<qa>  What is the name of the abnormalities that can indicate severe disease?Patients up to 21 years of age with childhood-onset mastocytosis may be eligible for this study. Candidates must have one or more of the following abnormalities, which indicate severe disease: enlarged liver or spleen; diffuse skin involvement; history of gastrointestinal bleeding or peptic ulcer; bone marrow biopsy with abnormal mast cells either in number or shape; elevated blood levels of the enzyme tryptase; or abnormal hemoglobin, white blood cells, platelets, or clotting factors. 