The investigators have successfully identified two novel genetic loci for MVP on chromosomes 11 and 13 and are searching for altered genes in these regions. This requires recruiting large families who may have MVP linked to these or other chromosomes; and obtaining DNA samples from 1,000-1,500 individually affected patients to study the relation between DNA markers throughout the genome and MVP. It is our expectation that the results of this study will lead to the discovery of gene(s) responsible for MVP. This will lead to improved understanding of the disease and, in turn, improved ability to treat and prevent progression in genetically susceptible individuals.