Both Parents’ Ages Linked to Autism Risk
By RONI CARYN RABIN
Published: February 8, 2010
Older mothers are more likely than younger ones to have a child with autism, and older fathers significantly contribute to the risk of the disorder when their partners are under 30, researchers are reporting.
In a study published online on Monday in the journal Autism Research, the researchers analyzed almost five million births in California during the 1990s, and 12,159 cases of autism diagnosed in those children ― a sample large enough to examine how the risk of autism was affected when one parent was a specific age and the other was the same age or considerably older or younger.
Previous research found that the risk of autism grew with the age of the father. The new study suggested that when the father was over 40 and the mother under 30, the increased risk was especially pronounced ― 59 percent greater than for younger men.
By contrast, for women 30 and older, the risk of autism rose 13 percent when the father was over 40.
Every five-year increase in a mother’s age raised her risk of having a child with autism by 18 percent; a 40-year-old woman’s risk was 50 percent greater than that of a woman who became a mother in her late 20s, and 77 percent higher than that of a woman under 25.
But while the number of California women giving birth in their 40s rose sharply in the 1990s, the researchers said that could not account for the sevenfold rise in autism during the decade.
“The rise in autism is occurring among children of parents of all ages,” said Janie F. Shelton, a graduate student in epidemiology at the University of California, Davis, who was the paper’s lead author. “We can’t say that the shifting trend of maternal age is responsible for the increased rates of autism.”
The new findings appeared to question the conclusions of earlier research suggesting that the risk of autism spectrum disorders increased with advancing paternal age, but not with advancing maternal age.
One such study analyzed a large Israeli military database and found that children of fathers 40 or older were more than five times as likely to have an autism disorder as those whose fathers were under 30.
An author of that study, Dr. Dolores Malaspina, a psychiatrist at New York University Langone Medical Center, said Monday that mothers and fathers were usually so close in age that small statistical differences could appear to shift the effect of advanced age from one parent to another.
“It’s important we not turn around and blame mothers,” Dr. Malaspina said. “The evidence is very, very strong that there is a paternal age effect.”
Independent and dependent contributions of advanced maternal and paternal ages to autism risk
Janie F. Shelton 1 *, Daniel J. Tancredi 2, Irva Hertz-Picciotto 1 3
1Department of Public Health Sciences, University of California, Davis
2Department of Pediatrics and the Center for Healthcare Policy and Research, University of California, Davis
3The UC Davis M.I.N.D Institute, Sacramento, California
email: Janie F. Shelton (firstname.lastname@example.org)
*Correspondence to Janie F. Shelton, Department of Public Health Sciences, MS1C, University of California Davis, California 95616
autism . maternal age . paternal age . effect measure modification . attributable risk . advanced maternal age . advanced paternal age . interaction
Reports on autism and parental age have yielded conflicting results on whether mothers, fathers, or both, contribute to increased risk. We analyzed restricted strata of parental age in a 10-year California birth cohort to determine the independent or dependent effect from each parent. Autism cases from California Department of Developmental Services records were linked to State birth files (1990-1999). Only singleton births with complete data on parental age and education were included (n=4,947,935, cases=12,159). In multivariate logistic regression models, advancing maternal age increased risk for autism monotonically regardless of the paternal age. Compared with mothers 25-29 years of age, the adjusted odds ratio (aOR) for mothers 40+ years was 1.51 (95% CI: 1.35-1.70), or compared with mothers <25 years of age, aOR=1.77 (95% CI, 1.56-2.00). In contrast, autism risk was associated with advancing paternal age primarily among mothers <30: aOR=1.59 (95% CI, 1.37-1.85) comparing fathers 40+ vs. 25-29 years of age. However, among mothers >30, the aOR was 1.13 (95% CI, 1.01-1.27) for fathers 40+ vs. 25-29 years of age, almost identical to the aOR for fathers <25 years. Based on the first examination of heterogeneity in parental age effects, it appears that women's risk for delivering a child who develops autism increases throughout their reproductive years whereas father's age confers increased risk for autism when mothers are <30, but has little effect when mothers are past age 30. We also calculated that the recent trend towards delayed childbearing contributed approximately a 4.6% increase in autism diagnoses in California over the decade.
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