Researchers led by Leslie Biesecker at the National Human Genome Research Institute found that Proteus syndrome results from a mutation in AKT1 that appears as a mosaic throughout the affected person's tissues. The condition is characterized by skin overgrowth and abnormal bone development. As they report in the New England Journal of Medicine, the researchers conducted exome sequencing of tissues from people with Proteus syndrome and found that 90 percent of the patients had a somatic AKT1 mutation.