THE ROLE OF TP53 MUTATIONS IN LOW-RISK MDS PATIENTS

ABSSUB-4894

Background: A negative prognostic impact of TP53 gene point mutations in the myelodysplastic syndrome (MDS) patients has not been intensively studied yet.

Aims: In this study we performed an analysis of:  the incidence of TP53 gene mutations in low-risk MDS patients, the effect of TP53 mutations on disease progression, the impact of treatment on mutated clones, the size of mutated clones with regard to the type of cell population and the effect of TP53 mutations on mRNA levels ofTP53, MDM2, MYC, and p21 genes.

Methods: TP53 mutations were analyzed in DNA from CD34+ or CD34- cells isolated from bone marrow of 103 patients included into cohort according to the International Prognostic Scoring System low risk or intermediate-1 risk using primers designed within the IRON-II study research consortium (Roche Applied Science) on the GS Junior system. If mutations were detected, we searched for mutations in the various cell populations (CD34+, CD34-, CD14+, CD3+, granulocytes) and at different time-points of the disease. TaqMan Gene Expression Assays were used to determine relative expression levels of mRNA of TP53, p21, MYC and MDM2 genes in CD34+ cells between patients with and without mutation.

Results: The overall incidence of TP53 mutations was 11.7 % (12/103), 3 patients had two mutated clones. The mutation frequency in low-risk MDS patients with and without del(5q) were 20.4% (11/54)  and 2.0% (2/49) respectively. The allele burden of mutation was in the range of 2.1 – 76.8 %. Out of the detected mutations were 14 missense and 1 nonsense. We found significant differences in the size of the mutated clone cells between bone marrow and peripheral blood. So far, 9 of 12 (75%) patients carrying mutations showed progression towards acute leukemia.

Patients with TP53 mutation showed 1.6-fold lower mRNA expression of TP53 (p=0.05) in CD34+ cells than those with wild type TP53. Non-significant change of mRNA expression of p21, MYC and MDM2 genes were detected between groups of patients with and without mutation.

Summary/Conclusion: Using sensitive next generation sequencing technology, that is able to detect mutations with low abundance, we confirmed in a large cohort of patients a significantly higher frequency of TP53mutations in low-risk MDS patients with del(5q) in comparison to those without del(5q). Furthermore, we found the association between presence of TP53 mutations and increased risk of leukemic transformation.  We were not able to detect a half of identified mutations by Sanger sequencing (<20% mutation burden).

Supported by grant (NT/13899, NT/14377, NT/14539) and the project for conceptual development of research organization (00023736) from the Ministry of Health of the Czech Republic.

Keywords: MDS, Mutation status, p53

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