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Tyrosinemia type 1 (Tyr 1) is an autosomal recessive condition caused by fumarylacetoacetate hydrolase (FAH) deficiency. Tyr 1 can cause severe liver disease, hypophosphatemic rickets, renal tubular dysfunction, and neurologic crises. If left untreated, most patients die of liver failure in the first years of life. Treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3 cyclohexanedione is available and is particularly effective when initiated in newborns. The incidence of Tyr 1 is approximately 1 in 100,000 live births.
While tyrosine can be determined by routine newborn screening, it is not a specific marker for Tyr I and often may be associated with common and benign transient tyrosinemia of the newborn. Succinylacetone (SUAC) is a specific marker for Tyr I, but is not detectable by routine newborn screening. This assay determines SUAC in newborn blood spots by tandem mass spectrometry. Additional follow-up testing may include confirmatory molecular analysis of the FAH gene.
Second-tier newborn screening for tyrosinemia type 1 (Tyr 1) in blood spots with nonspecific elevations of tyrosine
Diagnosis of Tyr 1
Follow-up of patients with Tyr 1
Normal: <5.0 mcM
Elevations of succinylacetone (SUAC) above the reference range are indicative of tyrosinemia type 1 (Tyr 1).
Patients with Tyr I who are treated with diet and/or 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3 cyclohexanedione (nitisinone) should have declining or normal values of SUAC.
Normal levels may be seen in affected individuals undergoing treatment.
An interpretive report will be provided.
1. Larochelle J, Alvarez F, Bussieres JF, et al: Effects of nitisinone (NTBC) treatment on the clinical course of hepatorenal tyrosinemia in Quebec. Mol Genet Metab 2012;107(1-2):49-54
2. Mitchell GA, Grompe M, Lambert M, Tanguay RM: Hypertyrosinemia. In The Metabolic and Molecular Bases of Inherited Disease. Eighth edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 1777-1805