NIH launches $140 million effort to investigate genetic variation in normal human cells and tissues. The National Institutes of Health is launching a new program, the Common Fund’s Somatic Mosaicism Across Human Tissues (SMaHT) Network, that aims to transform our knowledge of how much genetic variation there is in the cells and tissues throughout our bodies. Somatic mosaicism is a type of genetic variation that arises when our somatic (non-reproductive) cells are genetically different from each other. This somatic genetic variation occurs when some of our cells accumulate DNA changes over time. Read more.