FA2H deleterious single nucleotide variants in our study and in literature. (A) Distribution of R113Q in Family 2 and R113W in Family 3. In both families, mutations were shared by both affected siblings and inherited from a healthy parent. In Family 3, the sequence chromatograph of the mother showed a reduced signal for the mutation [the size of the allele T signal (in red) in the mother was twice lower than the signal observed in her affected children]. (B) We compared amino acid sequence conservation across species by aligning FA2H homologs using ClustalW (http://www.ebi.ac.uk/Tools/clustalw2/index.html). The R113 residue showed moderate conservation. (C) Localization of R113Q/R113W mutations and other reported mutations on a schematic representation of FA2H [8–11, 15–18]. Red squares represent transmembrane domains, the purple rectangle represents the cytochrome B5-like heme-binding domain, and green rectangles represent the catalytic domain. The D35Y mutation has been reported in patients with leukodystrophy with spastic paraparesis and dystonia , the R235 and R53_I58del mutations in patients with hereditary spastic paraplegia , and the R154C and Y170X mutations in patients with degeneration associated with brain iron accumulation . Splice site mutations predicted to result in skipping of exons 5-7(short gray line) and 2-7(long grey line) have been reported [9, 15].