https://www.bbc.com/news/articles/c241pn09qqjo**********
In the UK and across Europe, cousin marriage is coming under increased scrutiny - particularly from doctors, who warn that children of first cousins are more likely to experience an array of health problems.
And there's now some new, potentially worrying data from Bradford to add into that mix.
Researchers at the city's university are entering their 18th year of the Born in Bradford study. It's one of the biggest medical trials of its kind: between 2007 and 2010, researchers recruited more than 13,000 babies in the city and then followed them closely from childhood into adolescence and now into early adulthood. More than one in six children in the study have parents who are first cousins, mostly from Bradford's Pakistani community, making it among the world's most valuable studies of the health impacts of cousin marriage.
And when parents are cousins, they're more likely to both be carriers. A child of first cousins carries a 6% chance of inheriting a recessive disorder, compared to 3% for the general population.
But the Bradford study took a much broader view - and sheds fresh light. The researchers weren't just looking at whether a child had been diagnosed with a specific recessive disorder. Instead they studied dozens of data points, observing everything from the children's speech and language development to their frequency of healthcare to their performance at school. Then they used a mathematical model to try to eliminate the impacts of poverty and parental education - so they could focus squarely on the impact on "consanguinity", the scientific word for having parents who are related.
They found that even after factors like poverty were controlled for, a child of first cousins in Bradford had an 11% probability of being diagnosed with a speech and language problem, versus 7% for children whose parents are not related.
They also found a child of first cousins has a 54% chance of reaching a "good stage of development" (a government assessment given to all five year-olds in England), versus 64% for children whose parents are not related.
Aside from health concerns, there's another reason some people want to see cousin marriage banned: its impact on social cohesion. This is what's largely driving the debate in Scandinavia.
Back at the Bradford house, the beautician is putting her finishing touches to the hair of the three sisters, ahead of their big wedding at the weekend. Ayesha, the sister who is in a cousin marriage, is reflective and thoughtful about her own near decade-long relationship. "There are difficulties - we've been through lots together, we have sacrificed a lot," she says about her husband. "But we are happy together."
"I think even with love marriages you're going to have problems. They'll just be different ones."
***********