Study subjects had genetic confirmation with pathogenic variants in mitochondrial genes [30%: COX20 (OMIM#614698) n = 2, HADHA (OMIM#600890) n = 2, POLG (OMIM#174763) n = 1, FH (OMIM# 136850) n = 1], Friedreich-ataxia (21%: FXN (OMIM#606829) n = 4), spinocerebellar ataxia type-2 (15%: ATXN2 (OMIM#601517) n = 3), ataxia-telangiectasia (15%: ATM (OMIM#607585) n = 3), giant axonal neuropathy (10%: GAN (OMIM# 605379), n = 2), and 5% each in spastic paraplegia 7 (SPG7 (OMIM#602783) n = 1) and spastic paraplegia 15 (ZFYVE26 (OMIM# 612012) n = 1). The gene discussed is GAN; the disease is ataxia telangiectasia.