Though some genes are involved in ADpathogenesis, genetically inherited Alzheimer’s disease accounts only 10-12 percentof AD case (Blennow,de Leon et al. 2006).Onset of genetically identified forms of Alzheimer disease usually incident inearly life of individuals (Blennow,de Leon et al. 2006).The current idea is that there are atleast two types of AD- sporadic/late onsetand familial/early onset cases of Alzheimer disease.i.
FamilialAlzheimer’s disease (FAD)WhenAlzheimer disease is caused by inherited mutations in some genes it is termedas “familial Alzheimer disease (FAD)” (autosomal dominant Alzheimer disease(AD).FAD transfers risk factor generations to generation through the genes withmutations, several generation and thus many families are affected. Symptoms canbe observed before age of 60 years, and even may appear among persons between30 and 40 years old. Most of FAD can be attributed to The mutations in the amyloid precursor protein(APP) and presenilin 1 and 2 gene (2001).Mutations in the APP and presenilin genes lead to enhanced production of protein A?40 and A?42 (amyloid ?1-40and amyloid-?1-42)) that deposits in form of amyloid plaques and causes neuronaldeath (Selkoeand Schenk 2003).ii. SporadicAlzheimer’s diseaseOthercase, that does not caused due to autosomal-dominant inheritance are termed as sporadicAD. The inheritance of the allele of the apolipoprotein (APOE) is identified asmajor genetic risk factor.
Risk genes increase probability of diseaseprogression, but surety is always doubtful. Individual with a mutation in APOE4gene have 5-10 times more risk of developing Alzheimer disease. Table- 4.1shows the main genetic mutations associated with Alzheimer disease. Alzheimerdisease is caused by multiple factors through multiple mechanism disease