This month in The Journal

We often describe the functional effects of genetic variants using terms such as “loss of function” or “gain of function.” These terms have an origin in Muller’s morphs, a classification system published almost a hundred years ago. At that time, the structure of DNA and proteins were not known, and the interconnectedness of signaling pathways had not been discovered. While Muller’s morphs can still successfully categorize variants with a single effect, many complex variants do not fit into one of those boxes.