Two missense mutations causing tyrosinemia type 1 with presence and absence of immunoreactive fumarylacetoacetase.

Hereditary tyrosinemia type 1, due to a deficiency of fumarylacetoacetase (FAH), is characterized by progressive liver damage and renal tubular dysfunction and may occur in an acute or a chronic form. An Ala 134 to Asp (GCT to GAT) transition was found in one Turkish and two Norwegian patients with chronic tyrosinemia. SphI digestion of polymerase chain reaction (PCR) amplified genomic DNA identified the mutation and showed that the patients were heterozygous. All these patients had immunoreactive FAH protein in fibroblasts. Another Norwegian patient with chronic disease, without FAH immunoreactive material in fibroblasts, had a Pro 342 to Leu mutation (CCG to CTG). This mutation was identified by MspI digestion of PCR amplified genomic DNA, and the patient was heterozygous. Northern blotting showed FAH mRNA of normal size and amounts in all patients. Site directed mutagenesis and translation in a rabbit reticulocyte lysate demonstrated that both mutations abolished FAH activity.