Ataxia Telangiectasia (A-T) and Ataxia with Ocular Apraxia Type 1 (AOA1) are devastating neurological disorders caused by null mutations in the genome stability genes, A-T mutated (ATM) and Aprataxin (APTX), respectively. Our mechanistic understanding and therapeutic repertoire for treating these disorders are severely lacking, in large part due to the failure of prior animal models with similar null mutations to recapitulate the characteristic loss of motor coordination (i.e., ataxia) and associated cerebellar defects. By increasing genotoxic stress through the insertion of null mutations in both the Atm (nonsense) and Aptx (knockout) genes in the same animal, we have generated a novel mouse model that for the first time develops a progressively severe ataxic phenotype associated with atrophy of the cerebellar molecular layer. We find biophysical properties of cerebellar Purkinje neurons (PNs) are significantly perturbed (e.g., reduced membrane capacitance, lower action potential [AP] thresholds, etc.), while properties of synaptic inputs remain largely unchanged. These perturbations significantly alter PN neural activity, including a progressive reduction in spontaneous AP firing frequency that correlates with both cerebellar atrophy and ataxia over the animal’s first year of life. Double mutant mice also exhibit a high predisposition to developing cancer (thymomas) and immune abnormalities (impaired early thymocyte development and T-cell maturation), symptoms characteristic of A-T. Finally, by inserting a clinically relevant nonsense-type null mutation in Atm, we demonstrate that Small Molecule Read-Through (SMRT) compounds can restore ATM production, indicating their potential as a future A-T therapeutic.

Ataxia Telangiectasia (A-T) is caused by null mutations in the genome stability gene, ATM (A-T mutated). In mice, similar null mutations do not replicate A-T’s characteristic severe ataxia with associated cerebellar dysfunction and atrophy. By increasing genotoxic stress, through the insertion of null mutations in the Atm (nonsense) and related Aptx (knockout) genes, we have generated a novel A-T mouse that first develops mild ataxia, associated with abnormal Purkinje neuron (PN) activity and decreased size, progressing to severe ataxia correlated with further reduced PN activity as well as PN loss and overall cerebellar atrophy. These mice also exhibit high incidences of cancer and immune abnormalities that are all hallmarks of the human disorder. Enabled by the insertion of a clinically relevant nonsense mutation in Atm, we demonstrate that small molecule readthrough (SMRT) compounds can restore ATM production, indicating their potential as a future A-T therapeutic.

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