Michael Hoffman

Dietary calcium, vitamin D, VDR genotypes and colorectal cancer.

The vitamin D receptor (VDR) may importantly modulate risk of colorectal cancer either independently or in conjunction with calcium and vitamin D intake. We evaluate the association between calcium, vitamin D, dairy products, and VDR polymorphisms in 2 case‐control studies of colon and rectal cancer (n = 2,306 cases and 2,749 controls). Dietary intake was evaluated using a detailed diet history questionnaire. Two VDR polymorphisms were evaluated: an intron 8 Bsm 1 polymorphism and a 3′ untranslated region poly‐A length polymorphism (designated S for short and L for long). The SS genotype reduced risk of colorectal cancer for men (odds ratio [OR] = 0.71; 95% confidence interval [CI] = 0.55–0.92). High levels of calcium intake reduced risk of rectal cancer in women (OR = 0.39; 95% CI = 0.24–0.64) but were not associated with rectal cancer in men (OR = 1.02; 95% CI = 0.66–1.56). Similar reduced rectal cancer risk among women was observed at high levels of vitamin D (OR = 0.52; 95% CI = 0.32–0.85) and low‐fat dairy products (OR = 0.61; 95% CI = 0.39–0.94). High levels of sunshine exposure reduced risk of rectal cancer among those diagnosed when <60 years of age (OR = 0.62, 95% CI = 0.42–0.93). Examination of calcium in conjunction with VDR genotype showed that a significant 40% reduction in risk of rectal cancer was observed for the SS or BB VDR genotypes when calcium intake was low (p interaction = 0.01 for calcium interaction). For colon cancer, high levels of dietary intake of calcium, vitamin D, and low‐fat dairy products reduced risk of cancer for the SS or BB VDR genotypes, although the p for interaction was not statistically significant. These data support previous observations that high levels of calcium and vitamin D reduce risk of rectal cancer and provide support for a weak protective effect for the SS and BB VDR genotypes. The risk associated with VDR genotype seems to depend upon the level of dietary calcium and vitamin D and tumor site.

Sequence Variants in the Sulfonylurea Receptor (SUR) Gene Are Associated With NIDDM in Caucasians

NIDDM is a common heterogeneous disorder, the genetic basis of which has yet to be determined. The sulfonylurea receptor (SUR) gene, now known to encode an integral component of the pancreatic β-cell ATP-sensitive potassium channel, IKATP, was investigated as a logical candidate for this disorder. The two nucleotide-binding fold (NBF) regions of SUR are known to be critical for normal glucose regulation of insulin secretion. Thus, singlestrand conformational polymorphism analysis was used to find sequence changes in the two NBF regions of the SUR gene in 35 NIDDM patients. Eight variants were found; and three were evaluated in two Northern European white populations (Utah and the U.K.): 1) a missense mutation in exon 7 (S1370A) was found with equal frequency in patients (n = 223) and control subjects (n = 322); 2) an ACC→ACṮ silent variant in exon 22 (T761T) was more common in patients than in control subjects (allele frequencies 0.07 vs. 0.02, P = 0.0008, odds ratio (OR) 3.01, 95% CI 1.54–5.87); and 3) an intronic t→c change located at position –3 of the exon 24 splice acceptor site was also more common in patients than in control subjects (0.62 vs. 0.46, P < 0.0001, OR 1.91, 95% Cl 1.50–2.44). The combined genotypes of exon 22 C/T or T/T and intron 24 –3c/–3c occurred in 8.9% of patients and 0.5% of control subjects (P < 0.0001, OR 21.5,95% CI 2.91–159.6). These results suggest that defects at the SUR locus may be a major contributor to the inherited basis of NIDDM in Northern European Caucasians.

Variants of the VDR gene and risk of colon cancer (United States).

Objectives: Genetic factors involved in regulating cell growth, such as the vitamin D receptor (VDR) gene, may contribute to the etiology of colon cancer. Methods: Using data from a population-based case–control study of colon cancer and from a family-based study of cases with colon cancer and population-based controls, we evaluated the association between four variants of the VDR gene and risk of colon cancer. Results: The polyA (short), BsmI (BB), and TaqI (tt) variants of the VDR gene were in linkage disequilibrium in this mostly Caucasian population. These variants were associated with reduced risk of colon cancer (OR 0.5, 95% CI 0.3–0.9). The FokI variant was not associated with colon cancer risk. Although estimates of association were imprecise, there were suggestions that associations were slightly stronger for women than men, for people diagnosed at a younger age, and for those with proximal tumors. Consistent associations were observed from sporadic cases of colon cancer from a population-based study as well as from colon cancer cases from a family-based study. There were no interactions observed by family history. Conclusions: These data suggest that molecular variants of the VDR gene may be related to the development of colon cancer. To further define the impact of the VDR gene on cancer etiology, studies to evaluate the association of these variants with diet and lifestyle factors are needed.

MicroRNAs and Colon and Rectal Cancer: Differential Expression by Tumor Location and Subtype

MicroRNAs are thought to have an impact on cell proliferation, apoptosis, stress responses, maintenance of stem cell potency, and metabolism and are, therefore, important in the carcinogenic process. In this study, we examined 40 colon tumors, 30 rectal tumors, and 30 normal tissue samples (10 proximal colon, 10 distal colon, and 10 rectal paired with cancer cases) to examine miRNA expression profiles in colon and rectal tumors. MiRNA expression levels were adjusted for multiple comparisons; tumor tissue was compared with noncancerous tissue from the same site. A comparison of normal tissue showed 287 unique miRNAs that were significantly differentially expressed at the 1.5‐fold level and 73 with over a two‐fold difference in expression between colon and rectal tissue. Examination of miRNAs that were significantly differentially expressed at the 1.5‐fold level by tumor phenotype showed 143 unique miRNAs differentially expression for microsatellite instability positive (MSI+) colon tumors; 129 unique miRNAs differentially expressed for CpG Island Methylator Phenotype positive (CIMP+) colon tumors; 135 miRNAs were differentially expressed for KRAS2‐mutated colon tumors, and 139 miRNAs were differentially expressed for TP53‐mutated colon tumors. Similar numbers of differentially expressed miRNAs were observed for rectal tumors, although the miRNAs differentially expressed differed. There were 129 unique miRNAs for CIMP+, 143 unique miRNAs for KRAS2‐mutated, and 136 unique miRNAs for TP53‐mutated rectal tumors. These results suggest the importance of miRNAs in colorectal cancer and the need for studies that can confirm these results and provide insight into the diet, lifestyle, and genetic factors that influence miRNA expression.

Characterization of common BRCA1 and BRCA2 variants.

Many missense variants identified in BRCA1 and BRCA2, two genes responsible for the majority of hereditary breast and ovarian cancer, are of unclear clinical significance. Characterizing the significance of such variants is important for medical management of patients in whom they are identified. The aim of this study was to characterize eight of the most common reported missense mutations in BRCA1 and BRCA2 occurring in patients tested for hereditary risk of breast and ovarian cancers. The prevalence of each variant in a control population, co-segregation of the variant with cancer within families, location of the variant within the gene, the nature of the amino acid substitution and conservation of the wild-type amino acid among species were considered. In a control population, the BRCA1 variants M1652I, R1347G, and S1512I, were each observed at a frequency of 4.08%, 2.04%, and 2.04%, respectively, and the BRCA2 variants A2951T, V2728I, and D1420Y, were seen at 1.02%, 0.68%, and 0.34%, respectively. Although the BRCA2 variants T598A and R2034C were not seen in this group of controls, other clinical and published observations indicate that these variants are not deleterious. Based on epidemiological and biological criteria, we therefore conclude that the BRCA1 missense mutations R1347G, S1512I and M1652I, and the BRCA2 missense mutations T598A, D1420Y, R2034C, V2728I, and A2951T, are not deleterious mutations.

Role of CHEK2*1100delC in unselected series of non-BRCA1/2 male breast cancers.

Susan NEUHAUSEN, Alison DUNNING, Linda STEELE, Kazuko YAKUMO, Michael HOFFMAN, Csilla SZABO, Louise TEE, Caroline BAINES, Paul PHAROAH, David GOLDGAR* and Doug EASTON Division of Epidemiology, Department of Medicine, University of California, Irvine, CA, USA Human Cancer Genetics Research Group, Strangeways Research Laboratories, Cambridge, United Kingdom Cancer Research U.K. Genetic Epidemiology Unit, Strangeways Research Laboratories, Cambridge, United Kingdom Department of Family and Preventive Medicine, University of Utah, Salt Lake City, UT, USA International Agency for Research on Cancer, Lyon, France

Recessive Inheritance of Obesity in Familial Non—Insulin-Dependent Diabetes Mellitus, and Lack of Linkage to Nine Candidate Genes

Segregation analysis of body-mass index (BMI) supported recessive inheritance of obesity, in pedigrees ascertained through siblings with non-insulin dependent diabetes mellitus (NIDDM). BMI was estimated as 39 kg/m2 for those subjects homozygous at the inferred locus. Two-locus segregation analysis provided weak support for a second recessive locus, with BMI estimated as 32 kg/m2 for homozygotes. NIDDM prevalence was increased among those subjects presumed to be homozygous at either locus. Using both parametric and nonparametric methods, we found no evidence of linkage of obesity to any of nine candidate genes/regions, including the Prader-Willi chromosomal region (PWS), the human homologue of the mouse agouti gene (ASP), and the genes for leptin (OB), the leptin receptor (OBR/DB), the beta3-adrenergic receptor (ADRB3), lipoprotein lipase (LPL), hepatic lipase (LIPC), glycogen synthase (GYS), and tumor necrosis factor alpha (TNFA).

MicroRNA profiles in colorectal carcinomas, adenomas and normal colonic mucosa: variations in miRNA expression and disease progression

Summary Roughly 27% of miRNAs are commonly expressed in colonic tissue; of these, over 86% are dysregulated between carcinoma and normal tissue when applying a false discovery rate of 0.05. MiRNA expression from normal to adenoma to carcinoma varied by miRNA and its frequency of expression in the population.

Linkage Analysis of 19 Candidate Regions for Insulin Resistance in Familial NIDDM

As part of an ongoing search for diabetes susceptibility loci, we tested linkage with non-insulin-dependent diabetes mellitus (NIDDM) for 19 candidate loci or regions chosen for their potential to affect directly or indirectly the action of insulin. Loci were associated with insulin resistance, known effects on lipid metabolism, or effects on glucose metabolism or insulin action. Loci included the insulin-responsive (GLUT4) glucose transporter, hexokinase 2, glucagon, growth hormone, insulin receptor substrate 1 (IRS1), phosphoenolpyruvate carboxykinase, hepatic and muscle forms of pyruvate kinase, hepatic phosphofructokinase, the apolipoprotein B and the apolipoprotein A2 cluster, lipoprotein lipase, hepatic triglyceride lipase, the very-low-density-lipoprotein receptor, and the Pima insulin resistance locus on chromosome 4. For several candidates, no specific informative marker was available; consequently, we tested the surrounding region with highly informative markers. These regions included the diabetes-associated ras-like gene, rad, and the cholesterol ester–transfer gene, both mapped to chromosome 16. Additionally, we tested for linkage with markers at the tumor necrosis factor–α gene and the Friedreichs ataxia region. All regions were tested for linkage with microsatellite polymorphisms in >450 individuals from a minimum of 16 Caucasian families under parametric (LINKAGE 5.1) and nonparametric (affected pedigree member) models. On initial analysis, each region was rejected as a major diabetogenic locus under parametric models (logarithm of odds [LOD] <− 2) and nonparametric analyses, except growth hormone (LOD = 1.42; P < 0.005, nonparametric analysis) and IRS1 (P < 0.001, nonparametric analysis). Linkage of IRS1 and NIDDM was no longer significant when additional families were tested, and linkage of growth hormone under parametric analysis could likewise be rejected. However, under nonparametric, model-independent analysis, linkage to the growth hormone region remained suggestive. Additionally, possible evidence for linkage (P < 0.05) was found under nonparametric models for apolipoprotein A2 in an expanded sample of 29 families. We excluded multiple candidates as major diabetogenic loci, including fatty acid binding protein 2, IRS1, the insulin-responsive glucose transporter, and rad. However, the region around the growth hormone locus on chromosome 17 warrants further analysis in other populations.

The Genetics of NIDDM: An update

N on-insulin-dependent diabetes mellitus (NIDDM) is widely acknowledged as a genetic disease, although the mode of inheritance, degree of heterogeneity, and number of loci involved are all uncertain. A number of recent studies have addressed the role in NIDDM susceptibility of genes that encode proteins in the pathways of either insulin secretion or insulin-mediated glucose uptake into nonoxidative pathways. Defects have been identified that clearly alter the function of the insulin receptor gene and the glucokinase gene, but neither locus appears to be an important cause of common NIDDM. A single mutation in mitochondrial DNA also marks a relatively distinct but unusual form of maternally transmitted insulin-deficient diabetes. Although amino acid alterations or promoter region variants have been identified at several other loci, including the insulin and insulin-receptor substrate-1 (IRS-1) genes, the role of these variants is uncertain. None of the defects identified to date is likely to explain a significant proportion of susceptibility to typical NIDDM. However, the tools now exist to use the human gene map to search for diabetes susceptibility loci other than known (candidate) genes. Alternatively, both known genes and map loci may be tested for linkage to quantitative markers of diabetes susceptibility, such as diminished insulin sensitivity. Initial successes with the former approach (positional search) in maturity-onset diabetes of the young (MODY) and with mapping insulin sensitivity as a quantitative trait in Pima Indians promise to reveal new genes that are important to carbohydrate metabolism. These methods, combined with new patient resources, may identify major determinants of genetic susceptibility to NIDDM in the future. The genetic approach may ultimately lead to major advances in our understanding of NIDDM pathophysiology and to new therapeutic maneuvers that will prevent the phenotypic expression of a susceptible genotype.