We aimed to contrast rates of consanguinity among patients with bipolar I disorder (BP1) and controls in a population with customary consanguineous marriages (i.e., marriage between related individuals). Consanguinity increases risk for numerous monogenic and polygenic diseases. Whether the risk for BP1 increases with consanguinity has not been investigated systematically. Two independent studies were conducted in Egypt: (1) Case-control study 93 patients with BP1, 90 screened adult control individuals, and available parents. The inbreeding coefficient/consanguinity rate was estimated in two ways: using 64 DNA polymorphisms ("DNA-based" rate); and from family history data ("self report"); (2) Epidemiological survey: total of 1,584 individuals were screened, from whom self-reported consanguinity data were obtained for identified BP1 cases (n = 35) and 150 randomly selected, unaffected control individuals. DNA-based consanguinity rates showed significant case-control differences (P = 0.0039). Self-reported consanguinity rates were also elevated among BP1 patients in both samples (Study #1 OR = 2.66, 95% confidence intervals, CI: 1.34, 5.29; Study #2: OR = 4.64, 95% CI: 2.01, 10.34). In conclusion, two independent, systematic studies indicate increased consanguinity among Egyptian BP1 patients in the Nile delta region. Self-reported estimates of consanguinity are bolstered by DNA-based estimates, and both show significant case-control differences for BP1.
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