The exact diagnostic criteria for MCDD remain unclear but may be a useful diagnosis for people who do not fall into any specific category.
High frequency of idiosyncratic anxiety reactions such as sustained periods of uncontrollable giggling, giddiness, laughter, or "silly" affect that is inappropriate in the context of the situation.
More often attachments may appear friendly and cooperative but very superficial, based primarily on receiving material needs.
Disturbed attachments displaying high degrees of ambivalence to adults, particularly to parents/caregivers, as manifested by clinging, overly controlling, needy behavior, and/shifting or aggressive, oppositional behavior toward parents, teachers, or therapists are common.
Perplexity and easy confusability (trouble with understanding ongoing social processes and keeping one's thoughts "straight").
Multiple complex developmental disorder is likely to be caused by a number of different various genetic factors.