Option: (b) PSEN-1 1.    The PSEN-1 (Presenilin-1) gene mutation is the most commonly associated with early-onset Alzheimer's disease, particularly when the disease presents before age 65 and progresses rapidly. 2.    PSEN-1 is involved in the processing of amyloid precursor protein (APP), a key protein in Alzheimer's disease. Mutations in this gene result in abnormal cleavage of APP, leading to the formation of beta-amyloid plaques that contribute to the neurodegenerative process. 3.    Alzheimer's due to PSEN-1 mutations tends to present earlier in life, often between the ages of 30 and 60, and the disease progresses faster compared to the more common late-onset form of Alzheimer's. 4.    PSEN-1 mutations follow an autosomal dominant inheritance pattern, meaning an affected individual has a 50% chance of passing the mutation to offspring, leading to familial Alzheimer's disease. 5.    The mutation causes a defect in the gamma-secretase complex, leading to the overproduction of toxic amyloid-beta species, which accumulate in the brain and disrupt neural function. 6.    PSEN-1 mutations are more commonly seen in familial Alzheimer's, in contrast to the more sporadic late-onset form of the disease associated with APOE4 allele.

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