrosis (CF) has increased, more children have been diagnosed with CF in China. This study aimed to investigate medical and other challenges faced by pediatric CF patients in China.

METHOD

Treatments and treatment outcomes were retrospectively analyzed for 46 pediatric CF patients diagnosed from August 2009 to June 2019. Pre- and post-treatment results were compared using independent samples t-test.

RESULTS

Of 46 pediatric CF study patients, four died and five were lost to follow-up. Thirty-seven patients were monitored for 0.03 to 9.21 years; patients exhibited fewer attacks of respiratory tract infections after diagnosis (4.49 ± 2.13 episodes/year before diagnosis vs 1.97 ± 1.87 times/year after 1-year treatment, p < 0.05), significantly reduced sputum production and experienced 1.62 ± 1.71 exacerbations/year. Patient mean body mass index was 16.87 ± 3.53 and pancreatic malfunction persisted in 15 patients. For 17 children, no significant differences in lung function were found at follow-up as compared to lung function at diagnosis (FEV₁: 82.45% ± 16.56% vs 75.26% ± 22.34%, FVC: 87.18% ± 13.64% vs 86.99% ± 19.95%, FEF_75%: 46.51% ± 28.78% vs 36.63% ± 24.30%, P = 0.27, 0.97, 0.20, respectively). Pseudomonas aeruginosa (17/27) and bronchiectasis (22/22) were found during follow-up evaluation. Twenty-four patients (64.8%) maintained good adherence to therapies. Overall, azithromycin and tobramycin treatments were administered for 0.5-62 months and 0.5-48 months, respectively, and triggered no obvious adverse reactions.

CONCLUSION

No obvious declines in clinical presentation or lung function were found in Chinese pediatric CF patients after receiving standard therapeutic and active treatments, although malnutrition and low compliance were persistent challenges.

Autosomal Recessive Rod-Cone Dystrophy Associated With Compound Heterozygous Variants in ARL3 Gene

Purpose: ARL3 (ADP-ribosylation factor-like 3) variants cause autosomal dominant retinitis pigmentosa (RP) or autosomal recessive Joubert syndrome. We found a family with rod-cone dystrophy (RCD) and verified it was associated with compound heterozygous variants in ARL3 gene. Methods: Ophthalmic examinations including optical coherence tomography and electroretinogram (ERG) were performed. Targeted next generation sequencing (NGS) was performed for the proband using a custom designed panel. Sanger sequencing and co-segregation were conducted in the family members. Changes of protein structure mediated by the variants were studied in vitro. ARL3 protein stability and its interaction with RP2 protein were assessed by cycloheximide chase assay and co-immunoprecipitation (Co-IP) assay. Results: Visual acuity of the 18-year-old male proband was 0.25 in the right and 0.20 in the left eye, while his non-consanguineous parents and sister was normal. The proband showed signs of RCD, including nyctalopia, peripheral field loss, bone-spicule deposits in the retina, and reduced ERG responses. The father, aged 50 years old, showed visual acuity of 1.0 in both eyes. Unlike the proband, he presented late onset and mild cone-rod dystrophy (CRD), including macular atrophy, central scotomata, moderate reduction in photopic ERG responses. None of all the family members had hearing abnormality, mental dysplasia or gait instability. We identified two novel compound heterozygous variants (c.91A>G, p.T31A; c.353G>T, p.C118F) in ARL3 in the proband, while his father only had variant c.91A>G. Bioinformatics analysis indicated amino acid positions of the two variants are highly conserved among species. The in silico tools predicted the variants to be harmful. Protein structure analysis showed the two variants had potential to alter the protein structure. Based on the ACMG guidelines, the two variants were likely pathogenic. In addition, the ARL3 mutations destabilized ARL3 protein, and the mutation c.353G>T disrupted the interaction between ARL3 and RP2 in HEK293T cells. Conclusions: We showed novel compound heterozygous variants in ARL3 were associated with early onset of autosomal recessive RCD, while c.91A>G along may be associated with a late onset of dominant CRD. The two variants in ARL3 could be causative by destabilizing ARL3 protein and impairing its interaction with RP2 protein.

Identification of a novel homozygous variant in the CNGA1 gene in a Chinese family with autosomal recessive retinitis pigmentosa

Retinitis pigmentosa (RP) is a complex group of hereditary retinal dystrophies. Although >60 genes have been identified to be associated with non-syndromic RP, the exact genetic variant remains elusive in numerous cases of RP. In the present study, a Chinese pedigree affected by RP with autosomal recessive inheritance, including a total of seven members with one affected patient and six unaffected individuals, was recruited. Comprehensive ophthalmic examinations were performed on the proband and the proband's unaffected daughter. Genomic DNA was extracted from peripheral blood. Whole-exome sequencing (WES) was performed for the affected individual. The candidate pathogenic variant was verified by direct Sanger sequencing. The affected individual presented with classical clinical symptoms of RP. A novel homozygous variant, c.265delC (p.L89Ffs*3) in the cyclic nucleotide-gated channel subunit α 1 gene was identified in the affected patient. This homozygous variant was absent in other unaffected family members and 600 ethnicity-matched healthy controls. The variant was co-segregated with the disease phenotype in an autosomal recessive manner.