Impaired P50 sensory gating in Machado-Joseph disease.

OBJECTIVE: Machado-Joseph disease (MJD), an autosomal dominant spinocerebellar degeneration caused by an expanded CAG repeat on chromosome 14q32.1, is a disorder with wide range of neurological findings and brain regions involved. Studies evaluating neurophysiological parameters related to sensory gating in MJD are lacking.
METHODS: This study intends to investigate P50 suppression, an auditory mid-latency evoked potential in a test-conditioning paradigm, considered as an index of sensory gating function. Twelve patients with MJD, 24 normal subjects and 12 schizophrenic patients were evaluated.
RESULTS: MJD subjects had higher P50 ratios as compared to normal subjects (76.2 vs. 42.1%, P = 0.001), but similar to the group of schizophrenic patients. The difference from controls was due to greater test amplitudes (3.4 vs. 2.0 microV, P = 0.002), rather than to conditioning amplitudes. Latencies were higher for the MJD subjects than for controls (60.4 vs. 56.1 ms, P = 0.016).
CONCLUSIONS: MJD may present sensory gating dysfunction. However, the pattern of this dysfunction seems to slightly differ from that classically found in schizophrenia, were both test and conditioning amplitudes seem to be implicated. SIGNIFICANCE: These results point out the P50 paradigm as a potential tool for further neurophysiological surveying in MJD.