Brain and behaviour session 6: Alzheimer’s disease: Causes and treatments
Alzheimer's disease is one of several forms of dementia.
It affects 1 in 5 people over the age of 80 years.
Reduced glucose and neurotransmitter levels, build-up of amyloid plaques and
neurofibrillary tangles.
Brain atrophy (shrinkage).
Progressive neurodegeneration.
Average survival from initial diagnosis: 7 - 8 years
What causes Alzheimer’s disease?
1. Genetics
There is a form of AD known as ‘familial Alzheimer’s disease’
Very rare but more common in early onset cases.
The effects on the brain are almost indistinguishable from ‘normal’ AD.
It has a clear genetic basis.
Every cell in the body contains 23 pairs of chromosomes in its nucleus. One member
of each pair is inherited from the mother; the other from the father.
Chromosomes contain our DNA (de-oxyribose nucleic acid).
A gene is a section of DNA. A typical chromosome contains
1-2,000 genes. Most genes contain the instructions for manufacturing a specific
protein.
The total of all our genes is the genome. The human genome was mapped in 2003.
We have two copies of most genes: one from mother, one from father. Often, only
one of the two copies is active (‘expressed’).
Mutations occur when a gene is copied incorrectly. If the mutant gene is dominant,
its effects will be seen in the organism (‘phenotype’).
If the gene is recessive, its effects will only be seen in a person who inherits two
copies of the faulty gene, one from each parent. People with one copy are healthy
“carriers”.
Familial Alzheimer’s disease is associated with mutations to 3 different genes.
They all show a pattern of autosomal dominance; i.e., if you inherit a mutant gene
from either parent, you will develop early Alzheimer’s disease.
Children will have a 50% chance of inheriting the faulty gene, and therefore
developing AD.
Only 2% of people have familial Alzheimer’s with AD.
50% of people have early-onset AD (before aged 65) with familial Alzheimer’s
The genes responsible for familial AD are found on 3 different chromosomes.
Presenilin 1 (PS1) on chromosome 14
Presenilin 2 (PS2) on chromosome 1
Amyloid beta A4 precursor protein (APP) on chromosome 21
Each of these mutations causes a build-up of amyloid plaques in the brains of
affected individuals.
Genetic testing can identify whether an individual is carrying a mutant form of one of
the genes responsible for familial AD (and will therefore develop AD).
Remember: An individual carrying a mutation knows that if they have children, each
child has a 50% chance of inheriting familial AD.
Late onset AD
Alzheimer's disease is one of several forms of dementia.
It affects 1 in 5 people over the age of 80 years.
Reduced glucose and neurotransmitter levels, build-up of amyloid plaques and
neurofibrillary tangles.
Brain atrophy (shrinkage).
Progressive neurodegeneration.
Average survival from initial diagnosis: 7 - 8 years
What causes Alzheimer’s disease?
1. Genetics
There is a form of AD known as ‘familial Alzheimer’s disease’
Very rare but more common in early onset cases.
The effects on the brain are almost indistinguishable from ‘normal’ AD.
It has a clear genetic basis.
Every cell in the body contains 23 pairs of chromosomes in its nucleus. One member
of each pair is inherited from the mother; the other from the father.
Chromosomes contain our DNA (de-oxyribose nucleic acid).
A gene is a section of DNA. A typical chromosome contains
1-2,000 genes. Most genes contain the instructions for manufacturing a specific
protein.
The total of all our genes is the genome. The human genome was mapped in 2003.
We have two copies of most genes: one from mother, one from father. Often, only
one of the two copies is active (‘expressed’).
Mutations occur when a gene is copied incorrectly. If the mutant gene is dominant,
its effects will be seen in the organism (‘phenotype’).
If the gene is recessive, its effects will only be seen in a person who inherits two
copies of the faulty gene, one from each parent. People with one copy are healthy
“carriers”.
Familial Alzheimer’s disease is associated with mutations to 3 different genes.
They all show a pattern of autosomal dominance; i.e., if you inherit a mutant gene
from either parent, you will develop early Alzheimer’s disease.
Children will have a 50% chance of inheriting the faulty gene, and therefore
developing AD.
Only 2% of people have familial Alzheimer’s with AD.
50% of people have early-onset AD (before aged 65) with familial Alzheimer’s
The genes responsible for familial AD are found on 3 different chromosomes.
Presenilin 1 (PS1) on chromosome 14
Presenilin 2 (PS2) on chromosome 1
Amyloid beta A4 precursor protein (APP) on chromosome 21
Each of these mutations causes a build-up of amyloid plaques in the brains of
affected individuals.
Genetic testing can identify whether an individual is carrying a mutant form of one of
the genes responsible for familial AD (and will therefore develop AD).
Remember: An individual carrying a mutation knows that if they have children, each
child has a 50% chance of inheriting familial AD.
Late onset AD
