It was also found [6] that the post-translational modification of 17β-HSD10 regulates its mitochondrial abundance and its enzymatic activity as well as the formation of RNase P. Missense mutations at the HSD17B10 gene results in 17β-HSD10 loss-of-function mutants causing HSD10 deficiency [36,37,38,39,40,41,42,43,44,45], formerly referred to as 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency [46,47,48,49,50,51,52,53,54,55,56,57]—an inborn error in isoleucine metabolism. This evidence concerns the gene FSIP1 and HSD10 mitochondrial disease.