As pippap says, 'not very'. We can see many examples of 'close-kinship' arranged marriages amongst the Bangledeshi and Pakistani community in Britain. No doubt there will be more, and they will be increasingly dependent on a National Health System that was not set up to cater for self-inflicted genetic disorders. We have enough problems at the moment with obesity. The immigrant communities who bring in cousins from the sub-continent in arranged marriages are going to make life hard for their own kin-structure foremost, because we already have our own 'take' on the matter. Britain suffered from results of in-breeding before the regions were opened up by our transport revolution in the 18th-19th Centuries. Various isolated communities in areas like the Pennines, Snowdonia and the Scottish islands in-bred because of their isolation. The effects were eventually 'ironed-out' in the early years of the Health Service... We don't want it back again, thankyou very much.