Autism Recurrence Risks

Autism Spectrum Disorders (ASD) are neurodevelopmental disorders characterized by impairments in three main areas: social interaction, communication and restricted and repetitive behavior.  It occurs more often in males than in females, with a ratio of 4:1.  ASD includes individuals with classic autism as well as those with atypical or incomplete forms of autism.  The prevalence of ASD is approximately 1 in 150.  About 5-10% of cases of classic autism are due to an identifiable genetic disorder, which in many cases, has a known inheritance pattern and a specific recurrence risk.  These genetic disorders are typically identified by metabolic, chromosomal or molecular testing.

For families with a child who does not fall within this group of 5-10%, the risk of recurrence is often unknown and must be estimated.  Studies on twins have shown a concordance rate for autism to be between 30% and 60% for monozygotic (identical) and between 0% and 6% for dizygotic (fraternal) twins.  In addition, a concordance rate of approximately 90% for monozygotic twins was found for ASD, including cognitive delays and/or social problems, while only 10% of dizygotic twins were found to be concordant.  The higher rate of monozygotic concordance illustrates the strong influence of inherited genes and suggests that multiple genes are related to the cause of autism and autism-related traits.  This type of inheritance, where a combination of multiple genes and environment plays a role in the development of a condition or syndrome, is referred to as multifactorial.

The chart lists the estimated recurrence risks based on specific factors found in a family.  These risks are approximations based on past studies of families with autism or ASD.  It is important to note that the recurrence risks listed are for siblings born to the same parents AFTER identification of the affected individual.  The table applies to families in which the affected individuals are not known to have any identifiable genetic causation (e.g., a chromosome abnormality).

These risk figures represent an approximate average of the risk estimates reported in these studies:

1. Cook, E. H., Jr. (2001). Genetics of autism. Child Adolesc Psychiatr Clin N Am 10(2): 333-50.
2. Freitag, C. M. (2007). The genetics of autistic disorders and its clinical relevance: a review of the literature. Mol Psychiatry 12(1): 2-22.
3. Jorde, L. B., S. J. Hasstedt, et al. (1991). Complex segregation analysis of autism. Am J Hum Genet 49(5): 932-8.
4. Ritvo, E. R., L. B. Jorde, et al. (1989). The UCLA-University of Utah epidemiologic survey of autism: recurrence risk estimates and genetic counseling. Am J Psychiatry 146(8): 1032-6.
5. Simonoff, E. (1998). Genetic counseling in autism and pervasive developmental disorders. J Autism Dev Disord 28(5): 447-56.
6. Szatmari, P., M. B. Jones, et al. (1998). Genetics of autism: overview and new directions. J Autism Dev Disord 28(5): 351-68.
7. Whitelaw, C., P. Flett, et al. (2007). Recurrence risk in Autism Spectrum Disorder: a study of parental knowledge. J Paediatr Child Health 43(11): 752-4.