C. Leigh Pearce

Association of mis-sense substitution in SRD5A2 gene with prostate cancer in African-American and Hispanic men in Los Angeles, USA

BACKGROUND Prostate cancer is a very common disease in more-developed countries, but its cause is largely unknown. It is an androgen-dependent cancer, and androgens have been proposed as having a substantial role in predisposition to the disease. Thus, variations in androgen metabolism genes may affect risk of this disease. METHODS We screened 216 African-American and 172 Hispanic men with prostate cancer, and 261 African-American and 200 Hispanic healthy men (controls), from a large prospective cohort study (the Hawaii-Los Angeles Multiethnic Cohort Study) for a mis-sense substitution in the human prostatic (or type II) steroid 5alpha-reductase (SRD5A2) gene, the product of which controls metabolic activation of testosterone to dihydrotestosterone. This mis-sense substitution results in an alanine residue at codon 49 being replaced with threonine (A49T). We also reconstructed this mutation in the SRD5A2 cDNA, and overexpressed the enzyme in mammalian tissue culture cells. FINDINGS The A49T aminoacid substitution in the SRD5A2 gene increased the risk of clinically significant disease 7.2-fold in African-American men (95% CI=2.17-27.91; p=0.001) and 3.6-fold in Hispanic men (1.09-12.27; p=0.04). The mutant enzyme had a higher in-vitro Vmax than the normal enzyme (9.9 vs 1.9 nmol min(-1) mg(-1)). INTERPRETATION The A49T variant of the SRD5A2 gene may be a significant contributor to the incidence of prostate cancer in African-American and Hispanic men in Los Angeles. We estimate that the population attributable risk due to this aminoacid substitution for clinically significant disease is about 8% in both populations. Increased conversion of testosterone to dihydrotestosterone catalysed by this variant steroid 5alpha-reductase enzyme may be the cause of the increased risk.

Tagging Single Nucleotide Polymorphisms in Cell Cycle Control Genes and Susceptibility to Invasive Epithelial Ovarian Cancer

High-risk susceptibility genes explain <40% of the excess risk of familial ovarian cancer. Therefore, other ovarian cancer susceptibility genes are likely to exist. We have used a single nucleotide polymorphism (SNP)-tagging approach to evaluate common variants in 13 genes involved in cell cycle control-CCND1, CCND2, CCND3, CCNE1, CDK2, CDK4, CDK6, CDKN1A, CDKN1B, CDKN2A, CDKN2B, CDKN2C, and CDKN2D-and risk of invasive epithelial ovarian cancer. We used a two-stage, multicenter, case-control study. In stage 1, 88 SNPs that tag common variation in these genes were genotyped in three studies from the United Kingdom, United States, and Denmark ( approximately 1,500 cases and 2,500 controls). Genotype frequencies in cases and controls were compared using logistic regression. In stage 2, eight other studies from Australia, Poland, and the United States ( approximately 2,000 cases and approximately 3,200 controls) were genotyped for the five most significant SNPs from stage 1. No SNP was significant in the stage 2 data alone. Using the combined stages 1 and 2 data set, CDKN2A rs3731257 and CDKN1B rs2066827 were associated with disease risk (unadjusted P trend = 0.008 and 0.036, respectively), but these were not significant after adjusting for multiple testing. Carrying the minor allele of these SNPs was found to be associated with reduced risk [OR, 0.91 (0.85-0.98) for rs3731257; and OR, 0.93 (0.87-0.995) for rs2066827]. In conclusion, we have found evidence that a single tagged SNP in both the CDKN2A and CDKN1B genes may be associated with reduced ovarian cancer risk. This study highlights the need for multicenter collaborations for genetic association studies.

Common alleles in candidate susceptibility genes associated with risk and development of epithelial ovarian cancer

Common germline genetic variation in the population is associated with susceptibility to epithelial ovarian cancer. Microcell‐mediated chromosome transfer and expression microarray analysis identified nine genes associated with functional suppression of tumorogenicity in ovarian cancer cell lines; AIFM2, AKTIP, AXIN2, CASP5, FILIP1L, RBBP8, RGC32, RUVBL1 and STAG3. Sixty‐three tagging single nucleotide polymorphisms (tSNPs) in these genes were genotyped in 1,799 invasive ovarian cancer cases and 3,045 controls to look for associations with disease risk. Two SNPs in RUVBL1, rs13063604 and rs7650365, were associated with increased risk of serous ovarian cancer [HetOR = 1.42 (1.15–1.74) and the HomOR = 1.63 (1.10–1.42), p‐trend = 0.0002] and [HetOR = 0.97 (0.80–1.17), HomOR = 0.74 (0.58–0.93), p‐trend = 0.009], respectively. We genotyped rs13063604 and rs7650365 in an additional 4,590 cases and 6,031 controls from ten sites from the United States, Europe and Australia; however, neither SNP was significant in Stage 2. We also evaluated the potential role of tSNPs in these nine genes in ovarian cancer development by testing for allele‐specific loss of heterozygosity (LOH) in 286 primary ovarian tumours. We found frequent LOH for tSNPs in AXIN2, AKTIP and RGC32 (64, 46 and 34%, respectively) and one SNP, rs1637001, in STAG3 showed significant allele‐specific LOH with loss of the common allele in 94% of informative tumours (p = 0.015). Array comparative genomic hybridisation indicated that this nonrandom allelic imbalance was due to amplification of the rare allele. In conclusion, we show evidence for the involvement of a common allele of STAG3 in the development of epithelial ovarian cancer.

The impact of kidney function at highly active antiretroviral therapy initiation on mortality in HIV-infected women.

Background:In the early highly active antiretroviral therapy (HAART) era, kidney dysfunction was strongly associated with death among HIV-infected individuals. We re-examined this association in the later HAART period to determine whether chronic kidney disease remains a predictor of death after HAART initiation. Methods:To evaluate the effect of kidney function at the time of HAART initiation on time to all-cause mortality, we evaluated 1415 HIV-infected women initiating HAART in the Womens Interagency HIV Study. Multivariable proportional hazards models with survival times calculated from HAART initiation to death were constructed; participants were censored at the time of the last available visit or December 31, 2006. Results:Chronic kidney disease (estimated glomerular filtration rate less than 60 mL/min/1.73 m2) at HAART initiation was associated with higher mortality risk adjusting for age, race, hepatitis C serostatus, AIDS history, and CD4+ cell count (hazard ratio 2.23, 95% confidence interval: 1.45-3.43). Adjustment for hypertension and diabetes history attenuated this association (hazard ratio = 1.89, confidence interval: 0.94-3.80). Lower kidney function at HAART initiation was weakly associated with increased mortality risk in women with prior AIDS (hazard ratio = 1.09, confidence interval: 1.00-1.19, per 20% decrease in estimated glomerular filtration rate). Conclusions:Kidney function at HAART initiation remains an independent predictor of death in HIV-infected individuals, especially in those with a history of AIDS. Our study emphasizes the necessity of monitoring kidney function in this population. Additional studies are needed to determine mechanisms underlying the increased mortality risk associated with chronic kidney disease in HIV-infected persons.

No association between the SRD5A2 gene A49T missense variant and prostate cancer risk: lessons learned

The steroid 5-alpha reductase type II gene (SRD5A2) encodes the enzyme which converts testosterone (T) to the more active androgen dihydrotestosterone. A non-synonymous single-nucleotide polymorphism, A49T (rs9282858), in SRD5A2 has been implicated in prostate cancer risk; however, results have been inconsistent. In 1999, we reported a strong association between the A49T variant and prostate cancer risk among African-Americans and Latinos in the Hawaii-Los Angeles Multiethnic Cohort (MEC). We report here an updated analysis of MEC data including the five major ethnic groups of the MEC, an increased sample size, improved genotyping technology and a comprehensive meta-analysis of the published literature. We found a non-statistically significant positive association between prostate cancer risk and carrying either the AT or TT genotype [odds ratio (OR) = 1.16, 95% confidence interval (CI) 0.79-1.69] in the MEC. This finding is in contrast to our previous results of ORs of 3.28 and 2.50 for the association between prostate cancer risk and the variant in African-American and Latino men, respectively; this can be accounted for by genotyping error in our earlier study. Meta-analysis of the published literature, including the current MEC data, shows a summary OR of 1.13 (95% CI 0.95-1.34) for the A49T variant with prostate cancer risk among sporadic, unselected cases. After evaluating more than 6000 cases and 6000 controls, there is little evidence of a role for the SRD5A2 A49T variant in prostate cancer risk. Overall, this report highlights the importance of rigorous genotyping quality control measures and replication efforts in genetic association studies.

The Search for Host Genetic Factors of HIV/AIDS Pathogenesis in the Post-Genome Era: Progress to Date and New Avenues for Discovery

Though pursuit of host genetic factors that influence the pathogenesis of HIV began over two decades ago, progress has been slow. Initial genome-level searches for variations associated with HIV-related traits have yielded interesting candidates, but less in the way of novel pathways to be exploited for therapeutic targets. More recent genome-wide association studies (GWAS) that include different phenotypes, novel designs, and that have examined different population characteristics suggest novel targets and affirm the utility of additional searches. Recent findings from these GWAS are reviewed, new directions for research are identified, and the promise of systems biology to yield novel insights is discussed.

Role of Genetic Polymorphisms in Ovarian Cancer Susceptibility: Development of an International Ovarian Cancer Association Consortium

The value of identifying women with an inherited predisposition to ovarian cancer has become readily apparent with the identification of the BRCA1 and BRCA2 genes. Women who inherit a deleterious mutation in one of these genes have a very high lifetime risk of ovarian cancer (10–60%) and lesser risks of fallopian tube and peritoneal cancer. These highly lethal cancers are almost completely prevented by prophylactic salpingoophorectomy. BRCA1/BRCA2 mutation testing has become the accepted standard of care in families with a strong history of breast and/or ovarian cancer. This approach has the potential to reduce ovarian cancer mortality by about 10%. Although the ability to perform genetic testing for BRCA1 and BRCA2 represents a significant clinical advance, the frequency of mutations in these high penetrance ovarian cancer susceptibility genes in the general population is low (about 1 in 500 individuals). There is evidence to suggest that ovarian cancer susceptibility is affected by low penetrance genetic polymorphisms that are much more common. Although such polymorphisms would increase risk to a lesser degree, they could contribute to the development of many ovarian cancers by virtue of their high frequency in the population. It has been shown that the most powerful approach to studying low penetrance genes is an association study rather than a linkage study (1). Several groups have obtained funding to initiate such studies and these generally have focused on polymorphisms in candidate genes purportedly involved in ovarian biology or carcinogenesis. Over the last decade, initial reports from ovarian cancer association studies have been disappointing. Although numerous positive associations have been reported, in most cases these have not been confirmed by other groups. The accumulated experience to date has served to highlight how difficult it is to conduct statistically and methologically rigorous ovarian cancer association studies. The main issues are summarized below.

Host APOL1 genotype is independently associated with proteinuria in HIV infection

Proteinuria is associated with adverse clinical outcomes in HIV infection. Here we evaluated whether APOL1 risk alleles, previously associated with advanced kidney disease, is independently associated with proteinuria in HIV infection in a cross-sectional study of HIV-infected women in the Women’s Interagency HIV Study. We estimated the percent difference in urine protein excretion and odds of proteinuria (200 mg/g and higher) associated with two versus one or no APOL1 risk allele using linear and logistic regression, respectively. Of 1285 women successfully genotyped, 379 carried one and 80 carried two risk alleles. Proteinuria was present in 124 women; 78 of whom had proteinuria confirmed on a second sample. In women without prior AIDS, two risk alleles were independently associated with a 69% higher urine protein excretion (95% CI: 36%, 108%) and 5-fold higher odds of proteinuria (95% CI: 2.45, 10.37) versus one or no risk allele. No association was found in women with prior AIDS. Analyses in which women with impaired kidney function were excluded and proteinuria was confirmed by a second urine sample yielded similar estimates. Thus, APOL1 risk alleles are associated with significant proteinuria in HIV-infected persons without prior clinical AIDS, independent of clinical factors traditionally associated with proteinuria. Trials are needed to determine whether APOL1 genotyping identifies individuals who could benefit from earlier intervention to prevent overt renal disease.

Body Weight, Menopausal Hormone Therapy, and Risk of Breast Cancer

Publisher Summary Two observations hold the key to understand the relationship of ovarian hormones to breast cancer risk as it applies to the treatment of postmenopausal women. Earlier menopause, whether natural or through bilateral oophorectomy, reduces breast cancer risk. The rate of breast cell proliferation in the luteal phase of the menstrual cycle is about double the rate in the follicular phase, and the rate in the follicular phase is considerably higher than in the postmenopausal period. This chapter uses these two observations to build a basic mathematical model of breast cancer etiology. This model gives an understanding of the quantitative effect of obesity on risk. The epidemiologic data, including that found in the Womens Health Initiative randomized trials on the quantitative effects of menopausal estrogen therapy and menopausal estrogen-progestin therapy on breast cancer risk is summarized. Its integration with the model provides a comprehensive understanding of the effect of estrogen and progestin treatment on breast cancer risk.Publisher Summary Two observations hold the key to understand the relationship of ovarian hormones to breast cancer risk as it applies to the treatment of postmenopausal women. Earlier menopause, whether natural or through bilateral oophorectomy, reduces breast cancer risk. The rate of breast cell proliferation in the luteal phase of the menstrual cycle is about double the rate in the follicular phase, and the rate in the follicular phase is considerably higher than in the postmenopausal period. This chapter uses these two observations to build a basic mathematical model of breast cancer etiology. This model gives an understanding of the quantitative effect of obesity on risk. The epidemiologic data, including that found in the Womens Health Initiative randomized trials on the quantitative effects of menopausal estrogen therapy and menopausal estrogen-progestin therapy on breast cancer risk is summarized. Its integration with the model provides a comprehensive understanding of the effect of estrogen and progestin treatment on breast cancer risk.

Lowering oral contraceptive norethindrone dose increases estrogen and progesterone receptor levels with no reduction in proliferation of breast epithelium: a randomized trial☆☆☆★★★

BACKGROUND This study was conducted to compare breast epithelial-cell proliferation and estrogen and progesterone receptor levels in women taking one of two oral contraceptives (OCs) containing the same dose of estrogen but different doses of the progestin norethindrone (NET). STUDY DESIGN Thirty-three women were randomly assigned 1:1 to one of two OCs with 35-mcg ethinylestradiol (EE2) but different doses of NET - 1 or 0.4 mg. At the end of the active pill phase of the third OC cycle, a breast biopsy was performed and the percentages of epithelial cells of the terminal duct lobular units were measured for Ki67 (MIB1), progesterone receptors A and B (PRA and PRB, respectively), and estrogen receptor α (ERα). RESULTS The biopsies from 27 women had sufficient epithelium for analysis. The percentages of cells positive for PRA, PRB and ERα were approximately double with the lower progestin dose (PRA: p=.041; PRB: p=.030; ERα: p=.056). The Ki67 percentage was not reduced with the lower progestin dose (12.5% for 0.4-mg NET vs. 7.8% for 1.0-mg NET). CONCLUSIONS The increase in PRA-, PRB- and ERα-positive cells with the 60% lower progestin dose OC appears likely to account for its failure to decrease breast-cell proliferation. This breast-cell proliferation result is contrary to that predicted from the results of lowering the medroxyprogesterone acetate dose in menopausal hormone therapy.