The results presented here suggest that although the CHEK2 Y424H variant occurs at a highly conserved position, it does not seem to play a significant role in predisposition to PRCA. While the results do not exclude the possibility that this is a modest-risk predisposition allele in the AJ population, functional studies in yeast indicate that Y424H does not have a significant deleterious effect.
Previous studies of CHEK2
mutations in men with PRCA from the US, Finland, Poland, and Sweden have found conflicting results. Dong et al.
reported a total of 28 (4.8%) germline CHEK2
mutations (16 of which were unique) among 578 sporadic PRCA cases collected at the Mayo clinic compared to 6/423 (1.4%) unaffected men. Additional screening for CHEK2
mutations in 149 families with familial PRCA prostate cancer (a minimum of three men over at least two generations) revealed 11 mutations (5 unique) in nine families, but the frequency of CHEK2
mutations in the familial group was not significantly different from that in the control group [24
In a Finnish study of 120 patients with hereditary PRCA, 537 unselected PRCA cases, and 480 controls, the 1100delC variant was at an increased frequency among the patients with hereditary PRCA compared to controls (OR 8.24; 95% confidence intervals, CI 1.49–45.54; p=0.02) [25
]. The I157T missense variant also had significantly higher frequency among hereditary PRCA patients in Finland (OR 2.12; 95% C.I. 1.06–4.27; p=0.04). However, only small associations were found between patients with unselected PRCA cases and the variants 1100delC (odds ratio, OR 3.14; 95% confidence intervals, CI 0.65–15.16; p=.15) and I127T (odds ratio, OR 1.48; 95% confidence intervals, CI 0.89–2.46; p=.13). Cybulski et al.
studied three common Polish CHEK2
mutations, 1100delC, IVS2+1G>A, and I157T, in 98 familial PRCA cases, 690 unselected cases, and 1921 controls [22
]. They reported an OR of 2.2 (p=.04) for unselected PRCA cases and the protein-truncating alleles (1100delC and IVS2+1G>A) and an OR of 1.7 (p=.002) for the I157T variant [22
]. In the 98 familial cases (2.2 cases per pedigree), IVS2+1G>A had an OR of 12.1 (C.I. 2.8–51.4, p=.0002), 1100delC had an OR of 4.9 (C.I. 0.5–44.6 p=.11), I157T had an OR of 3.8 (C.I. 2.0–7.4, p=.00002), and at least one of the three variants was identified in 20.4% of familial cases [23
]. In contrast, in a recent study where the CHEK2
*1100delC variant was screened in 419 men diagnosed with PRCA in southern Sweden (145 sporadic cases and 274 familial/hereditary cases) the CHEK2
*1100delC variant was found in 1.2% of the cases (sporadic: 0.7%; familial: 1.6%; hereditary: 1.4%) and in 1.0% of the controls, indicating that CHEK2
*1100delC is not a clinically important high-risk variant for hereditary PRCA susceptibility in this population [26
]. By comparison, in the study presented here we found one 1100delC variant in 131 cases (0.76%) in the Montreal series compared to an established population frequency of 0.3% in Ashkenazi Jewish controls [45
]. However, the numbers of cases analyzed (131) is too small to draw any strong conclusions and it would be interesting to study larger numbers to investigate this further.
In summary, the most compelling CHEK2
variant identified in this study was Y424H. The complete conservation among eight vertebrate sequences plus sea urchin of Y at position 424 suggests that changing this amino acid may have biologically significant consequences, but the genetic and functional assay data presented here do not provide sufficient support for this view. Overall, based on the results of this study, we conclude that germline CHEK2
variants play a minor role, if any, in PRCA susceptibility in the AJ population and conservation alone is not a sufficient reason to suspect that an amino acid substitution in a protein may be pathogenic. Some ultra-conserved regions in human genome with no apparent functions have been reported [46
], supporting this conclusion.