Magnetic resonance spectroscopy (MRS) is one of few methods capable of measuring metabolite levels in vivo non-invasively and has been applied to analysis of R-2-HG levels in individuals with IDH1/2 mutant glioma.122, 123, 124 However, it remains unclear which R-2-HG-linked metabolic changes, beyond the increase of R-2-HG itself, are important in tumor development and which are bystanders in the processes of cellular transformation and tumorigenesis. The gene discussed is IDH1; the disease is central nervous system cancer.