A 6yearold boy is referred for genetic counseling. His medical record shows that he had mild congenital hearing loss, which worsened after he fell and hit his head. He has no dysmorphic features and a negative family history. A head CT scan performed after the fall noted bilateral enlargement of the vestibular aqueducts. Which of the following is the MOST likely cause?
A. connexin26 mutations
B. branchiootorenal syndrome C. mitochondrial A1555G mutation
D. Pendred syndrome