Nijmegen breakage syndrome (NBS), is a rare genetic disorder that is characterized by a small head size (microcephaly), immunodeficiency (weakened immune system), increased sensitivity to the effects of radiation exposure including medical x-rays and an increased risk of developing cancer, especially lymphoma or leukemia. Cancer treatment must be modified because conventional doses of chemotherapy may lead to severe even lethal life-threatening toxic complications. Since NBS patients are immunocompromised, they have an increased risk of developing infections (especially respiratory tract infections). NBS patients are born with a mutated gene that normally codes for a protein called nibrin. Nibrin helps repair DNA that has been damaged by chromosome breaks. Therefore, NBS patients are susceptible to chromosomal breakage, which leads to rearrangements of translocations. In other words, one piece of a chromosome is broken off and joined to another chromosome. Chromosomal rearrangements typically occur in chromosomes 7 and 14, both of which are involved in the development of the immune system. The syndrome is named after the city Nijmegen in the Netherlands, where the first case of NBS was described in 1998. The disorder is extremely rare. Most NBS patients are of Slavic or other European decent. However, a few cases have also been reported in New Zealand, Mexico, and the United States. Men and women are affected equally.