Parental genotypes in the risk of a complex disease.

Our understanding of the genetic etiology of complex disorders is still elusive. According to the common-variant/common-disease hypothesis, frequent functional polymorphisms are the best candidates for disease-susceptibility alleles. Implicitly, we also assume that disease-susceptibility alleles are preferentially transmitted from parents to the affected offspring and that this effect can be captured by the transmission/disequilibrium test (TDT). However, our study of genetic predisposition to childhood acute lymphoblastic leukemia suggests that a focus on the patient's genotype might, in certain instances, be misleading. Our results indicate that, at least at some loci, parental genetics might be of primary importance in predicting the risk of cancer in this pediatric model of a complex disease. Consequently, in addition to TDT, other complementary strategies will need to be simultaneously applied to dissect genetic predisposition to complex disorders.