Dementia is characterized by an insidious and progressive loss of memory, disorientation,
cognitive decline, and affective flattening.
Accompanied by neuropsychological deficits such as aphasia, apraxia, agnosia or
disturbances in executive functioning.
Behavioural symptoms such as withdrawl, depression, delusions, motor restlessness,
wandering or aggression may complicate dementia, particularly in the advanced stages of the
A person who has impaired ability to retrieve past interactions from autobiographical memory
may repsond with increasing irritability or anxiety in situations that are actually or perceived
Combination of memory loss with other cognitive disturbances leads to a profound
deterioration of social competence.
Dementia creates a substantial burden on patients’ spouses, children and other carers.
Most common form of demetia is Alzheimer’s disease (AD), which accounts for approx. two
thirds of all dementing disorders.
The prevelance of AD increases steadily from about 1% in people 65+, to over 20% in the
ninth decade of life.
In some populations worldwide, the rates for AD have been reported to be lower than in
The conversion rate of mild cognitive impairment (MCI) to dementia is between 25% and
50% at 2to3 year followup.
A variant of AD is dementia with Lewy bodies (DLB), which is often associated with
parkinsonism, visual hallucinations, fluctuating vigilance, and intolerance of antipsychotic
Vascular dementia (VD) is the secondmost common form of demetia in countries with high
prevalence and 20% cases overlap with AD.
Frontotemporal dementia (FTD) compromises a spectrum of nonAlzheimer diseases
affecting the frontal lobe with predominating behavioural symptoms and personality change.
Genetic risk factors
The risk for developing AD is increased in firstdegree relatives of patients with AD,
suggesting a heritable component.
By age 90, relatives of AD patients have a cumilative risk of 15% to 20% for developing AD
compared to 5% in controls. Double concordance rates in MZ twins : 30% to 80%
DZ twins : 10% to 40%
However, familial AD accounts for only 13% of early onset cases and less than 0.01% of all
Late onset AD is associated with polymorphisms of the apolopoproteinE family on
chromosome 19, with ApoE4 conveying the greatest risk for developing AD.
Environmental risk factors
Age is the most significant risk factor for AD.
People with down’s syndrome may develop the disorder in their 40s.
Poor education and oestrogen depletion at menopause have also been discussed as putative
risk factors for AD.
Humans possess three isoforms of ApoE, namely ApoE3, and ApoE4, the most common one
being ApoE3, ApoE4 is found in about 15% and ApoE2 found in about 8% of individuals.
Abeta is usually produced in a minor pathway of APP metabolism thrugh the action of beta
and gammasecretase mediated by the availability of intracellular cholestrol.
Excessive production of abnormal Abet