POLG and Cerebellar atrophy: Patients harbouring bi-allelic pathogenic variants in POLG (NM_002693.3), encoding the catalytic subunit of the mtDNA polymerase gamma (POLG)—the sole enzyme responsible for replication of mtDNA—also frequently develop mixed ataxia due to cerebellar atrophy and dorsal root ganglionopathy [28, 39].