Subacute sclerosing panencephalitis(SSPE) is a progressive and fatal neurological illness without established treatment. As the precise mechanism how measles virus (MV) causes SSPE is still unknown, full clarification of pathogenesis and pathophysiology is essential to establish effective strategy to treat the illness. Viral, host and environmental factors are involved in the development of SSPE. As host factors, immaturity of immune system and central nervous system are well recognized. Recently, we demonstrated that functional polymorphisms of MxA, interleukin(IL)-4 and interferon regulatory factor-1 (IRF-1) genes are associated with the development of SSPE in Japanese. High-density oligonucleotide microarray and subsequent quantitative reverse transcriptase-polymerase chain reaction demonstrated that the mRNA levels of granulysin were decreased in SSPE patients and were increased in measles patients, suggesting that granulysin might play a role in the host defense against MV and possibly be involved in the pathogenesis or pathophysiology of SSPE. In a Turkish study, association between angiotensin converting enzyme (ACE) gene polymorphism and SSPE was shown.