Nine patients with a microdeletion 15q11.2 between breakpoints 1 and 2 of the Prader-Willi critical region, possibly associated with behavioural disturbances.

Behavioural differences have been described in patients with type I deletions (between breakpoints 1 and 3 (BP1-BP3)) or type II deletions (between breakpoints 2 and 3) of the 15q11.2 Prader-Willi/Angelman region. The larger type I deletions appear to coincide with more severe behavioural problems (autism, ADHD, obsessive-compulsive disorder).