Early Manifestations, Diagnostic Pathways, and Epilepsy in Juvenile-Onset Huntington Disease: A Three-Patient Case Series and Systematic Review.

BACKGROUND: Juvenile-onset Huntington disease (JoHD) is a rare form of Huntington disease characterized by symptom onset at or before 20 years of age. Early manifestations are often non-choreic and may be attributed to developmental, psychiatric, movement, metabolic, or epileptic disorders. We described three molecularly confirmed cases and examined early manifestations, diagnostic pathways, and epilepsy. METHODS: We conducted a retrospective case series and a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 systematic review of PubMed, Scopus, and Web of Science Core Collection through 5 July 2026. The strict patient-level synthesis required attributable onset at or before 20 years, patient-specific molecular confirmation of a pathogenic HTT repeat expansion, and extractable clinical data. Complementary aggregate or linked reports using closely aligned JoHD criteria were retained for context but excluded from patient-level calculations. RESULTS: The cases included childhood-onset JoHD with drug-resistant epilepsy, adolescent-onset JoHD with progressive motor-cognitive decline and epilepsy in a known Huntington disease pedigree, and childhood-onset JoHD without available family history, in whom status epilepticus prompted renewed diagnostic evaluation. Ninety-three reports were included; of these, 81 contributed 228 unique patients and 12 provided complementary data. Early manifestations were heterogeneous and broadly consistent with previously described childhood-onset JoHD phenotypes. Diagnostic delay was extractable in 180/228 patients; among 172 with point estimates, the median was 4.0 years. Definite epilepsy was reported in 60/145 patients with ascertainable seizure status and was descriptively more frequent in childhood-onset (<10 years) than adolescent-onset (10-20 years) JoHD (49/84 [58.3%] vs. 11/57 [19.3%]). CONCLUSIONS: JoHD should be considered in children and adolescents with progressive multisystem neurological involvement, particularly when epilepsy occurs with developmental regression, gait or speech deterioration, pyramidal or extrapyramidal signs, basal-ganglia abnormalities, or a compatible family history.