Identification of two novel LRP5 mutations in families with familial exudative vitreoretinopathy

PURPOSE To investigate the clinical features and disease-causing mutations in two Chinese families with familial exudative vitreoretinopathy (FEVR). METHODS Clinical data and genomic DNA were collected for patients with FEVR. The coding exons and adjacent intronic regions of FZD4, LRP5, TSPAN12, and NDP were amplified with PCR, and the resulting amplicons were analyzed with Sanger sequencing. Wild-type and mutant LRP5 proteins were assayed for the Norrin/β-catenin pathway by luciferase reporter assays. RESULTS Two novel heterozygous mutations in the LRP5 gene were identified in two relatives--p.A422T and p.L540P. Typical FEVR fundus change and mild reduced bone mineral density (BMD) was found in the two patients and the affected parent. In the luciferase studies, both p.A422T and p.L540P mutants displayed a significant reduction of the luciferase activity in SuperTopFlash (STF) cells in response to Norrin (87% reduction for p.A422T and 97% reduction for p.L540P). Both patients had an additional LRP5 sequence change (p.Q816P in Patient 1 from the unaffected mother and p.T852M in Patient 2 verified as a new mutation). Luciferase assay showed no reduction for p.Q816P and 94.9% reduction for the new mutation p.T852M, suggesting that p.Q816P may be not pathogenic and p.T852M may be pathogenic. CONCLUSIONS Our findings demonstrated two new novel LRP5 mutations in Chinese patients with FEVR and mild reduced BMD. They emphasize the complexity of FEVR mutations and phenotypes.