A molecular model for sporadic human aneuploidy.

Aneuploidy is a leading cause of birth defects and a significant contributor to infertility in humans. Maternal age is the only well-established risk factor for gametic aneuploidy in the general population, with the underlying cause(s) yet to be identified. Here we present an extension of the 'two-hit' model for sporadic human aneuploidy. An important implication of this model is that the genetic makeup of an individual will influence the threshold where recombinationally at-risk oocytes (hit-1 events) become sensitive to the effects of advancing age (hit-2 events). Consequently, the age-related risk of gametic aneuploidy in many individuals is likely to differ significantly from the population average, and single nucleotide polymorphisms (SNPs) associated with altered risk should be identifiable.