Familial factors influence level of functioning in pervasive developmentaldisorder

Objective: To determine whether siblings with pervasive developmental disor ders (PDD) tend to have the same type and number of PDD symptoms or a simil ar level of functioning. Method: The familiar correlations for PDD subtype, symptom totals, adaptive behaviors, and nonverbal IQ were calculated for 9 4 children with PDD from 46 families. Results: On variables measuring PDD s ymptoms, only impairments in nonverbal communication and verbal/nonverbal s tatus tended to run true within families. There was no familial aggregation of PDD subtype. In contrast, measures of nonverbal IQ and adaptive behavio rs in socialization and communication showed a moderate degree of familial resemblance. The degree of familial resemblance did not change ii the analy sis was restricted only to those families in which both affected children m et criteria for autism. Conclusion: Insofar as the familial resemblance see n in PDD is due to genetic factors, these data provide some evidence that h igher- and lower-functioning PDD children may arise from separate genetic m echanisms. Current gene-mapping studies of PDD may need to take this eviden ce of genetic heterogeneity into account.