Several different types of autoimmune disease (MIM #109100) have been found to be associated with particular susceptibility alleles, even in the same family. For example, the Arg620Trp polymorphism of the PTPN22 gene (MIM *600716.0001) has been identified as a susceptibility allele in insulin-dependent diabetes mellitus, rheumatoid arthritis, systemic lupus erythematosus, and Hashimoto thyroiditis. The insertion/deletion polymorphism of angiotensin I-converting enzyme (ACE [MIM +106180.0001]) has been identified as a susceptibility allele for myocardial infarction, diabetic nephropathy, hemorrhagic stroke, ischemic stroke, and progression of severe acute respiratory syndrome. In addition, the indel polymorphism of ACE appears to be a QTL for stature. The Val66Met polymorphism of the gene encoding brain-derived neurotrophic factor (MIM *113505.0002) has been related to susceptibility to memory impairment, anorexia nervosa, bulimia nervosa, and bipolar affective disorder, as well as to protection against obsessive-compulsive disorder and modification of the age at onset of Parkinson disease.