Novel Exon 7 Deletions in TSPAN12 in a Three-Generation FEVR Family: A Case Report and Literature Review

Mutations in TSPAN12 gene causing familial exudative vitreoretinopathy

BACKGROUND

To report newly found TSPAN12 mutations with a unique form of familial exudative vitreoretinopathy (FEVR) and find out the possible mechanism of a repeated novel intronic variant in TSPAN12 led to FEVR.

RESULTS

Nine TSPAN12 mutations with a unique form of FEVR were detected by panel-based NGS. MINI-Gene assay showed two splicing modes of mRNA that process two different bands A and B, and mutant-type shows replacement with the splicing mode of Exon11 hopping. Construction of wild-type and mutant TSPAN12 vector showed the appearance of premature termination codons (PTC). In vitro expression detection showed significant down-regulated expression level of TSPAN12 mRNAs and proteins in cells transfected with mutant vectors compared with in wild-type group. On the contrary, translation inhibitor CHX and small interfering RNA of UPF1 (si-UPF1) significantly increased mRNA or protein expression of TSPAN12 in cells transfected with the mutant vectors.

CONCLUSIONS

Nine mutations in TSPAN12 gene are reported in 9 FEVR patients with a unique series of ocular abnormalities. The three novel TSPAN12 mutations trigger NMD would cause the decrease of TSPAN12 proteins that participate in biosynthesis and assembly of microfibers, which might lead to FEVR, and suggest that intronic sequence analysis might be a vital tool for genetic counseling and prenatal diagnoses.

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.