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Did you know that not all identical twins have the same DNA? Research estimates that in 15% of identical twin pairs, one twin has a sizable number of mutations the other twin does not have.

Though identical twins inherit the same DNA sequence from their parents, through changes (or variation) in DNA that occur throughout their lives, twins can acquire personal genomes that aren’t 100% identical to each other.

In fact, we all have personal genomes that consist of the DNA sequence we inherit from our parents and of changes to that DNA sequence that occur over time in individual cells.

Somatic mosaicism refers to the changes to our DNA that occur after we’re conceived and that lead to some cells in our body having different DNA sequences than other cells.

Although we know that certain kinds of somatic mosaicism can lead to cancer, we don’t know how much somatic mosaicism there is in our personal genomes or how much it impacts human biology or other disease processes.

To understand the influence of somatic mosaicism on human biology and disease, the NIH Common Fund’s Somatic Mosaicism across Human Tissues (SMaHT) Network will develop a catalog of somatic mosaicism in humans. The knowledge generated from this catalog will enable the SMaHT Network to deepen our understanding of how much variation there is within our personal genomes and what the consequences are on human health. It will catalyze research on the extent to which somatic mosaicism within personal genomes is associated with environmental exposures, influences human development and aging, and contributes to diseases and disorders, including undiagnosed diseases and disorders in the skin, muscle, brain, and immune system.