Early epileptic encephalopathies associated with STXBP1 mutations: Could we better delineate the phenotype?

STXBP1 (MUNC18.1), encoding syntaxin binding protein 1, is a gene causing epileptic encephalopathy. Mutations in STXBP1 have first been reported in early onset epileptic encephalopathy with suppression-bursts, then in infantile spasms and, more recently, in patients with non syndromic mental retardation without epilepsy. We analyzed clinical evolution and brain magnetic resonance imaging in 7 patients (6 females, 1 male) with early onset epileptic encephalopathies associated with STXBP1 mutations. We documented a peculiar brain MRI aspect characterized by frontal hypoplasia and a thin and dysmorphic corpus callosum. The course of the epilepsy was relatively benign. These clinical and neuroradiological features could orient the clinician in selecting patients' candidate to genetic testing for STXBP1 gene.

Barcia G ，Chemaly N ，Gobin S ，Milh M ，Van Bogaert P ，Barnerias C ，Kaminska A ，Dulac O ，Desguerre I ，Cormier V ，Boddaert N ，Nabbout R ... -  《-》

STXBP1-related encephalopathy presenting as infantile spasms and generalized tremor in three patients.

Dominant mutations in the STXBP1 gene are a recently identified cause of infantile epileptic encephalopathy without metabolic and structural brain anomalies. To date, 25 patients with heterozygous mutation or deletion of STXBP1 have been reported. A diagnosis of early infantile epileptic encephalopathy with suppression-burst (Ohtahara syndrome) was made in most of them, with infantile spasms and nonsyndromic infantile epileptic encephalopathy being the diagnosis in other patients. Although the phenotypic spectrum of STXBP1-related encephalopathy is emerging with evidence suggesting the relatively frequent involvement of this gene in infantile epileptic encephalopathies, accurate clinical descriptions of patients are still necessary to delineate this entity. The sequence of the STXPB1 gene was analyzed in 29 patients with early onset syndromic or nonsyndromic infantile epileptic encephalopathy without brain magnetic resonance imaging (MRI) anomalies and with normal chromosomal and metabolic checkup. Another patient with a complex phenotype was analyzed by comparative genomic hybridization (CGH) array. From the studied series, 2 of 29 patients were found to carry a de novo heterozygous mutation in STXBP1. One patient carried the recurrent p.Arg406His mutation and the other an insertion of 10 bases leading to a premature termination codon. CGH array experiment detected a deletion of 3-3.5 Mbp in the third patient with infantile epileptic encephalopathy and nail malformations. All three had infantile spasms associated with partial seizures that responded to antiepileptic drug therapy. Intellectual abilities were severely impaired in all of them. Generalized tremor was the main neurologic striking feature in the three patients, with one of them further displaying unilateral akinetic-hypertonic syndrome. Mutations in STXBP1 are relatively frequent in patients with infantile epileptic encephalopathies. STXBP1-related encephalopathy may present as drug-responsive infantile spasms with focal/lateralized discharges. Generalized tremor appearing after the first year of life may be a clue to the diagnosis in some patients.

Mignot C ，Moutard ML ，Trouillard O ，Gourfinkel-An I ，Jacquette A ，Arveiler B ，Morice-Picard F ，Lacombe D ，Chiron C ，Ville D ，Charles P ，LeGuern E ，Depienne C ，Héron D ... -  《-》

A novel mutation in STXBP1 gene in a child with epileptic encephalopathy and an atypical electroclinical pattern.

Romaniello R ，Zucca C ，Tenderini E ，Arrigoni F ，Ragona F ，Zorzi G ，Bassi MT ，Borgatti R ... -  《-》

Epileptic patients with de novo STXBP1 mutations: Key clinical features based on 24 cases.

Mutations in the syntaxin binding protein 1 gene (STXBP1) have been associated mostly with early onset epileptic encephalopathies (EOEEs) and Ohtahara syndrome, with a mutation detection rate of approximately 10%, depending on the criteria of selection of patients. The aim of this study was to retrospectively describe clinical and electroencephalography (EEG) features associated with STXBP1-related epilepsies to orient molecular screening. We screened STXBP1 in a cohort of 284 patients with epilepsy associated with a developmental delay/intellectual disability and brain magnetic resonance imaging (MRI) without any obvious structural abnormality. We reported on patients with a mutation and a microdeletion involving STXBP1 found using array comparative genomic hybridization (CGH). We found a mutation of STXBP1 in 22 patients and included 2 additional patients with a deletion including STXBP1. In 22 of them, epilepsy onset was before 3 months of age. EEG at onset was abnormal in all patients, suppression-burst and multifocal abnormalities being the most common patterns. The rate of patients carrying a mutation ranged from 25% in Ohtahara syndrome to <5% in patients with an epilepsy beginning after 3 months of age. Epilepsy improved over time for most patients, with an evolution to West syndrome in half. Patients had moderate to severe developmental delay with normal head growth. Cerebellar syndrome with ataxic gait and/or tremor was present in 60%. Our data confirm that STXBP1 mutations are associated with neonatal-infantile epileptic encephalopathies. The initial key features highlighted in the cohort of early epileptic patients are motor seizures either focal or generalized, abnormal initial interictal EEG, and normal head growth. In addition, we constantly found an ongoing moderate to severe developmental delay with normal head growth. Patients often had ongoing ataxic gait with trembling gestures. Altogether these features should help the clinician to consider STXBP1 molecular screening.

Di Meglio C ，Lesca G ，Villeneuve N ，Lacoste C ，Abidi A ，Cacciagli P ，Altuzarra C ，Roubertie A ，Afenjar A ，Renaldo-Robin F ，Isidor B ，Gautier A ，Husson M ，Cances C ，Metreau J ，Laroche C ，Chouchane M ，Ville D ，Marignier S ，Rougeot C ，Lebrun M ，de Saint Martin A ，Perez A ，Riquet A ，Badens C ，Missirian C ，Philip N ，Chabrol B ，Villard L ，Milh M ... -  《-》

Epileptic and nonepileptic features in patients with early onset epileptic encephalopathy and STXBP1 mutations.

STXBP1 (MUNC18-1) mutations have been associated with various types of epilepsies, mostly beginning early in life. To refine the phenotype associated with STXBP1 aberrations in early onset epileptic syndromes, we studied this gene in a cohort of patients with early onset epileptic encephalopathy. STXBP1 was screened in a multicenter cohort of 52 patients with early onset epilepsy (first seizure observed before the age of 3 months), no cortical malformation on brain magnetic resonance imaging (MRI), and negative metabolic screening. Three groups of patients could be distinguished in this cohort: (1) Ohtahara syndromes (n = 38); (2) early myoclonic encephalopathies (n = 7); and (3) early onset epileptic encephalopathies that did not match any familiar syndrome (n = 7). None of the patients displayed any cortical malformation on brain MRI and all were screened through multiple video-electroencephalography (EEG) recordings for a time period spanning from birth to their sixth postnatal month. Subsequently, patients had standard EEG or video-EEG recordings. We found five novel STXBP1 mutations in patients for whom video-EEG recordings could be sampled from the beginning of the disease. All patients with a mutation displayed Ohtahara syndrome, since most early seizures could be classified as epileptic spasms and since the silent EEG periods were on average shorter than bursts. However, each patient in addition displayed a particular clinical and EEG feature: In two patients, early seizures were clonic, with very early EEG studies exhibiting relatively low amplitude bursts of activity before progressing into a typical suppression-burst pattern, whereas the three other patients displayed epileptic spasms associated with typical suppression-burst patterns starting from the early recordings. Epilepsy dramatically improved after 6 months and finally disappeared before the end of the first year of life for four patients; the remaining one patient had few seizures until 18 months of age. In parallel, EEG paroxysmal abnormalities disappeared in three patients and decreased in two, giving place to continuous activity with fast rhythms. Each patient displayed frequent nonepileptic movement disorders that could easily be mistaken for epileptic seizures. These movements could be observed as early as the neonatal period and, unlike seizures, persisted during all the follow-up period. We confirm that STXBP1 is a major gene to screen in cases of Ohtahara syndrome, since it is mutated in >10% of the Ohtahara patients within our cohort. This gene should particularly be tested in the case of a surprising evolution of the patient condition if epileptic seizures and EEG paroxysmal activity disappear and are replaced by fast rhythms after the end of the first postnatal year.

Milh M ，Villeneuve N ，Chouchane M ，Kaminska A ，Laroche C ，Barthez MA ，Gitiaux C ，Bartoli C ，Borges-Correia A ，Cacciagli P ，Mignon-Ravix C ，Cuberos H ，Chabrol B ，Villard L ... -  《-》