This paper finds different variants in MEF2C are associated with forearm bone mineral density (BMD) compared to the MEF2C variants associated with femoral neck BMD. We conclude that these variants are likely independent signals that have different independent effects on the two BMD phenotypes. It is also possible that both associations arise from several rare causal variants on the same haplotype background. These results might suggest that the variants identified by GWAS are not causal, but the synthetic association created by rare variants with big effect size, however, this hypothesis will likely be tested as more sequencing studies emerge for BMD. (By Dr. Hou-Feng Zheng, http://jmg.bmj.com/content/early/2013/04/08/jmedgenet-2012-101287 )