TRICHOTHIODYSTROPHY WITHOUT PHOTOSENSITIVITY - BIOCHEMICAL, ULTRASTRUCTURAL AND DNA-REPAIR STUDIES

A case of trichothiodystrophy (TTD) without photosensitivity is reported in an 8-year-old girl. Electron microscopic (EM) examination of the keratinocytes showed fibrillary bundles in the cytoplasm thinner and less electron dense than those of the normal cells and large membrane-bound vacuoles filled with granular-filamentous material. These findings could indicate a disturbance in the protein metabolism in tissues of ectodermal origin, explaining also the functional abnormalities of the central nervous system in TTD patients. The results of cellular DNA repair studies after UV irradiation in cultured fibroblasts showed normal levels of unscheduled DNA synthesis. This finding indicates that UV hypersensitivity is not constantly present in TTD

Evoked cochlear potentials in the barn owl

Gross electrical responses to tone bursts were measured in adult barn owls, using a single-ended wire electrode placed onto the round window. Cochlear microphonic (CM) and compound action potential (CAP) responses were evaluated separately. Both potentials were physiologically vulnerable. Selective abolishment of neural responses at high frequencies confirmed that the CAP was of neural origin, while the CM remained unaffected. CAP latencies decreased with increasing stimulus frequency and CAP amplitudes were correlated with known variations in afferent fibre numbers from the different papillar regions. This suggests a local origin of the CAP along the tonotopic gradient within the basilar papilla. The audiograms derived from CAP and CM threshold responses both showed a broad frequency region of optimal sensitivity, very similar to behavioural and single-unit data, but shifted upward in absolute sensitivity. CAP thresholds rose above 8 kHz, while CM responses showed unchanged sensitivity up to 10 kHz