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Birth order effects on nonverbal IQ scores in autism multiplex families JOURNAL OF AUTISM AND DEVELOPMENTAL DISORDERS Spiker, D., Lotspeich, L. J., DiMiceli, S., Szatmari, P., Myers, R. M., Risch, N. 2001; 31 (5): 449-460

Abstract

Lord (1992) published a brief report showing a trend for decreasing nonverbal IQ scores with increasing birth order in a sample of 16 autism multiplex families, and urged replication in a larger sample. In this report, analyses of nonverbal IQ scores for a sample of 144 autism multiplex families indicated that nonverbal IQ scores were significantly lower in secondborn compared with firstborn siblings with autism. This birth order effect was independent of gender as well as the age differences within sib pairs. No such birth order effects were found for social or communicative deficits as measured by the Autism Diagnostic Interview-Revised (ADI-R), but there was a modest tendency for increased scores for ritualistic behaviors for the firstborn sibs. Further, there were no gender differences on nonverbal IQ scores in this sample. Results are discussed in terms of implications for genetic studies of autism.

View details for Web of Science ID 000172802000002

View details for PubMedID 11794410