Brainstem frequency-following responses in Rett syndrome.

The brainstem frequency-following response (FFR) is a short-latency evoked response that reflects waveform properties of periodic auditory stimuli. Unlike neural activity evoked by transient stimuli, the FFR originates in phase-locked neurons that provide unique information concerning the early processing of auditory inputs. FFRs elicited by a pure tone were recorded from 9 Rett syndrome patients (age 26-55 years, mean = 34.4 years) and compared with those of 18 normal infants (age 2-10 months, mean = 5.0 months), and 113 young adult (age 18-30 years, mean = 22.2 years) controls. The Rett syndrome pattern indicated considerable intersubject latency variability and poor intrasubject repeat reliability except for brief FFR components which were consistently synchronized. The pattern observed in Rett syndrome was similar in certain respects to that observed in infants, but both patterns differed from those of adults, who showed larger amplitudes and consistent waveform synchrony. Clinical and neuropathologic data indicate developmental arrest rather than a neurodegenerative process in Rett syndrome. The present results are consistent with this interpretation. Neurophysiologic studies may identify markers that are distinctive in Rett syndrome and make it possible to monitor changes with age and disease process.