Using linear mixed models (an increasingly popular methodology), Visscher and colleagues recently estimated the proportion of variance in liability to schizophrenia attributable to single nucleotide polymorphisms (SNPs) genotyped on commonly used arrays [1••]. These SNPs are chosen for typing because they are relatively common (allele frequencies greater than 5%). The researchers were able to put a lower limit on the genetic contribution: about one-quarter of the variance in liability was explained by common variants, refuting claims that common variants have only a small role in the genetic cause of schizophrenia. Conversely this means the remaining variation in susceptibility could be attributable to rare variants.
