Family tree, mutation analysis, and yeast functional assay. A. ATA-2-TO family tree suggested an autosomal recessive transmission, but clinical data from the father and the mother (died at 37 yrs) were incomplete. Below the segregation of three microsatellite markers surrounding the SETX gene show a homozygous region in the three affected individuals. Subject II.7 had subclinical myoclonus (see text). The presence of SETX c.6269C > T and AFG3L2 c.346G > A mutations are indicated below each subject. B. Electropherograms of SETX c.6269C > T and AFG3L2 c.346G > A mutations with accompanying amino acid changes. C. Evolutionary conservation of glycine at position 116 in the AFG3L2 protein. The position is conserved in all vertebrates analyzed. D. Yeast functional assay of p.Gly116Arg mutation  m-AAA proteases are evolutionarily highly conserved from human through to S. cerevisiae where both homo-oligomeric Yta12 (AFG3L2 orthologue), and hetero-oligomeric Yta10 (SPG7 orthologue) - Yta12 subunits are present. These proteins can be substituted with the human orthologues in order to study specific missense changes. In Δyta10Δyta12 yeast cells (ΔΔ) the synthesis of mitochondrial-encoded respiratory chain subunits is impaired and cells are unable to perform aerobic respiration, growing only on carbon fermentable source [Yeast extract Peptone and Dextrose (glucose): YPD] [4-6] and not on a non-fermentable source (Yeast extract Peptone and Glycerol: YPG). Δyta10Δyta12 yeast transfected with human AFG3L2 is able to grow on YPG, whereas human AFG3L2G116R is unable. The co-transfection of SPG7 and AFG3L2G116R rescued the phenotype.