The duplication/inversion 15q11 or isodicentric 15 chromosome (inv dup(15) or idic(15)) syndrome is a chromosomal disorder with distinctive clinical findings characterized by early central hypotonia, developmental delay and intellectual deficit, epilepsy, and autistic behavior.

An abnormality of skull shape characterized by a decreased anterior-posterior diameter. That is, a cephalic index greater than 81%. Alternatively, an apparently shortened anteroposterior dimension (length) of the head compared to width.