Analysis of MYO7A in a Moroccan family with Usher syndrome type 1B: novel loss-of-function mutation and non-pathogenicity of p.Y1719C.

Purpose: Mutations in the MYO7A gene are responsible for Usher syndrome type 1B (USH1B), the most common USH1 subtype, which accounts for the largest proportion of USH1 cases in most populations. Molecular genetic diagnosis in Usher syndrome is well established and identification of the underlying mutations in Usher patients is important for confirmation of the clinical diagnosis and genetic counseling. Methods: We analyzed a large consanguineous USH1 family from Morocco and linked the disease in this family to the MYO7A/USH1B locus. Results: We identified the frequently described missense change p.Y1719C. In addition, we found the homozygous c.1687G>A mutation in the last nucleotide of exon 14, which is predicted to result in aberrant splicing and may lead to loss of MYO7A transcript. We further showed that p.Y1719C is not disease-causing but does represent a frequent polymorphism in the Moroccan population, with an estimated carrier frequency of 0.07. Conclusions: This finding has an important impact for molecular diagnosis and genetic counseling in USH1B families.