Autosomal dominant non-syndromic hearing loss caused by a novel mutation in MYO7A: A case report and review of the literature

Select autosomal dominant DFNA11 deafness mutations activate Myo7A in epithelial cells

Myosin-7A (Myo7A) is a motor protein crucial for the organization and function of stereocilia, specialized actin-rich protrusions on the surface of inner ear hair cells that mediate hearing. Mutations in Myo7A cause several forms of genetic hearing loss, including autosomal dominant DFNA11 deafness. Despite its importance, the structural elements of Myo7A that control its motor activity within cells are not well understood. In this study, we used cultured kidney epithelial cells to screen for mutations that activate the motor-dependent targeting of Myo7A to the tips of apical microvilli on these cells. Our findings reveal that Myo7A is regulated by specific IQ motifs within its lever arm, and that this regulation can function at least partially independent of its tail sequence. Importantly, we demonstrate that many of the DFNA11 deafness mutations reported in patients activate Myo7A targeting, providing a potential explanation for the autosomal dominant genetics of this form of deafness.

Identification of a novel compound heterozygous pathogenic variant in MYO7A causing Usher syndrome type IB in a Chinese patient: a case report

Herein, we report the clinical and genetic features of a patient with Usher syndrome type IB to improve our collective understanding of the disorder. The patient was a teenaged boy with congenital profound hearing loss, progressive visual loss, and vestibular hypoplasia; his parents were phenotypically normal. His pure tone audiometry hearing thresholds were 100 dB at all frequencies, and distortion product otoacoustic emission was not elicited at any frequencies in either ear. Moreover, an auditory brainstem response test at 100 dB normal hearing level revealed no relevant response waves, and a caloric test showed vestibular hypoplasia. Fundus examination revealed retinitis pigmentosa and a reduced visual field. The use of high-throughput sequencing technology to screen the patient's family lineage for deafness-related genes revealed that the patient carried a compound heterozygous pathogenic variant of MYO7A: c.541C > T and c.6364delG. This pathogenic variant has not previously been reported. Our findings may provide a basis for genetic counseling, effective treatment, and/or gene therapy for Usher syndrome.