Spinocerebellar ataxia type 1 (SCA1) is characterized by adult-onset cerebellar degeneration with attendant loss of motor coordination. Bulbar function is eventually impaired, and patients tend to die from inability to clear the airway. We asked whether motor neuron degeneration is at the root of bulbar dysfunction by studying SCA1 knock-in mice. We analyzed spinal cord and brainstem motor neurons in SCA1 knock-in (Atxn1154Q) mice at 1, 3, and 6 months of age. Specifically, we assessed breathing physiology, diaphragm histology and electromyography, and motor neuron histology and immunohistochemistry. Atxn1154Q mice show progressive neuromuscular respiratory abnormalities, neurogenic changes in diaphragm, and motor neuron degeneration in the spinal cord and brainstem. The latter is accompanied by reactive astrocytosis and accumulation of Atxn1 aggregates in the motor neuron nuclei. This dovetails with previous observations in SCA1 patient tissue. Atxn1154Q mice develop bulbar dysfunction because of motor neuron degeneration. These findings confirm the Atxn1154Q line as a SCA1 model with face and construct validity for this understudied disease feature. Furthermore, this model is suitable to study the pathogenic mechanism driving motor neuron degeneration in SCA1 and perhaps other degenerative motor neuron diseases. From a clinical standpoint, the data indicate that pulmonary function testing and employment of non-invasive ventilator support could be beneficial in SCA1 patients. The physiological tests used in this study may serve as valuable biomarkers for future therapeutic interventions and clinical trials.

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