Cohort study of genotype and clinical phenotype in 34 families with familial exudative vitreoretinopathy

Objective To observe and analyze the genotype and clinical phenotype in 34 families of familial exudative vitreoretinopathy associated with (FEVR) gene variation. Methods Cohort study. Thirty-four FEVR families, in which the patients and both of their parents were all found to have FEVR-related gene mutations (proband 34 cases, 67 eyes; parents 68 cases, 136 eyes), were included in the study. These patients were identifIed from 722 FEVR patients through genetic screening, which diagnosed in Department of Ophtalmology of Xinhua Hospital and Tianjin Medical University Eye Hospital from January 2010 to December 2018. The probands and their parents underwent a comprehensive ophthalmological examination appropriate to their age, including BCVA, intraocular pressure, axial length, slit lamp examination, indirect ophthalmoscopy, FFA or color fundus photography or wide field color fundus photography. According to the severity of the disease, the clinical manifestations were divided into severe phenotype and mild phenotype. Thirty-four normal healthy people over 40 years old were included as the control group. The peripheral blood samples of FEVR family members and control group members were collected, and the genes known to be involved in FEVR, such as FZD4, LRP5, NDP, TSPAN12, ZNF408 and KIF11, were analyzed by next generation sequencing molecular genetics. The data were statistically analyzed by SPSS. The counting data was expressed in numbers or rates, and tested by Kruskal-Wallis test and χ2 test to find out the existence of significant difference. Results In 67 eyes of the 34 probands, 48 eyes (71.64%) were classified into severe phenotype and 19 eyes (28.36%) were mild phenotype. In 136 eyes of 68 parents of the proband patients, 76 eyes (55.88%) were normal, 60 eyes (44.12%) were classified into mild phenotype, and no severe phenotype was found. A total of 65 variants of FEVR-related genes were detected in the 34 probands, of which LRP5 mutation was the most common (64.61 %), followed by FZD4 (12.31%), NDP (10.77%), TSPAN12 (6.15%), ZNF408 (4.62%) and KIF11 (1.54%). Missense mutations were the most common variant in FEVR-related genes. However, the results of correlation analysis indicated that there was no significant correlation between the type of mutation and the severity of clinical phenotype (H=1.775, P=0.620). Among the 65 mutation types, 21 types have been previously identified and 44 were novel in this study. Thirty-nine eyes of 20 cases had only one single pathogenic mutation gene but with multiple mutation sites, 26 eyes of 13 cases carried 2 relevant pathogenic mutation genes, and 2 eyes in one case had 3 pathogenic mutation genes. The mutation frequencies of LRP5, NDP, ZNF408, FZD4, TSPAN12 and KIF11 genes in probands were significantly higher than those in control group, and the difference was statistically significant. The total mutation frequencies of LRP5, NDP, ZNF408, FZD4, TSPAN12 and KIF11 genes in proband group were significantly higher than those in control group (χ2=64.702, P <0.001). Conclusions In the FEVR families, the most frequent mutations were those in LRP5, followed by FZD4, NDP, TSPAN12,ZNF408 and KIF11. Missense mutation is the most common type of FEVR-related gene mutation, but there is no significant correlation between the clinical phenotype and gene variation type. Most of the probands were with severe clinical phenotype, while most of the parents with FEVR pathogenic gene mutation showed normal or mild manifestations. Key words: Retinal diseases/genetics; Genotype; Mutation; Familial exudative vitreoretinopathy