Summary An investigation of 22 new patients with Shwachman‐Diamond syndrome (SDS) and the follow‐up of 14 previously reported cases showed that (i) clonal chromosome changes of chromosomes 7 and 20 were present in the bone marrow (BM) of 16 out of 36 cases, but if non‐clonal changes were taken into account, the frequency of anomalies affecting these chromosomes was 20/36: a specific SDS karyotype instability was thus confirmed; (ii) the recurrent isochromosome i(7)(q10) did not include short arm material, whereas it retained two arrays of D7Z1 alphoid sequences; (iii) the deletion del(20)(q11) involved the minimal region of deletion typical of myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML); (iv) only one patient developed MDS, during the rapid expansion of a BM clone with a chromosome 7 carrying additional material on the short arms; (v) the acquisition of BM clonal chromosome anomalies was age‐related. We conclude that karyotype instability is part of the natural history of SDS through a specific mutator effect, linked to lacking SBDS protein, with consequent clonal anomalies of chromosomes 7 and 20 in BM, which may eventually promote MDS/AML with the patients’ ageing.

An investigation of 14 patients with Shwachman syndrome (SS), using standard and molecular cytogenetic methods and molecular genetic techniques, showed that (1) the i(7)(q10) is not, or not always, an isochromosome but may arise from a more complex mechanism, retaining part of the short arm; (2) the i(7)(q10) has no preferential parental origin; (3) clonal chromosome changes, such as chromosome 7 anomalies and del(20)(q11), may be present in the bone marrow (BM) for a long time without progressing to myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML); (4) the del(20)(q11) involves the minimal region of deletion typical of MDS/AML; (5) the rate of chromosome breaks is not significantly higher than in controls, from which it is concluded that SS should not be considered a breakage syndrome; (6) a specific kind of karyotype instability is present in SS, with chromosome changes possibly found in single cells or small clones, often affecting chromosomes 7 and 20, in the BM. Hence, we have confirmed our previous hypothesis that the SS mutation itself implies a mutator effect that is responsible for MDS/AML through these specific chromosome anomalies. This conclusion supports the practice of including cytogenetic monitoring in the follow-up of SS patients.

acquired TTP but with an atypical presentation. A suboptimal response to PEX, defined as the absence of a steadily declining lactate dehydrogenase level and an increase in the platelet count after 4-5 days of daily PEX in the context of ADAMTS13 >10%, would lead us to consider therapy with eculizumab over intensified PEX or immune-based therapy as might be considered in TTP.

BackgroundAn interstitial deletion of the long arms of chromosome 20, del(20)(q), is frequent in the bone marrow (BM) of patients with myelodysplastic syndromes (MDS), acute myeloid leukemia (AML), and myeloproliferative neoplasms (MPN), and it is recurrent in the BM of patients with Shwachman-Diamond syndrome (SDS), who have a 30-40% risk of developing MDS and AML.ResultsWe report the results obtained by microarray-based comparative genomic hybridization (a-CGH) in six patients with SDS, and we compare the loss of chromosome 20 material with one patient with MDS, and with data on 92 informative patients with MDS/AML/MPN and del(20)(q) collected from the literature.ConclusionsThe chromosome material lost in MDS/AML/MPN is highly variable with no identifiable common deleted regions, whereas in SDS the loss is more uniform: in 3/6 patients it was almost identical, and the breakpoints that we defined are probably common to most patients from the literature. In some SDS patients less material may be lost, due to different distal breakpoints, but the proximal breakpoint is in the same region, always leading to the loss of the EIF6 gene, an event which was related to a lower risk of MDS/AML in comparison with other patients.

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BackgroundThe results of cytogenetic investigations on unbalanced chromosome anomalies, both constitutional and acquired, were largely improved by comparative genomic hybridization on microarray (a-CGH), but in mosaicism the ability of a-CGH to reliably detect imbalances is not yet well established. This problem of sensitivity is even more relevant in acquired mosaicism in neoplastic diseases, where cells carrying acquired imbalances coexist with normal cells, in particular when the proportion of abnormal cells may be low.We constructed a synthetic mosaicism by mixing the DNA of three patients carrying altogether seven chromosome imbalances with normal sex-matched DNA. Dilutions were prepared mimicking 5%, 6%, 7%, 8%, 10% and 15% levels of mosaicism. Oligomer-based a-CGH (244 K whole-genome system) was applied on the patients' DNA and customized slides designed around the regions of imbalance were used for the synthetic mosaics.Results and conclusionsThe a-CGH on the synthetic mosaics proved to be able to detect as low as 8% abnormal cells in the tissue examined. Although in our experiment some regions of imbalances escaped to be revealed at this level, and were detected only at 10-15% level, it should be remarked that these ones were the smallest analyzed, and that the imbalances recurrent as clonal anomalies in cancer and leukaemia are similar in size to those revealed at 8% level.

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Monosomy 7 is one of the most frequent chromosome changes observed in patients with myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML), and it may also be found superimposed to the Philadelphia chromosome in chronic myelocytic leukaemia (CML) in accelerated or blastic phase. It is even more common in secondary MDS/AML, and is associated with a variety of Mendelian and non-Mendelian predisposing disorders or in the so-called monosomy-7 families, where it recurs in subjects developing MDS/AML.1 Also partial monosomy 7 due to structural rearrangements (which thus has a different mechanism of origin as compared to monosomy, that is chromosome breakage vs non-disjunction) is frequently found in association with all the disorders mentioned above, but a single common region of deletion has not yet been identified. Familial cases indicated as unlikely the action of an oncosuppressor gene in the pathogenesis of MDS/AML associated with monosomy 7,1 and its role is thought to be mediated by gene dosage effects, recently investigated by microarray analysis.2 The presence of monosomy 7 portends a poor clinical outcome, both in MDS3 and in AML,4 and hence the clinical relevance of accurate monitoring of the abnormal clone during the course of the disease. We present here data concerning the methods to monitor the consistency of the monosomic clone and the parental origin of the chromosome 7 loss. As to the first point, the monitoring results obtained with cytogenetic techniques were compared with those of a newly developed method based on real-time quantitative polymerase chain reaction (RQ-PCR)5, which we suggest is more reliable. As to the parental origin of the lacking chromosome 7, some data are already available in the literature,6 and our aim was to further contribute to clarifying the issu