We collected data on 48 patients from 38 families with guanidinoacetate methyltransferase (GAMT) deficiency. Global developmental delay/intellectual disability (DD/ID) with speech/language delay and behavioral problems as the most affected domains was present in 44 participants, with additional epilepsy present in 35 and movement disorder in 13. Treatment regimens included various combinations/dosages of creatine-monohydrate, l-ornithine, sodium benzoate and protein/arginine restricted diets. The median age at treatment initiation was 25.5 and 39 months in patients with mild and moderate DD/ID, respectively, and 11 years in patients with severe DD/ID. Increase of cerebral creatine and decrease of plasma/CSF guanidinoacetate levels were achieved by supplementation with creatine-monohydrate combined with high dosages of l-ornithine and/or an arginine-restricted diet (250 mg/kg/d l-arginine). Therapy was associated with improvement or stabilization of symptoms in all of the symptomatic cases. The 4 patients treated younger than 9 months had normal or almost normal developmental outcomes. One with inconsistent compliance had a borderline IQ at age 8.6 years. An observational GAMT database will be essential to identify the best treatment to reduce plasma guanidinoacetate levels and improve long-term outcomes.

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IMPORTANCE Reports of pediatric-onset stiff-man syndrome (SMS) are rare. This may be an underrecognized disorder in child neurology practice.OBJECTIVE To describe patients with disorders in the SMS spectrum beginning in childhood. DESIGN, SETTING, AND PARTICIPANTSThis study was a medical record review and serological evaluation conducted at child and adult neurology clinics at the Mayo Clinic, Rochester, Minnesota. Systematic review of the literature was conducted of patients who presented from 1984-2012 with onset of symptomatic SMS occurring at age 18 years or younger. MAIN OUTCOMES AND MEASURESResponse to symptomatic and immunotherapies, patient and physician reported, including modified Rankin scale. RESULTSWe identified 8 patients with childhood-onset SMS, representing 5% of patients with SMS evaluated at Mayo Clinic during a period of 29 years (4 were girls). The median age at symptom onset was 11 years (range, 1-14 years). The diagnosis in 3 patients was not established until adulthood (median symptom duration at diagnosis, 14 years; range, 0-46 years). The phenotypes encountered were: classic SMS (n = 5, involving the low back and lower extremities), variant SMS (n = 2, limited to 1 limb [with dystonic posture] or back), and progressive encephalomyelitis with rigidity and myoclonus (n = 1). Initial misdiagnoses included functional movement disorder (n = 2), generalized dystonia and parkinsonism (n = 1), and hereditary spastic paraparesis (n = 1). Six patients had 1 or more coexisting autoimmune disorders: type 1 diabetes mellitus (n = 4), thyroid disease (n = 2), and vitiligo (n = 2). Serologic study results revealed glutamic acid decarboxylase 65-IgG in all cases (median value, 754 nmol/L; range, 0.06-3847 nmol/L; normal value, Յ0.02 nmol/L) and glycine receptor antibody in 3 cases. Improvements were noted with symptomatic therapy (diazepam, 6 of 6 patients treated, and oral baclofen, 3 of 3 treated) and immunotherapy (intravenous immune globulin, 3 of 4 treated and plasmapheresis, 3 of 4 treated). The 3 patients with glycine receptor antibody all improved with immunotherapy. At last follow-up, 4 patients had mild or no symptoms, but 4 had moderate or severe residual symptoms and required maintenance symptomatic therapy (n = 5) and immunotherapy (n = 4). Ten of 12 pediatric SMS cases identified by literature review had a severe whole-body phenotype resembling progressive encephalomyelitis with rigidity and myoclonus.CONCLUSIONS AND RELEVANCE Childhood-onset SMS is a rare but underrecognized and treatable disorder. Serological and electrophysiological testing aid diagnosis.

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There has been one previous report of a cohort of patients with variants in Chromodomain Helicase DNA-binding 3 ( CHD3 ), now recognized as Snijders Blok-Campeau syndrome. However, with only three previously-reported patients with variants outside the ATPase/helicase domain, it was unclear if variants outside of this domain caused a clinically similar phenotype. We have analyzed 24 new patients with CHD3 variants, including nine outside the ATPase/helicase domain. All patients were detected with unbiased molecular genetic methods. There is not a significant difference in the clinical or facial features of patients with variants in or outside this domain. These additional patients further expand the clinical and molecular data associated with CHD3 variants. Importantly we conclude that there is not a significant difference in the phenotypic features of patients with various molecular disruptions, including whole gene deletions and duplications, and missense variants outside the ATPase/helicase domain. This data will aid both clinical geneticists and molecular geneticists in the diagnosis of this emerging syndrome.