The YG22 transgenic founder line carries a single copy of the human FXN gene with one GAA trinucleotide repeat sequence of 190 repeats. High levels of human FXN gene product (mRNA or protein) are detected by RT-PCR and Western blot analysis. 40-50% of the endogenous mouse Fxn gene product (protein) is detected by Western blot analysis in mice heterozygous for the targeted mutation alone. Mice that are homozygous for the targeted allele and hemizygous for the transgene exhibit an age dependent, tissue specific expansion of the GAA repeat, with expansion accumulation in the CNS (particularly cerebellum), similar to the human pathology. The GAA triplet repeat exhibits intergenerational instability. Mice that are homozygous for the targeted allele and hemizygous for the transgene exhibit progressive retinal degeneration, impaired and decreased locomotor activity and coordination, and an increase in body weight. At 9 months of age, muscle strength is decreased. Although, histological analysis reveals progressive vacuolation of the dorsal root ganglia, no abnormalities or loss of cerebellar Purkinje cells were detected. Iron deposition in cardiac tissue of 14-18 month old mice is observed. Dorsal root ganglia neurons contain lipofuscin deposits, and large axons are swollen and exhibit secondary demyelination. Cardiomyocytes contain lipofuscin deposits, free glycogen accumulation and disrupted mitochondria. Mitochondrial respiratory chain function is decreased and oxidized protein levels are increased. This mutant mouse strain may be useful in studies of Friedreich's Ataxia. 
 Importation of this model was supported by the Friedreich's Ataxia Research Alliance (FARA) .

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Mice that are homozygous for the Fxntm1Mkn (frataxin) targeted allele and hemizygous for the Tg(FXN)YG22Pook (frataxin, human) transgene, display an age dependent, tissue specific expansion of the GAA repeat, with expansion accumulation in the CNS (particularly cerebellum), similar to the human pathology of Friedreich's Ataxia. They also exhibit progressive retinal degeneration, impaired and decreased locomotor activity and coordination, an increase in body weight, and neurodegeneration. Our preclinical efficacy testing services offer scientific expertise and an array of target-based and phenotype-based outcome measures, both in vivo and at endpoint, for flexible study designs and assay development in mouse models of Friedreich's Ataxia. <a href="https://www.jax.org/jax-mice-and-services/in-vivo-pharmacology/neurobiology-services">See our full service platform</a>.

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