Marriage between first cousins doubles risk of birth defects, say researchers

20.09.2013 14:46

Marriage between first cousins
doubles the risk of children being
born with birth defects, according to
a study seeking answers to the higher
than expected rates of deaths and
congenital abnormalities in the
babies of the Pakistani community.
Researchers have concluded that the
cultural practice of marriage between
first cousins is a bigger factor than
any other – outweighing the effects of
deprivation in parts of Bradford,
where the study was carried out.
Marriage to a blood relative
accounted for nearly a third (31%) of
all birth defects in babies of Pakistani
The risk of having a baby with birth
defects – usually heart or nervous
system problems which can
sometimes be fatal – is still small, but
it rises from 3% in the general
Pakistani population to 6% among
those married to blood relatives. The
researchers also found a doubling of
the risk in the babies of white British
women who were over the age of 34.
That increased risk, rising from 2% to
4%, is already known.
Every year there are about 90 more
baby deaths than would be expected
in the Pakistani community in
England and Wales because of birth
defects. But the issue is highly
sensitive because marriage within
families is an established cultural
Previous studies have caused
controversy but the lead author of the
paper, Dr Eamonn Sheridan from
Leeds University, said there has been
strong community involvement in the
Born in Bradford study, which has
been following the health of 13,500
babies delivered in the Bradford
Royal Infirmary between 2007 and
"The issue is incredibly sensitive,"
said Sheridan. "There has been a
terrific amount of community
engagement in the Born in Bradford
study from the word go. The
community has not been surprised by
the findings."
Local health professionals received
training in raising the issues with
people in the Pakistani community, so
that it became an acceptable topic for
discussion. The Muslim clerical
community was also involved.
In the multi-ethnic study, published in
the Lancet , the researchers looked at
a range of factors that might play a
part in birth defects, including
deprivation, obesity and smoking in
Socioeconomic status did not explain
the birth defects, even though two-
thirds of the babies came from the
most deprived fifth of the UK
population. Maternal smoking,
alcohol use and obesity were not
found to be risk factors in this
population. Greater education in
mothers was a protective factor in all
Professor Neil Small from the
University of Bradford, who co-led
the research, said: "This is the first
study that has been able to explore all
causes of congenital anomaly in a
population where there are sufficient
numbers in both consanguineous
[related by blood] and non-
consanguineous groups to come to
reliable conclusions.
"Clear and accessible information on
these small but significant avoidable
risks should be widely disseminated to
local communities and be included as
part of antenatal counselling and in
the planning of healthcare services."
It is difficult to advocate changes in
other people's cultural traditions, but
Sheridan said a shift in practice that
would save babies' lives was not
without hope. "The only other big
cohort study is of the Pakistani
community in Norway. The incidence
of first-cousin union in that
community is now declining," he
Partly that would be because of
gradual adaptation to Norwegian
culture, but since 2009 when the
study was published, there had been a
health education campaign to inform
people of the risks.
"It is something we can aspire to," he
said, "but I don't think there will be
any quick fixes."