Natural history of SGCE-associated myoclonus dystonia in children and adolescents.

Aim: To investigate the natural progression of SGCE-associated myoclonus dystonia from symptom onset in childhood to early adulthood.

Method: Myoclonus and dystonia were monitored using rating scales in two cohorts of participants from Spain and the Netherlands. Individual annualized rates of change were calculated and longitudinal trends were assessed using Bayesian mixed models. Psychiatric features were evaluated cross-sectionally in the Spanish cohort.

Results: Thirty-eight patients (21 males, 17 females) were evaluated at a mean age (SD) of 10 years (4 years 7 months; range 2-21 years) and 14 years 2 months (4 years 8 months; range 4-25 years). We observed a significant worsening of action myoclonus, global dystonia, and dystonia during writing (mean annual increases of 1.356, 0.226, and 0.518 in the Unified Myoclonus, Burke-Fahn-Marsden, and Writer's Cramp Rating Scales respectively). Accordingly, participants perceived a significant worsening in their speech, writing, and walking abilities. Twenty-six of 32 participants suffered from anxiety (n = 13), obsessive-compulsive disorder (n = 9), and attention-deficit/hyperactivity disorder (n = 8).

Interpretation: This study demonstrates that, unlike in the adult population, myoclonus dystonia syndrome in childhood and adolescence follows a progressive course that can be debilitating in the early stages of life. These findings, along with a high prevalence of psychiatric symptoms, highlight the need for early therapeutic interventions to prevent long-term motor and psychological sequelae.