Late-onset cluster seizures and intellectual disability associated with a novel truncation variant in SMC1A

SMC1A variants are known to cause Cornelia de Lange Syndrome (CdLS) which encompasses a clinical spectrum of intellectual disability, dysmorphic features (long or thick eyebrows, a hypomorphic philtrum and small nose) and, in some cases, epilepsy. More recently, SMC1A truncating variants have been described as the cause of a neurodevelopmental disorder with early-childhood onset drug-resistant epilepsy with seizures that occur in clusters, similar to that seen in PCDH19-related epilepsy, but without the classical features of CdLS. Here, we report the case of a 28-year-old woman with a de novo heterozygous truncating variant in SMC1A who unusually presented with seizures at the late age of 12 years and had normal development into adulthood.