The Test for Severe Impairment

It is expected that the number of people with dementia will reach 66 million by 2030 and 115 million by 2050 [1]. It has also been noted that the number of cases of early onset dementia and young onset dementia (under 65 and under 45 respectively), while still infrequent are rising [2]. Overall prevalence rates of 5–7% have been reported in those over 60 [3] with prevalence rates of 2–10% for those under 65 years reported [1]. As has been widely reported, these figures are starkly different to those seen in a population of people with intellectual disabilities (ID), and in particular for those with Down syndrome (DS). Individuals with DS have a third copy of chromosome 21, trisomy 21, and this leads to 4–5 time the expression of amyloid precursor protein (APP) [4]. This overexpression of APP leads to increased amyloid deposition in the brain. This in turn leads to an increase in amyloid B deposition [5], where Amyloid B is known as a key contributor to Alzheimer’s disease (AD). A number of positron emission tomography (PET) studies have shown abnormal amyloid binding in individuals with DS [6] with abnormal binding found in those as young as 39 [7]. Thus, while these studies have shown neuropathological hallmarks prior to the fourth decade, the average age of clinical diagnosis has been found to be between 51 and 56, with an average duration of 3.5–6 years [8–10].