Autism and Maternal Age Linked
Reported February 11, 2010
(Ivanhoe Newswire) — Older mothers are significantly more likely to have a child with autism, regardless of the father’s age, although advanced paternal age is associated with elevated autism risk when the father is older and the mother is under 30.
A study at University of California, Davis, found the incremental risk of having a child with autism increased by 18 percent — nearly one fifth — for every five-year increase in the mother’s age. A 40-year-old woman’s risk of having a child later diagnosed with autism was 50 percent greater than that of a woman between 25 and 29 years old.
“This study challenges a current theory in autism epidemiology that identifies the father’s age as a key factor in increasing the risk of having a child with autism,” lead author Janie Shelton, of the UC Davis Department of Public Health Sciences, was quoted as saying. “It shows that while maternal age consistently increases the risk of autism, the father’s age only contributes an increased risk when the father is older and the mother is under 30 years old. Among mothers over 30, increases in the father’s age do not appear to further increase the risk of autism.”
Autism is a pervasive developmental disorder of deficits in social skills and communication, as well as repetitive and restricted behaviors, with onset occurring prior to age 3. Abnormal brain development, probably beginning in the womb, is fundamental to the behaviors that characterize autism. Current estimates place the incidence of autism at between 1 in 100 and 1 in 110 children in the United States.
The researchers consulted the electronic records for all births in California between January 1, 1990, and December 31, 1999. They then identified electronic records of children born during the study period who later received an autism diagnosis, defined as a diagnosis of full-syndrome autism at a California Regional Center.
Births where demographic information about parents was not available were excluded. Instances of multiple births were analyzed separately. The exclusions brought the total size of the study sample to approximately 4.9 million births and 12,159 cases of autism.
According to senior author Irva Hertz-Picciotto, professor of public health sciences at the UC Davis MIND Institute, why having an older parent places a child at risk for autism is not known.
“We still need to figure out what it is about older parents that puts their children at greater risk for autism and other adverse outcomes so that we can begin to design interventions,” Picciotto was quoted as saying.
One possible clue comes from a 2008 UC Davis study that found some mothers of children with autism had antibodies to fetal brain protein, while none of the mothers of typical children did. Advancing age has been associated with an increase in auto-antibody production.
The study also suggests epigenetic changes over time “may enable an older parent to transfer a multitude of molecular functional alterations to a child
thus epigenetics may be involved in the risks contributed by advancing parental age as a result of changes induced by stresses from environmental chemicals, co-morbidity or assistive reproductive therapy.”
SOURCE: Autism Research, February 8, 2010