Chromosome Fragile Site

Chromosomes are the structures that hold genes, the units of heredity that code for the basic instructions for the development, reproduction, and maintenance of organisms. Fragile sites are heritable locations on chromosomes that have a tendency to break or appear as a gap or constriction. Fragile sites are classified as common (present in all people) or rare (present in at least 1 out of 20 people and heritable). A few rare fragile sites are induced by depletion of folate/thymidine, bromodeoxyuridine (an antiviral and antineoplastic agent used in the treatment of primary brain tumors), distamycins (antibiotics), and aphidicolin (an antiviral antibiotic produced by Cephalosporium aphidicola and other fungi).

Common fragile sites do not appear to be associated with any disease. In contrast, rare fragile sites are all associated with disease conditions. For example, in humans, one fragile site is associated with the X-linked mental retardation. In total, 21 human fragile sites have been characterized: eight rare fragile sites and 13 common human fragile sites. Although most rare fragile sites have been studied mostly in humans, they have also been described in a wide variety of mammals. Fragile sites are thought to genetically predispose Boxer dogs to mast cell tumor Since their discovery, fragile sites have been implicated in constitutional and cancer chromosome rearrangements and recent studies suggest that fragile sites may serve as markers of chromosome damage during early tumor formation.


  1. Chromosomes: Organization and Function. Adrian T. Sumner
  2. Bromodeoxyuridine induces chromosomal fragile sites in the canine genome. Stone DM, Stephens KE.
  3. Common fragile sites as targets for chromosome rearrangements. Martin F. Arlta, Sandra G. Durkina, Ryan L. Raglanda and Thomas W. Glover
  4. Small Animal Clinical Oncology. Stephen J. Withrow, E. Gregory MacEwen

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