The characteristics of digenic familial exudative vitreoretinopathy.

Aim: To describe and analyse the clinical and genetic characteristics of digenic familial exudative vitreoretinopathy (FEVR).
Methods: The study cohort consisted of patients with FEVR (n = 13) to identify patients with two mutations in two different genes. A genetic analysis of the LRP5, FZD4, TSPAN12, and ZNF408 genes was performed with next-generation sequencing (NGS). The genotype data obtained from the patients with FEVR were analysed and correlated with their clinical manifestations. They were then further evaluated in conjunction with other data that were available for these genes. The probands and parents/relatives underwent comprehensive age-appropriate ophthalmic examinations.
Results: The medical history and genetic reports of 487 patients with FEVR were reviewed. In all, we identified 13 probands (2.67%, 13/487) with simultaneous mutations in two disease-causing genes. A total of 25 of mutations were found, including10 in FZD4, 8 in LRP5, 3 in ZNF408, 2 in NDP, and 2 in TSPAN12. The most frequent mutations were those in FZD4 and LRP5. We identified 8 mutations that had previously been identified and 17 novel variants. Among 26 eyes, 65.38% exhibited a phenotype, and 10 (38.46%) were stage 4, while 7 (26.92%) were stage 5.
Conclusions: This is the first study to report a group of patients with digenic FEVR. In most affected eyes, the stage was more severe than stage 3. We speculate that the phenotype of FEVR is more severe in patients with digenic rather than monogenic variants of FEVR-related genes.