by Jos Van der Poel
Down’s syndrome is a genetic disorder (in stead of two these persons have three chromosomes 21) that besides a number of physical characteristics leads to intellectual impairment.
It occurs in one out of every 1.000 births. Life expectancy of people with Down’s syndrome has increased substantially over the last century: about 50 % of them will reach the age of 60. Because of the trisomie 21 people with Down’s syndrome have an overexpression of the amyloid precursor protein. Amyloid is the main ingredient of the plaques, which are found in the brains of people with Alzheimer’s disease.
Symptoms and course
Not all persons with Down’s syndrome show evidence of cognitive deterioration or other clinical evidence of dementia even after extended periods of observation.
Clinical symptoms at first are increasing depression, indifference and a decline in social communication. Later symptoms are: seizures in previously unaffected persons, changes in personality, loss of memory and general functions, long periods of inactivity or apathy, hyperactive reflexes, loss of activity of daily skills, visual retention deficits, loss of speech, disorientation, increase in stereotyped behaviour and abnormal neurological signs.
Average age of onset is 54 years and average interval from diagnosis to death is less than 5 years.
Especially for brothers and sisters who are confronted with the responsibility for (the care of) their sibling with Down’s syndrome when their parents have died. It is distressing when this person develops Alzheimer’s disease at a relatively young age. Not only are they loosing the person they (often) love very much, but the burden of care gets heavier.
Causes and risk factors
In Down’s syndrome the development of Alzheimer’s disease seems to be linked directly to the overexposure to APP. The ApoE2 gene seems to have a protective effect in Down’s syndrome too, but whether ApoE4 increases the risk of Alzheimer’s disease in Down’s syndrome is not clear yet. Men and women seem to be equally susceptible.
Down’s syndrome originates in an extra copy of chromosome 21.
At least 36 % of the people with Down’s syndrome aged 50 – 59 years and 65 % aged 60 and older are affected by dementia. Brain changes associated with Alzheimer’s disease are found in 96 % of all adults with Down’s syndrome.
Diagnosing dementia in people with Down’s syndrome is very difficult, as the dementia symptoms are often masked by the existing intellectual impairment. Several screening and evaluation procedures have been developed. These evaluations must be performed at select intervals, thus comparing with the person’s previous score. Definitive diagnosis is only available after death.
Care and treatment
Because of limited personel in small scale living settings for people with an intellectual impairment, persons with dementia often have to move (back) to an institution for mentally retarded people. Research has shown that donepezil (Aricept®) has a positive though not significant effect.
Ongoing research/Clinical trials
Erasmus University Rotterdam (Evenhuis HM)
- Beer EFG de; De effecten van donepezil bij Downsyndroom; Down + Up 2003; 62
- Lott IT, Head E; Down syndrome and Alzheimer’s disease: a link between development and aging; Ment Ret Dev Dis 2001; 7
- Visser FE; Down en Alzheimer in perspectief; dissertation 1996
- Down’s Syndrome and Alzheimer’s Disease; Briefing North West Training & Development Team (1995)
- Dementia an Intellectual Disabilities; Fact sheet Alzheimer’s Disease International (s.a.)
Last Updated: Friday 09 October 2009