Diseases with DNA damage-processing defects.

Xeroderma pigmentosum, Cockayne's syndrome, ataxia telangiectasia, Fanconi anemia, and Bloom's syndrome are autosomal recessive diseases with cellular defects in the ability to process DNA damage. Although these diseases are rare, they are seen occasionally in practice and provide insight into the mechanisms of DNA repair and replication in humans. The authors will review the clinical and cytological presentation of each disease, the genetic heterogeneity, as inferred by complementation analysis, and the differentiating characteristics of each. The authors will conclude with a discussion of the state of current research on each disease and possible directions for future research.