I am not understanding the polarized comments here. There is a major amount of hashgocho involved in the producing of children and their genetic coding. Parents do not have the control over that. With what science does know, we need to be cautious, and relatives marrying can possibly involve increased risk of combining of recessive genes. Dor Yeshurim does a superb and excellent job in testing for everything known, and it has the access to test for additional issues if there is reason to suspect, as with relatives. In fact, I have examined the situation quite carefully, and it seems that Dor Yeshurim has a better track record than the “average” lab.
For families that have no identified cases of illness for the past few generations, it stands to reason that there is a statistically lower risk. Regardless, if you ask R’ Eckstein of Dor Yeshurim, he will recommend against relatives marrying.
In my family, intra-family marriages have happened, and there have been no problems B”H. Everyne who considered such a shidduch did meticulous homework before proceeding. HKB”H should continue to protect all of Klal Yisroel.