Recent genome-wide sequencing efforts have led to the identification of a number of new candidate genes involved in the pathogenesis of myeloid neoplasms. Among them, variations in isocitrate dehydrogenase genes (IDH1 and IDH2) have been identified in several hematologic malignancies. IDH1 and IDH2 mutations have been found in 8–10% and 15% of patients with acute myeloid leukemia, res pectively, especially in those having normal karyotype (NK-AML). Both gene mutations were recently also reported in myelodysplastic syndromes and chronic myeloproliferative disorders, and were associated with a high rate of leukemic transformation and poor prognosis [1–3]. A few studies have been published on somatic mutations of IDH1 and IDH2 in chronic myelomonocytic leukemia (CMML). The reported incidence of these mutations in CMML ranged from 0 to 9%[3–7], although their prognostic relevance remains uncertain. All reported IDH1 mutations involve the R132 residue, while IDH2 mutations involve either the R140 or the R172 residue. Mutations in IDH decreased affinity to isocitrate, displaying a neomorphic catalytic activity toward α-ketoglutarate, producing an accumulation of 2-hydroxyglutarate [2, 8–10]. It is currently believed that these intracellular changes facilitate oncogenic pathways, including activation of hypoxia-inducible factor-1 α (HIF-1 α). Nevertheless, their relative contribution is still unclear [2]. In the present study, we evaluated the incidence of the IDH1 and IDH2 mutations at the time of diagnosis in a series of 70 adult patients with CMML (Table I). We developed a high-resolution melting (HRM) assay on a

LightCycler® 480 to detect somatic mutations of the fourth exon of IDH1 and IDH2 genes using reported primers [11]. Genomic DNA was isolated from bone marrow samples at the time of diagnosis. All cases were tested in duplicate in each run using both mutated and wild-type IDH1 or IDH2 samples provided by the Hospital La Fe Biobank. The analysis of melting curves clearly distinguished between the group of wild-type DNA and the variant carrier samples. For the duplicates of each sample, the curves practically overlapped, either in the same assay or between assays. All results were confirmed by direct sequencing on an ABI PRISM 310 DNA Analyzer (Applied Biosystems, Foster City, CA). Sequence analysis was verified by GenBank accession numbers NT_005403. 17 and NT_010274. 17. All mutations were confirmed at least twice. Two of the 70 patients (3%) showed the IDH1 mutation R132H as a result of a c. G395A change. Both mutations were identified in patients with CMML-1. In addition, seven patients (10%) showed single nucleotide polymorphism (SNP) rs11554137 located in codon 105 (IDH1105GGC_T)(Figure 1). This polymorphism is present in about 7.5% of the European population (http://www. ncbi. nlm. nih. gov/projects/SNP). However, in a previous IDH mRNA study, patients with at least one IDH1105GGT allele had a significantly higher expression of IDH1 mRNA than patients with two IDH1105GGC alleles, and there was a negative impact on prognosis in patients with NK-AML [12]. Probably due to the small sample size, IDH1 variations, including SNP rs11554137, were not associated with any clinical or biological features or outcome. IDH2 mutations were not detected in the present series. The HRM method showed a high sensitivity and specificity for mutational screening, since no mutations were missed as compared with those identified with Sanger sequencing. Although several methods have been used to detect gene alterations (denaturing high performance liquid chromatography [DHLPC …