Abstract
Background: Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive inherited metabolic disorder caused by the fumerylacetoacetate hydrolase enzyme deficiency. It is characterized by liver dysfunction and/ or failure, renal tubular dysfunction. If left untreated it may lead to Fanconi syndrome and neurological crisis (porphyria-like crisis). Nitisinone is the recommended therapy for HT1 in combination with tyrosine and phenylalanine restricted diet.
Case Presentation: In this report, we present 3 years and 8-months-old boy who was referred to the Metabolic Clinic after his cousin was diagnosed with HT1. His history was significant for pleural effusion at 8 months of age which contributed to pulmonary tuberculosis. His alpha-fetoprotein was checked (for no apparent reason) at one and a half years of age and was elevated. Upon evaluation at 3 years and 8 months at our facility, his succinylacetone was significantly elevated. Liver function tests and coagulation results were also mildly elevated. Liver ultrasound was routine apart from gallstones. Targeted mutation testing revealed a fumarylacetoacetate hydrolase gene’s homozygous pathogenic variant (c.982C>T; p. Gln328*).
Conclusion: In conclusion, we presented a patient with an unusual, late presentation of HT1, to highlight the clinical variability in this rare, treatable metabolic disease.

Key words: Tyrosinemia Type I, Hereditary TyrosinemiaType 1, Nitisinone, FAH, Fumarylacetoacetate Hydrolase