Type I Tyrosinemia
What Your Test Results Mean:
Carriers typically do not show symptoms of tyrosinemia; however, you may be at an increased risk to have a child affected with tyrosinemia depending on your partner’s carrier status. Carrier testing of your partner is recommended as well as consulting with a genetic counselor.
Type I Tyrosinemia is an inherited metabolic disorder that may present with failure to thrive, diarrhea, vomiting, jaundice, and an increased tendency to bleed. Pathogenic variants in the FAH gene cause a decrease in a liver enzyme called fumarylacetoacetate hydrolase, which cause a dangerous accumulation of tyrosine or its byproducts and are toxic to the liver, kidneys, and other organs and tissues. Type I tyrosinemia can potentially lead to liver and kidney failure, as well as affect the nervous system. Those with this disorder have an increased risk for having liver cancer.
A restriction of tyrosine in the diet is recommended for those affected. A metabolic specialist and dietician typically manage care of individuals with the disorder. Lifespan is not typically decreased in treated individuals; however, death may occur in undetected and untreated individuals early in life.
How the Genetics Works:
Type I tyrosinemia is an autosomal recessive disorder caused by pathogenic variants in the FAH gene. All individuals have two copies of the FAH gene. Carriers of type I tyrosinemia have a variant in one copy of the FAH gene while individuals with the disorder have variants in both copies of their FAH genes, one inherited from each parent. Risk for two carriers to have a child with the disorder is 25%.
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