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

Hindawi Publishing Corporation Anemia Volume 2010, Article ID 565268, 7 pages doi:10.1155/2010/565268 Clinical Study Diagnostic Overlap between Fanconi Anemia and the Cohesinopathies: Roberts Syndrome and Warsaw Breakage Syndrome Petra van der Lelij, Anneke B. Oostra, Martin A. Rooimans, Hans Joenje, and Johan P. de Winter Department of Clinical Genetics, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands Correspondence should be addressed to Johan P. de Winter, Received 13 April 2010; Accepted 10 June 2010 Academic Editor: John S. Waye Copyright © 2010 Petra van der Lelij et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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. 1. Introduction Fanconi anemia (FA) is a recessive chromosomal instability syndrome that is clinically characterized by a wide variety of symptoms including growth retardation and developmental abnormalities such as malformed digits, absent radii, and microcephaly. Additional common features include a progressive bone marrow failure and pronounced cancer predisposition. Because the FA phenotype is so diverse and variable, diagnosis on the basis of clinical features alone is often difficult [1–3]. The ultimate diagnosis of FA has been based on a hyperresponsiveness of FA cells to chromosome breakage by DNA cross-linking agents, such as diepoxybutane (DEB) and mitomycin C (MMC), or on excessive cell cycle arrest in the G2/M phase of the cell cycle, both spontaneously and after treatment with MMC [4–6]. In a number of patients, spontaneous genetic reversion can correct FA mutations in haematopoietic stem cells, leading to mosaicism in the blood. The reverted cells may (partially) correct the bone marrow failure [7–11]. In mosaic FA patients, the overall cross-linker hypersensitivity is less pronounced, because in the blood of such patients phenotypically normal cells exist in addition to FA cells. As genetic reversion has not been observed in tissues other than blood, performing the test on the patient’s skin fibroblasts helps to avoid this complication. An occasional patient suffering from Nijmegen breakage syndrome or some hitherto undefined disorder has been noted to score positive in the FA chromosomal breakage test [12–14]. Cellular hypersensitivity to MMC has also been reported for a distinct class of syndromes, the so-called “cohesinopathies”. These are caused by mutations in genes involved in the process of sister chromatid cohesion [15] and include Cornelia de Lange syndrome, Roberts syndrome [16–18], and the recently described Warsaw Breakage syndrome [19]. Due to a highly variable clinical phenotype, 2 Roberts syndrome (RBS) patients may exhibit symptoms overlapping with those of FA. RBS is an extremely rare, autosomal recessive disorder characterized by severe pre- and postnatal growth retardation, craniofacial abnormalities, and symmetric limb defects, features that are also observed in FA. RBS is caused by mutations in ESCO2, which encodes an acetyltransferase that is involved in sister chromatid cohesion [20]. Affected individuals show varying degrees of malformations involving symmetric reduction in the number of digits and the length or presence of bones in the arms and legs [21]. So far, no clear correlation between the type of mutation and clinical phenotype has been observed [22–24]. Most cases of RBS result in spontaneous abortion, stillbirth, or neonatal death; mental retardation is often observed, with various degrees of severity. At the cellular level, RBS patients show specific cytogenetic features, mainly consisting of metaphase chromosomes displaying repulsion of heterochromatic regions, leading to a railroad-track appearance of the chromosomes. This cytogenetic feature is used in the diagnosis of RBS and may be followed by mutational analysis of ESCO2. Recently, an individual was described with mutations in another gene involved in sister chromatid cohesion, DDX11/ChlR1, which encodes an XPD-like DNA helicase. This novel cohesinopathy, called Warsaw breakage syndrome (WABS), is mainly characterized by severe growth retardation and microcephaly [19]. The patient representing this syndrome was initially suspected to suffer from a chromosomal instability syndrome and was therefore tested for chromosomal breakage in an FA-specific diagnostic test. Metaphase preparations revealed cohesion defects (as in RBS), that is, railroad-track appearance of chromosomes due to premature centromere division (PCD); in addition to this feature, a high proportion of metaphases showed premature chromatid separation (PCS), in particular after treatment with MMC. Here we report that patients suffering from RBS or WABS may be misdiagnosed as having FA based on excessive MMCinduced chromosomal breakage in primary lymphocyte cultures and/or on an increased arrest of primary skin fibroblasts in the G2/M phase of the cell cycle. However, detailed cytogenetic analysis of unchallenged lymphocyte cultures should reveal the presence of railroad track-like chromosomes in RBS and WABS, which are not known to occur in unchallenged FA lymphocyte cultures. We conclude that in the diagnostic work-up for FA, cytogenetic examination should include the scoring of cohesion defects in unbanded metaphase preparations, in order to exclude the cohesinopathies RBS and WABS. 2. Methods 2.1. Patients. All affected individuals investigated (Table 1) have been reported before. RBS patients with homozygous mutations in ESCO2 and heterozygous carriers (mothers) were as follows: VU1174 (c.1457 1458delAG) (Turkey); VU1199 (c.877 878delAG) (Turkey) and VU1200 (mother (...truncated)