Do FISH Lesions Have Any Role in the Pathogenesis and Outcome of Chromosomally Normal MDS?

The chromosomal pattern is one of the most relevant parameters to make an accurate diagnosis and predict disease outcome of MDS patients. However, in about 40–50% of patients, mostly low-risk MDS, conventional cytogenetics (CC) does not reveal any defect and thus it is not informative. In this MDS subset FISH with specific probes may identify clonal defects and improve CC results. In addition, recent aCGH data suggest that these patients may present novel lesions affecting unsuspected chromosomal regions harbouring genes with a crucial role in MDS pathogenesis.

Based on these findings the principal goal of the present study was to establish whether FISH with probes specific for chromosomal regions most commonly involved in MDS along with additional probes exploring chromosomal areas which alteration has been revealed by recent aCGH studies was truly able to unmask clonal cryptic defects in chromosomally normal MDS. Additional aims were to establish whether these defects consisted in either gains/losses or balanced rearrangements, to identify the potential affected genes and to evaluate any possible influence on OS and progression free interval (PFI).

The ninety-eight consecutive chromosomally normal MDS patients analysed in the present study came to our observation in the period January 2005-December 2010. They were thirty-seven females and sixty-one males, median age 64 years (range 22–77). Eighteen patients were classified as RARS, 27 as RA, one as CRMDS, 15 as RCMD, 16 as RAEB-1 and 21 as RAEB-2. Considering IPSS score, 38 patients were considered low-risk, 36 intermediate-1 risk and 18 intermediate-2 risk and 6 as high-risk. Median follow-up was 33 months (range 1–84). At the time of the study four patient have died. FISH probes were chosen based on the frequency of their involvement in MDS and their Mb position determined using UCSC genome browser on Human Mar. 2003 assembly. They were obtained from BACPAC Resources Center at C.H.O.R.I. (Oakland, USA), labelled and applied as previously described. The probes applied were the followings: RP11-912D8 (19q13.2); RP11-196P12 (17q11.2); RP11-269C4 (14q12); RP11-351O1 (10q21.3); RP11-144G6 (10q11.2); RP11-122A11 (7q34); RP11-951K18 (5q13.1); RP11-101K5 (4p14); RP11-544H14 (2q33). i-FISH cut-off values were fixed at 10%.

An abnormal FISH pattern was revealed in 30 patients (33.7%). A single defect was revealed in 31 patients (31.6%) and more than two defects in 8 (26.7). Twenty-two patients (22.4%) presented a single defect, whereas 9 (9.1%) more than two defects. Band 19q13.2, 14q12, 4p14, 5q13.1, 7q34, 17q11.2, 7q22, 10q11.2, 10q21.3 and 2p33 deletions had an incidence of 54.8%, 25.8%, 16.1%, 12.9%, 12.9%, 12.9%, 9.6%, 6.4% and 3.2%. The RP11-196P12 covers the RDM-1 gene which encodes for a motif found in the RAD52 protein involved in DNA double strand breaks and homologous recombination and the RP11-144G6 covers the ANXA8L1 gene over-expressed in AML. Thus, these two genes are now analysed with additional molecular tests in order to check whether they may be affected by mutations. An abnormal FISH pattern was observed in 4/18 (22.2%) RARS, in 5/27 (18.5%) RA, in 4/15 (26.6%) RCMD, in 6/16 (37.5%) RAEB-1 and in 12/21 (57.1%) RAEB-2. Considering IPSS, an abnormal FISH pattern was revealed in 7/38 (18.4%) low-risk, in 12/36 (33.3%) intermediate-1 risk, in 9/18 (50%) intermediate-2 risk and in 3/6 (50%) high-risk patients. Disease evolution occurred in a total of 21 patients (2 RARS, 5RA, 6 RAEB-1 and 7 RAEB-2), 11 (one RARS, 2 RA, 5 RAEB-1 and 2 RAEB-2) presented an abnormal FISH pattern. At least two chromosomal deletions were observed in 7/11 patients.

i) FISH reveals novel not expected karyotype defects, mostly deletions, in about 32% of chromosomally normal MDS; ii) some deletions pinpoint genes involved in DNA repair; iii) an abnormal FISH pattern correlates with advanced and int-2, high-risk MDS; iii) the presence of more than two lesions seems to associate with an increased risk of disease progression.

No relevant conflicts of interest to declare.