Following are predispositions to Alzhiemer’s desease except :
**Core Concept**
Early-onset Alzheimer's disease is a rare form of the disease characterized by the onset of symptoms before the age of 65, often linked to specific genetic mutations. The most well-known genetic risk factors for Alzheimer's disease are the APOE ε4 allele, APOE ε2 allele, and mutations in the APP, PSEN1, and PSEN2 genes.
**Why the Correct Answer is Right**
The APOE ε4 allele is a well-established risk factor for late-onset Alzheimer's disease. It is a variant of the Apolipoprotein E gene that plays a crucial role in lipid metabolism and neuronal function. Carriers of the APOE ε4 allele are at increased risk of developing Alzheimer's disease, particularly those with a family history of the disease. In contrast, the APOE ε2 allele is considered a protective factor against Alzheimer's disease.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as there are no known predispositions to Alzheimer's disease associated with this choice.
**Option B:** Down syndrome is a known predisposition to Alzheimer's disease due to the presence of an extra copy of chromosome 21, which carries the APP gene. Individuals with Down syndrome have a high risk of developing Alzheimer's disease, often beginning in their 40s.
**Option C:** Vascular dementia is a type of dementia caused by reduced blood flow to the brain, often resulting from stroke or small vessel disease. While vascular dementia is a common cause of cognitive decline, it is not a predisposition to Alzheimer's disease.
**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that individuals with Down syndrome have a high risk of developing Alzheimer's disease, often beginning in their 40s. This is due to the presence of an extra copy of chromosome 21, which carries the APP gene.
**Correct Answer: B. Down syndrome**