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Genetic and neurodevelopmental spectrum of SYNGAP1 -associated intellectual disability and epilepsy

2016; BMJ; Volume: 53; Issue: 8 Linguagem: Inglês

10.1136/jmedgenet-2015-103451

1468-6244

Cyril Mignot, Celina von Stülpnagel, Caroline Nava, Dorothée Ville, Damien Sanlaville, Gaëtan Lesca, Agnès Rastetter, Benoît Gachet, Yannick Marie, Georg Christoph Korenke, Ingo Borggraefe, Dorota Hoffman‐Zacharska, Elżbieta Szczepanik, Mariola Rudzka‐Dybała, Uluç Yiş, Hande Çağlayan, Arnaud Isapof, Isabelle Marey, Eleni Panagiotakaki, Christian Korff, Eva Rossier, Angelika Rieß, Stefanie Beck‐Woedl, Anita Rauch, Christiane Zweier, Juliane Hoyer, André Reis, М. Б. Миронов, M. Yu. Bobylоva, К. Yu. Мukhin, Laura Hernandez‐Hernandez, Bridget H. Maher, Sanjay M. Sisodiya, Marius Kuhn, Dieter Glaeser, Sarah Weckhuysen, Candace T. Myers, Heather C. Mefford, Konstanze Hörtnagel, Saskia Biskup, Johannes R. Lemke, Delphine Héron, Gerhard Kluger, Christel Depienne,

Lysosomal Storage Disorders Research

Objective We aimed to delineate the neurodevelopmental spectrum associated with SYNGAP1 mutations and to investigate genotype–phenotype correlations. Methods We sequenced the exome or screened the exons of SYNGAP1 in a total of 251 patients with neurodevelopmental disorders. Molecular and clinical data from patients with SYNGAP1 mutations from other centres were also collected, focusing on developmental aspects and the associated epilepsy phenotype. A review of SYNGAP1 mutations published in the literature was also performed. Results We describe 17 unrelated affected individuals carrying 13 different novel loss-of-function SYNGAP1 mutations. Developmental delay was the first manifestation of SYNGAP1 -related encephalopathy; intellectual disability became progressively obvious and was associated with autistic behaviours in eight patients. Hypotonia and unstable gait were frequent associated neurological features. With the exception of one patient who experienced a single seizure, all patients had epilepsy, characterised by falls or head drops due to atonic or myoclonic seizures, (myoclonic) absences and/or eyelid myoclonia. Triggers of seizures were frequent (n=7). Seizures were pharmacoresistant in half of the patients. The severity of the epilepsy did not correlate with the presence of autistic features or with the severity of cognitive impairment. Mutations were distributed throughout the gene, but spared spliced 3′ and 5′ exons. Seizures in patients with mutations in exons 4–5 were more pharmacoresponsive than in patients with mutations in exons 8–15. Conclusions SYNGAP1 encephalopathy is characterised by early neurodevelopmental delay typically preceding the onset of a relatively recognisable epilepsy comprising generalised seizures (absences, myoclonic jerks) and frequent triggers.