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Cousin marriage doubles birth defect risk

Older white mothers also have doubled risk – but absolute risk is small

Louise Prime

Thursday, 04 July 2013

Children whose parents are first cousins are twice as likely to have birth defects as those whose parents are unrelated, and consanguinity accounts for almost a third of all birth defects among Pakistani babies in Bradford, research has shown. The study, published online first in The Lancet, also showed that older white mothers have double the risk of having birth defects compared with younger mothers – though absolute risks remain small.

The Born in Bradford (BiB) project is following the health of 13,500 babies born in Bradford Royal Infirmary between 2007 and 2011. The BiB researchers found that overall rates of congenital anomalies are nearly twice as high in this cohort as the national mean (305.74 vs. 165.90 per 10,000 live births), and they investigated the effect of various clinical and maternal risk factors on the risk of birth anomalies.

One of the factors they looked at was consanguineous marriage – about 37% of marriages among people of Pakistani origin in the study were between first cousins, compared with fewer than 1% in people of white British origin. Overall, 18% of the babies in this study were born to parents who were first cousins, but this rose to 37% for babies of Pakistani origin.

The researchers found that consanguineous marriage more than doubled babies’ risk of birth defects, from 3% to 6%; this was not explained by differences in socioeconomic status. They calculated that consanguinity accounted for almost a third (31%) of all birth defects in babies of Pakistani origin.

The other factor that significantly increased the risk of birth defects, for babies of white British women, was maternal age greater than 34 years, which almost doubled the rate, from 2% to 4%.

Highly educated mothers, of any ethnic origin, had about half the risk of having birth defects compared with less educated women.

The authors concluded: “Consanguinity is a major risk factor for congenital anomaly ... Our findings will be valuable in health promotion and public health, and to those commissioning antenatal, paediatric, and clinical genetic services. Sensitive advice about the risks should be provided to communities at increased risk, and to couples in consanguineous unions, to assist in reproductive decision making.”

The author of an accompanying editorial added: “In view of the high community support for the Born in Bradford programme, a complementary substudy to determine the effects of consanguinity and community endogamy [when individuals marry within the same ethnic, class, or social group] on adult-onset diseases would be an invaluable investment for the future.”

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