Detection of microsatellite instability and loss of heterozygosity in Myelodysplastic Síndromes

VAZQUEZ, MARÍA LORENA; BELLI, CAROLINA; TACHI, C; FANAL, D; VENICA, A; ALBERBIDE, J; NUCIFORA, E; LARRIPA, IRENE; FUNDIA, ARIELA

Punta del Este, Uruguay

Congreso; XXXI World Congress of the International Society of Hematology 2007; 2007

ISH

The onset of myelodysplastic syndrome (MDS) has been associated to genomic instability, which is frequently due to deficiencies in mismatch repair (MMR) or tumor-suppressor genes (TSG). To verify whether both mechanic¡sm might be involved In MDS genomic instability, microsatellite instability (MSI) and loss of heterozygosity (LOH) were analyzed. Bone marrow samples from 21 untreated patients (12 females/ 9 males) with a mean age of 70.7 years (range 38-93) were studied. Myelodysplastic DNA was obtained from non-adherent mononuclear cells, while constitutional DNA was extracted from polymorphonuclear cells. Nine STR chosen from the MSI colon cancer reference panel (BAT 25, BAT 26, D2S123 and D18S58) or located at points involved in MDS and acute leukemia (D5S209, CRTL, CSF1RT, D7S525 and TP53) were analyzed by PCR and electrophoresis on native polyacrylamide gels silver stained. FLT3 mutations were also studied. The colon panel revealed MSI only in one patient (4.8%) at D18S58. Employing hematological STR, 5 cases (23.8%) presented alterations at 1 or 2 STR: CSF1RT, CRTL and TP53, being classified as MSI-low according international criteria. Two cases presented LOH at TP53, D5S209 and D7S525. The mean frequency of mutated STR/individual showed a significant difference between hematological markers (0.08±0.03) respect to colon STR (0.01±0.03) (Student test, p=0.007), suggesting that colon markers are insensitive for MDS. Only 1/10 cases showed one D835 FLT3 mutation in addition to MSI and LOH. The low frequency of LOH suggests that putative TSG at the loci studied are not involved in genomic instability. These findings allows to identify a subset of patients with MSI-low, not due to MMR mutations but probably related to other genetic alterations, critical in MDS development