Risk Factors

A number of risk factors are associated with dementia. Concerning Alzheimer’s disease, there are a number of factors associated with early-onset Alzheimer’s disease and late-onset Alzheimer’s disease.

Early-Onset Alzheimer ’s Disease

Onset before the age of 65 often indicates a genetic cause. Single gene mutations at one of three loci of the following genes account for most of these cases:

– Beta Amyloid Precursor Protein
– Presenellin 1
– Presenellin 2

 

Late-Onset Alzheimer’s Disease

Both genetic and environmental (lifestyle) factors influence the onset of Alzheimer’s disease.

Genetic Factors

A genetic polymorphism, the apolipoprotein E (ApoE) gene e4 allele greatly increases risk of suffering from dementia, about 25% of the population having one or two copies. (Saunders et. Al, 1993).

Given the fact that one identical twin can suffer from dementia and the other not, there is a strong environmental influence.

Environmental Factors

Cross-sectional and case-control studies suggest associations of Alzheimer’s disease with limited education, head injury and depression, as reviewed in World Alzheimer Report 2009.

Modifiable Risk Factors

There are a number of modifiable risk factors, including Cardiovascular Risk Factors (CVRF) and cardiovascular disease (CVD), smoking (Luchsinger et.al, 2005), diabetes (Ott et. al, 1999), hypertension and hypercholesterolaemia (Kivipelto et. al, 2001).

Metabolic syndrome has been associated with incident cognitive decline (Yaffe et. al, 2004), insulin resistance with impaired executive functions (Abbatecola et. al, 2004). In addition atherosclerosis has also been associated with Alzheimer’s disease (Casserly et. al, 2004), the underlying factors being the apoE e4 gene, hypertension, increased fat intake and obesity, raised cholesterol, diabetes, metabolic syndrome, smoking and systemic inflammation.

 

References

Abbatecola AM, Paolisso G, Lamponi M, Bandinelli S, Lauretani F, LAuner L et al. Insulin resistance and executive dysfunction in older persons. J Am Geriatr Soc 2004 October; 52 (10): 1713-8.

Abbatecola AM, Paolisso G, Lamponi M, Bandinelli S, Lauretani F, LAuner L et al. Insulin resistance and executive dysfunction in older persons. J Am Geriatr Soc 2004 October; 52 (10): 1713-8.

Casserly I, Topol E. Convergence of atherosclerosis and Alzheimer’s disease: inflammation, cholesterol, and misfolded proteins. Lancet 2004 April 3; 363 (9415):1139-46.

Kivipelto M, Helkala EL, Laakso MP, Hanninen T, Hallikainen M, Alhainen K et al. Midlife vascular risk factors and risk of dementia in later life: longitudinal, population based study. BMJ 2001 June 16; 322 (7300): 1447-51.

Luchsinger JA, Reitz C, Honig LS, Tang MX, Shea S, Mayeux R. Aggregation of vascular risk factors and risk of incident Alzheimer disease. Neurology 2005 August 23; 65(4): 545-51.

Ott A, Breteler MM, van Harskamp F, Claus JJ, van der Cammen TJ, Grobbee DE et al. Prevalence of Alzheimer’s disease and vascular dementia: association with education. The Rotterdam study (see comments). BMJ 1995; 310 (6985): 970-3.

Prince Martin, ed. “The global prevalence of dementia” World Alzheimer Report 2009. Alzheimer Disease International. London: Alzheimer’s Disease International, 2009.25-46.

Prince Martin and Jackson Jim, ed. “What is Dementia?”World Alzheimer Report 2009. Alzheimer Disease International. London: Alzheimer’s Disease International, 2009.13-24.

Saunders AM, Strittmatter WJ, Schmechel D, St. George Hyslop PH, Pericak-Vance MA, Joo SH et al. Association of apolipoprotein E allele e4 with late-onset familial and sporadic Alzheimer’s disease.Neurology 1993, 43:1467-72.

Yaffe K, Kanaya A, Lindquist K, Simonsick EM, Harris T, Shorr Rl et al. The metabolic syndrome, inflammation, and risk of cognitive decline. JAMA 2004 November 10; 292 (18):2237-42.