Consanguinuity and older mothers increase risk of birth defects

8 July 2013

New research has shown that children born to older mothers and parents who are also blood relations are at greater risk of birth defects.
Birth defects are a varied group of abnormalities present at birth, ranging from chromosomal disorders such as Down’s Syndrome and inherited diseases such as haemophilia to physical malformations such as cleft palate and spina bifida. They are a leading cause of infant death and disability around the world; in many countries and populations they are the single most common cause of childhood deaths. Incidence in the UK varies between different ethnic groups, being highest among Pakistani populations.
Researchers from the Universities of Bradford and Leeds examined the factors that affect the rates of birth defects (also called congenital disorders or anomalies) in different ethnic groups. They examined records from more than 11,000 babies of 43 different ethnicities from the Born in Bradford study of babies born in 2007-13, and found that 386 (3%) had some form of birth defect. This was around twice the national rate.
They then used questionnaire data from the mothers of babies with at least one recorded birth defect and clinical data to examine factors potentially associated with birth defects. The two factors found to be linked with greatest increased risk, approximately double, were older maternal age (over 34) and parental consanguinity (blood relationships). Conversely, socio-economic status (deprivation levels) had no effect, whilst higher levels of maternal education halved the risk for all ethnic groups.
The researchers concluded that ‘consanguinity is a major risk factor for congenital anomaly’ and underlies the higher rate of birth defects observed in Pakistani populations, accounting for almost a third of cases. They propose that health professionals should advise parents of increased risks in a sensitive manner, especially in communities at increased risk and for couples in consanguineous unions, ‘to assist in reproductive decision making’.
More than a billion people are thought to live in communities where consanguineous marriage is common, so the new evidence of increased risk of birth defects is important. This research is valuable because it included sufficient numbers of babies from different ethnicities (the most common being Pakistani and white British) to produce reliable results, and controlled for factors such as deprivation, revealing the independent risk conferred by consanguinity.
In his accompanying commentary Alan Bittles observes that information on the nature of consanguinity was limited, demarcated by first-cousin or other blood relationship between the parents only. In some communities, whole lineages based on marriages between specific groups (such as the Biraderi networks in the UK Pakistani community) may also have increased the risk of recessive genetic disorders. Clearly, a whole range of genetic, environmental and social factors may affect the incidence of birth defects in different populations.
The PHG Foundation Health Needs Assessment Toolkit for Congenital Disorders was developed to allow health planners around the world to evaluate rates of birth defects in individual countries or communities, compare them with those in other areas, and tailor national and local services and policies to reduce the adverse health impacts. This is because although information about causes, frequency, prevention and care for birth defects in any population may be useful, the variability between different populations and sub-populations must be taken into account in planning health services. The toolkit also provides specific resources for the local development of services to prevent and treat congenital disorders.

In a separate piece of work, the PHG Foundation is also providing the evaluation for a project to increase awareness and understanding of genetic disorders among ethnic minority groups in the UK. Based in Birmingham where levels of infant mortality have been amongst the highest in England and continue to be above the national average, the Enhanced Genetic Services Project (EGSP) aims to improve access to genetic services and reproductive advice among ethnic minorities, especially the local Pakistani community and particularly those in consanguineous unions, and ultimately to reduce levels of infant mortality and disability. 

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