FUNGAL METABOLIC MODEL FOR HUMAN TYPE-I HEREDITARY TYROSINEMIA

Type I hereditary tyrosinaemia (HT1) is a severe human inborn disease resulting from loss of fumarylacetoacetate hydrolase (Fah), Homozygous disruption of the gene encoding Fah in mice causes neonatal lethality, seriously limiting use of this animal as a model, We report here that fahA, the gene encoding Fah in the fungus Aspergillus nidulans, encodes a polypeptide showing 47.1% identity to its human homologue. fahA disruption results in secretion of succinylacetone (a diagnostic compound for human type I tyrosinaemia) and phenylalanine toxicity. We have isolated spontaneous suppressor mutations preventing this toxicity, presumably representing loss-of-function mutations in genes acting upstream of fahA in the phenylalanine catabolic pathway. Analysis of a class of these mutations demonstrates that loss of homogentisate dioxygenase (leading to alkaptonuria in humans) prevents the effects of a Fah deficiency, Our results strongly suggest human homogentisate dioxygenase as a target for HT1 therapy and illustrate the usefulness of this fungus as an alternative to animal models for certain aspects of human metabolic diseases.