Hemochromatois-Associated Gene Mutations in Patients with Myelodysplastic Syndromes with Refractory Anemia and Ringed Sideroblasts.

Complex interaction between a multitude of genetic variants may be responsible for differential susceptibility to specific diseases, and be responsible for phenotypic variability and heterogeneity of clinical presentations. Such a variability in clinical features confounded for many years investigations into the pathogenesis of myelodysplastic syndromes (MDS). We made a curious observation of increased ferritin levels in some newly diagnosed patients with MDS RARS (refractory anemia with ringed sideroblasts) in whom transfusional iron-overload was unlikely due to very low transfusion burden. Hence, we hypothesized that RARS patients may harbor hemochromatosis-related mutations, which could contribute to the pathophysiology of this particular subset of MDS. We studied a cohort of 109 MDS patients; 42 with RARS, and 67 with other forms of MDS (18 RA, 12 RAEB, 7 RAEB-T, 1 CMML, and 29 MDS/MPD overlap). All patients were genotyped using restriction fragment length polymorphism (RFLP) method, designed to detect presence of C282Y and H63D mutations of the HFE gene. We found significantly higher frequency of heterozygozity for the C282Y mutation in 21% of RARS patients (vs 9% in control population, n=2016, p= 0.017) while H63D genotype was not increased. The possible pathogenic role of this finding in RARS was supported by the normal distribution of mutant HFE alleles in patients with other forms of MDS (5% vs. 9%, p =0.35). Interestingly, 3/7 patients with RA not fulfilling the RARS criteria, but having increased numbers of ringed sideroblasts (<15%) also showed heterozygozity for either C282Y or H63D allele. To correlate the presence of C282Y allele with clinical features of RARS patients, we have performed a subset analysis. Within this group we have included patients with a rather nebulous and rare form of MDS, provisionally subclassified by WHO as RARS with thrombocytosis (RARSt); 7 of these patients (n=10) were found to have either C282Y or H63D allele resulting in a frequency of 30% and 40% of C282Y or H63D allele, respectively. The combined prevalence of either of these alleles in the control population is 33% (vs. 70% in RARSt, p=.01). Previously, we have demonstrated that RARSt patients are characterized by a high prevalence of the V617F JAK2 mutation (Szpurka et al, Blood 2006) suggestive of the pathophysiologic derivation of this syndrome from MPD rather than MDS. Consequently, we have tested the frequency of HFE gene variants associated with hemochromatosis in patients with MPD and Jak2 mutations. Of note is that patients with RARS harbored more C282Y alleles than those with other forms of MDS or MPD with Jak2 mutation (except for those with RARSt; (21% vs 5% and 3%, p =0.036 and .012, respectively). We conclude that hemochromatosis associated mutations may contribute to the pathogenesis of RARS. In patients with MPD and Jak2 mutation, concomitant presence of hemachromatosis-predisposing HFE variants may result in the unusual presentation associated with ringed sideroblasts.