[Developmental and epileptic encephalopathy 85 caused by SMC1A gene truncating variation: 4 cases report and literature review].

To summarize the clinical phenotype of patients with developmental and epileptic encephalopathy 85 caused by SMC1A gene truncating variation. The clinical data of 4 patients with epileptic encephalopathy caused by SMC1A gene truncating variation from August 2016 to June 2020 were analyzed retrospectively. Related literatures up to October 2021 with the key words "SMC1A" "Developmental and epileptic encephalopathy 85" "SMC1A, epilepsy" and "SMC1A, truncating" in PubMed, CNKI, and Wanfang databases were searched. Relevant literature was summarized and reviewed. These 4 patients were all female. The onset age of seizure were all in the infantile period. They were admitted to the hospital at 3, 2, 11 and 18 months respectively. Focal seizures occurred in all 4 patients, while 1 of them experienced infantile spasm. The characteristic of cluster was observed in all of them with an interval of 14 days to 5.0 months. The seizures were all refractory to different kinds of anti-seizure medications. All 4 patients had severe developmental retardation with microcephaly (head circumference<-2 ). The interictal electroencephalogram (EEG) was characterized by diffuse slow wave. The 4 SMC1A gene variants were p.Gly655fs, p.Glu811fs, p.Arg412fs and p.Ile143fs, all of which were frameshift variation after parental validation. There were another 17 cases with SMC1A gene truncating variation reported in 6 English articles and 1 Chinese article. Among these 21 patients, who were all female, the onset of seizures occurred between 0.5 and 18.0 months of age. Seventeen cases (81%) had the characteristics of cluster attacks, and the intervals of attack cycles were different. Seizure types included generalized tonic-clonic seizure (12 cases (57%)), focal seizure (11 cases(52%)), myoclonic(4 cases(19%)), spasm (4 cases(19%)), atypical absence (3 cases(14%)), tonic seizure (2 cases (10%)), and atonia (1 case(5%)). In addition, 4 cases (19%) had status epilepsy. All patients had moderate to severe mental retardation. Microcephaly was found in all patients. Among 18 cases,EEG in 8 cases had diffuse slow wave background. Brain magnetic resonance imaging (MRI) was normal in 13 cases (62%). Other MRI changes included cerebellar atrophy (3 cases), thin corpus callosum (3 cases), and lateral ventricular enlargement (2 cases). Twenty patients did not respond well to antiepileptic drugs. The clinical phenotypes of patients with epilepsy encephalopathy 85 caused by SMC1A gene truncating variation are characterized by female, early-onset, clustering of seizures, development delay and microcephaly. Diffuse slow waves are shown in interictal EEG in partial. Response to treatment and prognosis are poor.