Susceptibility to Philadelphia-Positive acute Lymphoblastic Leukemia (ALL) Is Associated with a Germline Polymorphism In the ANRIL (CDKN2BAS) Locus.

Among genes that are supposed to be involved in altered molecular pathways leading to leukemogenesis, the CDKN2A/B locus is particularly noteworthy since it encodes for the INK4-class cyclin dependent kinase inhibitors p15 INK4B, p16 INK4A and p14 ARF, which act as tumor suppressors. The CDKN2A/B locus has been found to be inactivated in several haeamatologic malignancies mainly due to deletion, aberrant repression or epigenetic silencing, whereas little is known about the potential role of its single nucleotide polymorphisms (SNPs) in leukemia susceptibility. To investigate whether polymorphisms within this broad genomic region can correlate with increased susceptibility to haeamatologic malignancies, an association study was performed by genotyping 23 SNPs spanning the MTAP, CDKN2A/B and CDKN2BAS loci, as well as relative intergenic regions, in a case-control cohort made up of 332 samples: 149 leukemia patients, including Philadelphia positive (Ph+) ALL (n=92) and acute myeloid leukemia (AML) samples (n=57), and 183 unrelated healthy controls. Ph+ ALL patients showed a median age of 52 years (18-78 years); 24 cases (26%) expressed the p210 oncoprotein, 62 (67%) the p190 and 6 (7%) both the proteins. AML patients showed a median age of 53 years (21-71 years) and they included FAB-M0, M1, M2, M3, M4, M5, miscellaneous cytogenetic abnormalities and normal karyotype subtypes. 6 SNPs were selected on the basis of their previous association with several diseases, such as coronary artery disease (rs2891168, rs518394, rs564398, rs10757278), type 2 diabetes mellitus (rs564398), frailty (rs2811712). The remaining 17 SNPs were selected among those included in the Affymetrix Genome-Wide Human SNP Array 6.0 to deepen the SNPs coverage for the examined region. Genotyping was performed using iPLEX Gold technology and MassARRAY high-throughput DNA analysis with Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (Sequenom, Inc., San Diego, CA). Furthermore, all leukemia samples were also previously genotyped using the GeneChip® Human Mapping 250K NspI and Genome-Wide Human SNP 6.0 (Affymetrix). A total of 17 SNPs, spanning the 9p genomic interval that encompasses the MTAP, CDKN2A/B and CDKN2BAS loci, were successfully genotyped and used for investigating their potential associations with the leukemia phenotypes. Five SNPs (rs1012713, rs10965179, rs34011899, rs3731232, rs3218010) with Minor Allele Frequency (MAF) <0.05 in cases and controls, as well as one SNP (rs3931609) showing >20% missing call rates, were instead excluded from the association analysis. Potential population stratification affecting the control sample was ruled out as its genotypes distribution satisfies the Hardy-Weinberg equilibrium criterion. Among the 17 SNPs, rs564398, mapping to the CDKN2BAS locus that encodes for ANRIL antisense non-coding RNA, showed a statistically significant correlation with the ALL phenotype, with a risk pattern that was compatible with an overdominant model of disease susceptibility and an Odd Ratio (OR) of 2 (95% CI, 1.20 to 3.33; p= 7.1 x 10-3). Since a co-ordinated regulation of ANRIL and p14/ARF, p16/CDKN2A, p15/CDKN2B transcription has been already observed in both physiologic and pathologic conditions, we hypothesized that rs564398 association reflects a condition of high linkage disequilibrium between such polymorphism and a causative variant that is able to alter CDKN2A/B expression profiles by changing ANRIL dosage, thus leading to abnormal proliferative boosts and consequent increased ALL susceptibility. Supported by European LeukemiaNet, AIL, AIRC, FIRB 2006, PRIN 2008, Ateneo RFO grants, Project of integrated program (PIO), Programma di Ricerca Regione – Università 2007 – 2009.