<scp>CGG</scp> Repeat Expansion in <scp> <i>GIPC1</i> </scp> is Associated with Childhood‐Onset Hereditary Ataxia

BACKGROUND: Hereditary ataxias are genetically heterogeneous; however, despite major advances in next-generation sequencing technologies, 20%-54% of childhood-onset cases remain genetically undiagnosed. OBJECTIVE: To elucidate the genetic etiology of childhood-onset hereditary ataxia. METHODS: Oxford Nanopore long-read genome sequencing (LRS) was performed in two unrelated Chinese patients with clinically suspected childhood-onset hereditary ataxia. RESULTS: Both patients presented with childhood-onset, slowly progressive ataxia, accompanied by mild cognitive impairment. Brain magnetic resonance imaging demonstrated cerebellar atrophy, and electromyography showed neurogenic damage. Muscle biopsy revealed fiber-type grouping, indicative of neurogenic changes, with no evidence of primary myopathy. LRS detected pathogenic-length CGG repeat expansions (>100 repeats) in GIPC1, which were validated by repeat-primed polymerase chain reaction. CONCLUSIONS: These findings expand the phenotypic spectrum associated with GIPC1 CGG repeat expansion and define a novel subtype of childhood-onset hereditary ataxia accompanied by mild cognitive impairment and neurogenic involvement. © 2026 International Parkinson and Movement Disorder Society.