Mantel-Haenszel statistics supported these results. The familial load of depression differed significantly by proband diagnoses (log-rank χ24 = 14.5; P = .006). Relatives of patients with EOD showed the most depression compared with relatives of patients with AD and controls (log-rank χ2 = 14.1 and 6.30, respectively; P ≤ .01). However, comparisons of relatives of probands with EOD vs LOD or comorbid AD/depression were inconclusive (log-rank χ2 = 1.41 [P = .23] and 2.45 [P = .12], respectively). Relatives of probands with AD showed the lowest occurrence of depression (log-rank tests: AD vs controls, χ2 = 3.36, P = .07; AD vs EOD, χ2 = 14.1, P<.001; AD vs LOD, χ2 = 6.72, P = .01; and AD vs comorbid AD/depression, χ2 = 3.42, P = .06). Patients with LOD, comorbid AD/depression, and controls did not differ in their familial loads of depression (LOD vs controls, χ2 = 1.12, P = .29; comorbid patients vs controls, χ2 = 0.06, P = .81; and LOD vs comorbid AD/depression, χ2 = 0.35, P = .55). However, relatives of patients with LOD showed a small, but significant, increase in LOD after the age of 80 years. Of 64 relatives of patients with LOD, 4 (6%) developed depression after this age, as contrasted with 2 (2%) of 85 relatives of persons with AD, 1 (2%) of 65 such relatives of persons with EOD, and 0 of the 145 control relatives and the 51 relatives of probands with comorbid AD/depression (χ24 = 11.5; P = .02).