The discovery of the cause of a rare hereditary disease that makes sufferers insensitive to pain may lead to the discovery of more effective painkillers. Researchers at the Kumamoto University School of Medicine in Japan examined DNA from four people suffering from CIPA or chronic insensitivity to pain with anhidrosis (inability to sweat). They found that defects in the gene that makes tyrosine kinase-A (TRKA) -- a receptor on embryonic neurons -- prevents the maturity of infant neurons into specialised sensory cells. As a result, the nerve cells die, causing the inability to detect tissue damage and feel pain. The finding, claim researchers, can form the basis for developing painkillers.