Behçet's disease (BD) is an idiopathic, chronic, relapsing, multi-systemic vasculitis characterized by recurrent oral and genital aphthous ulcers, ocular disease and skin lesions. Prevalence of BD is highest in countries along the ancient silk road from the Mediterranean basin to East Asia. By comparison, the prevalence in North American and Northern European countries is low. Gastrointestinal manifestations of Behçet's disease are of particular importance as they are associated with significant morbidity and mortality. Although ileocecal involvement is most commonly described, BD may involve any segment of the intestinal tract as well as the various organs within the gastrointestinal system. Diagnosis is based on clinical criteria - there are no pathognomonic laboratory tests. Methods for monitoring disease activity on therapy are available but imperfect. Evidence-based treatment strategies are lacking. Different classes of medications have been successfully used for the treatment of intestinal BD which include 5-aminosalicylic acid, corticosteroids, immunomodulators, and anti-tumor necrosis factor alpha monoclonal antibody therapy. Like inflammatory bowel disease, surgery is reserved for those who are resistant to medical therapy. A subset of patients have a poor disease course. Accurate methods to detect these patients and the optimal strategy for their treatment are not known at this time.

Behçet disease is a chronic inflammatory systemic disorder, characterized by a relapsing and remitting course. It manifests with oral and genital ulcerations, skin lesions, uveitis, and vascular, central nervous system and gastrointestinal involvement. The main histopathological finding is a widespread vasculitis of the arteries and veins of any size. The cause of this disease is presumed to be multifactorial involving infectious triggers, genetic predisposition, and dysregulation of the immune system. As the clinical expression of Behçet disease is heterogeneous, pharmacological therapy is variable and depends largely on the severity of the disease and organ involvement. Treatment of Behçet disease continues to be based largely on anecdotal case reports, case series, and a few randomized clinical trials.

The diversity in our genome is crucial to understanding the demographic history of worldwide populations. However, we have yet to know whether subtle genetic differences within a population can be disentangled, or whether they have an impact on complex traits. Here we apply dimensionality reduction methods (PCA, t-SNE, PCA-t-SNE, UMAP, and PCA-UMAP) to biobank-derived genomic data of a Japanese population (n = 169,719). Dimensionality reduction reveals fine-scale population structure, conspicuously differentiating adjacent insular subpopulations. We further enluciate the demographic landscape of these Japanese subpopulations using population genetics analyses. Finally, we perform phenome-wide polygenic risk score (PRS) analyses on 67 complex traits. Differences in PRS between the deconvoluted subpopulations are not always concordant with those in the observed phenotypes, suggesting that the PRS differences might reflect biases from the uncorrected structure, in a trait-dependent manner. This study suggests that such an uncorrected structure can be a potential pitfall in the clinical application of PRS.

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This is the first study to give population-based estimates of rheumatic diseases in Lebanon. The high burden calls for public health attention for early detection, control and prevention of these conditions. Point prevalence of individual diseases was within the range of results from other COPCORD surveys with some variations that can be attributed to differences in methodology and geo-ethnic factors.

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