Birth order, sibship size, childhood environment and immune-related disorders and risk of lymphoma in lymphoid cancer families

Familial aggregation of lymphoid cancers and immune-related disorders suggests a role for genetic susceptibility; however, few studies examine environmental factors. According to the hygiene hypothesis, adult-onset-immune-related diseases may be a consequence of reduced childhood infectious exposures and aberrant immune development. In a cohort of 196 multiple-case lymphoid cancer families, we analyzed environmental factors related to the hygiene hypothesis.