Myxomatous mitral valve disease (MMVD) is also known as mitral regurgitation, degenerative mitral valve disease and endocardiosis.  Myxomatous Mitral Valve Disease, often referred to as simply Mitral Valve Disease (MVD), is a common heart condition in dogs, particularly in small to medium-sized breeds and some toy breeds. Research into the genetics of MMVD in dogs has revealed that genetic factors can influence the severity and progression of the disease. While I don't have information on specific NEBL variants, I can explain that studies have identified certain genes and genetic markers associated with an increased risk of developing MMVD, as well as the rate of disease progression.