In addition to their role in primary mitochondrial disease, heterozygous germline variants in other complex II subunits and assembly factors (including SDHA, SDHB, SDHC, SDHD and SDHAF2) are associated with paragangliomas, phaeochromocytomas and gastrointestinal stromal tumours [3]. This evidence concerns the gene SDHB and mitochondrial disease.