Editing Repeated sequence (DNA) (section)

=== Friedreich's Ataxia ===
[[Friedreich's ataxia]] is a type of ataxia that has an expanded repeat sequence GAA in the frataxin gene.<ref>{{cite journal | vauthors = Bürk K | title = Friedreich Ataxia: current status and future prospects | journal = Cerebellum & Ataxias | volume = 4 | issue = 1 | pages = 4 | date = 2017 | pmid = 28405347 | pmc = 5383992 | doi = 10.1186/s40673-017-0062-x | doi-access = free }}</ref> The frataxin gene is responsible for producing the frataxin protein, which is a mitochondrial protein involved in energy production and cellular respiration.<ref>{{cite journal | vauthors = Mazzara PG, Muggeo S, Luoni M, Massimino L, Zaghi M, Valverde PT, Brusco S, Marzi MJ, Palma C, Colasante G, Iannielli A, Paulis M, Cordiglieri C, Giannelli SG, Podini P, Gellera C, Taroni F, Nicassio F, Rasponi M, Broccoli V | display-authors = 6 | title = Frataxin gene editing rescues Friedreich's ataxia pathology in dorsal root ganglia organoid-derived sensory neurons | journal = Nature Communications | volume = 11 | issue = 1 | pages = 4178 | date = August 2020 | pmid = 32826895 | pmc = 7442818 | doi = 10.1038/s41467-020-17954-3 | bibcode = 2020NatCo..11.4178M }}</ref> The expanded GAA sequence results in the silencing of the first intron resulting in loss of function in the frataxin protein. The loss of a functional ''FXN'' gene leads to issues with mitochondrial functioning as a whole and can present phenotypically in patients as difficulty walking.