Based on millions of children born in Sweden since
the 1970s, researchers say those born to fathers older than 45 were
significantly more likely to develop autism, bipolar disorder,
attention deficit hyperactivity disorder and schizophrenia than
those born to much younger fathers.
The analysis of all the births in Sweden over 28 years also found
that children of older fathers were at heightened risk for substance
abuse, suicide and academic failure.
"Historically, the focus has been on the mothers' age at
childbirth," lead author Brian D'Onofrio told Reuters Health. "This
study is adding to a growing body of research that suggests we also
need to consider fathers' age at childbearing."
In the largest study to date on the effects of paternal age,
D'Onofrio, an Indiana University psychologist, worked with
Karolinska Institute researchers to analyze the civil and medical
records of more than 2.6 million children born in Sweden between
1973 and 2001.
Several past studies have suggested that the age of a child's father — and even of its grandfather — can affect many aspects of the
child's physical and psychological health for a lifetime (see
Reuters article of March 20, 2013, here:
D'Onofrio and his colleagues wanted to look specifically at mental
health in kids born to older fathers and began by comparing all the
kids in their data pool to each other and seeing which children were
most at risk of specific psychological disorders.
Fathers aged 45 to 79 years old were considered older, and the
average age of older dads in the study was 49, D'Onofrio said. The
younger fathers were 20 to 24 years old.
In their analysis, the researchers also wanted to eliminate social
and environmental factors that could influence how kids turned out,
so they compared individual children to their own eldest sibling — born when the parents were potentially much younger — as well.
In that comparison, the children born to older fathers were 25 times
more likely to be diagnosed with bipolar disorder, 13 times more
likely to be diagnosed with attention deficit hyperactivity disorder
and 3.5 times more likely to suffer from autism than children born
to fathers aged 20 to 24.
Children of older fathers also were more than twice as likely to
attempt suicide and to become substance abusers, 1.6 times more
likely to receive failing grades and 1.7 times more likely to drop
out of school, the team reported in JAMA Psychiatry.
D'Onofrio said his findings from the sibling comparisons so
"shocked" him that he spent months adding new variables to see if he
could shrink the discrepancies or make them disappear. He could not.
Nonetheless, he pointed out, the chance of an older father having a
mentally ill child remains small.
The study found 2,424 cases of autism out of about 900,000 children
born between the years 1992 and 2001 and 6,819 cases of bipolar
disorder out of 2.3 million children born from 1973 to 1997.
"We are not saying that all children born to older men are going to
have psychiatric problems," D'Onofrio said. "Couples, along with
their doctors and society at large, need to consider the advantages
and disadvantages of delaying childbearing."
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"How that plays out in terms of medical practice is certainly up
for debate," D'Onofrio said.
Dr. Fred Volkmar, a psychiatrist and director of the Child Study
Center at the Yale School of Medicine said the new study would not
change his advice to prospective parents. "Any time you have a baby,
there's risk," he said.
Epidemiologist Irva Hertz-Picciotto of the University of
California, Davis, agrees there's evidence that paternal age may
contribute to the development of autism, which she has studied
extensively. But Hertz-Picciotto, who was not involved in the new
study, told Reuters Health she thinks the sibling comparisons
overstate the effect of paternal age because mothers' and fathers'
ages are so interrelated.
"If the father has aged, so has the mother," she said. "From my
perspective, that's a shaky analysis."
The new study also did not examine the possible role of older
couples' use of infertility treatments on childhood mental illness,
though D'Onofrio said the researchers plan to do that analysis.
The birth rate for U.S. women aged 40 to 44 years old rose by 2
percent a year from 2000 to 2012, according to government
statistics. Average childbearing age has increased steadily for both
men and women since the 1970s, with the average age increasing four
years for women and three years for men, D'Onofrio said.
A previous study of Icelandic children diagnosed with autism and
schizophrenia identified paternal age at conception as the single
largest risk factor for passing on new gene mutations (see Reuters
article of August 22, 2012, here: reut.rs/1cq3AYg)
In that study, about two more new gene mutations appeared in
offspring for every year of increase in a father's age — meaning the
number of new mutations passed on by fathers would double every 16.5
years from puberty onwards.
That possible explanation the new study's results makes sense to
Volkmar. "As fathers get older, their sperm basically degrades.
There is potential for small errors to creep in," he said, but other
mechanisms could also be at work.
"It's not impossible," he said, "that older fathers are getting
married later because they're strange people, and it takes them
longer to find a mate."
JAMA Psychiatry, online Feb. 26, 2014.
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