This is the first large scale study of candidate genes for association involving a unique set of diverse familial lymphoid malignancies and several findings are noteworthy. SNPs in
BCL2 were associated with all three diseases. Although BCL2 is a strong candidate gene, there were no overlapping SNPs among the three lymphomas. Since more than 50 SNPs were tested, chance is a plausible explanation for the findings observed. We found that SNPs in
IL10 were significantly associated with both WM and CLL patients.
IL10 is involved in several pathways that are potentially relevant for lymphomagenesis. The rs1800890 SNP in the promoter of
IL10 (-3575T>A) has previously been found to be associated with NHL in case-controls studies (
Lan, et al 2006,
Rothman, et al 2006). In our study, the same variant allele was associated with both CLL and WM. In addition,
IL10 is close to a linkage peak on chromosome 1 that we previously identified in a genome wide linkage study of families at high risk for WM (
McMaster, et al 2006). Our findings of SNPs associated with similar ORs in CLL and WM are consistent with the familial aggregation and gene expression studies and support a close biological relationship between them.
SNPs in
IL6 were also associated with HL and WM.
IL6 is involved in lymphocyte differentiation and is upregulated in HL (
Gutierrez, et al 2007,
Nagel, et al 2005,
Vener, et al 2000) (
Nagel, et al 2005,
Vener, et al 2000). A promoter polymorphism in
IL6 (rs1800795,174G>C) was reported to be associated with HL (
Cordano, et al 2005,
Cozen, et al 2004). However, this SNP was not genotyped either in our sample or the HapMap samples so we do not know if it is in linkage disequilibrium with our associated SNPs.
IL6 is also near a linkage peak on chromosome 7 that we identified in families at high risk for HL (
Goldin, et al 2005b).
IL6 is a strong candidate for WM as well since studies have also shown upregulation of IL6 levels in WM tumors. (
Chng, et al 2006,
Gutierrez, et al 2007).
We identified several other genes that are promising but require additional replication. The associations of
FASLG, TRAIL and
TRAIL-receptor 1 with CLL are noteworthy as these genes are all involved in the extrinsic apoptosis pathway and prior studies show altered function in CLL B-cells (
Dicker, et al 2005,
Kaufmann and Steensma 2005,
Scholz and Cinatl 2005). One of the SNPs in the
TRAIL gene also showed similar ORs in both CLL and WM. The possible associations of both the
IL1R1 and
IL4R genes with HL are noteworthy. The binding of
IL1R1 to its agonist activates
NFKB, which is constitutively expressed in HL cells (
Stylianou and Saklatvala 1998).
IL4R has been found to be highly expressed in Hodgkin-Reed Sternberg cells and is being studied as a molecular target for drug development in HL (
Kawakami, et al 2005).
Our study is limited by sample size but we selected familial lymphoma patients (including the rare subtype WM), which increases the power of association studies. Houlston and Peto (
Houlston and Peto 2003) have shown that collecting cases with two or more affected relatives increases the power to identify rare low penetrance variants. They showed that for cases with two additional affected relatives, the number of cases required detecting an effect with OR of 2.0 with 1% population prevalence is four- to five-fold reduced compared to using unselected cases.
It is likely that multiple genes are involved in susceptibility to familial lymphoid malignancies. A previous genome-wide linkage scan in high risk CLL families found evidence for multiple susceptibility gene regions (
Sellick, et al 2007). A recent genome-wide association study of CLL cases compared to controls also suggested an underlying multiple-gene model where six risk loci were identified (
IRF4, PRKD2, SP140, GRAMD1B, BCL2L11) (
Di Bernardo, et al 2008). In our study, 2 SNPs in two of those genes were also associated with CLL, although they were not the same SNPs. They were rs11681263 in
BCL2L11 on chromosome 2 with p=0.01, and rs6900384 in
IRF4 on chromosome 6 with p=0.03 (data not shown).
In summary, our study has replicated a reported association of IL10 SNPs with lymphoid malignancies and an association of the IL6 gene with HL. The TRAIL gene findings are also promising given that both CLL and WM were associated with the same SNPs. Our findings also support other data suggesting a close biological relationship between CLL and WM. Future genome-wide association studies and linkage studies are needed to confirm the findings and further clarify the role of genetic variants in relationship to risk of developing lymphoid malignancies.