15q13.3 microdeletion (microdel15q13.3) syndrome is characterized by a wide spectrum of neurodevelopmental disorders with no or subtle dysmorphic features. Epidemiology Its prevalence is unknown; nearly 150 cases have been reported, including a subset of healthy relatives of affected individuals. Males are more likely to be symptomatic. Clinical description The syndrome manifests in childhood or later in life. Patients present with developmental delay, mainly in speech acquisition, cognitive impairment in about half of the cases (usually mild, sometimes moderate to severe), idiopathic generalized epilepsy (IGE, including childhood or juvenile absence epilepsy, juvenile myoclonic epilepsy (see these terms) and epilepsies with generalized tonic-clonic seizures), neurobehavioral disorders of the autistic or psychotic spectrum (including impaired expressive language, poor eye contact, repetitive movements, hyperactivity, impulsive and/or aggressive behavior, and disturbed social interactions). Subtle dysmorphic features may be present (down-slanting palpebral fissures, prominent nasal tip, large ears, strabismus, clinodactyly of the 5th finger, pigmented naevi ).