Marrying blood relatives and genetic risk

Families from all communities can be affected by genetic disorders.

Sri Lankan wedding
* Image source below

However, some types of genetic disorders – known as recessive disorders - are more common among families where couples are blood relatives, for example cousins.

Everyone carries at least one changed gene that can be harmful and could cause a recessive disorder, so there is a risk of recessive genetic disorders in all communities.

If partners are not related to each other the chance of them carrying the same changed (faulty) genes is very low because these changed genes are rare. Therefore, the chance of a baby born to unrelated couples inheriting two copies of the same changed gene is very low. So, most recessive genetic conditions are rare in populations that marry outside the family.


However, if partners are close blood relatives – such as cousins - then they share a large part of their genetic make-up and there is a higher chance that they we will share the same changed gene, and be a ‘carrier couple’.

Newly wedded Japanese couple
** Image source below

For carrier couples there is a chance that their children will inherit two copies of the same gene (receiving one each from both the mother and the father) and so be affected by a recessive genetic disorder. So, in populations where many people marry close relatives recessive genetic disorders are found in higher numbers.

Of the UK communities that have cousin couples, the Pakistani origin community is the largest with the highest level of cousin marriage. Therefore, there are more ‘carrier couples’ among the Pakistani population and a higher chance of babies receiving two copies of the same changed gene than among other populations where close relative marriage is less common.






* By Peter van der Sluijs (Own work) [GFDL or CC-BY-SA-3.0-2.5-2.0-1.0], via Wikimedia Commons

** By Christian Habisreutinger from Switzerland / Japan / Hong Kong (Wedding) [CC-BY-2.0], via Wikimedia Commons