Amyloid pathology in the diagnosis and treatment of cognitive decline and dementia in patients with Down syndrome.

Down syndrome (DS) is the most frequent cause of mental retardation and occurs
in about 1 out of 1000 newborns. Due to improved medical care the
life-expectancy of persons with DS has dramatically increased. Currently about
half of all DS patients reaches the age of 60 years or over. Consequently,
these patients are also being confronted with the consequences of ageing.
Especially among DS patients one of the first manifestations of ageing is
cognitive decline, ultimately resulting in dementia, most frequently of the
Alzheimer*s disease type (AD). The overall prevalence of AD among DS patients
is about 15%, while this is about 80% among those between 60-70 years. (the AD
prevalence within this age-stratum is about 5% among patients without DS). The
high prevalence makes dementia the most important risk factor for morbidity and
mortality among DS patients.
The most common explanation for this observation is a gradual increase in the
number of amyloid plaques in the brain because the amyloid encoding gene, the
APP gene, is on the in DS triplicated chromosome 21.
However, not every DS patient becomes demented, however until now it is not
possible to predict who will become demented or who will not. Getting to know
this may be very relevant since early intervention by for example cognitive
training in the progression from cognitive decline towards dementia may be
possible and postpone cognitive decline.
Two important predictive factors for the development of dementia have emerged
from the literature namely amyloid metabolites and certain genotypes. It is now
possible to measure the degree of *amyloid pathology* in plasma by the
determination of the amyloid fragments Abeta1-40 en 1-42. A possible genetic
factor that increases the susceptibility for AD could be the presence of an
APOE4 allele. It has never investigated whether these factors also play a role
in the prediction of AD in patients with DS. If so, than early determination of
these factors could aid in the prediction of AD in patients with DS, still
without cognitive deterioration.
It is not known how these factors may relate to dementia in patients with Down
syndrome, but the occurrence of brain changes seem a plausible explanation.
However to date, the radiological substrate of dementia in DS patients is
unknown, while it has been characterized in great detail for AD patients
(including hippocampal and cortical atrophy). Detailed knowledge on underlying
radiological mechanisms on the structural changes involved in dementia in DS
patients may provide a better insight on those DS who may develop DS or who
will not.

To investigate the relation between the amyloid metabolism (as measured by
plasma Abeta1-40 en 1-42) and the incidence of dementia in DS patients and the
investigate whether there is interaction with vascular or genetic factors with
respect to this relation.
Secondly, we want to investigate whether the underlying radiological substrate
of dementia among DS patients.

longitudinal cohort study.

To the best of our knowledge the burden and risks associated with participation
is limited as all questionnaires and additional investigations used are used on
a routine basis, also in patients with Down syndrome and outweighs the expected
benefits of a better understanding of the etiology of cognitive decline in Down
patients and possible treatment options this may have. As the objective of the
study specifically addresses a research question within the "Down research
field" this question can only be addressed by asking for the participation of
patients with Down syndrome.
Due to the expertise of specialized physicians within the field of mentally
retarded people and people who guide the participants on a daily basis we will
immediately be notified when a participants does not want to continue with the
study.

The actual burden consists of some questionnaires, 1 time a blood withdrawal,
routine physical examination and a MRI scan. These are routine investigations.