Sunday, September 14, 2008

p53 Protein

p53 protein overexpression in Shwachman-Diamond syndrome / In reply
Archives of Pathology & Laboratory Medicine, Oct 2002 by Dror, Yigal, Elghetany, M Tarek, Alter, Blanche P

To the Editor.-We read with great interest the paper of Drs Elghetany and Alter in the April 2002 issue of the ARCHIVES.1 Shwachman-Diamond syndrome (SDS) is an autosomal recessive multisystemic disorder characterized by varying degrees of marrow failure and a high propensity for malignant myeloid transformation into myelodysplastic syndromes (MDS) and acute myeloid leukemia.2-4 The authors found p53 overexpression in bone marrow biopsies from 9 patients with SDS. None of the bone marrow biopsies from patients with acquired aplastic anemia or acquired cytopenias and none of those from individuals in the control group had overexpression of p53 protein. Very interestingly, p53 overexpression in patients with SDS was comparable to p53 results in 46 bone marrow specimens from patients with refractory anemia. Refractory anemia is a subtype of MDS.
Although neither the method for selecting patients nor the clinical phenotype of the patients was specified in the paper, the authors' work is important and furthers our understanding of the relationship between SDS and MDS. Myelodysplastic syndrome is a preleukemic, stem cell disease with peripheral blood cytopenia, ineffective hematopoiesis, and varying degrees of bone marrow cellularity and dysplasia. Shwachman-Diamond syndrome meets many of these criteria2: it is a stem cell disorder with peripheral cytopenia, ineffective hematopoiesis,5,6 and varying degrees of bone marrow cellularity, and it carries a significantly increased risk of leukemia.2-4 In addition, scattered mild dysplastic changes in the erythroid, myeloid, and megakaryocytic precursors are commonly seen on careful examination of bone marrow biopsies of patients with SDS2 and are part of the syndrome. Further, the close relationship between SDS and MDS is reflected by similar defects in marrow stromal support of normal hematopoiesis,5 increased apoptosis mediated through the Fas pathway,6 a high frequency of clonal marrow cytogenetic abnormalities,2 and as the authors showed also by a prevalence of p53 protein overexpression that is similar to that in patients with refractory anemia.1 Therefore, SDS seems to be a myelodysplastic disorder from its inception. We therefore consider SDS to be refractory anemia 2 or refractory cytopenia according to the CCC (category-cytology-- cytogenetics) classification of childhood MDS.7 When we refer to malignant myeloid transformation in SDS, we mean stages beyond refractory anemia, namely refractory cytopenia with cytogenetic abnormality, refractory anemia with ring sideroblasts, refractory anemia with dysplasia, refractory cytopenia with excess blasts, or leukemia.
We have recently analyzed bone marrow mononuclear cells from 11 patients with SDS (2 had a clonal marrow cytogenetic abnormality), and we did not find mutations in exons 2 through 11 of the p53 gene.2 Therefore, p53 protein overexpression in SDS can result from either upregulation of the functional p53 gene (as the authors postulated) or posttranslational modification of the protein, rendering it more stable than the wild type protein, which normally cannot be detected.
Marrow Failure and Myelodysplasia Programme
Division of Hematology/ Oncology
The Hospital for Sick Children and the University of Toronto
Toronto, Ontario, Canada M5G 1X8
1. Elghetany MT, Alter BP. p53 Protein overexpression in bone marrow biopsies of patients with Shwachman-Diamond syndrome has a prevalence similar to that of patients with refractory anemia. Arch Pathol Lab Med. 2002;126:452-455.
2. Dror Y, Durie P, Ginzberg H, et al. Clonal evolution in marrows of patients with Shwachman-Diamond syndrome: a prospective 5-year follow-up study. Exp Hematol. 2002;30:659-669.
3. Mack DR, Forstner GG, Wilschanik M, Freedman MH, Durie PR. Shwachman syndrome: exocrine pancreatic dysfunction and variable phenotypic expression. Gastroenterology. 1996;111:15931602.
4. Smith OP, Hann IM, Chessells JM, Reeves BR, Milla P. Haematological abnormalities in Shwachman-Diamond syndrome. Br] Haematol. 1996;94: 279-284.
5. Dror Y, Freedman MH. Shwachman-Diamond syndrome: an inherited preleukemic bone marrow failure disorder with aberrant hematopoietic progenitors and faulty marrow microenvironment. Blood 1999;94:3048-3054.
6. Dror Y, Freedman MH. Shwachman-Diamond syndrome marrow cells show abnormally increased apoptosis mediated through the Fas pathway. Blood. 2001;97:3011-3016.
7. Mandel K, Dror Y, Poon A, Freedman MH. Practical classification of pediatric MDS. J Pediatr Hematol Oncol. 2002;24:343-352.
In Reply.-We thank Dr Dror for his comments in support of our recent article.1 Our patients were unselected, and included all of those whose samples were available between November 1999 and November 2000. None of the patients with Shwachman-Diamond syndrome (SDS) had cytogenetic clones, and their bone marrow morphology did not show significant dysplastic features. Thus, p53 overexpression was the hallmark of the similarity between SDS and refractory anemia (RA). Dr Dror raises the interesting question regarding the relationship between this syndrome and RA. Although we agree with Dr Dror that SDS shares common features with RA, it may not be appropriate to classify all patients with this syndrome as having RA at the time of diagnosis. Other bone marrow failure syndromes, such as Fanconi anemia and Diamond-Blackfan anemia, share some features with RA as well.2,3 We are concerned that labeling SDS as RA may prompt an aggressive mode of treatment that may not be supported by data other than these similarities. Moreover, there are some indications that myelodysplastic syndromes evolving from an inherited bone marrow disease may not have the same biological behavior as primary myelodysplastic syndromes in children.4 Longterm prospective studies and the continued search for an underlying molecular defect for SDS should shed some light on this rare disease and its relationship to RA.

For information on Shwachman-Diamond Syndrome check out Shwachman-Diamond America