FGF14 (fibroblast growth factor 14) is a protein involved in nervous system development and function, with a key role in regulating voltage-gated sodium channel distribution in cerebellar Purkinje and granule cells 1. The gene functions through protein binding and cell-cell signaling mechanisms to support neurogenesis and signal transduction 2. Pathogenic intronic GAA repeat expansions (≥250 repeats) in FGF14 cause spinocerebellar ataxia 27B (SCA27B), a dominantly inherited late-onset cerebellar ataxia 23. SCA27B is characterized by slowly progressive cerebellar syndrome presenting around age 60, with core features including oculomotor disorders (particularly downbeat nystagmus), episodic ataxia, and dysautonomia 43. Disease progression is mild, with patients requiring mobility aids only after 8 years of illness 4. Clinically, FGF14 expansions represent one of the most frequent genetic causes of adult-onset ataxia, accounting for 9-61% of previously undiagnosed late-onset cerebellar ataxia cases across different populations 56. Importantly, 4-aminopyridine demonstrates promising symptomatic benefits, with 86% of treated patients reporting clinically relevant responses 45. The identification of FGF14 as a major disease gene has significantly improved diagnostic yield and opened new therapeutic opportunities for this previously elusive cause of adult-onset neurodegeneration.