Further evidence that d-glycerate kinase (GK) deficiency is a benign disorder

Abstract d -Glyceric aciduria is caused by deficiency in d -glycerate kinase (GK) due to recessive mutations in the GLYCTK gene. GK catalyzes the conversion of d -glycerate to 2-phosphoglycerate which is an intermediary reaction in the catabolism of serine and fructose. Deficiency of GK leads to accumulation of d -glycerate, which may be detected in urine organic acid analysis. Debate exists as to whether this is a benign or disease-causing disorder as the reported phenotypes vary significantly. We report two siblings from a consanguineous Pakistani family. The index case is a 5 year old boy with severe autism and global developmental delay. His urine organic acid analysis showed markedly increased excretion of glycerate, determined as d -form by enantioselective gas chromatography. There was no oxalic aciduria. His younger sister (3 years old) is asymptomatic and developmentally normal (already bilingual). Her urine showed similar amounts of d -glycerate. Both children are homozygous for the novel mutation c.767C > G in exon 5 of the GLYCTK gene, predicted to affect the enzyme by replacing the evolutionarily conserved Proline with Arginine (P256R). Both parents are heterozygous carriers. These cases support the view that d -glycerate kinase deficiency is a benign disorder. Long term follow-up studies with a greater number of individuals may be required for further confirmation.