The Genetics of Adipose Tissue Function and Its Link to Type 2 Diabetes and Heart Disease

Overview

Obesity is a major risk factor for Type 2 diabetes. However, two obese people of the same height and weight can have very different risks of the condition. As a greater proportion of the population is becoming obese, scientists need to understand more about why some people develop Type 2 diabetes at lower weight and why some people stay healthy despite being obese. The investigators and others provided evidence for genetic factors associated with higher weight for a given height but lower risk of diabetes, lower cholesterol and fat levels, lower blood pressure and lower risk of heart disease. The investigators showed that people who carry these genetic factors are able to store extra fat in a safe place, which is under the skin, as they gain weight. The proposed project aims to establish whether or not these genetic factors are associated with better development and function of fat tissue in storing extra fat. It is thought that a healthy and functional fat tissue in the human body has a key role in modifying the risk of diseases such as Type 2 diabetes, heart disease and hypertension. Volunteers from Exeter 10,000 who gave their permission to contact them about further research will be recruited to the study. In those that agree, detailed body size measures, including body composition assessments by the BodPodTM machine will be recorded, a blood sample will be collected, and a small subcutaneous abdominal fat biopsy will be collected to measure fat cell size and from which a sample will be stored for future analyses. The results between people with and without the particular genetic changes of interest will be compared. Knowing more about these genetic changes and how fat cells work could help to improve understanding of the factors that predispose, delay or protect obese individuals from Type 2 diabetes and other metabolic disturbances.

Introduction: Diabetes is the most common chronic metabolic disease and is a major source of morbidity and mortality. It is one of the biggest healthcare challenges facing the United Kingdom's (UK) National Health Service (NHS) with more than 2.6 million adults diagnosed in the UK, with the vast majority (90%) having Type 2 diabetes (T2D). It is anticipated that the numbers will continue to rise, in part due to the increasing levels of obesity in the population. Type 2 diabetes is characterised by high blood glucose levels in the context of increasing insulin resistance and reduced beta cell function, and this can develop over several years with individuals unaware of the problem. Research groups in Exeter are leading efforts to identify the genetic factors that influence why some people develop Type 2 diabetes despite relative leanness, whilst many obese people do not get the disease. The investigators have identified many such factors but now wish to study them in more detail to understand the role of a healthy and functioning adipose tissue in the disease mechanism. This study builds on a previous 'recruit by genotype' study to explore the size of fat cells in people carrying the most genetic factors for being fatter but healthier (fATDIVA (for Adipose Tissue DIabetes VAriants) NCT02505321). The investigators will expand on the range of genetic variations to be undertaken in the research volunteers. The preliminary data from fATDIVA helped to secure prestigious funding from Diabetes UK to expand this work to improve understanding of the complex processes that lead to Type 2 diabetes. The investigators are trying to understand how genetic variations cause differences in the human ability to store fat. The hypothesis to be tested is that individuals carrying different genetic variations have different abilities to store fat under the skin as subcutaneous fat tissue. This could lead to an improved understanding of subcutaneous fat storage. It is very unlikely that scientists will be able to reverse substantially the rising numbers of people becoming overweight or obese as they age, therefore this study's findings could be important in identifying how to reduce the risk of disease caused by obesity. Study Design: This is a prospective observational study that will take place over a 30 month period (March 2019 to August 2021). Study participants: All participants will be identified from existing research cohorts managed by the National Institute for Health Research (NIHR) Exeter Clinical Research Facility (Exeter CRF) and recruitment will be facilitated within the Exeter CRF. Under over-arching ethical approval 09/H0106/75, approximately 8900 anonymised DNA samples have whole genome genotype data. Subject Selection: The researchers will provide the Exeter Clinical Research Facility (Exeter CRF) with a list of the sample numbers that fulfil the inclusion criteria. The Exeter CRF will approach these individuals on the researcher's behalf to ask if they would be willing to provide body fat measures, a blood sample and an abdominal fat biopsy. Participants would be invited to a single visit lasting up to 2 hours at the Exeter CRF for data and sample collection. Interested participants will then be contacted directly by a member of the study team who will be responsible for the recruitment process, providing more detailed verbal and written project-specific information. The investigators will aim to target men only to increase power for two reasons. First, men and women have different body shape and different fat distribution. Men tend to store the extra fat in abdominal subcutaneous adipose tissue while women tend to store it in the lower body. Second, the study of fat biopsy samples in women could be affected by menopause which could cause bias in the data. However, as the target sample size is 500 and the number of men who fulfil the inclusion criteria is approximately 3000, this will be reviewed after a year. If projections indicate that the target sample size will not be met, women will also be recruited in the second year.