employed. viral vectors, such as the retrovirus, that incorporate the gene into the genome result in long-term effects. this, coupled with the bone marrow stem cells, has been successful in treating individuals with x-scid. in one particular trial by cavazzana-calvo et al., ten children were treated with gene therapy at infancy for x-scid. nine of the ten were cured of x-scid. however, about three years after treatment, two of the children developed t-cell leukemia due to insertion of the il2rg gene near the lmo2 gene and thereby activating the lmo2 gene (a known oncogene). a third child developed leukemia within two years of that study being published, likely as a direct result of the therapy. this condition is known as insertional mutagenesis, where the random insertion of a gene interferes with the tumor suppressor gene or stimulates an oncogene. there is currently no approved gene therapy on the market, but there are many clinical trials into which x-scid patients may enroll. therefore, research in the field of gene therapy today and in the future is needed to avoid the occurrence of leukemia. in particular, research into the use of insulator and suicide genes is warranted as this may prevent cancer from developing. the insulator gene inhibits the activation of adjacent genes. on the other hand, the suicide gene is stimulated when a tumour begins to form, and this will result in the deactivation of the therapeutic gene. moreover, the use of restriction enzymes such as the zinc-finger nuclease (zfn) is being studied. the zfn allows the researcher to choose the site of gene integration. vector safety is important in the field of gene therapy, hence vectors that self-inactivate the promoter and enhancer (sin) and adenoviruses that creates no immune response are prominent areas of research for vector biologists. prognosis x-linked scid is a known pediatric emergency which primarily affects males. if the appropriate treatment such as intravenous immunoglobulin supplements, medications for treating infections or a bone marrow transplant is not administered, then the prognosis is poor. the patients with x-linked scid usually die two years after they are born. for this reason, the diagnosis of x-linked scid needs to be done early to prevent any pathogens from infecting the infant. however, the patients have a higher chance of survival if the diagnosis of x-linked scid is done as soon as the baby is born. this involves taking preventative measures to avoid any infections that can cause death. for example, david vetter had a high chance of having x-linked scid because his elder sibling had died due to scid. this allowed the doctors to place david in the bubble and prevented infections. in addition, if x-linked scid is known to affect a child, then live vaccines should not be administered and this can save the infant's life. live attenuated vaccines, which consist of weakened pathogens inserted into the body to create an immune response, can lead to death in infants with x-linked scid. moreover, with proper treatments, such as a bone marrow transplant, the prognosis is good. the bone marrow transplant has been successful in treating several patients and resulted in a full immune reconstitution and the patient can live a healthy life. the results of bone marrow transplant are most successful when the closest human leukocyte antigen match has been found. if a close match is not found, however, there is a chance of graft-versus-host-disease which means the donor bone marrow attacks the patient's body. hence, a close match is required to prevent any complications. epidemiology there is no information on birth ratios/rates, but "x-linked scid is the most common form of scid and it has been estimated to account for 46% to 70% of all scid cases."