A polymorphism in the 3′ UTR of <i>IRF4</i> linked to susceptibility and pathogenesis in chronic lymphocytic leukaemia and Hodgkin lymphoma has limited impact in multiple myeloma (2010)

Multiple myeloma is a malignancy of plasma cells with a complex aetiology and there is a limited understanding of how constitutional genetic variation may play a role in its pathogenesis. Strong racial predisposition and weak familial predisposition support constitutional genetic variants as having some role in the development of monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma. The first evidence for the existence of common, low-penetrance susceptibility variants linked to a haematological malignancy (Di Bernardo et al, 2008) was a genome-wide association study in chronic lymphocytic leukaemia (CLL) that identified six previously unreported risk loci. The strongest statistical evidence for an association with CLL disease causation was a G>A variant (rs872071) on chromosome 6p25·3 mapping to the 3′ UTR of the IRF4 (interferon regulatory factor 4) gene and subsequently associated with a significantly shorter treatment-free survival (TFS) (Allan et al, 2010). This allele is also associated with an increased risk of developing Hodgkin lymphoma (Broderick et al, 2010) and other polymorphisms in IRF4 have also been associated with B cell malignancies (Do et al, 2010; Gathany et al, 2010). IRF4 is a key protein in multiple myeloma (Heintel et al, 2008; Shaffer et al, 2008) and in B cell and plasma cell development (Busslinger, 2004; Klein & Della-Favera, 2007) and this provides a strong rationale for investigating rs872071 in multiple myeloma and MGUS. Three hundred and seventy-eight unselected multiple myeloma cases (mean age ± standard deviation (SD) 66·5 ± 12·3 years) and 99 unselected MGUS cases (mean age 68·2 ± 11·5 years) were recruited through treating centres within the Heart of England NHS Trust, Leeds Teaching Hospitals NHS Trust and Newcastle-upon-Tyne NHS Trust between 1990 and 2005. Healthy controls (n = 771, mean age 48·4 ± 14·3 years) were recruited between 1991 and 1996 as part of a population-based case-control study of adult acute leukaemia (Kane et al, 1999). Three hundred and fifty-two (93·1%) multiple myeloma cases and all of the MGUS cases and controls were self-reported to be British and of European ancestry. The collection of DNA samples for research purposes was approved by Research Ethics Committee and by the respective Hospital Trust Research and Development Committee in accordance with the tenets of the Declaration of Helsinki. Genotyping for rs872071 was performed using DNA from peripheral blood or bone marrow by competitive allele-specific polymerase chain reaction single nucleotide polymorphism genotyping system (KASPar®) chemistry (KBiosciences, Hoddesdon, UK) and data quality was determined as previously described (Allan et al, 2010). Unadjusted and age/sex adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using unconditional logistic regression for individuals of European ancestry only. Multiple myeloma patients were treated either as part of a clinical trial (Medical Research Council Myeloma VII, VIII or IX studies) or according to national guidelines. The Chi-squared test was used to examine the distribution of categorical variables as a function of genotype status. Comparisons of overall survival between genotype groups were determined using the log-rank test. A P-value of 0·05 was used to define statistical significance. Genotype frequencies for rs872071 in Europeans were in accordance with Hardy-Weinberg equilibrium for multiple myeloma cases (P = 0·49), MGUS cases (P = 0·16) and controls (P = 0·85), providing no evidence of population stratification (Table I). There was no association of rs872071 status with multiple myeloma or MGUS in either an unadjusted analysis (data not shown) or with adjustment for age and sex (Table I). The rs872071 variant was not associated with haemoglobin level, creatinine or β-2 microglobulin (Table II). Outcome data was available for 155 multiple myeloma patients (85 deaths) with a median follow-up time of 40·2 months. Three clinical parameters were significantly associated with worse survival – low haemoglobin level (P = 0·001), high creatinine level (P < 0·0001) and high β-2 microglobulin (P < 0·0001) and a high calcium was weakly associated (P = 0·085). The rs872071 variant was not significantly associated with overall survival (P = 0·921) (data not shown). There was an association for the G allele (i.e. GG or GA genotype) with hypercalcaemia (P = 0·03; Table II) and the effect was gender specific. Female carriers of the high-risk allele were significantly more likely to have hypercalcaemia than non-carriers (P = 0·01) but the association was not seen in males (P = 0·64) (data not shown). The biological explanation for this association with hypercalcaemia in myeloma is unclear. Despite this gene being strongly implicated in myeloma biology (Shaffer et al, 2008), we have not found any strong evidence that this common allelic variant has any significant pathological relevance in myeloma. However, our study was insufficiently powered to exclude rs872071 acting as a very low penetrance risk allele for myeloma. Further work is needed to understand the relevance and functional consequences of not only this polymorphism but other potentially functional polymorphisms in the IRF4 gene region in order to better understand their impact in lymphoid malignancies. We are grateful to the patients and their clinicians who participated in this study. This work was supported by Leukaemia Research.