[Auditory brainstem responses in group A xeroderma pigmentosum]

Xeroderma pigmentosum has been known to result from disturbance in the repair of injured DNA caused by the ultra violet light. According to cell fusion studies, this disease is classified into 8 groups. Among these groups, group A (A-XP) shows the most severe type of neurological disturbance. Slowly progressive diffuse impairment both in the central and the peripheral nervous systems has been reported. Although hearing loss occurs in all the patients, few papers have described the chronological changes of this disability. This study aimed to clarify the development of audiological abnormalities in A-XP patients. We recorded auditory brainstem evoked responses (ABRs) in 20 Japanese children with A-XP. All patients had homozygous intron 3 splicing mutations of xeroderma pigmentosum group A complementing gene, the most common type mutations in Japan. ABR threshold, peak latency of 5th wave and the peak interval latency between the 1st and 5th waves (I-V interpeak latency) were measured, and were compared with those obtained from age-matched controls. ABRs were well detected in all patients examined under 4 years old. The I-V interpeak latencies became shorter with age as in the controls. In 3 ears, the 5th wave was recorded without 1st wave. In 4 ears which no ABRs were detected with 90 dBHL stimulation, the only 5th wave was detected. No waves were obtained from the patients aged over 10 years. The current study revealed that ABR disturbance in A-XP patients became obvious after 4 years of age. In addition, no ABR was found to be identified after 10 years of age. During 4 to 10 years of age, some patients showed the elevation of the threshold of the 5th wave. In A-XP patients, the peripheral nerve was hypothesized to be affected earlier than the central pathway involved in ABR.