A homozygous in-frame duplication within the LRRCT consensus sequence of CFAP410 causes cone-rod dystrophy, macular staphyloma and short stature

Double Hyperautofluorescence Rings as a Sign of CFAP410-related Retinopathy

Purpose

Variants in CFAP410 have been reported to cause retinal dystrophy with or without systemic symptoms. This study was designed to characterize the fundus changes of patients with biallelic variants in CFAP410.

Methods

Variants in CFAP410 were identified through whole exome sequencing and targeted exome sequencing of 10,530 probands. Biallelic variants in CFAP410 were evaluated by comprehensive in silico analysis and confirmed by Sanger sequencing and segregation analysis. Ocular phenotypes including fundus photographs, scanning laser ophthalmoscopy, autofluorescence images, ERG, and optical coherence tomography were characterized.

Results

Nine patients from eight families were homozygotes or compound heterozygotes for a total of four variants in CFAP410, including c.144-6_159del (novel), c.340_351dup, c.347C>T, and c.545+1G>A. Three patients were diagnosed with cone-rod dystrophy, and the remaining six patients with RP. Among eight patients performed with ultra-wide scanning laser ophthalmoscopy, double hyperautofluorescence rings inside and outside of the macular vascular arcades were observed in six patients, and the remaining two older patients demonstrated single hyperautofluorescence ring surrounded by pigmentation. CFAP410-associated retinopathy in early stage was generally tapetoretinal degeneration without noticeable bone spicule pigmentation, with more severe degeneration in the inferior nasal retina. ERG recordings delineated a severely reduced cone response and mildly to severely reduced rod response. Posterior staphyloma was seen in seven patients who underwent optical coherence tomography examinations.

Conclusions

The present study demonstrates the fundus characteristics of patients with biallelic variants in CFAP410 and expands the genotype-phenotype spectrum of CFAP410-related retinal degeneration, in which posterior staphyloma together with double hyperautofluorescence rings might be common peculiar signs.

Pathogenicity and functional analysis of CFAP410 mutations causing cone-rod dystrophy with macular staphyloma

Background

Cone-rod dystrophy (CORD) caused by pathogenic variants in CFAP410 is a very rare disease. The mechanisms by which the variants caused the disease remained largely unknown. CFAP410 pathogenic variants were identified in a cone-rod dystrophy with macular staphyloma patient. We explored the pathogenicity and performed functional analysis of two compound heterozygous mutations.

Methods

A 6-year-old boy complained decreased vision for 1 year, underwent ocular examinations together with systemic X-ray check. Blood sample was taken for targeted next generation sequencing (Tg-NGS). Pathogenicity of identified variants was determined by ACMG guideline. Mutated plasmids were constructed and transferred to HEK293T cells. Cell cycle, protein stability, and protein ubiquitination level was measured.

Results

The best-corrected visual acuity of proband was 0.20 bilaterally. Fundus showed macular staphyloma and uneven granular pigment disorder in the periphery of the retina. SS-OCT showed thinning and atrophy of the outer retina, residual ellipsoid zone (EZ) in the fovea. Scotopic and photopic ERG responses severe reduced. Two heterozygous missense pathogenic variants, c.319 T > C (p.Tyr107His) and c.347 C > T (p.Pro116Leu) in exon 4 of the CFAP410, were found and were pathogenic by the ACMG guideline. In vitro, pathogenic variants affect cell cycle. Immunofluorescence and western blotting showed that the mutant proteins decreased expression levels protein stability. Meanwhile, co-IP data suggested that ubiquitination level was altered in cells transferred with the mutated plasmids.

Conclusion

Compound heterozygous pathogenic variants c.319 T > C and c.347 C > T in CFAP410 caused CORD with macular staphyloma. The pathogenic mechanisms may be associated with alternations of protein stability and degradation through the ubiquitin-proteasome pathway.

C21orf2 variants causing inherited retinal disease: A review of what we know and a report of two new suspected cases

Variants in the C21orf2 (CFAP410) gene have recently been associated with the development of retinitis pigmentosa, an inherited condition characterized by degeneration of the retina. In this article, we describe 34 previously reported cases of C21orf2 variant-associated retinopathies and present two new suspected cases.