Bilateral progressive coats-type exudative retinopathy in Usher syndrome type IIIA from c.528T>G Clarin 1 (CLRN1) mutation

Purpose To describe bilateral, progressive, Coats-type exudative retinopathy in a boy with Usher syndrome type IIIA. Methods An interventional case report from a tertiary referral center. Results A 9-year-old boy with a hearing loss of medium severity diagnosed 4 y earlier developed nyctalopia and began to stumble on objects, leading to suspicion of a visual field defect. His visual acuity (VA) was 20/50 OD and 20/40 OS with no significant refractive error. The RPE was distinctly flecked. Dilated retinal vessels with a confluent accumulation of subretinal lipid were seen temporally, OD, and two similar smaller lesions without obvious vascular pathology, OS. The vitreous showed diffuse cellular or lipoid deposits. The ERG was almost isoelectric and Goldmann visual fields were constricted. Two months later, vision had deteriorated to 20/100 and exudates extended to the macula, OD. He underwent bilateral peripheral cryocoagulation. Genetic testing uncovered the predominant Finnish c.528T>G homozygous mutation of CLRN1 (clarin-1). During the next 8 months, exudates slowly regressed with vision improvement to 20/40, OD, but the telangiectasias appeared leading to extension of exudation to the macular area, OS. Twenty months after a second cryocoagulation, OS, the exudates remain regressed bilaterally with 20/40 vision, OD, and 20/30 vision, OS. Conclusion Bilateral Coats-like exudative retinopathy is well known from diverse types of retinitis pigmentosa and from Usher syndrome type II unrelated to CLRN1. It has not been reported in Usher syndrome type IIIA, which predominates in Finland, highlighting the possibility that other genes may may contribute to Coats’ type retinitis pigmentosa.