The epidemiology of mental retardation: Challenges and opportunities in the new millennium

Abstract

There are a number of problems and challenges in relating the science of epidemiology to mental retardation (MR). These relate to how MR is defined and classified and how these definitions may change over time. These as well as other differences in ascertainment sources and methods need to be considered when comparing MR prevalence over time and place. On the other hand, advances in technology also provide new and efficient methods of data collection both by data linkage and by use of web-based methods to study rare diseases. While prevalence studies have not been individually reviewed, we have examined the range of data including recent studies relating to how prevalence differs according to age, gender, social class and ethnicity. Some problems with available etiological classification systems have been identified. Recent etiological studies, most of which use different classification systems, have been reviewed and explanations have been postulated to account for differences in results. Individual risk factors for MR are considered whilst the option of considering a population as opposed to a high risk strategy to MR prevention is raised. This might well involve improving the social milieu surrounding the occurrence of individual risk factors. The impact of biotechnological advances such as antenatal and neonatal screening and assisted reproduction on MR are discussed. The issue of how inequalities in access to technology may impact on case identification and even have the potential to further widen inequalities is raised. The importance of extending the use of epidemiological tools to study the social, health and economic burden of MR is also emphasized. However, in order to apply to MR the "prevention-intervention-research" cycle, which surely underpins all epidemiology, it is vital to ensure that the methodological challenges we raise are adequately addressed.

Genetic and clinical specificity of 26 symptomatic carriers for dystrophinopathies at pediatric age

“…The prevalence of intellectual disability is estimated at B2-3% in the general population and males are more often affected than females. 31 Considering a prevalence of 3%, which is likely to be an overestimation in female population, we found a significantly higher proportion of carriers with cognitive impairment in our series versus in the general population (P ¼ 0.002).…”

The Prevalence and Incidence of Mental Ill-Health in Adults with Autism and Intellectual Disabilities

“…This population ascertainment therefore differs from "administratively" defined populations, as it was through general practitioners/family physicians, not just services provided for persons with intellectual disabilities. Reviewing the existing literature reveals that there are many contributing factors that make the prevalence of intellectual disabilities amongst the adult population far from clear, with it additionally varying with time, country and region, age group, socio-economic factors, and the definition of intellectual disabilities used (Leonard and Wen, 2002),. The population rate of 0.33 per 1,000 is in keeping with other recent population ascertainments/estimates in Europe (Farmer et al 1993;McGrother et al, 2001;van Schrojenstein Lantman-de Valk HM et al, 2006;Wullink, Van Schrojenstein Lantman de-Valk, Dinant, & Metsemakers, 2007), and is lower than that found amongst children and young persons because of the short life expectancy of persons with intellectual disabilities, combined with their gradual skill development as described above.…”

Excess of runs of homozygosity is associated with severe cognitive impairment in intellectual disability

“…1 The genetic causes of ID have been largely investigated in the past decades, but because of a male prevalence of ID, research was mainly focused on X-linked forms until recently. Molecular karyotyping is the most common technique used today in ID investigation, and gross chromosomal abnormalities explain up to 15% of the cases.…”