A chromosomal disorder with distinctive clinical findings characterized by early central hypotonia, developmental delay and intellectual deficit, epilepsy, and autistic behavior. Facial dysmorphism is absent or subtle and major malformations are rare. The syndrome is usually sporadic and not inherited and results from an abnormal extra chromosome in each cell containing mirror-image segments of genetic material. The isodicentric chromosome is made up of two extra copies of a segment of genetic material from chromosome 15, which is attached end-to-end. Typically this copied genetic material includes a region of the chromosome called 15q11-q13. [from
SNOMEDCT_US]