[Clinical and genetic analysis of a patient with tyrosinemia type I but without elevated succinylacetone]

To analyze the clinical manifestation and genetic mutation of a child with tyrosinemia type I but without elevated succinylacetone.

Clinical data of the patient was collected. Tandem mass spectrometry and gas chromatography mass spectrometry were used to analyze the blood amino acid and urine organic acid component of the proband. DNA was extracted from the child and his parents and used for mutation analysis.

The proband was of acute type, with features including hepatomegaly, jaundice, anemia and tendency of bleeding. Serum levels of Tyrosine, Methionine and Phenylalanine were 397.12 μmol/L, 896.16 μmol/L and 292.52 μmol/L, respectively, which all distinctly exceeded the normal levels. The level of phenyllactic acid and 4-hydroxyphenyl-lactic acid of proband's urine were 17.4 μmol/L and 417.0 μmol/L, respectively, which also exceeded the normal levels, but the level of succinylacetone was within the normal range. Compound heterozygous mutations of the FAH gene, namely c.634delT (p.L212Wfs*20) and c.455G>A (p.W152X), were detected in the proband, which were both predicted to be pathogenic and were inherited from her father and mother, respectively.

For children with tyrosinemia type I, detection of urine succinylacetone by gas phase mass spectrometry can be negative. The diagnosis of tyrosinemia type I must rely on genetic testing and/or enzymatic assaying.