Recent evidence suggests that a family of nerve growth factors exist, each effective for a certain population of neurons. Human fibroblasts make a NGF similar to mouse submaxillary NGF in both its immunoreactive and biological properties. However, fibroblasts from patients with the genetically inherited disease familial dysautonomia contain a NGF which is immunoactive but has very low biological activity. Mouse brain contains a factor which is NGF-like by immunoassay but has no biological activity. This factor increases in the cerebella of the pcd mutant mouse as the Purkinje cells die out and astrocytes proliferate. The PC12 pheochromocytoma cell line has been used to study the biological effects of NGF and whether these effects require NGF-receptor endocytosis. Transglutaminase is present in the cells and can be induced by butyrate treatment - the effect of this treatment on the NGF response is being studied.