The Fanconi anaemia pathway orchestrates incisions at sites of crosslinked DNA.

Fanconi anaemia (FA) is a rare, autosomal recessive, genetically complex, DNA repair deficiency syndrome in man. Patients with FA exhibit a heterogeneous spectrum of clinical features. The most significant and consistent phenotypic characteristics are stem cell loss, causing progressive bone marrow failure and sterility, diverse developmental abnormalities and a profound predisposition to neoplasia. To date, 15 genes have been identified, biallelic disruption of any one of which results in this clinically defined syndrome. It is now apparent that all 15 gene products act in a common process to maintain genome stability. At the molecular level, a fundamental defect in DNA repair underlies this complex phenotype. Cells derived from FA patients spontaneously accumulate broken chromosomes and exhibit a marked sensitivity to DNA-damaging chemotherapeutic agents. Despite complementation analysis defining many components of the FA DNA repair pathway, no direct link to DNA metabolism was established until recently. First, it is now evident that the FA pathway is required to make incisions at the site of damaged DNA. Second, a specific component of the FA pathway has been identified that regulates nucleases previously implicated in DNA interstrand crosslink repair. Taken together, these data provide genetic and biochemical evidence that the FA pathway is a bona fide DNA repair pathway that directly mediates DNA repair transactions, thereby elucidating the specific molecular defect in human Fanconi anaemia.