Friedreich's ataxia (FRDA) is an autosomal recessive inherited disorder characterized by progressive gait and limb ataxia, dysarthria, areflexia, loss of vibratory and position sense, and a progressive motor weakness of central origin. Additional features include hypertrophic cardiomyopathy and diabetes. Large GAA repeat expansions in the first intron of the FXN gene are the most common mutation underlying FRDA. Patients show severely reduced levels of a FXN-encoded mitochondrial protein called frataxin.

Friedreich's ataxia: Past, present and future

Novel gene-based therapies for disease will depend in many cases on long-term persistent transgene expression. To develop gene therapy strategies for Friedreich's ataxia (FRDA), we have examined the persistence of transgene expression in the brain in vivo provided by the entire 135 kb FXN genomic DNA locus delivered as an infectious bacterial artificial chromosome (iBAC) herpes simplex virus type 1 (HSV-1)-based vector injected in the adult mouse cerebellum. 

Infectious delivery and long-term persistence of transgene expression in the brain by a 135-kb iBAC-FXN genomic DNA expression vector

Short-chain quinones are described as potent antioxidants and in the case of idebenone have already been under clinical investigation for the treatment of neuromuscular disorders. Due to their analogy to coenzyme Q10 (CoQ10), a long-chain quinone, they are widely regarded as a substitute for CoQ10. However, apart from their antioxidant function, this provides no clear rationale for their use in disorders with normal CoQ10 levels. Using recombinant NAD(P)H:quinone oxidoreductase (NQO) enzymes, we observed that contrary to CoQ10 short-chain quinones such as idebenone are good substrates for both NQO1 and NQO2. 

NQO1-Dependent Redox Cycling of Idebenone: Effects on Cellular Redox Potential and Energy Levels

Friedreich ataxia (FRDA) is an autosomal recessive disorder characterized by neurodegeneration and cardiomyopathy, and is the most common inherited ataxia. About 98% of individuals with FRDA are homozygous for an expansion of a GA A trinucleotide repeat sequence within the first intron of the FXN gene. The remaining individuals are compound heterozygotes for a GAA expansion and a point mutation. Pathogenic GAA expansion alleles are in the size range of 60 to >1300 repeats. The presence of a GAA repeat expansion results in the inhibition of FXN gene expression, reduced levels of full-length FXN transcript, and an insufficiency of the mitochondrial protein frataxin (1–4). Overall, an inverse correlation has been found between the size of the smaller GAA expansion and transcript levels, the amount of residual frataxin produced, and the age of onset of disease symptoms (5–9).

Detection of interruptions in the GAA trinucleotide repeat expansion in the FXN gene of Friedreich ataxia