The Journal of Pediatrics completed a retrospective chart review on 196 children less than 6 years of age with various developmental disabilities. Sixty three of the children (32%) were reported to exhibit self injurious behaviors. When comparing the children with self injurious behaviors and those without no differences were seen between the two groups regarding "developmental level, expressive or receptive language level, mobility status or sensory functioning, or in rates of identification with cerebral palsy, seizure disorders, or autism". Differences were seen in the self injurious group regarding higher parental report of "destructive behaviors, hurting others or unusual habits".
Reference: William E. MacLean, Raymond C. Tervo, John Hoch, Mark Tervo, Frank J. Symons Self-Injury among a Community Cohort of Young Children at Risk for Intellectual and Developmental Disabilities The Journal of Pediatrics