Measuring serum melatonin in postmenopausal women: Implications for epidemiologic studies and breast cancer studies

<div><p>Background</p><p>Circulating melatonin is a good candidate biomarker for studies of circadian rhythms and circadian disruption. However, epidemiologic studies on circulating melatonin are limited because melatonin is secreted at night, yet most epidemiologic studies collect blood during the day when melatonin levels are very low, and assays are lacking that are ultrasensitive to detect low levels of melatonin reliably.</p><p>Objective</p><p>To assess the performance of a refined radioimmunoassay in measuring morning melatonin among women.</p><p>Methods</p><p>We used morning serum samples from 47 postmenopausal women ages 48–80 years without a history of breast cancer who participated in the San Francisco Bay Area Breast Cancer Study, including 19 women who had duplicate measurements. The coefficient of variation (CV) and intraclass coefficient (ICC) were estimated using the random effect model.</p><p>Results</p><p>Reproducibility for the assay was satisfactory, with a CV of 11.2% and an ICC of 98.9%; correlation between the replicate samples was also high (<i>R</i> = 0.96). In the 47 women, serum melatonin levels ranged from 0.6 to 62.6 pg/ml, with a median of 7.0 pg/ml.</p><p>Conclusion</p><p>Our results suggest that it is possible to reliably measure melatonin in postmenopausal women in morning serum samples in large epidemiologic studies to evaluate the role of melatonin in cancer etiology or prognosis.</p></div

<i>SEPP1</i> Influences Breast Cancer Risk among Women with Greater Native American Ancestry: The Breast Cancer Health Disparities Study

<div><p>Selenoproteins are a class of proteins containing a selenocysteine residue, many of which have been shown to have redox functions, acting as antioxidants to decrease oxidative stress. Selenoproteins have previously been associated with risk of various cancers and redox-related diseases. In this study we evaluated possible associations between breast cancer risk and survival and single nucleotide polymorphisms (SNPs) in the selenoprotein genes <i>GPX1</i>, <i>GPX2</i>, <i>GPX3, GPX4, SELS, SEP15, SEPN1, SEPP1, SEPW1, TXNRD1</i>, and <i>TXNRD2</i> among Hispanic/Native American (2111 cases, 2597 controls) and non-Hispanic white (NHW) (1481 cases, 1586 controls) women in the Breast Cancer Health Disparities Study. Adaptive Rank Truncated Product (ARTP) analysis was used to determine both gene and pathway significance with these genes. The overall selenoprotein pathway P_ARTP was not significantly associated with breast cancer risk (P_ARTP = 0.69), and only one gene, <i>GPX3</i>, was of borderline significance for the overall population (P_ARTP =0.09) and marginally significant among women with 0-28% Native American (NA) ancestry (P_ARTP=0.06). The <i>SEPP1</i> gene was statistically significantly associated with breast cancer risk among women with higher NA ancestry (P_ARTP=0.002) and contributed to a significant pathway among those women (P_ARTP=0.04). <i>GPX1, GPX3</i>, and <i>SELS</i> were associated with Estrogen Receptor-/Progesterone Receptor+ status (P_ARTP = 0.002, 0.05, and 0.01, respectively). Four SNPs (<i>GPX3</i> rs2070593, rs<i>GPX4</i> rs2074451, <i>SELS</i> rs9874, and <i>TXNRD1</i> rs17202060) significantly interacted with dietary oxidative balance score after adjustment for multiple comparisons to alter breast cancer risk. <i>GPX4</i> was significantly associated with breast cancer survival among those with the highest NA ancestry (P_ARTP = 0.05) only. Our data suggest that <i>SEPP1</i> alters breast cancer risk among women with higher levels of NA ancestry. </p> </div

Range of morning melatonin levels and reproducibility of serum melatonin assays in postmenopausal non-Hispanic white women.

<p>Range of morning melatonin levels and reproducibility of serum melatonin assays in postmenopausal non-Hispanic white women.</p

<em>RAD51</em> and Breast Cancer Susceptibility: No Evidence for Rare Variant Association in the Breast Cancer Family Registry Study

<div><h3>Background</h3><p>Although inherited breast cancer has been associated with germline mutations in genes that are functionally involved in the DNA homologous recombination repair (HRR) pathway, including <em>BRCA1</em>, <em>BRCA2</em>, <em>TP53</em>, <em>ATM</em>, <em>BRIP1</em>, <em>CHEK2</em> and <em>PALB2,</em> about 70% of breast cancer heritability remains unexplained. Because of their critical functions in maintaining genome integrity and already well-established associations with breast cancer susceptibility, it is likely that additional genes involved in the HRR pathway harbor sequence variants associated with increased risk of breast cancer. <em>RAD51</em> plays a central biological function in DNA repair and despite the fact that rare, likely dysfunctional variants in three of its five paralogs, <em>RAD51C, RAD51D,</em> and <em>XRCC2,</em> have been associated with breast and/or ovarian cancer risk, no population-based case-control mutation screening data are available for the <em>RAD51</em> gene. We thus postulated that <em>RAD51</em> could harbor rare germline mutations that confer increased risk of breast cancer.</p> <h3>Methodology/Principal Findings</h3><p>We screened the coding exons and proximal splice junction regions of the gene for germline sequence variation in 1,330 early-onset breast cancer cases and 1,123 controls from the Breast Cancer Family Registry, using the same population-based sampling and analytical strategy that we developed for assessment of rare sequence variants in <em>ATM</em> and <em>CHEK2.</em> In total, 12 distinct very rare or private variants were characterized in <em>RAD51</em>, with 10 cases (0.75%) and 9 controls (0.80%) carrying such a variant. Variants were either likely neutral missense substitutions (3), silent substitutions (4) or non-coding substitutions (5) that were predicted to have little effect on efficiency of the splicing machinery.</p> <h3>Conclusion</h3><p>Altogether, our data suggest that <em>RAD51</em> tolerates so little dysfunctional sequence variation that rare variants in the gene contribute little, if anything, to breast cancer susceptibility.</p> </div

Plot of the density function of beta distributions parameterized by mean and heterogeneity factor .

<p>On each subplot the density is shown for two choices of namely  = 0.2 (solid line) and  = 0.25 (dotted lines).</p

Rare genetic variants of <i>RAD51</i> identified in the BCFR.

*<p>A protein multiple sequence alignment (PMSA) including 15 sequences from Human to Drosophila (Dmel) was used to obtain scores for Align-GVGD and for SIFT (Median sequence conservation of 4.32 substitutions per position).</p><p>NA, not applicable.</p

Plot of estimate of proportion of African ancestry from STRUCTURE by participating AABC study.

<p>Plot of estimate of proportion of African ancestry from STRUCTURE by participating AABC study.</p

Principal components plots of AABC and selected HapMap samples.

<p>Principal components plots of AABC and selected HapMap samples.</p

Quantile-quantile plot of p-values from association tests in the hypothesized case-control study in which cases from the CBCS and controls from the MEC are used.

<p>The plotted values indicate adjustment for 0 (uncorrected heavy solid line), 1 (dashed line), 10 (dotted line) and 200 (thin solid line) eigenvectors, by using these components in the calculation of .</p

Plot of non-centrality parameter for the Bourgain test for a case-control study using two incompletely admixed populations as sources of cases and controls respectively.

<p>The parameters chosen refer to a test of a variant associated with disease which has 40 percent overall allele frequency and which is associated with a 10 percent difference in frequency between cases and controls (OR = 1.5 per copy). Cases are assumed to have average admixture percentage of 20 percent and controls 25 percent. The within population heterogeneity is specified by a single common heterogeneity parameter as used in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1001096#pgen-1001096-g001" target="_blank">Figure 1</a>.</p