Fumarylacetoacetate Hydrolase (FAH)

In an individual homozygous for pseudodeficiency of FAH and in 3 hereditary tyrosinemia type I families also carrying the pseudodeficiency allele, Western blotting of fibroblast extracts showed that the pseudodeficiency allele gave very little immunoreactive FAH protein, whereas Northern analysis revealed a normal amount of FAH mRNA. All the pseudodeficiency alleles were found to carry a C-to-T transition in nucleotide 1021, predicting an arg341-to-trp substitution. Site-directed mutagenesis and expression in a rabbit reticulocyte lysate system demonstrated that the arg341-to-trp mutation gave reduced FAH activity and reduced amounts of the full-length protein. The normal and the mutated sequences could be distinguished by BsiEI restriction digestion of PCR products.