Tyrosinemia type II: Mutation update, 11 novel mutations and description of 5 independent subjects with a novel founder mutation.

BACKGROUND: Tyrosinemia type II, also known as Richner-Hanhart Syndrome, is an extremely rare autosomal recessive disorder, caused by mutations in the gene encoding hepatic cytosolic tyrosine aminotransferase, leading to the accumulation of tyrosine and its metabolites which cause ocular and skin lesions, that may be accompanied by neurological manifestations, mostly intellectual disability. AIMS: To update disease-causing mutations and current clinical knowledge of the disease. MATERIALS AND METHODS: Genetic and clinical information were obtained from a collection of both unreported and previously reported cases. RESULTS: We report 106 families, represented by 143 individuals, carrying a total of 36 genetic variants, 11 of them not previously known to be associated with the disease. Variants include 3 large deletions, 21 non-synonymous and 5 nonsense amino-acid changes, 5 frameshifts and 2 splice variants. We also report 5 patients from Gran Canaria, representing the largest known group of unrelated families sharing the same P406L mutation. CONCLUSIONS: Data analysis did not reveal a genotype-phenotype correlation, but stressed the need of early diagnosis: All patients improved the oculocutaneous lesions after dietary treatment but neurological symptoms prevailed. The discovery of founder mutations in isolated populations, and the benefits of early intervention, should increase diagnostic awareness in newborns.

Maternal and fetal tyrosinemia type I.

A 22 year-old woman with tyrosinemia type I (HT1) married her first cousin who is heterozygous for the same FAH mutation for which the patient is homozygous. During her pregnancy she was treated with diet (prescribed tyrosine intake 300 mg/day), and nitisinone (60 mg/day). Median plasma tyrosine levels were 560 µmol/L (range: 375-838, n = 21) and nitisinone 51 µmol/L (range: 41-57, n = 3) during pregnancy. She gave birth to a clinically healthy girl affected with tyrosinemia type 1. Birth was normal (birth weight 2615 g) and the baby had normal liver function, normal plasma alpha-fetoprotein concentrations, low urinary excretion of phenolic acids and no detectable succinylacetone. At birth, the baby had hypertyrosinemia (860 µmol/L in blood cord) and nitisinone levels of 14 µmol/L. Following molecular confirmation of the diagnosis of HT1 specific treatment began on day 15 by which time she had detectable urinary succinylacetone.