Marrying your cousin? Think again.

4 07 2013

First cousins who marry run twice the risk of
having a child with genetic abnormalities,
according to the findings of a study in the
English city of Bradford, published Friday in
The Lancet. The city, which has a high proportion of South
Asian immigrants and their descendants
among its population, served as a microcosm
for examining the risk of blood relative
couplings. About 37 percent of marriages among people
of Pakistani origin in the study involved first
cousins, compared to less than one percent of
“British unions”, said the researchers. University of Leeds investigator Eamonn
Sheridan led a team that pored over data from
the “Born in Bradford” study, which tracks the
health of 13,500 babies born at the city’s main
hospital between 2007 and 2011. Out of 11,396 babies for whom family details
were known, 18 percent were the offspring of
first-cousin unions, mainly among people of
Pakistani heritage. A total of 386 babies — three percent — were
born with anomalies ranging from problems in
the nervous, respiratory and digestive systems,
to urinary and genital defects and cleft palates. This Bradford rate was nearly twice the
national average, said the study. Other factors blamed for genetic flaws, such as
alcohol consumption, smoking and social
deprivation, can be ruled out, it said. “Thirty-one percent of all anomalies in children
of Pakistani origin could be attributed to
consanguinity” or marriage between first
cousins, said the study. The authors say theirs was the first study to
delve into the causes of congenital
abnormalities in a broad population. Co-researcher Neil Small said that in absolute
terms, the risk from consanguineous marriage
was still small. The study noted, in fact, that the risk was about
the same as for older white British mothers —
an age deemed to be 34 years and above. Even so, “sensitive advice (about) avoidable
risks” should be disseminated to communities
and couples in consanguineous unions, he
said. The findings should also inform health
professionals in antenatal care and genetic
testing. The paper said 90 infant deaths a year among
Pakistani mothers in England and Wales could
be attributed to congenital anomalies. Consanguinity is a deeply rooted social
phenomenon, The Lancet noted. “More than one billion people worldwide
currently (live) in communities where
consanguineous marriages are commonplace.”

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