OBJECTIVE:

To determine complement C4 protein concentrations in the plasmas of autistic subjects and their family members.

DESIGN:

Cross-sectional study.

SETTING:

Center for Persons with Disabilities and the Department of Biology, Utah State University, Logan.

PARTICIPANTS:

Forty-two autistic subjects (34 males [81%] and eight females [19%]), 50 of their biologic parents, 21 siblings, and 105 normal subjects (56 females [53%] and 49 males [47%]; all white) living in northern Utah.

INTERVENTIONS:

None.

METHODS:

The enzyme-linked immunosorbent assay was used to determine C4 protein concentrations in autistic subjects.

MAIN RESULTS:

Plasma concentration (median, 14.7 g/L of the C4B protein) in autistic patients was significantly (P = .01) decreased compared with that of normal subjects (median, 22.4 g/L). The C4B concentrations in parents and siblings of autistic children were decreased, but not significantly. The C4A protein concentrations in the plasma of autistic subjects and their family members were normal.

CONCLUSION:

Decreased protein concentrations of C4B may be associated with autism.