See:
https://www.nature.com/articles/ejhg2014218


Abstract:
"Druze individuals rarely marry outside their faith (often practicing consanguinity) and are thus believed to form a genetic isolate. To comprehensively characterize the genetic structure of the Druze population, we recruited and genotyped 40 parent-offspring trios from the Upper Galilee in Israel and the Golan Heights, attempting to capture different extended families (clans) across various geographical locations. Principal component (PC) and ADMIXTURE analyses demonstrated that Druze are close to, yet distinct from, other Middle-Eastern groups (Bedouins and Palestinians), supporting the Druze’s Middle-Eastern origin and their recent genetic isolation. Reconstruction of the Druze demographic history using identical-by-descent (IBD) segments suggested an ≈15-fold reduction in population size taking place ≈22–47 generations ago, close to the documented time of the foundation of the Druze faith at the 11th century. Combining the Galilee and Golan Druze genotypes with previously published data on Druze from the Carmel (Israel) and Lebanon demonstrated that all four Druze communities are genetically distinct. The Lebanese group shared less IBD segments (within the group and with other groups) compared with the Israeli Druze and showed higher heterozygosity (suggesting less consanguinity), but was less diverse in PC space. These findings suggest complex recent and ancient demographic history of the Druze population."


"Our study did not establish whether the Druze arose as a single founder group (and only then split to communities), or alternatively, whether each community descended from a unique ancestral population (by accepting the Druze religion), followed by homogenization by gene flow. A combination of these two scenarios is also possible, namely, a single ancestral group followed by admixture with local populations. Currently, we cannot rule out either option, since the Druze communities we studied are genetically closer to each other than to other Middle-Eastern populations, but at the same time are genetically distinct. We also did not identify the ancestral founder population (in case such a single population existed) or which of the four communities studied is closest to that founder population. Evidence from this study, in particular with respect to Lebanese Druze, is ambiguous: Lebanese Druze clustered more closely on PCA but shared significantly less IBD segments. These patterns are not necessarily contradicting (ie, they could represent different time scales; see also McVean40 for interpretation of PCA results), but are nevertheless not decidedly informative regarding Druze origins. Since the Druze population was only recently established (≈1000 years ago by historical accounts), we expect that with more data (eg, a finer mapping of Middle-Eastern populations as well as larger sample sizes) and improved modeling, questions of Druze origins will be further clarified. Additionally, sampling of more Druze communities (eg, from Syria) will be necessary to validate the conclusions reached in this study. Finally, due to the consanguineous nature of this population and hence its importance in medical genetics, we believe that the trio-based data set that we generated will be indispensable in mapping and investigating medically-relevant haplotypes."

This refusal to allow converts has cost them; all that consanguinity in marriages (47%), has resulted in a significant genetic load.

These practices mean they haven't absorbed the SSA which flowed into Bedouin groups and Palestinians, and so they are closer to Europeans.