Beta-alanine and beta-aminoisobutyric acid levels in two siblings with dihydropyrimidinase deficiency.

Dihydropyrimidinase (DHP) deficiency is an inborn error of the pyrimidine degradation pathway, affecting the hydrolytic ring opening of the dihydropyrimidines. In two siblings with a complete DHP deficiency and a variable clinical presentation, a normal concentration of s-alanine and strongly decreased levels of s-aminoisobutyric acid were observed in plasma, urine and CSF. No major differences were observed for the concentrations of the s-amino acids in plasma and urine between the symptomatic and asymptomatic sibling. Thus, the relevance of the shortage of s-aminoisobutyric acid for the onset of a clinical phenotype in patients with DHP deficiency remains to be established.