SDHB and proximal spinal muscular atrophy: Genes coding for proteins involved in mitochondrial OXPHOS — succinate dehydrogenase complex flavoprotein subunits A, B, and C (SDHA, SDHB, and SDHC, respectively; code for proteins in complex II), mitochondrial cytochrome c oxidase subunits I and II (MT-CO1 and MT-CO2, respectively; code for proteins in complex IV), and ATP synthase F0 subunit 6 and ATP synthase F1 subunit α (MT-ATP6 and ATP5A) — all showed reduced transcription in SMA iHeps, but this was not correlated to severity of SMA phenotype (Figure 6A).