Allosteric communication between non-contacting sites in proteins plays a fundamental role in biological regulation and drug action. While allosteric gain-of-function variants are known drivers of oncogene activation, the broader importance of allostery in genetic disease and protein evolution is less clear. Here, we integrate large-scale experimental measurements and neural network models to provide evidence that allostery is a widespread cause of loss-of-function variant pathogenicity in human genetic diseases. In addition, our analyses reveal a conserved distance-dependent decay of allosteric mutational effects outside of protein active sites. As an important mechanism of pathogenicity, allostery needs to be better mapped, understood, and predicted across the human proteome.