Omer T. Njajou

A mutation in SLC11A3 is associated with autosomal dominant hemochromatosis

Hereditary hemochromatosis (HH) is a very common disorder characterized by iron overload and multi-organ damage. Several genes involved in iron metabolism have been implicated in the pathology of HH (refs. 1–4). We report that a mutation in the gene encoding Solute Carrier family 11, member A3 (SLC11A3), also known as ferroportin, is associated with autosomal dominant hemochromatosis.

Telomere length is paternally inherited and is associated with parental lifespan.

Telomere length (TL) is emerging as a biomarker for aging and survival. To evaluate factors influencing this trait, we measured TL in a large homogeneous population, estimated the heritability (h2), and tested for parental effects on TL variation. Our sample included 356 men and 551 women, aged 18–92 years, from large Amish families. Mean TL in leukocytes was measured by quantitative PCR (mean: 6,198 ± 1,696 bp). The h2 of TL was 0.44 ± 0.06 (P < 0.001), after adjusting for age, sex, and TL assay batch. As expected, TL was negatively correlated with age (r = −0.40; P < 0.001). There was no significant difference in TL between men and women, consistent with our previous findings that Amish men lived as long as Amish women. There was a stronger and positive correlation and association between TL in the offspring and paternal TL (r = 0.46, P < 0.001; β = 0.22, P = 0.006) than offspring and maternal TL (r = 0.18, P = 0.04; β = −0.02, P = 0.4). Furthermore, we observed a positive correlation and association between daughters TL and paternal lifespan (r = 0.20, P < 0.001; β = 0.21, P = 0.04), but not between daughters TL and maternal lifespan (r = −0.01, β = 0.04; both P = not significant). Our data, which are based on one of the largest family studies of human TL, support a link between TL and aging and lifespan and suggest a strong genetic influence, possibly via an imprinting mechanism, on TL regulation.

Association Between Telomere Length, Specific Causes of Death, and Years of Healthy Life in Health, Aging, and Body Composition, a Population-Based Cohort Study

Although telomere length (TL) is known to play a critical role in cellular senescence, the relationship of TL to aging and longevity in humans is not well understood. In a large biracial population-based cohort, we tested the hypotheses that elderly persons with shorter TL in peripheral white blood cells have poorer survival, shorter life span, and fewer years of healthy life (YHL). Associations were evaluated using Cox proportional hazard models and linear regression analyses where appropriate. TL (in kilo base pairs) was not associated with overall survival (hazard ratio 1.0; 95% confidence interval 0.9-1.1) or death from any specific underlying cause including infectious diseases, cancer, or cardiac and cerebrovascular diseases. TL, however, was positively associated with more YHL (beta = 0.08 +/- 0.04, p = .03). Findings suggest that TL may not be a strong biomarker of survival in older individuals, but it may be an informative biomarker of healthy aging.

Association between oxidized LDL, obesity and type 2 diabetes in a population-based cohort, the Health Aging and Body Composition study

Accumulating evidence suggests a cross‐sectional association between oxidative stress and type 2 diabetes (T2D). Systemic oxidative stress, as measured by oxidized LDL (oxLDL), has been correlated with visceral fat. We examined the relationship between oxLDL, and T2D‐ and obesity‐related traits in a bi‐racial sample of 2985 subjects at baseline and after 7 years of follow‐up.

Mutations in the hemochromatosis gene (HFE), Parkinson's disease and parkinsonism.

Iron overload increases oxidative stress and may lead to neurodegenerative disease like Parkinsons disease (PD). We studied the role of mutations in the hemochromatosis gene HFE in PD and other parkinsonism (non-PD PS) in two population-based series. The first series consisted of 137 patients with PD and 47 with non-PD PS, and the second of 60 patients with PD and 25 with non-PD PS. In the first series, PD patients were significantly more often homozygous for the C282Y mutation than controls (P=0.03). Patients with non-PD PS in both series were more often carriers for the C282Y mutation than controls (P=0.009, P=0.006, respectively). Our data are hampered by small numbers, yet suggest that the C282Y mutation increases the risk of PD and non-PD PS. The rarity of this genotype requires a large series of patients to prove our hypothesis.

Shorter telomeres are associated with obesity and weight gain in the elderly

Objective:Obesity and shorter telomeres are commonly associated with elevated risk for age-related diseases and mortality. Whether telomere length (TL) may be associated with obesity or variations in adiposity is not well established. Therefore, we set out to test the hypothesis that TL may be a risk factor for increased adiposity using data from a large population-based cohort study.Design:Levels of adiposity were assessed in six ways (obesity status, body mass index (BMI), the percentage of body fat or % body fat, leptin, visceral and subcutaneous fat mass) in 2721 elderly subjects (42% black and 58% white). Associations between TL measured in leukocytes at baseline and adiposity traits measured at baseline, and three of these traits after 7 years of follow-up were tested using regression models adjusting for important covariates. Additionally, we look at weight changes and relative changes in BMI and % body fat between baseline and follow-up.Results:At baseline, TL was negatively associated with % body fat (ß=−0.35±0.09, P=0.001) and subcutaneous fat (ß=−2.66±1.07, P=0.01), and positively associated with leptin after adjusting for % body fat (ß=0.32±0.14, P=0.001), but not with obesity, BMI or visceral fat. Prospective analyses showed that longer TL was associated with positive percent change between baseline and 7-year follow-up for both BMI (ß=0.48±0.20, P=0.01) and % body fat (ß=0.42±0.23, P=0.05).Conclusion:Our study suggests that shorter TL may be a risk factor for increased adiposity. Coupling with previous reports on their reversed roles, the relationship between adiposity and TL may be complicated and may warrant more prospective studies.

Angiotensin-Converting Enzyme Gene Insertion/Deletion Polymorphism and Breast Cancer Risk

Background: The renin-angiotensin system plays an important role in homeostasis and lately, its main effector, angiotensin II, has been attributed with angiogenic and growth factor actions in the breast tissue. Previous studies have shown that the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene accounts for the variability of ACE plasma concentrations. The use of ACE inhibitors and the ACE I/D polymorphism may be linked to breast cancer risk. In this study, we evaluate the relationship of the ACE I/D polymorphism with breast cancer risk in Caucasian postmenopausal women. Methods: The ACE I/D polymorphism was genotyped in 4,117 women participants in the Rotterdam Study. Baseline information was obtained through a questionnaire. We conducted a logistic regression and survival analysis to assess the risk of breast cancer by the ACE genotype. Results: The DD carriers showed a significantly increased risk of developing breast cancer when compared with the II carriers (odds ratio, 1.86; 95% confidence interval, 1.06-3.27; P = 0.03). This association remained after adjusting for other risk factors, including body mass index, age at menarche, age at menopause, hormone replacement therapy, and hypertension. Our survival analysis showed that the cancer-free survival was significantly reduced in DD compared with II carriers (hazard ratio, 1.80; 95% confidence interval, 1.07-3.01; P = 0.03). Conclusions: Our results suggest that the ACE I/D polymorphism plays an important role in breast cancer risk and disease-free survival in Caucasian postmenopausal women.

A population-based study of the effect of the HFE C282Y and H63D mutations on iron metabolism

The C282Y and H63D mutations in the HFE gene are important causes of hemochromatosis. In the elderly, these mutations might be associated with increased morbidity because of the lifelong accumulation of iron. In a population-based sample of the elderly, we determined the value of genotyping for HFE mutations to screen for subclinical hemochromatosis. HFE genotype frequencies were determined in a random group of 2095 subjects (55 years and over). In this random group, we selected within the six genotype groups a total of 342 individuals and measured their serum transferrin saturation, iron and ferritin levels. We also estimated the heritability and parameters needed to evaluate screening, including the sensitivity, specificity, positive and negative predictive values (PPV, NPV) of HFE genotypes. Iron parameters were significantly increased in subjects homozygous, heterozygous or compound heterozygous. The effect of the mutations was more pronounced in men than in women. For the H63D mutation, an allele dose effect was observed. The HFE gene explained about 5% of the variability in serum iron indices. The PPV for hemochromatosis for the C282Y homozygous was 100% in men and 67% in women. The NPV of the wild-type allele was 97% for both men and women. The sensitivity of both mutations was 70% for men and 52% for women and the specificity was 62% for men and 64% for women. Our study shows that the HFE C282Y and H63D are determinants of iron parameters in the elderly and will be effective in detecting individuals at high risk of hemochromatosis. However, when screening based on these two mutations, some individuals with subclinical hemochromatosis will be missed.

Heritability of Serum Iron, Ferritin and Transferrin Saturation in a Genetically Isolated Population, the Erasmus Rucphen Family (ERF) Study

Background: Iron has been implicated in the pathogenesis of various disorders. Mutations in the HFE gene are associated with an increase in serum iron parameters. The aim of this study was to estimate the heritability in serum iron parameters explained by HFE. Methods: Ninety families (980 subjects) were included in the present analysis. Heritability estimation was conducted using the variance component method. The likelihood ratio test was used to compare models. Phenotypic and genetic correlations between serum iron parameters were calculated. Results: The heritability (h2 ± SE) estimates were 0.23 ± 0.07 (p < 0.0001) for iron, 0.29 ± 0.09 (p < 0.0001) for ferritin and 0.28 ± 0.07 (p < 0.0001) for transferrin saturation while adjusting for age, age2 and sex. The HFE genotypes explained between 2 to 6% of the sex and age-adjusted variance in serum iron, ferritin and transferrin saturation. There was a high genetic correlation between serum iron parameters, suggesting pleiotropy between these traits. Conclusion: A substantial proportion of the variance of iron, ferritin and transferrin saturation can be explained by additive genetic effects, independent of sex and age. The HFE genotypes explained a considerable proportion of serum iron parameters and may be an important factor in the complex iron network.

Mutations in the Hemochromatosis Gene (HFE) and Stroke

Background and Purpose— Increased serum iron is found to be a risk factor for stroke. Carriers of HFE C282Y and H63D mutations have elevated serum iron levels and may have an increased risk for stroke. We studied the association between HFE gene mutations, carotid atherosclerosis, and stroke. Methods— We compared the frequency of the HFE C282Y and H63D gene mutations in 202 prevalent and incident cases of stroke with that of 2730 controls from a population-based study, the Rotterdam Study. The influence of HFE mutations on the relationship between hypertension, smoking, and stroke was studied by use of a logistic regression model. In the analyses of hypertension, we used noncarriers and nonhypertensives as reference; in the analysis of smoking, we used noncarriers and those who never smoked as the reference group. Furthermore, we studied the mean intima-media thickness of the common carotid artery in relation to hypertension, smoking, and the HFE genotype in subjects without stroke. Results— The percentage of both C282Y and H63D carriers in cases (43.7%, n=87) did not differ significantly (P =0.09) from that of controls (37.6%, n=986). The odds ratio for stroke for HFE carriers who also suffered from hypertension was 3.0 (95% CI, 1.9 to 4.6), and for HFE carriers who were also smokers, the odds ratio for stroke was 2.6 (95% CI, 1.4 to 5.0). The mean±SD intima-media thickness of the carotid artery was 0.77±0.14 mm for noncarriers without a history of hypertension or smoking compared with 0.81±0.17 mm for HFE carriers who smoked (P <0.004) and 0.84±0.20 mm for HFE carriers who were hypertensive (P <0.001). Conclusions— Mutations in the HFE gene were not significantly related to stroke or atherosclerosis in the carotid artery. The HFE gene may modify the relationship between smoking and stroke.