The contribution of distinct genes to overlapping phenotypes suggests that such genes share ancestral origins, membership of disease pathways, or molecular functions. A recent study by Liu and colleagues identified mutations in TCF20, a paralog of RAI1, among individuals manifesting a novel syndrome that has phenotypes similar to those of Smith-Magenis syndrome (a disorder caused by disruption of RAI1). This study highlights how structural similarity among genes contributes to shared phenotypes, and shows how this relationship can contribute to our understanding of the genetic basis of complex disorders.