Children of either younger or older parents carry an increased risk of
bipolar disorder. This risk is greater if you were born to a mother
or father younger than 20 years old, if your mother was older than 35, or
your father was older than 45. This tendency gives a ‘U-Shaped Curve’,
showing increased risks for younger and older parents. This work is
presented at the ECNP Congress in Vienna, after recent publication in the
peer-reviewed journal European Neuropsychopharmacology.
Bipolar disorder, where sufferers can swing from moods of elation to
moods of extreme depression, is one of the most common serious mental
illnesses, affecting around 2% of people, and carries a high risk of
suicide and premature death. It is known to have high heritability; if
one parent has bipolar disorder there’s a 15% to 30% chance that this
will be passed on to their children.
Study leader Dr Giovanna Fico, of the University of Barcelona, said:
“Parental age is a
factor which affects many conditions, such as fertility and some
neuropsychiatric disorders. What we have found is slightly unusual
because both younger and older parents carry an increased risk of having
a child with bipolar disorder. The increased risk is moderate, but real.
We can speculate that younger parents may be affected by environmental
factors, such as socio-economic problems, lack of support, but also
stress or immunological factors, and that older parents may have genetic
factors coming into play, but the truth is we don’t really know”.
The researchers, from Spain, Italy, Australia and the Netherlands,
undertook a systematic review of studies from various countries which
relate bipolar disorder to age. In total the studies included 13,424,760
participants, of whom 217,089 had bipolar disorder. They found that older
men were more at risk than other groups of having a child with bipolar
disorder. These men had 29% higher odds of having a baby with bipolar
disorder than fathers aged 25 to 29 while older women had 20% higher odds
than mothers aged 25 to 29. In parents younger than 20 years the
increased odds were 23% (for mothers) to 29% (for fathers). All analyses
were corrected for biasing factors, like familial history for bipolar
disorders and the age of the other parent.
Giovanna Fico said “Again,
we must stress that this risk is moderate, and it must be kept in
perspective. However, for those already at risk, age is another factor
that should be taken into consideration, and so it may be that doctors
need to counsel both younger and older couples if they have a risk of
bipolar disorder. We also see this U-shaped curve in some other
conditions, such as autism and some cardiovascular diseases”.
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