To date, genome-wide association studies have focused on variants that influence the magnitude of a trait, but evidence from several species suggests that phenotypic variability has some degree of genetic control. A study has now identified the first example of an individual genetic variant associated with variability of a complex trait. Yang et al. conducted a meta-analysis of genome-wide association studies for phenotypic variability in body mass index and height and found a SNP at the FTO locus that is associated with variability in body mass index. The authors found no SNPs that were associated with variability in height. As this study included ~170,000 samples, it suggests that most SNPs are not associated with phenotypic variability (or that they have very small effects on variability).