Tyrosinemia type I is caused by mutations – or genetic changes – in the FAH gene. This gene encodes for the FAH protein, which is required in the last step of breaking down the amino acid tyrosine.
Now if the FAH gene is altered, the FAH protein will not be produced properly and will no longer be able to perform its normal function. This leads to the improper breakdown of tyrosine, causing various metabolic products to accumulate. This in turn results in damage to the liver, kidneys, and nerves.
Tyrosinemia type I is found in around one in 100,000-120,000 people. It occurs much more frequently in Scandinavia, Finland, and Quebec (Canada). It can be passed on by parents to their children, as an autosomal-recessive disease.