Hereditary dysfunction of the brain stem auditory pathways as the major cause of speech retardation

Grossly abnormal auditory brain stem responses (ABR) and abnormally high stapedius reflex thresholds were found in 2 pairs of siblings, not akin. Pure tone audiometry showed moderate to moderately severe hearing impairment in all 4 subjects, but neither the ABR findings nor the stapedius reflex thresholds were compatible with pure cochlear lesions. In all the cases the benefit from using hearing aids was conspicuously poor, and the development of oral language markedly retarded, one pair of siblings being essentially incapable of oral--aural communication. A cousin to one of the pairs of siblings showed similar but less pronounced symptoms and signs. Intelligence was judged to be normal in all 5 individuals and neurologic examination did not reveal CNS abnormalities besides the hearing impairment. We assume dysfunction of the brain stem auditory pathways to be the main cause of the speech retardation in the 2 pairs of siblings and the abnormality to be hereditary in nature.