Alzheimer's disease (AD) can be classified into two main types based on its genetic nature: sporadic and hereditary.
Sporadic Alzheimer's disease
- Prevalence: The majority of AD cases are sporadic, accounting for over 95% of all cases
- Onset: Sporadic AD typically presents with a late onset, usually between 80-90 years of age
- Pathophysiology: The sporadic form of AD is characterized by the failure to clear the amyloid-β (Aβ) peptide from the interstices of the brain
- Genetic factors: While the exact cause of sporadic AD is unknown, it is believed to be a heterogeneous disease caused by aging in concert with a complex interaction of both genetic and environmental risk factors . A large number of genetic risk factors for sporadic disease have been identified
Hereditary Alzheimer's disease
- Prevalence: Hereditary or familial AD is very rare, accounting for a small proportion of all AD cases
- Onset: Familial AD is characterized by an early onset, often before the age of 65
- Pathophysiology: Familial AD is caused by mutations in the amyloid precursor protein and presenilin genes, both linked to Aβ metabolism
- Genetic factors: Familial AD is an autosomal dominant disease, meaning that each family member has a 50% chance of inheriting the mutation, which confers a lifetime dementia risk of over 95%
In conclusion, while both sporadic and hereditary forms of AD share common pathological features, they differ in terms of prevalence, age of onset, and genetic factors. The sporadic form is more common, typically presents later in life, and is influenced by a complex interplay of genetic and environmental factors. In contrast, the hereditary form is rare, presents earlier, and is caused by specific genetic mutations.