Mutation of p53 gene does not play a critical role in myelodysplastic syndrome and its transformation to acute leukaemia

Prognostic molecular markers in myelodysplastic syndromes

Cytogenetic findings in myelodysplastic syndromes play an important role in diagnosis, prognostication and clinical decision making. Therefore, they became an important aspect in scoring systems such as the International Prognostic Scoring System (IPSS) and the WHO-adapted Prognostic Scoring System (WPSS). Ongoing efforts to refine the categorization of karyotypes with regard to prognosis and therapeutic options will change scoring systems in the near future. In order to learn more about the pathophysiology of myelodysplastic syndromes, various molecular genetic aberrations are identified and their impact on prognosis discussed. New screening methods such as gene expression or single nucleotide polymorphism analysis are good candidates to find entrance in clinical practice in the future as they are useful tools in further elucidation of the underlying defects in myelodysplastic syndromes and the development of more specific classifications of the disease concerning risk assessment.

Genetic testing in the myelodysplastic syndromes: molecular insights into hematologic diversity

The myelodysplastic syndromes (MDS) are associated with a diverse set of acquired somatic genetic abnormalities. Bone marrow karyotyping provides important diagnostic and prognostic information and should be attempted in all patients who are suspected of having MDS. Fluorescent in situ hybridization (FISH) studies on blood or marrow may also be valuable in selected cases, such as patients who may have 5q- syndrome or those who have undergone hematopoletic stem cell transplantation. The MDS-associated cytogenetic abnormalities that have been defined by karyotyping and FISH studies have already contributed substantially to our current understanding of the biology of malignant myeloid disorders, but the pathobiological meaning of common, recurrent chromosomal lesions such as del(5q), del(20q), and monosomy 7 is still unknown. The great diversity of the cytogenetic findings described in MDS highlights the molecular heterogeneity of this cluster of diseases. We review the common and pathophysiologically interesting genetic abnormalities associated with MDS, focusing on the clinical utility of conventional cytogenetic assays and selected FISH studies. In addition, we discuss a series of well-defined MDS-associated point mutations and outline the potential for further insights from newer techniques such as global gene expression profiling and array-based comparative genomic hybridization.

p53 protein overexpression in bone marrow biopsies of patients with Shwachman-Diamond syndrome has a prevalence similar to that of patients with refractory anemia

CONTEXT

Shwachman-Diamond syndrome (SDS) is a rare inherited disorder characterized by pancreatic insufficiency, neutropenia, and in some patients, metaphyseal dysostosis. Patients with SDS are at a high risk for development of bone marrow failure, myelodysplastic syndrome, and acute leukemia. The p53 gene plays a major role in cell-cycle regulation, particularly in the presence of a genetic alteration in DNA, a critical step for the initiation of leukemogenesis. p53 gene up-regulation and p53 protein overexpression may occur as a cellular reaction to significant DNA damage. Shwachman-Diamond syndrome and refractory anemia patients have close similarities in the prevalence of acute leukemia and in cell-cycle changes in bone marrow cells. This similarity was further investigated for p53 protein overexpression using archived tissue from patients with hematologic diseases having various leukemic propensities, including SDS and refractory anemia.

METHODS

Immunohistochemical staining for p53 protein overexpression was performed on bone marrow biopsies from 9 patients with SDS. These specimens were compared with biopsies from 71 patients with acquired hematologic disorders with variable risk levels for leukemia, including acquired aplastic anemia (n = 14), refractory anemia (n = 46), and various acquired cytopenias (n = 11), as well as 37 control subjects.

RESULTS

p53 protein overexpression was identified only in patients with SDS and in patients with refractory anemia; these groups exhibited comparable prevalences of 78% and 72%, respectively. None of the patients with acquired aplastic anemia, acquired cytopenias, or in the control group showed overexpression of p53 protein.

CONCLUSION

The prevalence of p53 protein overexpression in SDS is significantly different from that in acquired aplastic anemia and acquired cytopenias, but it is similar to the prevalence in refractory anemia. We speculate that p53 protein overexpression in this bone marrow failure syndrome may represent an early indicator of significant DNA genetic alteration, which is a crucial step in the process of leukemogenesis.

Study of p53 in elderly patients with myelodysplastic syndromes by immunohistochemistry and DNA analysis

We analyzed the tumor suppressor gene product, p53, in elderly patients with myelodysplastic syndromes (MDS) and in overt leukemia patients after transformation from MDS using immunohistochemical techniques. We examined 52 MDS patients (mean age 79 years, range 68 to 96) from the time of initial diagnosis to death or development of overt leukemia. p53 protein was detected by immunohistochemistry (IHC) in 8/52 patients (15%) at initial diagnosis: 1/26 with refractory anemia (RA), 0/4 with RA with ringed sideroblasts, 3/11 with RA with an excess of blasts (RAEB), 3/8 with RAEB in transformation, and 1/3 with chronic myelomonocytic leukemia. We also analyzed gene mutations in patients with positive IHC. p53 mutations were detected in 3/8 (38%) patients. IHC-positive patients had a significantly higher incidence of leukemic transformation and the presence of a complex karyotype with monosomy 17. IHC-positive cells included blasts as well as mature myeloid cells, erythroblasts, and megakaryocytes. Scrutiny of our data in combination with previous data revealed that patients with positive IHC in multilineage cells were older than those in whom positivity was noted mostly in myeloblasts. This suggests that p53 IHC positivity with a multilineage pattern may be a characteristic of MDS in older patients.

TP53 mutations in myelodysplastic syndrome

Mutations of the TP53 tumor suppressor gene, contributing to the development and progression of a wide variety of human malignancies, are found in some of the patients with myelodysplastic syndromes (MDS). Previous reports revealed that TP53 mutations were found in 0-25% of patients with MDS and are closely associated with a complex abnormal karyotype including such chromosomal losses as -5/5q-, -7/7q- and/or 17p-, which are known to be frequent in therapy-related leukemias. We have also detected TP53 mutation in 10 (14%) of 70 patients with MDS. All of the mutations were detected at the time of diagnosis, which suggest the TP53 mutation may play a role in the development of MDS. Those patients with a TP53 mutation had a poor prognosis regardless of leukemic transformation or not. The reported mutational spectra of TP53 in MDS and ANLL differ from those of colon and lung cancers. Compared with other hematological disorders, the spectrum of TP53 mutations in MDS and ANLL is assumed to be associated with pathogenic exposure to known or unknown carcinogens, as suggested by the chromosomal findings. Further studies are required to clarify the pathogenesis of this heterogenous disease entity.

Mutations of the p53 gene in myelodysplastic syndrome and overt leukemia

We analysed p53 mutations in 24 patients with myelodysplastic syndrome (MDS) and overt acute myeloid leukaemia after a period of MDS, using polymerase chain reaction-single strand conformation polymorphism analysis. In exons 5 to 8, mobility shifts were detected in five of the 24 patients. Sequence analysis was subsequently performed, and four missense mutations (16.7%) and one silent nucleotide substitution were identified. Patients harbouring mutations were characterized as having advanced disease. Loss of the wild type allele was observed in three of the four patients with missense mutations. No mobility shifts of the N-ras or FMS gene were detected in these four patients. We next analysed the correlation of the p53 mutations with the progression of MDS in three patients. The mutation was accompanied by the progression in two of the three patients. These findings suggest that mutations of the p53 gene are associated with progression in some cases of MDS, while being compatible with stable disease or clonal evolution in others.

Epidemiological and etiological aspects of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are increasingly recognized as a cause of bone marrow failure, and are at least as frequent as acute myeloid leukemias. While the overall incidence is about 2-4/100,000/year, incidence figures rise steeply with age. Incidence rates of 20-30/100,000/year in persons over 70 demonstrate that MDS are among the most common hematological neoplasias in this age group. However, due to difficulties of diagnosis and classification, patient registration in population-based registers is far from complete. As a prerequisite for truly representative statistics, future revisions of disease classification systems must incorporate MDS as a separate group of disorders. The difficulties in conducting epidemiological studies also impede the identification of risk factors for the development of MDS. Current knowledge of occupational risk factors is also reviewed here. More rapid progress in our understanding of MDS may come from recent advances in methodology that have begun to shed some light on the cytogenetic and molecular aspects of leukemogenesis in general, and MDS in particular. Non-random chromosomal changes can be found in about 50% of cases at diagnosis, but they are probably late events in the evolution of MDS, reflecting the progressive genomic instability of the premalignant clone. Proto-oncogene mutations have also been suggested to be relevant to the pathogenesis of MDS, but longitudinal studies of point mutations of the N-ras proto-oncogene revealed that such events, although often associated with rapid deterioration and transformation to AML, also appear to be late events during the course of disease. Therefore, it remains a major challenge to identify those lesions that initiate the multistep development of preleukemia. As the incidence of MDS correlates strongly with age, it is reasonable to presume that age-dependent changes of the hematopoietic system may play a role in the initiation of MDS. Aging is probably associated with a compromised marrow reserve through reduction in the size of the stem cell pool. Through increased proliferative activity, the remaining stem cells may be particularly vulnerable to mutagenic insults. Immunological attack on stem cells, mitochondrial DNA mutations, and the regulatory influence of the hematopoietic microenvironment must also be considered as possibly contributing to the early stages of MDS.

Spontaneous and carcinogen-induced tumorigenesis in p53-deficient mice

Using gene targeting techniques, mice that have been generated with two germ-line p53 null alleles (homozygotes) develop normally but are highly susceptible to early onset spontaneous tumours. Here, we show that mice with a single null p53 allele (heterozygotes) produced in the same way are also susceptible to spontaneous tumours, but with a delayed onset compared to homozygotes. The most frequent tumour type in homozygotes was malignant lymphoma; in heterozygotes, osteosarcomas and soft tissue sarcomas predominated. Heterozygous mice treated with a liver carcinogen, dimethylnitrosamine, showed a decreased survival time in comparison to treated wild type mice, suggesting that the p53-deficient mice may be useful for some in vivo carcinogenesis assays.