Rare & Mosaic Disorders Molecular Research

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Overall Approach of the laboratory The laboratory uses a translational research approach to study human malformations and overgrowth disorders. In the clinical arena (study HG200388), we operate several clinical research protocols to assess the range of severity, spectrum of malformations, natural history of pleiotropic developmental and overgrowth disorders, and therapeutic studies. We use the tools of modern molecular biology to determine the molecular pathogenesis of these disorders. These include high throughput sequencing, positional cloning, microarray expression and microarray CGH analysis, cell and tissue culture studies to assess cell biologic functions and abnormalities of gene products, and the creation and analysis of animal mouse models of human genetic disease, and now we have developed therapeutic protocols for several of these diseases. Overgrowth syndromes Building on our prior successes with PIK3CA-related fibroadipose overgrowth (Lindhurst et al, 2012) and Proteus syndrome (Lindhurst et al, 2011), we have now identified targets for therapeutic intervention. These discoveries have shown that the mutations that cause mosaic overgrowth also are major contributors to the pathogenesis of cancer. Because of the intense work in the pharmaceutical industry on cancer drugs, we have used two such agents for therapeutics of overgrowth. We are using single-cell cloned fibroblast lines from patients with Proteus syndrome to test therapeutic agents. By titrating dosage of agents against assays of cell death and proliferation we have measured the potential effect of these agents for future clinical development. These preclinical data supported our successful application for an IND to use this compound to treat affected patients. Modeling Proteus syndrome Following on our discovery of the cause of this disorder in 2011 we have been successful in modeling this disorder in mice. While the Happle hypothesis (mosaicism for a mutation lethal in the non-mosaic state) is completely consistent with all recognized features of the disorder, it is impossible to prove this in human studies. To that end, we have created a mouse model of Proteus syndrome by creating a conditional knock-in allele for the p.Glu17Lys mutation (the mutation that affects all known patients with this disorder). We have shown that these animals have the predicted 100% embryonic lethality and a range of abnormalities consistent with the human syndrome. We are now planning therepeutic experiments for this model system. We have also demonstrated abnormalities in vascular remodeling. Genotype-Phenotype studies in mosaic disorders We have developed tissue sampling and culture methods coupled with custom-engineered mutation assays to detect the 5 known mutations in these genes in patients thought to be affected with this disorder and now routinely perform this as a patient screening method. This will allow us to support the activities in our clinical research project (HG200388) to reclassify these phenotypes. For any patients in whom this analysis is negative, we feed these samples into our next generation sequencing analysis pipeline using the intrapatient exome mosaic comparison approach that we have pioneered. We have also initiated studies of the molecular pathogenesis of tumors in Proteus syndrome in collaboration with NCI.