Trichothiodystrophy (brittle sulfur-deficient hair) is a marker for several 
autosomal recessive neurocutaneous syndromes with neurological manifestations 
and mental retardation. In Tay syndrome, the trichothiodystrophy is accompanied 
by congenital ichthyosis, short stature, delayed physical and mental development 
and pyramidal tract signs with increase in muscular tone and brisk tendon 
reflexes. The pathogenesis of these neurological manifestations is not fully 
elucidated. We present a case of Tay syndrome in which a cranial MRI revealed an 
almost total lack of myelin within the cerebral hemispheres and a patchy 
hypomyelination of the cerebellum. In accordance, a strongly prolonged visual 
evoked response pointed to a dysfunction of the white matter in Tay syndrome.