Cindy Boer

The Gut Microbiome of Childen and Adults | 205 5.1 Introduction The human gut microbiome is dynamic, shaped by multiple factors and has been shown to play an important role in human health. Several studies have reported an association between alterations in the composition of the gut microbiome and various gastrointes- tinal (GI)[1-9] and non-GI[10-15] disease conditions in both children and adults. These changes in composition of the microbiome (known as dysbiosis) and their associations with health and disease have led to an increased interest in the complex microbial com- munity of the gut[16,17]. However, our understanding of the relationship between the gut microbiome and health and disease still remains superficial at best. A fundamental issue hampering progress in this respect is that our lack of knowledge on the compo- sition and variation of the gut microbiome across the human lifespan remains limit- ed. So far, most microbiome studies have been relatively small in terms of sample size and have usually focused on specific diseases and phenotypes, with most publications having used a case-control study design, what makes the analyses more vulnerable to methodological challenges. A better understanding of the variation in microbiome com- position (from stool or other sources) and its role in the aetiology of chronic diseases can be achieved through the study of large and well-characterized population-based cohorts, which generate rich information on many different physiological parameters, disease status, medication use, dietary intake, and other layers of “omics” data from individual participants. Up to now, microbiome studies have focused mainly on adult populations, whereas it has been shown that the intestinal microbiome undergoes dynamic chang- es in diversity and composition during the human lifespan and particularly during development; with the most substantial changes believed to occur throughout child- hood[18-20]. Interestingly, emerging data suggest that early alterations in the gut mi- crobiome are associated with an increased risk of developing diseases later in child- hood and adulthood e.g., asthma[21,22] and Crohn’s disease[23]. These studies were, however, limited by low sample sizes. If the field of microbiota dynamics is to move for- ward, it requires studies in well-characterized general population cohorts of different ages, including studies investigating paediatric cohorts. So far, a complete description of diversity, compositional and functional differences between children and adults in a large, homogeneous and population-based cohorts have not been reported. The above-mentioned considerations prompted us to profile the stool microbi- ome composition of children and adults within two large, independent and extensively characterized population-based cohorts: the Generation R Study (GenR, visit at 9 years) and the Rotterdam Study (RS, sub-cohort RSIII-2). In this publication, we report our