First time hearing about this. I'm surprised the whole region isn't massively degenerated after centuries of traditional incest. The numbers are pretty staggering
However, that's racist-adjacent so I doubt there's any actual research or scientific basis for it. They certainly have much higher rates of genetic diseases. As noted in that Wikipedia article: "While babies of Pakistani heritage accounted for roughly 3.4% of all births in the UK (2005), "they had 30% of all British children with recessive disorders and a higher rate of infant mortality," according to research done by the BBC.[46]"