Familial pellagra-like skin rash with neurological manifestations

A 14-year-old boy of Arabic origin presented with a pellagra-like rash and neurological manifestations including ataxia, dysarthria, nystagmus, and coma. There was a striking response to oral nicotinamide. The laboratory findings were not typical of Hartnup disease: aminoaciduris and indicanuria were absent and there was no evidence of tryptophan malabsorption. Tryptophan loading did not induce tryptophanuria nor did it increase excretion of xanthurenic or kynurenic acids. These findings support the possibility of a block in tryptophan degradation. The family history suggests a genetically-determined disorder.