Lockhart et al., "Compound heterozygous FXN
mutations and clinical outcome in friedreich ataxia," Annals of Neurology, vol.
The researchers used a transgenic mouse model that expresses two mutant human FXN transgenes, and exhibits the resulting progressive neurological degeneration and muscle weakness
The HSPCs engrafted and soon differentiated into macrophages in key regions of the mice's brain and spinal cord where they appeared to transfer wildtype FXN into deficient neurons and muscle cells.
The three DNA sequences of FXN , FMR1 , and DMPK  genes involved in the 3 TNR expansion diseases were examined for methylation status in patients and controls in previous studies.
Sequences from FXN, FMR1, and DMPK genes were divided into three classes of region, always methylated (AM), variably methylated (VM), and never methylated (NM), where the regions that are variably methylated are aberrantly methylated in patients and the always and never methylated regions are methylated and nonmethylated, respectively, in both patients and controls.
)j = [1/2][F([U.sup.+.sub.j]) x [n.sub.j] + F([U.sup.-.sub.j]) x [n.sub.j] - [absolute value of A]([U.sup.+.sub.j] - [U.sup.-.sub.j])] (9)
FA is now known to be an autosomal recessive trinucleotide repeat disorder, with the most common mutation being an expanded GAA triplet repeat in intron 1 on both alleles of FXN. Whereas unaffected individuals can have 5-30 GAA repeats, people affected by FA have 70-1000 repeats (12).
The ability to measure frataxin, the reduced gene product of FXN, in a high-throughput immunoassay will provide not only the ability to perform population screening and presymptomatic diagnosis, but also a biomarker to be used to measure disease progression or response to clinical trials.
GD = Tm - Tb + ((TM - Tm/2) + [(TM - 25).sup.2]/2.(TM - Tm)) x fxn
The molecular abnormality in more than 97% of patients is GAA trinucleotide repeat expansion in intron 1 of the FXN
Most patients with FRDA are homozygous for expansion in the GAA trinucleotide repeat sequence in the first intron of FXN. These expansions impair gene expression, but up to 3% of FRDA patients have other molecular defects, such as point mutations within the FXN coding region and exonic deletions, which can complicate confirmation of a clinical diagnosis by molecular analysis exclusively (8).
Molecular genetic analyses for detecting GAArepeat expansions within intron 1 or mutations in the FXN coding sequence itself are currently used to confirm a clinical suspicion of FRDA.