Serum fatty acid profiling in patients with SDHx mutations: New advances on cellular metabolism in SDH deficiency.

Apart from the oncometabolite succinate, little studies have appeared on extra-mitochondrial pathways in Succinate Dehydrogenase (SDH) genetic deficiency. The role of NADH/NAD+ redox status and dependent pathways was recently emphasized. Therein, fatty acid (FA) metabolism data were collected here in 30 patients with a loss of function (LOF) variant in one SDHx gene (either with a pheochromocytoma/paraganglioma (PPGL) or asymptomatic) and in 22 wild-type SDHx controls (with PPGL or asymptomatic). Blood acylcarnitines in two patients, peroxisomal biomarkers, very long-chain saturated FA (VLCFA), and C20 to C24 n-3 polyunsaturated fatty acids (PUFA), in all patients were measured by mass spectrometry. Preliminary data showed elevated even and odd long- and very long-chain acylcarnitines in two patients with a SDHB variant. In the whole series, no abnormalities were observed in biomarkers of peroxisomal β-oxidation (C27-bile acids, VLCFAs and phytanic/pristanic acids) in SDHx patients. However, an increased hexaene to pentaene PUFA ratio ([TetraHexaenoic Acid + DocosaHexaenoic Acid]/[n-3 DocosaPentaenoic Acid + EicosaPentaenoic Acid]) was noticed in patients with SDHC/SDHD variants vs patients with SDHA/SDHB variants or controls, suggesting a higher degree of unsaturation of PUFAs. Within the group with a SDHx variant, Eicosapentaenoate/Tetracosahexaenoate ratio, as an empiric index of shortening/elongation balance, discriminated patients with PPGL from asymptomatic ones. Present findings argue for stimulated elongation of saturated FAs, changes in shortening/elongation balance and desaturation rates of C20-C24 PUFAs in SDH-deficient patients with PPGL. Overall, oxidation of NADH sustained by these pathways might reflect or impact glycolytic NAD+ recycling and hence tumor proliferation.