Congenital lipomatous overgrowth with vascular, epidermal, and skeletal anomalies (CLOVES) is a sporadically occurring, nonhereditary disorder characterized by asymmetric somatic hypertrophy and anomalies in multiple organs. We hypothesized that CLOVES syndrome would be caused by a somatic mutation arising during early embryonic development. Therefore, we employed massively parallel sequencing to search for somatic mosaic mutations in fresh, frozen, or fixed archival tissue from six affected individuals. We identified mutations in PIK3CA in all six individuals, and mutant allele frequencies ranged from 3% to 30% in affected tissue from multiple embryonic lineages. Interestingly, these same mutations have been identified in cancer cells, in which they increase phosphoinositide-3-kinase activity. We conclude that CLOVES is caused by postzygotic activating mutations in PIK3CA. The application of similar sequencing strategies will probably identify additional genetic causes for sporadically occurring, nonheritable malformations.

Objective We generated knock-in mice that express a tamoxifen-inducible Cre recombinase from the Prg4 locus (Prg4GFPCreERt2), and used these animals to fate-map the progeny of Prg4-positive articular cartilage cells at various ages. Methods We crossed Prg4GFPCreERt2 mice to Rosa26floxlacZ or Rosa26mTmG reporter strains, administered tamoxifen to the double heterozygous offspring at different ages, and assayed Cre-mediated recombination by histochemistry and/or fluorescence microscopy. Results In 1-month-old mice, the expression of the Prg4GFPCreERt2 allele mirrors expression of endogenous Prg4 and, when tamoxifen is given for 10 days, causes Cre-mediated recombination in ~70% of the superficial-most chondrocytes. Prg4GFPCreERt2 expressing cells are mostly confined to the top three cell layers of the articular cartilage in 1-month-old mice, but descendants of these cells are located in deeper regions of the articular cartilage in aged mice. At embryonic day 17.5, Prg4GFPCreERt2 expressing cells are largely restricted to the superficial-most cell layer of the forming joint, yet at approximately 1 year, progeny of these cells span the depth of the articular cartilage. Conclusions Our results indicate that Prg4-expressing cells located at the joint surface in the embryo serve as a progenitor population for all deeper layers of the mature articular cartilage. Also, our data reveal that Prg4GFPCreERt2 is expressed by superficial chondrocytes in young mice, but expands into deeper regions of the articular cartilage as the animals age. The Prg4GFPCreERt2 allele should be a useful tool for inducing efficient Cre-mediated recombination of floxed alleles at sites of Prg4 expression.