NMNAT1 and spinocerebellar ataxia 7: Remarkably, reduced NAD+ production in the nucleus and low expression of the NMNAT1 gene (the main gene involved in NAD+ production) were found in SCA7 neural progenitor cells (NPC), which might result in decreased NAD+ availability in mitochondria; decreased levels of NADH can consequently disturb the electron donor system that drives oxidative phosphorylation at the inner mitochondrial membrane [16].