Key features of this disorder are intellectual disability, language impairment and behavioural anomalies.
All individuals have mild to severe intellectual disability comorbid with severely impaired language development.
Behavioral issues are commonly observed, including irritability, low tolerance to frustration, hyperactivity, anxiety, aggressiveness or autistic traits.
Epilepsy is reported in one third of the individuals (absence, febrile, Rolandic or tonic-clonic seizures). Brain imaging is generally normal.
Additional recurrent features are hypotonia, motor delay, facial dysmorphism (hypotelorism, down-slanting palpebral fissures, and epicanthus), visual problems (strabismus, visual impairment and visual tracking difficulty), gastro-intestinal issues (feeding difficulties, reflux and constipation), breathing irregularities and scoliosis.