ARID1B mutations have been identified as the most common cause of CSS and also in children with intellectual disability who have subtle features of CSS, but who would not have been diagnosed with this syndrome on the basis of their phenotype alone.24 However, we suggest that certain features of CSS, such as the pattern of hair distribution (synophrys, sparse scalp hair but increased body hair) and fifth finger hypoplasia in combination, should lead to CSS being included in differential diagnoses for children with a neurodevelopmental disorder. This evidence concerns the gene ARID1B and neurodevelopmental disorder.