SDHB and mitochondrial disease: An alternative aetiology (bi-allelic DARS2 variants) has been established for the clinically-affected individual in whom compound heterozygous c.541-2A>G and c.423+20T>A SDHB splicing variants were initially suspected; so, although the pathogenicity of the c.541-2A>G variant that affects the conserved donor sequence is not in question, it has yet to be implicated in mitochondrial disease [26].