Clinical implications and classification of the constitutive fragile sites.

Constitutive fragile sites (c-fra) comprise the more prevalent but less recognised suite of fragile sites in eukaryotes. They differ from the heritable (rare) suite of fragile sites (h-fra) in several significant ways. In the present report, data concerning the c-fra so far recognised are reviewed in connection with their origin, classification, use as positive controls for cell culture conditions inducing the fra(X), and their presumptive relationships to the characteristic breakpoints in the neoplasias and in constitutional chromosome rearrangements.