Profiling of intracellular metabolites produced from galactose and its potential for galactosemia research

BACKGROUND: Clinical outcome of patients with a classical presentation of galactosemia (classical patients) varies substantially, even between patients with the same genotype. With current biomarkers, it is not possible to predict clinical outcome early in life. The aim of this study was to develop a method to provide more insight into galactose metabolism, which allows quantitative assessment of residual galactose metabolism in galactosemia patients. We therefore developed a method for galactose metabolite profiling (GMP) in fibroblasts using [U-(13)C]-labeled galactose. METHODS: GMP analysis was performed in fibroblasts of three classical patients, three variant patients and three healthy controls. The following metabolites were analyzed: [U(13)C]-galactose, [U(13)C]-galactose-1-phosphate (Gal-1-P) and [(13)C(6)]- uridine diphosphate(UDP)-galactose. The ratio of [U(13)C]-Gal-1-P/ [(13)C(6)]-UDP-galactose was defined as the galactose index (GI). RESULTS: All patient cell lines could be distinguished from the control cell lines and there was a clear difference between variant and classical patients. Variant patients had lower levels of [U(13)C]-galactose and [U(13)C]-Gal-1-P than classical patients (though substantially higher than healthy controls) and higher levels of [(13)C(6)]-UDP-galactose than classical patients (though substantially lower than healthy controls) resulting in a different GI in all groups. CONCLUSIONS: GMP in fibroblasts is a sensitive method to determine residual galactose metabolism capacity, which can discriminate between patients with a classical presentation of galactosemia, patients with a variant presentation and healthy controls. GMP may be a useful method for early prognostication after further validation in a larger cohort of patients representing the full phenotypic spectrum of galactosemia.