On chromosome 5q31.1, antagonistic signals for AD and psoriasis have previously been attributed to IL13. 10,11,21 We here show that IL13 polymorphisms specifically influence AD risk, whereas opposing signals map to RAD50. The Rad50 protein, a component of the MRN complex (Mre11, Rad50, and Nbs1), is involved in DNA double-strand break repair but has no known function directly related to AD or psoriasis. This evidence concerns the gene IL13 and Alzheimer disease.