Towards Untangling the Ageing Riddle in People with Intellectual Disabilities: An Overview of Research on Frailty and Its Consequences

Josje D. Schoufour, Dederieke Maes-Festen, Alyt Oppewal, and

Heleen M. Evenhuis

Frailty as a Measure of Ageing in the General Population

One of the biggest challenges Western society is currently facing is the shift in age distribution towards older age groups. These trends are accompanied by a greater burden of chronic diseases, social isolation, hospitalisation, disabilities, and healthcare costs. Research is required to better understand the process of ageing and methods to preserve health as long as possible. Several methods have been proposed to study ageing and age-related conditions. One such method is frailty. Frailty is the accumulation ot age-related conditions in many physiological systems that eventually lead to increased vulnerability to adverse health outcomes including tails, disabilities, hospitalisation, and mortality (Clegg, Young, Iliffe, Rikkert, & Rockwood, 2013). Frailty has been shown a very useful concept in research to study ageing and has even been proposed a measure for biological age (Mitnitski et ah, 2015). In the general population, the interest in frailty has led to increased knowledge about the risk factors and consequences of frailty, resulting in a broad range of screening instruments and preventative strategies. For example, an incredible amount of knowledge has been gathered about lifestyle factors that contribute to frailty leading to interventions aiming to prevent or slow onset (Apostolo et ah, 2018; Brinkman et ah, 2018; Tieland, Trouwborst, & Clark, 2018). Furthermore, several screening instruments are being used in among others in hospitals to identify frail older adults (Rocha, Marmelo, Leite-Moreira, & Moreira- Gonfalves, 2017; Theou, Campbell, Malone, & Rockwood, 2018; Walston, Buta, & Xue, 2018).

Frailty can be measured using different operationalisations and methods. The two most frequently used approaches internationally to measure frailty (Bouillon et ah, 2013) are the frailty ‘phenotype’ developed by Fried and colleagues (Fried et ah, 2001), and the frailty index developed by Rockwood and Mitnitski (Mitnitski, Mogilner, & Rockwood, 2001). The frailty phenotype is based on five clinical core features (unintended weight loss, weakness, slowness, low physical activity, and poor endurance or exhaustion). People with at least three of these features are defined as frail, people with one or two are considered pre-frail and people with none are called robust. In contrast, the frailty index is a quantitative measure of frailty, based on non-specific accumulation of health impairments, also called deficits. These deficits can be symptoms, signs, diseases, disabilities, or laboratory data (Mitnitski et ah, 2001; Rockwood, Abeysundera, & Mitnitski, 2007). Although the content of a frailty index is flexible, deficits need to adhere to several rules to be included in it. A deficit can only be included if (1) The deficit can be considered an aspect of health (2) The deficit is associated with age (3) The deficit does not saturate too early or is very rare (4) Together, the deficits must cover different health aspects and (5) At least 20—30 deficits must be included (Middleton, Kirkland, Mitnitski, & Rockwood, 2010; Mitnitski et al., 2001). In addition to these commonly used operationalisations of frailty, many others exist. They differ in content but all aim to identify people at risk for deterioration ot health.

Frailty as a Measure of Ageing in People with Intellectual Disabilities

There is a lack of comprehensive insight into the effect of ageing on health and independence of people with ID (Reppermund & Trollor, 2016). Although premature ageing and its genetic basis have been established in people with Down syndrome (Horvath et al., 2015), there is little evidence indicating a more rapid ageing process in those with other causes of ID. Frailty could be a very useful method to better understand the ageing process of people with ID to understand it they experience premature ageing.

Methods to measure frailty from the general population may not be applied to older adults with ID. Indeed, given the characteristics ot the population of older adults with ID, it could be that when you apply a diagnostic measure developed for the general population, the majority of people with ID would be found frail. In that case, frailty would not appear to be a distinctive concept in this population. Additionally, the relationship between frailty and age-related disability, intensively discussed tor the general older population (Fried, Ferrucci, Darer, Williamson, & Anderson, 2004; Theou, Rockwood, Mitnitski, & Rockwood, 2012), seems even more complicated for a population with lifelong disabilities. Where disabilities are life-long they are more likely to result in frailty than be a result of frailty, as is usually the case in the general population (Abelian van Kan et al., 2008; Fried et al., 2004; Theou et al., 2012).

Although frailty measures from the general population cannot be simply implemented in people with ID, several research groups used the frailty approach to better understand ageing in people with ID. In this chapter we review the approaches that were applied, how the results help to better understand ageing and frailty in this population and discuss future research directions (Figure 24.1). More specifically, within this chapter we will address the following questions:

  • 1. Is it feasible to measure frailty in older adults with ID?
  • 2. How frail are older people with ID compared to older people from the general population?
  • 3. Does frailty predict deterioration of health and (relative) independence in the same way as it does in the general population?
  • 4. Which characteristics are associated with frailty?
  • 5. Which recommendations can be made for future research and clinical practice?
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