Glycerol kinase deficiency: Residual activity explained by reduced transcription and enzyme conformation

Damayanti Rusli Sjarif, Christina Hellerud, Johannes K.Ploos van Amstel, Willem J. Kleijer, Wolfgang Sperl, Dedier Lacombe, Jõrn Oliver Sass, Frits A. Beemer, Marinus Duran, Bwee Tien Poll-The

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7 Citations (Scopus)

Abstract

Four unrelated patients with glyceroluria ranging from 7 to 170 mmol/l were studied. The activity of glycerol kinase (GK) in cultured fibroblasts was determined with a specific enzyme assay and with two indirect methods, that is, incorporation into macromolecules of [14C] from [14C]glycero and its oxidation to [14C]CO2. Exon amplification and RT-PCR were used to identify mutations. In patient 1, with low activity in all three assays, we identified a c.1194A>C (E398D) missense mutation. In patient 2 with a considerable activity of the GK enzyme (22% of reference), oxidation to [14C]CO2 (37%) and a high incorporation of [14C] into macromolecules (92%), we identified a c.182T>C (L61P) mutation that causes the enzyme to have a higher Km for glycerol (∼ 300 μM) than normals (2-8 μM). In patient 3, the GK activity estimated by the three different methods ranged from 16 to 22% of reference. Analysis of mRNA from the GK gene revealed three alternatively spliced transcripts. A mutation in intron 3 (g.16835G>A) resulted in an insertion of a cryptic exon between exon 2 or 3 and exon 4. Patient 4 with minor glyceroluria (7 mmol/l) and normal plasma glycerol concentration had normal activity with all three assay methods, thus excluding GK deficiency (GKD) as a cause of slight glyceroluria. To evaluate fully patients with glyceroluria, one needs to measure the GK activity and relate this and the clinical data to genetic findings. Residual enzyme activities in cultured fibroblasts can be found in GKD patients with severe clinical symptoms.

Original languageEnglish
Pages (from-to)424-432
Number of pages9
JournalEuropean Journal of Human Genetics
Volume12
Issue number6
DOIs
Publication statusPublished - 1 Jun 2004

Keywords

  • Enzyme assay
  • Glycerol kinase deficiency
  • Glyceroluria
  • Mutation analysis

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