Genetic Deciphering of Early-Onset and Severe Retinal Dystrophy Associated with Sensorineural Hearing Loss

Abstract

The specific association of Leber congenital amaurosis (LCA) or early-onset severe retinal dystrophy (LCA-like) with sensorineural hearing loss (SHL) is uncommon. Recently, we ascribed some of these distinctive associations to dominant and de novo mutations in the β-tubulin 4B isotype-encoding gene (TUBB4B), providing a link between a sensorineural disease and anomalies in microtubules behavior. Here, we report 12 sporadic cases with LCA/SHL or LCA-like/SHL and no TUBB4B mutation. Trio-based whole exome sequencing (WES) identified disease-causing mutations in 5/12 cases. Four out of five carried biallelic mutations in PEX1 (1/4) or PEX6 (3/4), involved in peroxisome biogenesis disorders from Zellweger syndrome characterized by severe neurologic and neurosensory dysfunctions, craniofacial abnormalities, and liver dysfunction to Heimler syndrome associating SHL, enamel hypoplasia of the secondary dentition, nail abnormalities, and occasional retinal disease. Upon reexamination, the index case carrying PEX1 mutations, a 4-year-old girl, presented additional symptoms consistent with Zellweger syndrome. Reexamination of individuals with PEX6 mutations (1/3 unavailable) revealed normal nails but enamel hypoplasia affecting one primary teeth in a 4-year-old girl and severe enamel hypoplasia of primary teeth hidden by dental prosthesis in a 50-year-old male, describing a novel PEX6-associated disease of the Zellweger/Heimler spectrum. Finally, hemizygosity for a CACNA1F mutation was identified in an 18-year-old male addressed for LCA/SHL, redirecting the retinal diagnosis to congenital stationary night blindness (CSNB2A). Consistent with the pure CSNB2A retinal involvement, SHL was ascribed to biallelic mutations in another gene, STRC, involved in nonprogressive DFNB16 deafness.