The addition of genetic information to either of the phenotype based risk models (using the simple gene count or the genetic risk function) did not improve discrimination (table 1). Because part of the information included in the family history component of a risk score could reflect carriage of common genotypes, this may have undermined the incremental value of genetic information for predicting risk. However, the variants we studied explain only a small proportion of the familial aggregation of diabetes, and a formal analysis of the effect of inclusion or exclusion of the family history variable had almost no effect on the area under the receiver operating characteristics curve (data available on request).36
