ATN1 encodes atrophin-1, a transcriptional corepressor that functions as a nuclear protein involved in transcriptional regulation and neurodevelopmental processes 1. The protein acts as a corepressor through recruitment of NR2E1 and interaction with transcriptional machinery to regulate gene expression 1. ATN1 contains a polyglutamine (polyQ) tract encoded by CAG repeats in exon 5, and pathogenic expansions of these repeats cause dentatorubral-pallidoluysian atrophy (DRPLA), a rare autosomal dominant neurodegenerative disorder characterized by cerebellar ataxia, myoclonus, epilepsy, dementia, and psychiatric symptoms 2. Additionally, heterozygous variants in the HX repeat motif of ATN1 cause CHEDDA syndrome (congenital hypotonia, epilepsy, developmental delay, and digital anomalies), a distinct neurodevelopmental condition 3. In DRPLA pathogenesis, expanded polyQ-containing atrophin-1 accumulates diffusely in neuronal nuclei, leading to nuclear dysfunction, protein aggregation, and neuronal loss particularly affecting the globus pallidus and brainstem nuclei 14. Whole genome sequencing shows high sensitivity (97.3%) and specificity (99.6%) for detecting ATN1 repeat expansions clinically 5. Currently, no disease-modifying treatments exist for DRPLA 2.