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Fig. 1 Mitomycin C (MMC)-induced chromosomal breakage in phytohemagglutinin-stimulated T-lymphocyte cultures distinguishes FA (middle) from non-FA individuals (upper chart). The lower chart represents a mosaic FA patient, showing two types of lymphocytes, one responding as FA and one responding as the healthy control. (View this art in color at www.dekker.com.)

with overlapping clinical symptoms. In this test, T lymphocytes in a peripheral blood sample are stimulated to divide and cultured for 3 days in the presence of various concentrations of a cross-linking agent (mitomycin C or diepoxybutane), after which chromosomal aberrations (chromatid breaks and chromosomal interchange figures) are quantified in metaphase spreads. Figure 1 shows results obtained for three individuals, a healthy control, an FA patient, and an FA patient with lymphocyte mo-saicism. The latter patient has two populations of T lymphocytes in roughly equal proportions: cells that respond as FA next to cells that respond as healthy control cells. The latter cells, which have originated by spontaneous reversion of one pathogenic allele at the disease locus, tend to increase with time. Therefore, some mosaic FA patients may score negative for the FA diagnosis in this test. Such patients may still be diagnosed by using skin fibroblasts, in which mosaicism has thus far not been noted.[3]

The chromosomal breakage test, originally developed by Auerbach et al.,[20] has been used for both postnatal and prenatal diagnoses and is still considered the standard test for diagnosing all genetic subtypes of FA. However, the test does not seem to distinguish FA from Nijmegen breakage syndrome,[21] which is why further testing is recommended by mutation screening (see below).

Alternative Tests

An alternative way to confirm FA is based on cell cycle analysis using flow cytometry. This test is based on the observation that FA cells (T lymphocytes or skin fibroblasts) tend to become arrested in the G2 phase of the cell cycle.[22] However, this test may fail to diagnose cases with overt leukemia or high levels of lymphocyte mosaicism.

Recently, FANCD2 western blotting has been reported as an alternative procedure to diagnose FA.[23] In this case, growth-stimulated T lymphocytes are tested for the occurrence of the ubiquitinated isoform of FANCD2, which readily reveals FA in cases where this isoform is not detected. This is a very convenient alternative for diagnosing 90% of all FA patients. However, the subtypes FA-D1 and -J, which are defective downstream of FANCD2 ubiquitination, are not diagnosed. In addition, true FA cases with a significant level of lymphocyte mosaicism may not be diagnosed as FA. In negative but still highly suspicious cases, the diagnostic workup may be extended to include additional tests, such as chromosomal breakage analysis in lymphocytes or fibro-blasts.[20'24]

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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