Bone marrow failure may be caused by chromosome anomalies exerting effects on RUNX1T1 gene

Abstract

Background: The majority of the cases of bone marrow failure syndromes/aplastic anaemias (BMFS/AA) are non-hereditary and considered idiopathic (80-85%). The peripheral blood picture is variable, with anaemia, neutropenia and/or thrombocytopenia, and the patients with idiopathic BMFS/AA may have a risk of transformation into a myelodysplastic syndrome (MDS) and/or an acute myeloid leukaemia (AML), as ascertained for all inherited BMFS. We already reported four patients with different forms of BMFS/AA with chromosome anomalies as primary etiologic event: the chromosome changes exerted an effect on specific genes, namely RUNX1, MPL, and FLI1, leading to the disease.

Results: We report two further patients with non-hereditary BM failure, with diagnosis of severe aplastic anaemia and pancytopenia caused by two different constitutional structural anomalies involving chromosome 8, and possibly leading to the disorder due to effects on the RUNX1T1 gene, which was hypo-expressed and hyper-expressed, respectively, in the two patients. The chromosome change was unbalanced in one patient, and balanced in the other one.

Conclusions: We analyzed the sequence of events in the pathogenesis of the disease in the two patients, including a number of non-haematological signs present in the one with the unbalanced anomaly. We demonstrated that in these two patients the primary event causing BMFS/AA was the constitutional chromosome anomaly. If we take into account the cohort of 219 patients with a similar diagnosis in whom we made cytogenetic studies in the years 2003-2017, we conclude that cytogenetic investigations were instrumental to reach a diagnosis in 52 of them. We postulate that a chromosome change is the primary cause of BMFS/AA in a not negligible proportion of cases, as it was ascertained in 6 of these patients.

Keywords: Chromosome 2; Chromosome 8; Chromosome structural anomalies; Pancytopenia; RUNX1T1 gene; Severe aplastic anaemia.

Fig. 1

Patient 1: a-CGH profiles of chromosomes 1 (a) and 8 (b). In the enlarged view (at the right) the locations of the genes GFI1 (chromosome 1) and RUNX1T1 (chromosome 8) in evidence (arrows)

Fig. 2

Relative expression of RUNX1T1 in the BM of patient 1. The green bars refer to the patient and the red bars to 6 controls’ average values: two control housekeeping genes were used, UBC (left) and HPRT1 (right). Standard error is shown for controls

Fig. 3

Cut-out of the chromosomes involved in the rearrangement in patient 2. In a and c the Q-banded chromosomes (normal 2 and 8 at the left). In b the painting result on the normal chromosome 2 (left) and on the rearranged one (right) with the chromosome 2 library. In d the result of dual color painting with chromosomes 2 and 8 libraries on the normal chromosome 8 (left) and on the rearranged one (right). In e the dual color FISH with the chromosome 2 library (red) and a probe recognizing the entire sequence of the RUNX1T1 gene, part of the system to detect the AML1/ETO translocation (Table 1) (green)

Fig. 4

Relative expression of RUNX1T1 in the BM of patient 2. The blue bars refer to the patient and the red bars to 6 controls’ average values: two control housekeeping genes were used, UBC (left) and HPRT1 (right). Standard error is shown for controls