Hypereosinophilic syndrome (HES) is a rare blood disease in which the body produces too many of a particular type of leukocyte (white blood cell) called eosinophils. Eosinophils normally help the body fight allergies and certain types of infections. Hypereosinophilic syndrome may provoke cardiomyopathy, pulmonary disease, neuropathy, skin lesions, etc. If left untreated, HES is progressively fatal. It is treated with glucocorticoids such as prednisone. The addition of the monoclonal antibody mepolizumab may reduce the dose of glucorticoids.
Although the cause of hypereosinophilic syndrome is unknown, there are clues which indicate it begins in a person's genes. Researchers have found that in some people with HES, 2 genes somehow combine to form a new combination gene. This "fusion gene" causes the body to make a protein known as a kinase (KY-nase), which causes some white blood cells to multiply excesively. People with HES might have different symptoms, depending on which parts of the body are affected. These symptoms may include: tiredness, shortness of breath, cough, muscle pain, rashes, etc.