Abstract
The best-studied examples of genetically defined developmental disorders, such as Down syndrome (trisomy 21) and velocardiofacial syndrome (del22q11), have been known since before the genomic era and were initially recognized as distinct syndromes based on their own unique constellation of dysmorphic and multisystem features. For example, Down syndrome is characterized by the co-occurrence of several dysmorphic features, including a flattened facial profile, slanted palpebral fissures, protruding tongue, and transverse palmar crease, with accompanying hypotonia, cardiac issues, and developmental delay.(1) None of these features in isolation is specific to Down syndrome, and all features are not present in all cases, but the co-occurrence of multiple features from this set is a specific and sensitive marker for the presence of trisomy 21. To what extent might similar principles apply to the patterning of cognitive and behavioral features across different neurogenetic syndromes?