De Novel Heterozygous Copy Number Deletion on 7Q31.31-7Q31.32 Involving TSPAN12 Gene with Familial Exudative Vitreoretinopathy in a Chinese Family.

AIM:To investigate the genetic and clinical characteristics of patients with a large heterozygous copy number deletion on 7q31.31-7q31.32.METHODS:A family with familial exudative vitreoretinopathy (FEVR) phenotype was included in the study. Whole-exome sequencing (WES) was initially used to locate copy number variations (CNVs) on 7q31.31-31.32, but failed to detect the precise breakpoint. The long-read sequencing, Oxford Nanopore sequencing Technology (ONT) was used to get the accurate breakpoint which is verified by quantitative real-time polymerase chain reaction (QPCR) and Sanger Sequencing.RESULTS:The proband, along with her father and younger brother, were found to have a heterozygous 4.5 Mb CNV deletion located on 7q31.31-31.32, which included the FEVR-related gene TSPAN12. The specific deletion was confirmed as del(7)(q31.31q31.32)chr7:g.119451239_123956818del. The proband exhibited a phase 2A FEVR phenotype, characterized by a falciform retinal fold, macular dragging, and peripheral neovascularization with leaking of fluorescence. These symptoms led to a significant decrease in visual acuity in both eyes. On the other hand, the affected father and younger brother showed a milder phenotype.CONCLUSION:The heterozygous CNV deletion located on 7q31.31-7q31.32 is associated with the FEVR phenotype. The use of long-read sequencing techniques is essential for accurate molecular diagnosis of genetic disorders.