Tyrosinemia type I

Tyrosinemia type 1 is a disorder of amino acid metabolism characterized by hepatorenal manifestations.

The prevalence is estimated at 1 case between two million.

In childhood acute form, onset occurs between 15 days and 3 months old, hepatocellular necrosis associated with vomiting, diarrhea, jaundice, hypoglycemia, edema, ascites and signs of bleeding. Sepsis is a common complication, and the appearance of tubulopathy, associated with loss of phosphate and hypophosphatemic rickets. Also it described a form of late-onset manifested by vitamino-resistant rickets, caused by tubulopathy.
If left untreated, the acute form may be complicated by neurologic crises with porphyria, polyneuritis and dystonia, and in rare cases, can be characteristic features present in the disease. It is often the occurrence of malignant hepatomas.

The disease is transmitted by autosomal recessive traits and is caused by a deficiency in fumaryl-acidoacetasa (FAH, 15q23-q25), an enzyme involved in the catabolism of tyrosine. FAH deficiency leads to inhibition of delta-aminolevulinate hydratase D, a key enzyme in the synthesis of porfobilinógenos.

The diagnosis is confirmed by detection of increased delta-aminolevulinic in urine and the characteristic profiles of gas chromatography urine acid, which show increasing levels of succinyl-acetone. Assays of enzymatic activity in fibroblasts FAH, are also possible and may be useful for diagnosis.

The treatment is based on the administration of nitisinone (NTBC, combined with dietary protein restriction to prevent hypertyrosinemia. Despite treatment, some patients develop hepatoma with elevated alpha-fetoprotein and require liver transplant.

GENE OR REGION STUDIED

• FAH