a group of syndromic forms of congenital anomalies due to a gene mutation or chromosomal aberration, united by one common feature – behavioral features and mental retardation. This group also includes states of unknown origin, but with characteristic behavioral reactions, such as rAS, Rett syndrome (see Rett syndrome). Children have a recognizable appearance, they are characterized by field behavior, so they must be recognized and distinguished from undifferentiated forms of mental retardation in order to prevent repeated family cases. Many forms of behavioral phenomena have a common behavioral feature – hyperactivity with attention deficit, which can also be an independent syndrome and not accompanied by mental retardation. As a rule, if a child without good reason (postnatal brain damage, sensory deficit, pedagogical neglect) is not able to learn complex skills and stereotypical forms of behavior and special pretentious movements prevail, then you should think about a violation of his mental development.