A high level of succinylacetone (SA) in blood is a sensitive, specific newborn screening marker for hepatorenal tyrosinemia type 1 (HT1, MIM 276700) caused by deficiency of fumarylacetoacetate hydrolase (FAH).
The finding that the Fah gene in wild-type mice is highly expressed only in cell types that develop a phenotype in mutants, and the fact that Fah deficiency determines the human liver disease hereditary tyrosinemia type 1 (HT1), suggested that disruption of the Fah gene was responsible for the lethal albino phenotype.
Recently, we identified a splice mutation and two nonsense mutations in the fumarylacetoacetate hydrolase gene in two patients from Quebec with tyrosinemia type I.
Children born with fumarylacetoacetate hydrolase (FAH) mutations suffer from Hepatorenal Tyrosinemia Type 1 (HT-1) resulting in renal dysfunction, liver failure, neurological impairments, and cancer.
A mosaic pattern of immunoreactive fumarylacetoacetase (FAH) protein was found in liver tissue in 15 of 18 tyrosinemia type I patients of various ethnic origins.
The severe type I tyrosinemia, caused by a deficiency of fumarylacetoacetate hydrolase which functions downstream of HPD in the tyrosine degradation pathway, is often associated with decreased expression of HPD, and interestingly, inhibition of HPD activity seems to ameliorate the clinical symptoms of type I tyrosinemia.
To determine the utility of this approach, cells were isolated from the livers of non-heart-beating cadaveric mice long after death and transplanted into fumarylacetoacetate hydrolase-deficient mice, a model for the human metabolic liver disease hereditary tyrosinemia type I and a stringent in vivo model for hepatic cell transplantation.
The mechanistic insights reported here pave the way for the development of pharmacological chaperones that target FAH to tackle the severe disease HT1.
The human fumarylacetoacetase gene: characterisation of restriction fragment length polymorphisms and identification of haplotypes in tyrosinemia type 1 and pseudodeficiency.
(6) Fumarylacetoacetate hydrolase (FAH) deficiency (tyrosinemia type I) may lead to hypermethioninemia secondary either to liver damage and/or to accumulation of fumarylacetoacetate, an inhibitor of the high K(m) MAT.
In summary, the extent of mutation reversion of the FAH gene in the liver of HTI patients was inversely correlated with the clinical severity of the disease, suggesting that the corrected hepatocytes play a substantial protective role in liver function.