Auditory neuropathy spectrum disorder and related auditory features in patients with hearing loss associated with the MT-TS1 m.7471dup variant

The m.7471dup variant of mitochondrial-tRNA Ser (UCN) (MT-TS1) is associated with sensorineural hearing loss (SNHL), neurological abnormalities, or both. Phenotypic variations in SNHL associated with the m.7471dup variant were the focus of our investigation. Five Japanese families carrying the variant were subjected to comprehensive genetic and clinical evaluations and audiometric testing. Notably, two families presented with auditory neuropathy spectrum disorder (ANSD), and two other families presented with auditory brainstem response thresholds much higher than those expected from the pure-tone audiometry results, which is analogous to ANSD. This is the first study to demonstrate that the m.7471dup variant can be associated with ANSD or similar characteristics. The penetrance of the m.7471dup variant was 71.4 % overall, with 100 % penetrance in cases with homoplasmy and 42.9 % penetrance in cases with heteroplasmy. Disease onset was congenital or early onset (≤ 6 years) in 80 % of the patients. The hearing levels ranged from normal to profound, and four subjects presented with neurological or psychiatric abnormalities. About 80 % of subjects who had newborn hearing screening passed the screening, suggesting late-onset or progressive hearing loss. These findings underscore the importance of rigorous follow-up evaluations, genetic counseling, and evaluation of educational environment considerations for patients carrying the m.7471dup variant.