D-2-hydroxyglutaric , L-2-hydroxyglutaric and combined D,L-2-hydroxyglutaric acidurias
Our laboratory is specialized in the biochemical and genetic diagnostics on the above mentioned diseases. Usually, an increase of total 2-hydroxyglutarate (2HG) is observed in the urinary organic acid screening, and subsequent enantiomeric separation of the two forms of 2-HG is performed on our laboratory by an LC-MS/MS based assay. Over the years we have identified the genes related to D-2-HGA (i.e. D2HGDH and IDH2) and combined D,L-2HGA (SLC25A1). Moreover, by using stable-isotope labelled substrates we have identified that alpha-ketoglutarate is the precursor both D2HG and L2HG. In oncology, heterozygous mutations in either IDH1 or IDH2 are frequently observed, which lead to the genesis of a neomorph enzyme that produces vast amounts of D-2-HG. In AML patients harboring mutations in IDH1/2, we have, in a collaboration with the Manchester AML Oncology group (UK), shown that the plasma assessment of D-2-HG and L-2-HG serves as a perfect marker for their IDH1/2 mutation. In a longitudinal study it was shown that the plasma assessment of D-2-HG and L-2-HG can be used to monitor the success of the treatment. Future research will focus more on this biomarker potential for those cancer types that harbor IDH1/2 mutations, and we offer our dedicated LC-MS/MS to other research groups interested in D-2-HG and L-2-HG.
Pyridoxine Dependant Epilepsy ( α-AASA dehydrogenase deficiency)
In an international collaboration we have (in 2006) unraveled the underlying cause of Pyridoxine Dependant Epilepsy. This has provided us a sensitive urinary biomarker for this condition i.e. alpha-amino adipic semialdehyde ( α-AASA) which we measure by LC-MS/MS. We have recently reported that α-AASA is also increased in Molybdenum Cofactor and Sulfite Oxidase deficiencies and we therefore have included the measurement of S-sulfocysteine in our LC-MS/MS assay allowing us to discriminate, in one single run, between a primary α-AASA increase due to Antiquitin deficiency and a secondary increase of α-AASA in Molybdenum cofactor and Sulfite Oxidase deficiencies. In a recent cohort consisting of individuals with a clinical response to pyridoxine supplementation and normal levels of α-AASA, it was shown that in some cases their disease was caused by mutations in the PNPO gene (encoding pyridoxamine phosphate oxidase). For this disease entity, no consistent biomarker is currently available, and molecular investigations on the PNPO gene are reconmmended for those pyridoxine responsive individuals. Future research will focus on theα-AASA metabolism and neurotoxicity and B6 metabolism.
Inborn errors of metabolism in the pentose phosphate pathway
We study the pathophysiology and metabolism of disorders in the pentose phosphate pathway (PPP). We have so far found four novel defects in the PPP: transaldolase deficiency, ribose-5-phosphate isomerase (RPI) deficiency, transketolase deficiency and sedoheptulokinase deficiency with unique polyol and sugar profiles. Although the enzymes of these defects are located in the same pathway the clinical phenotypes are completely different. Transaldolase deficiency is a disorder with multi-organ involvement, especially the liver, while RPI deficiency is a neurological disorder with leuco-encephalopathy, transketolase deficiency is characterized by short stature, developmental delay and congenital heart defects, while sedoheptulokinase deficiency seems to be a benign disorder or one with large differences in clinical presentation. We study the metabolism of C5-C7 polyols, sugars and sugar phosphates which are linked to the pentose phosphate pathway.
Pentose phosphate pathway and oxidative stress
The major function of the oxidative stage of the PPP is the production of NADPH from NADP+. NADPH is an important cofactor in the defence of oxidative stress caused by reactive oxygen species. We study the intermediates of the PPP (sugar-phosphates, seven-carbon sugars and polyols) in different tissues and cell lines to determine the role of the PPP in different situations.