Single nucleotide polymorphism to disclose severe side-effects or proper dosage for each patient.

Recently, the importance of single nucleotide polymorphism (SNP) has been stressed. The discovery of the disease-related gene can disclose disease susceptible or resistant persons, such as noted in persons resistant to AIDSvirus infection. Genetic polymorphism is also important in drug-responsiveness, and also in the occurrence of severe side effects in each patient. Azathioprine is one of the most frequently used immunosuppressants in the treatment of autoimmune diseases, such as systemic lupus erythematosus, polyand dermato-myositis, and polyarteritis nodosa. Although infrequent, we sometimes experience marked leukopenia during the treatment with azathioprine, which forced us to stop use of the drug immediately. Azathioprine, mercaptopurine and thioguanine are