(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
