Chromosomal instability in hereditary tyrosinemia type I.

Autopsy of a 4-year-old girl with hereditary tyrosinemia type I revealed a hepatocellular carcinoma in addition to cirrhosis and renal tubular dysplasia. Cytogenetic studies performed on a skin fibroblast culture demonstrated greatly increased chromosome breakage, which affected 71% of the cells. This suggests that the development of hepatoma, which is frequent in this syndrome, and the presence of dysplastic changes of hepatocytes in nontumorous liver are related to genetic instability caused by accumulation of intermediates of tyrosine catabolism, which are natural alkylating agents (e.g., maleylacetoacetate and fumarylacetoacetate). The other microscopic structural changes seen, such as renal tubular atypia, pancreatic islet cell hyperplasia, and focal necrosis of cortical neurons, may also be partly due to DNA damage caused by the accumulation of abnormal metabolites produced in patients with type 1 tyrosinemia.