DNA repair defects and chromosome instability disorders

Reduced hematopoietic reserves in DNA interstrand crosslink repair-deficient Ercc1-/- mice

The ERCC1-XPF heterodimer is a structure-specific endonuclease involved in both nucleotide excision repair and interstrand crosslink repair. Mice carrying a genetic defect in Ercc1 display symptoms suggestive of a progressive, segmental progeria, indicating that disruption of one or both of these DNA damage repair pathways accelerates aging. In the hematopoietic system, there are defined age-associated changes for which the cause is unknown. To determine if DNA repair is critical to prolonged hematopoietic function, hematopoiesis in Ercc1-/- mice was compared to that in young and old wild-type mice. Ercc1-/- mice (3-week-old) exhibited multilineage cytopenia and fatty replacement of bone marrow, similar to old wild-type mice. In addition, the proliferative reserves of hematopoietic progenitors and stress erythropoiesis were significantly reduced in Ercc1-/- mice compared to age-matched controls. These features were not seen in nucleotide excision repair-deficient Xpa-/- mice, but are characteristic of Fanconi anemia, a human cancer syndrome caused by defects in interstrand crosslink repair. These data support the hypothesis that spontaneous interstrand crosslink damage contributes to the functional decline of the hematopoietic system associated with aging.

Response to DNA-damaging agents in cultured cells from patients with X-linked duchenne muscular dystrophy phenotype: male DMD, female DMD, possible carriers

Using blood cultures the response to gamma (γ) radiation was examined in a male DMD and his mother, in a female DMD and her mother and in a normal control. In a series of experiments chromosome aberrations were determined after 3 separate γ-irradiation dose levels: 0, 150, 300 rads. The DMD patients showed a response to ionising radiations different from control, in fact the percentage of aberrations was lower than the control. In this preliminary study a slight difference between normal and possible carriers was also found.