Cluster 1A tumours have pathogenic variants in enzymes of the tricarboxylic acid (TCA) cycle, including in the genes encoding the different subunits of succinate dehydrogenase SDHA, SDHB, SDHC, SDHD and the assembly factor SDHAF2 (collectively SDHx), fumarate hydratase FH, isocitrate dehydrogenase IDH1/2, malate dehydrogenase 2 MDH2, glutamic-oxaloacetic transaminase 2 GOT2 and, rarely, the also metabolism-related SCL25A11 and SUCLG2 [11]. The gene discussed is SDHD; the disease is neoplasm.