Summary
Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant precursor to multiple myeloma (MM). Though several genetic variants have been identified for MM, none have been identified for MGUS. Recently, Broderick et al. conducted a GWAS of MM and identified three novel loci at 3p22.1 (rs1052501), 7p15.3 (rs4487645) and 2p23.3 (rs6746082) associated with MM risk. We examined the association of these variants with MGUS in a clinic-based case-control study of 391 MGUS cases and 365 controls. We also attempted to replicate the reported association with MM (243 MM cases, 365 controls). We found rs1052501 associated with increased risk of both MGUS (OR=1.32; 95% CI, 1.02 to 1.72; p=0.04) and MM (OR=1.39; 95% CI, 1.04, 1.86; p=0.03). However, there were no associations with the other two loci, rs6746082 and rs4487645, for either MGUS or MM. We identified one genetic variant that may exert its influence on MM through its association with MGUS.
Keywords: genetic variation, MGUS, MM, single nucleotide polymorphism
Monoclonal gammopathy of undetermined significance (MGUS) is the most prevalent clonal plasma cell proliferative disorder, present in over 3% of the population aged 50 years and older, with a rate of progression to malignancy of 1% per year. (Kyle, et al 2006, Kyle, et al 2002) MGUS has been shown to precede MM in almost all cases. (Landgren, et al 2009b) We, and others, have shown evidence for a familial component to MGUS, with first-degree relatives of MM or MGUS probands having a 2.5 fold increased risk of MGUS, indicative of an underlying genetic predisposition. (Landgren, et al 2009a, Vachon, et al 2009)
While several genetic variants have been identified for MM, none have been identified that are associated with MGUS. (Greenberg, et al 2012) Broderick et al. (Broderick, et al 2011) recently conducted the first genome-wide association study (GWAS) of MM using case-control studies from the United Kingdom and Germany and identified three novel loci at 3p22.1 (rs1052501 in ULK4), 7p15.3 (rs4487645) and 2p23.3 (rs6746082) associated with risk of MM, although the latter did not reach genome wide significance (p<5×10−8). Here, we investigate whether these three loci for MM risk are also associated with risk of MGUS in order to provide evidence that genetic variation influences MM through MGUS. We also attempt to replicate the association of these loci with MM within a case-control study of MM.
Material and methods
Cases (MGUS/MM) and controls
The ascertainment of MGUS and MM cases and controls as well as examination of genetic variation in these populations was approved by the Mayo Clinic Institutional Review Board.
MGUS and MM cases were sampled from the Mayo Clinic regional practice. Specifically, all patients from Minnesota, Iowa and Wisconsin who were found to have MGUS on a clinical blood test between 2005 through 2009 and had provided research authorization were asked to participate in a case-control study of MGUS. MGUS was diagnosed by serum immunofixation. MGUS cases provided informed consent, a blood sample, and completed a detailed questionnaire. Of 973 eligible MGUS cases, 388 (40%) participated and were used for the current analysis; of these, 318 (81.3%) had a detectable M protein on serum protein electrophoresis or SPEP. Incident MM cases were also sampled from MM cases seen between 1998 and 2007 at the Mayo Clinic and within nine months of their initial diagnosis. Eligible cases had provided prior consent and a blood sample for research studies of MM. A total 243 of MM cases from the seven states, including Minnesota, Iowa, Wisconsin, North Dakota, Michigan, South Dakota, and Illinois were used for analyses.
Clinic-based controls (n=378) enrolled between 2002 and 2010 into an ongoing Mayo Clinic case-control study of non-Hodgkin lymphoma (Cerhan, et al 2011) were used as the comparison group for both MM and MGUS cases. Briefly, controls were recruited from the General Internal Medicine clinics. Controls had to be at least 20 years old, a resident of Minnesota, Iowa, or Wisconsin at the time of appointment, and have no personal history of lymphoma, leukemia, or HIV infection; none of the controls had a history of MM or known MGUS.
Genotyping
Genotyping of rs1052501, rs4487645, and rs6746082 was performed using TaqMan SNP Genotyping Assays (Applied Biosystems, Carlsbad, California). In addition to the 1012 case and control samples, an extra two duplicates and three related controls (CEPH-NA10858, CEPH-NA10859, and CEPH-NA11875) were genotyped on each plate. Among the 24 duplicates and CEPH controls, the concordance rates were 100% for all three single nucleotide polymorphisms (SNPs). Sample call rate was >97%. We assessed departures from Hardy-Weinberg equilibrium (HWE) among controls using an exact test. (Wigginton, et al 2005) None of the SNPs showed departure from HWE.
Statistical analyses and considerations
Odds ratios and 95% confidence intervals from logistic regression were used to evaluate the associations between the three SNPs with risk of MGUS and of MM assuming an additive model. Analyses were also performed adjusting for age, and after excluding those who did not have a detectable M protein on SPEP (n=70).
Results: Discussion
The SNP at 3p22.1 (rs1052501 in ULK4) was associated with both MGUS and MM (Table II). Specifically, the C allele was associated with a 30% increased risk of MGUS (OR=1.32; 95% CI, 1.02 to 1.72; p=0.04) and 40% increased risk of MM (OR=1.39; 95% CI, 1.04 to 1.86; p=0.03). Risk estimates were similar to those previously reported.(Broderick, et al 2011) We failed to replicate the associations for rs6746082 and rs4487645 (Table II) with MM. (Broderick, et al 2011) We also found no significant association of these two SNPs with MGUS. Results (not shown) were virtually unchanged with adjustment for age and when restricted to the 318 MGUS cases who had a detectable M protein on SPEP.
Table II.
Association of genetic variation with MGUS and MM.
| rsID | Chromosome | Locus | Variation | MGUS | MM | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
| |||||||||||
| N (case/control) | MAF (case/control) | OR (95% CI) | p | N (case/control) | MAF (case/control) | OR (95% CI) | p | ||||
| rs1052501 | 3 | 41925398 | T > C | 378/365 | 0.20/0.15 | 1.32 (1.02, 1.72) | 0.04 | 238/365 | 0.21/0.15 | 1.39 (1.04, 1.86) | 0.03 |
| rs4487645 | 7 | 21938240 | C > A | 378/365 | 0.32/0.34 | 0.90 (0.72, 1.12) | 0.33 | 238/365 | 0.33/0.34 | 0.95 (0.74, 1.22) | 0.68 |
| rs6746082 | 2 | 25659244 | A > C | 378/365 | 0.22/0.18 | 1.24 (0.96, 1.60) | 0.1 | 238/365 | 0.20/0.18 | 1.14 (0.85, 1.53) | 0.38 |
Rs1052501 maps to ULK4, which encodes a kinase with serine/threonine activity. While recently found to be associated with MM, rs1052501 has also been shown to have associations with essential hypertension in women and Korean populations. (Ho, et al 2011, Hong, et al 2010) Evidence presented here demonstrates that there is a modest association between rs1052501 and MGUS and suggests that this polymorphism or the causal variant that it represents, may exert its influence on MM through initiation of the precursor, MGUS. Whether rs1052501 (or the other two loci) are associated with progression from MGUS to MM needs to be examined.
While there have been several polymorphisms reported to be associated with MM, (Greenberg, et al 2012) this is the first study to evaluate whether these genetic risk factors for MM also influence MGUS. (Abazis-Stamboulieh, et al 2007, Broderick, et al 2011, Chapman, et al 2011, Hayden, et al 2007) Genetic variants associated with MM may be associated with the initiation of MGUS (the necessary precursor), the progression of MGUS to MM, or both. We were not able to evaluate the association of this SNP with progression. Although there are known biological markers associated with risk of progression from MGUS to MM (including abnormal free light chain ratio and immunoglobulin subtype), it remains difficult to predict which of the 3% of the population with MGUS will progress to malignancy. (Dispenzieri, et al 2010, Kyle, et al 2002, Rajkumar, et al 2005) Genetic variants should be complementary to these predictions.
We did not find an association of either 7p15.3 (rs4487645) or 2p23.3 (rs6746082) with MM or MGUS. Lack of statistical power is certainly a possibility given our sample size; however, our risk estimates for MM were greatly attenuated relative to the studies reported in Broderick et al who reported risk estimates of 1.38 (95%CI: 1.28–1.50) and 1.29 (95%CI: 1.17–1.42), respectively. Also, we were not able to adequately examine the associations between polymorphisms and MGUS by specific isotype, which would be relevant since IgA and IgG MGUS are more likely to progress to MM.
In summary, we have validated the association between 3p22.1 (rs1052501) and MM, and have also shown this polymorphism to be associated with MGUS, the premalignant condition. Future studies will need to examine whether this locus is associated with progression to MM or MGUS subtypes.
Table I.
Baseline characteristics of MGUS and multiple myeloma, cases and controls.
| MM cases (243) | MGUS cases (388) | Controls (n=378) | |
|---|---|---|---|
| Gender | |||
| Male (n, %) | 146 (60.1) | 234 (60.3) | 222 (58.7) |
| Female (n, %) | 97 (39.9) | 154 (39.7) | 156 (42.3) |
| Age group, n (%) | |||
| <50 | 33 (13.6) | 43 (11.1) | 78 (20.6) |
| 50–59 | 65 (26.8) | 65 (16.7) | 96 (25.4) |
| 60–69 | 80 (32.9) | 120 (30.9) | 99 (26.2) |
| 70+ | 65 (26.7) | 160 (41.3) | 105 (27.8) |
| Monoclonal protein concentration | |||
| Less than 1.5 g/dL | 66 (27.2) | 27 (7.0) | N/A |
| 1.5 g/dL or more | 177 (72.8) | 361 (93.0) | N/A |
| Monoclonal immunoglobulin isotype, n (%)* | |||
| IgA | 57 (23.6) | 39 (10.1) | N/A |
| IgM | 1 (0.4) | 55 (14.2) | N/A |
| Light chain only | 30 (12.4) | 1 (0.3) | N/A |
| Biclonal | 5 (2.1) | 37 (9.6) | |
| Other | 10 (4.1) | ||
Acknowledgments
This work was supported, in part, by the National Cancer Institute, National Institutes of Health, Bethesda, MD (CA107476, CA100707, CA 83724, and CA92153) and by the NIH/NCRR CTSA Grant Number TL1 RR024152. The work was also supported, in part, by the Jabbs Foundation, Birmingham, United Kingdom and the Henry J. Predolin Foundation, USA.
This project was supported by NIH/NCRR/NCATS CTSA Grant Number UL1 RR024150. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.
Footnotes
Author contributions
SLS and CMV conceived of the study question and were responsible for study design and overseeing the project. CMV, SLS, and AJG wrote the paper with comments from all coauthors; JRC, ML, CMV, SVR and RAK contributed study populations, and interpreted study findings; DJS, SKM, DRL, CLC performed all statistical analyses and contributed to their interpretation; ADN, AML and RBD provided scientific input and interpretation of analyses; all coauthors read and approved the paper.
Disclosure conflict-of-interest
The authors declare no competing financial interest.
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