Which of the following statements about early onset Alzheimer’s disease (AD) is true?
The early onset form of the disease is characterized by many sporadic cases in the population.
Incorrect
The early onset form of AD is likely not related to genetic variants.
Incorrect
The mutations of PSEN1 gene are associated with the most severe form of the disease.
Correct! More than 150 PSEN1 gene mutations have been identified in patients with early-onset Alzheimer disease. Mutations in the PSEN1 gene are the most common cause of early-onset Alzheimer disease, accounting for up to 70 percent of cases. The mutations in this gene result in the production of abnormal protein product that leads to the overproduction of a longer-toxic version of amyloid that builds up in the brain and forms amyloid clumps- a characteristic feature of AD. These toxic plaques likely lead to the death of neurons and progressive signs/symptoms of this disease.
Most of the variants in genes responsible for early onset AD are triplet repeat mutations.
Incorrect
Why is genetic testing of the APOE gene for AD risk generally not recommended?
The genetics of AD are completely unknown at this time.
Incorrect
Knowing APOE genotype does not predict AD for an individual.
Correct! APOE ε4 is a risk-factor or susceptibility gene because it increases a person's risk of developing the disease. However, inheriting an APOE ε4 allele does not mean that a person will definitely develop Alzheimer's. Some people with an APOE ε4 allele never get the disease, and others who develop Alzheimer's do not have any APOE ε4 alleles.
It is not possible to identify genotype in AD.
Incorrect
Predictive testing for AD is highly accurate but no treatment is available.
Correct! A haploid sperm ferlitizing a diploid egg can result in an extra set of chromosomes because the egg is not haploid.
Why are people with Down syndrome at risk for developing AD as they age?
The have an extra copy of the APP gene because of trisomy 21.
Correct! People with Down's syndrome have an extra copy of chromosome 21 and as a consequence there will be three copies of the genes on this chromosome, including key genes related to amyloid, tau and the development of AD. The amyloid precursor protein (APP) gene is located upon chromosome 21. APP is processed into amyloid-beta, which forms the plaques seen in the brains of people with Alzheimer's disease. It is thought that the extra copy of APP is responsible for the early onset of Alzheimer's disease in people with Down's syndrome.
They already have a deficit in memory, so with aging memory is even more at risk.
Incorrect
They are more likely to have a positive family history for AD.
Incorrect.
Mutations in the PSEN2 gene are more common with Down syndrome.
Incorrect