Several cultural or religious groups claim descent from a common ancestor. The extent to which this claimed ancestry is real or socially constructed can be assessed by means of genetic studies. Syed is a common honorific title given to male Muslims belonging to certain families claiming descent from the Prophet Muhammad through his grandsons Hassan and Hussein, who lived 1,400 years ago and were the sons of the Prophet’s daughter Fatima. If all Syeds really are in direct descent from Hassan and Hussein, we would expect the Y chromosomes of Syeds to be less diverse than those of non-Syeds. Outside the Arab world, we would also expect to find that Syeds share Y chromosomes with Arab populations to a greater extent than they do with their non-Syed geographic neighbours. In this study, we found that the Y chromosomes of self-identified Syeds from India and Pakistan are no less diverse than those non-Syeds from the same regions, suggesting that there is no biological basis to the belief that self-identified Syeds in this part of the world share a recent common ancestry. In addition to Syeds, we also considered members of other hereditary Muslim lineages, which either claim descent from the tribe or family of Muhammad or from the residents of Medinah. Here, we found that these lineages showed greater affinity to geographically distant Arab populations, than to their neighbours from the Indian subcontinent, who do not belong to an Islamic honorific lineage.
The results are pretty simple. First:
1) The Syed lineages don't exhibit a "Syed modal haplotype." What you should see is a Syed haplotype of ~50%, and then a range of other lineages which introgressed through people lying about their origins or women being unfaithful to their husbands. Instead there are a wide range of haplotypes. Being Syed is an honorific.
2) I don't think that they really prove higher Arab ancestry as such. They include really diverse populations, from Algerians to Israeli Arabs to Sudanese. The Islamic Honorific Lineages are somewhat closer to these groups, but that could be generic West Asian ancestry. For example, Persian. Or perhaps more African ancestry in cosmopolitan Syed lineages. Or, perhaps Syeds are just former high caste Hindus, who have more West Asian affinities.
Below is the PCA and list of Y chromosomal haplogroups. The paper is free at the link above.