Tyrosinemia

Test

• Bacterial inhibition assay of tyrosine

Genetics

• Autosomal recessive
• 2:94,000 in 1991
• Nonbreastfeeding Canadian Inuits: 1 in 16

Pathology

• Neonatal tyrosinemia and increased excretion of tyrosine and its metabolites are not uncommon in premature infants.  Type I tyrosinemia (tyrosinosis) is caused by a deficiency of faumarylacetoacetase.  Type II tyrosinemia (Richner-Hanhart Syndrome) is caused by a deficiency of hepatic tyrosine aminotransferase, the rate-limiting enzyme of tyrosine catabolism.

Diagnosis

• Neonatal tyrosinemia -- lethargy, difficulty swallowing, impaired motor activity, prolonged jaundice, and increased levels of galactose, phenyalanine, histidine and cholesterol.  Mild acidosis in about half of the infants.
• Type I acute form -- cabbage-like odor, failure to thrive, vomiting, diarrhea, hepatomegaly, fever, jaundice, edema, melena, and progressive liver disease, which can lead to death in the first year of life.
• Type I chronic form -- milder, chronic liver disease, renal tubular dysfunction (Fanconi syndrome), hypophosphatemic rickets.  Death in the first decade of life.
• Type II -- an oculocutaneous syndrome, findings present in infancy or early childhood.  Skin lesions begin with or after the eye lesions.  Long term effects include conreal scarring and glaucoma.  Mental retardation sometimes reported.

Treatment

• Most cases of neonatal type are transient and can be controlled by reducing protein intake.  Therapy with a diet low in tyrosine and phenylalanine is curative in type II.  Liver transplantation has been beneficial in type I

Acknowledgment

Also see other Inborn Errors of Metabolism.
 

Genetics

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