[Analysis of IVD gene variants in four children with isovalerate acidemia].

OBJECTIVE
To detect variants of IVD gene among 4 neonates with suspected isovalerate acidemia in order to provide a guidance for clinical treatment.


METHODS
111 986 newborns and 7461 hospitalized children with suspected metabolic disorders were screened for acyl carnitine by tandem mass spectrometry. Those showing a significant increase in serum isovaleryl carnitine (C5) were analyzed for urinary organic acid and variants of the IVD gene.


RESULTS
Four cases of isovalerate acidemia were detected, which included 2 asymptomatic newborns (0.018‰, 2/111 986) and 2 children suspected for metabolic genetic diseases (0.268‰, 2/7461). The formers had no obvious clinical symptoms. Analysis of acyl carnitine has suggested a significant increase in C5, and urinary organic acid analysis has shown an increase in isovaleryl glycine and 3-hydroxyisovalerate. Laboratory tests of the two hospitalized children revealed high blood ammonia, hyperglycemia, decreased red blood cells, white blood cells, platelets and metabolic acidosis. The main clinical manifestations have included sweaty foot-like odor, feeding difficulty, confusion, drowsiness, and coma. Eight variants (5 types) were detected, which included c.158G>A (p.Arg53His), c.214G>A (p.Asp72Asn), c.548C>T (p.Ala183Val), c.757A>G (p.Thr253Ala) and 1208A>G (p.Tyr403Cys). Among these, c.548C>T and c.757A>G were unreported previously. None of the variants was detected by next generation sequencing of 2095 healthy newborns, and all variants were predicted to be likely pathogenic based on the guidelines from the American College of Medical Genetics and Genomics.


CONCLUSION
The incidence of isovalerate acidemia in Liuzhou area is quite high. Screening of metabolic genetic diseases is therefore recommended for newborns with abnormal metabolism. The discovery of novel variants has enriched the mutational spectrum of the IVD gene.