Hirschhorn 2009; Kraft and Hunter 2009). Factors invoked to explain the “missing heritability” include polygenic effects (very large numbers of polymorphisms having very small effects), undiscovered rare variants, copy-number variants that have yet to be systematically analyzed, and interactions among genes, or between genes and environmental factors (Maher 2008; Phillips 2008; Goldstein 2009). Investigation of these potential sources of undiscovered phenotypic variation can lead to novel genetic discoveries, provide new insights into biological pathways involved in disease, and potentially provide clues to environmental interventions capable of mitigating genetic risk.
