Diagnostic Overlap between Fanconi Anemia and the Cohesinopathies: Roberts Syndrome and Warsaw Breakage Syndrome

Abstract

Fanconi anemia (FA) is a recessively inherited disease characterized by multiple symptoms including growth retardation, skeletal abnormalities, and bone marrow failure. The FA diagnosis is complicated due to the fact that the clinical manifestations are both diverse and variable. A chromosomal breakage test using a DNA cross-linking agent, in which cells from an FA patient typically exhibit an extraordinarily sensitive response, has been considered the gold standard for the ultimate diagnosis of FA. In the majority of FA patients the test results are unambiguous, although in some cases the presence of hematopoietic mosaicism may complicate interpretation of the data. However, some diagnostic overlap with other syndromes has previously been noted in cases with Nijmegen breakage syndrome. Here we present results showing that misdiagnosis may also occur with patients suffering from two of the three currently known cohesinopathies, that is, Roberts syndrome (RBS) and Warsaw breakage syndrome (WABS). This complication may be avoided by scoring metaphase chromosomes-in addition to chromosomal breakage-for spontaneously occurring premature centromere division, which is characteristic for RBS and WABS, but not for FA.

Figure 1

Chromosomal breakage in stimulated T lymphocytes from patients with FA, RBS, or WABS. A chromosomal breakage test, routinely utilized for the diagnosis of FA, was carried out on various individuals, as indicated (RBS: Roberts syndrome; WABS: Warsaw Breakage syndrome; FA: Fanconi anemia: FA mosaic, FA patient with hematopoietic mosaicism; Con-1 to -3: healthy controls, that is, parents of an affected individual; Con-4 and -5: healthy controls, noncarriers; see Table 1). Whole-blood PHA-stimulated T lymphocyte cultures were exposed to various concentrations of MMC for 72 h and analyzed for chromosomal breakage. Only results for the untreated (blue bars) and the highest concentration of MMC (300 nM, purple bars) are shown. Percentages of cells with the indicated number of chromatid-type break events per cell are shown.

Figure 2

Cell cycle analysis of primary skin fibroblasts from individuals with FA, RBS, or WABS. Cells were treated with 50 or 100 nM MMC, for 72 h. Cell cycle profiles were obtained and the percentages of cells in G2/M phase of the cell cycle were determined. Averages of at least two experiments are shown, with standard errors of the mean.

Figure 3

(a) Cohesion defects in lymphocyte cultures from patients with FA, RBS, or WABS. Metaphases prepared from untreated cultures (−) or treated with 150 nM MMC (+) which had previously been evaluated for chromosomal breakage were reevaluated for the presence of cohesion defects. The percentages of cells containing the indicated number of railroad chromosomes (RR) or total premature centromere separation (PCS) were determined, as summarized in the histograms. (b) Illustrations of the various aberrations scored in the analysis.