Telomere length measurement in UK Biobank: advancing understanding of biological ageing and age-related diseases

Why do some individuals develop age-associated diseases such as coronary artery disease (CAD) early while others go through their entire life without being affected? The answer to this question is profoundly important for both understanding these diseases as well as healthy ageing. Because of their age-association, we have proposed that these diseases, at least to some extent, are manifestations of accelerated biological (as distinct from chronological) ageing. In this project, we will investigate this hypothesis by measuring a marker of biological ageing called telomere length (TL). Telomeres are structures that cap our chromosomes at each end. People are born with telomeres of different lengths and as cells divide a small amount of telomere is lost each time. Furthermore, the amount lost is known to be increased by some of the same factors that influence the risk of some age-related diseases. Importantly, cells "sense" their TL and become senescent and subsequently die when TL reaches a critically short value. Thus, TL acts as a biological clock that determines cell behaviour and lifespan. Translating this to a whole person, those born with shorter telomeres or whose telomeres attrition faster may "biologically" age more quickly than others. In turn, this could explain why some people develop specific age-associated diseases at an earlier age while others can remain healthy to an advanced age despite similar life exposures. In support of our hypothesis, in previous work we and others have shown an association between shorter mean TL in DNA from blood cells (leucocytes) (LTL) and risk of several chronic diseases, including CAD. Other studies have shown correlations between LTL and diet, life-style characteristics and disease risk factors such as obesity and smoking. However, many of the findings require further definitive evidence especially of a prospective nature i.e. whether variation in LTL predicts future occurrence of age-related disease. UK Biobank provides an ideal cohort to undertake such research. It comprises 500,000 participants, aged 45-69 years at enrolment, recruited UK-wide. A vast amount of information has been collected on each participant including data on diet, lifestyle, behaviour and risk factors and on existing diseases. By linkage to a variety of health-related records, information is also being collected on new diseases as they occur. Each participant is having their DNA typed using a genome-wide array. Using a method that we have optimised to achieve high throughput, we propose to measure LTL of all 500,000 UK Biobank participants. Standardised measurement of LTL in all participants in one go will enable a wide-range of hypotheses to be explored and provide a long-term enhancement of UK Biobank whose value will only increase with time as more disease outcomes accrue. Furthermore, we will be taking advantage of a one-off opportunity that has presented itself from an ongoing genotyping project in UK Biobank. By using the residual DNA samples left over from this project to measure LTL, we will avoid the substantial costs of further DNA extraction, quantification and arraying that would otherwise be required. Using the data we will: (i) Identify personal, environmental and life-style factors that correlate with LTL, which may be determinants of LTL. (ii) Characterise associations of LTL with cardiovascular traits/risk factors as well as with selected cardiovascular disease outcomes that occur after enrolment into the study. (iii) Test whether LTL is likely to be a causative factor in cardiovascular diseases using genetic methods, which, if positive, would support the biological ageing hypothesis and potentially open up new strategies for prevention and treatment. (iv) Make the data widely available to enable other researchers to test the association of LTL with other age-associated diseases, such as dementia and cancers, and with the likelihood of healthy ageing and longevity.