Glycerol Kinase Missense Mutations Provide Structure-Function But Not Genotype-Phenotype Insights. |[dagger]| 641

Intragenic mutations within the glycerol kinase gene (GK) on Xp21 are associated with hyperglycerolemia and glyceroluria in all affected individuals. In some families, affected individuals have acute episodes associated with potentially life-threatening, but reversible deterioration of central nervous system function, while in others the biochemically affected individuals have completely benign clinical courses. The crystal structure of E. coli GK was solved at 2.6A resolution (Hurley et al., Science 259:673, 1993). Our goal was to identify mutations in the human GK gene, and, based on the high degree of similarity between the prokaryotic and human genes, use these mutations to attempt to ascertain structure-function and genotype-phenotype relationships. We used an automated sequencer (ABI 377) to analyze patients' genomic and/or cDNA sequences. We observed missense mutations in three unrelated males, two asymptomatic adults with hyperglycerolemia determined incidentally (A862G::N288D and A1313G::Q438R) and an infant who was evaluated because of neonatal asphyxia but no subsequent problems (T1283C::M428T). A fourth missense mutation (D440V) was reported in a 14 yo male with GK deficiency and mental retardation(Walker et al, Am J Hum Genet 58:1205, 1996). These mutations occur either: in an amino acid (M428) corresponding to an alanine in E. coli GK that interacts with ADP and is part of a cluster of three residues interacting with ADP; near this cluster and involving residues absolutely conserved in E. coli, B. subtilis and human GK (Q438 and D440); or in an amino acid (N288) that is identical in these three organisms and is close to a conserved block of residues involved in ADP and glycerol binding. We conclude that the missense mutations in the GK gene reported to date alter amino acids with defined functions or that are highly conserved. However, we are unable to relate the patients' genotypes to their phenotypes. ERBM is an Acad Assoc, Corning Nichols Inst, San Juan Capistrano, CA.