De novo variants in PHF21A cause intellectual developmental disorder with behavioral abnormalities and craniofacial dysmorphism with or without seizures: A case report and literature review

•The core phenotypes of IDDBCS include neurodevelopmental delay, craniofacial abnormalities, and overgrowth.•ADHD, hypotonia, epilepsy, ASD, and sleep disorders are common symptoms of IDDBCS.•DEE is the dominant phenotype of epilepsy, especially IESS. PHF21A may be a candidate gene for DEE.•De novo variants are the main mode of inheritance. The most common types of variants are frameshift variants, and the variant p.Arg580* in PHF21A is located at a mutation hot spot.