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African-Americans, Alzheimer’s Disease, and the effects of epimutations on cognition

March 20, 2010

In my first few posts, I posit that racial differences in I.Q. scores may be partially related to racial differences in nutrition and environment. ‘Epigenetics’ provides a mechanism for this gene-environment interaction to occur.

What is epigenetics and what proof is there of its existence in humans? This explains it pretty clearly:

Interestingly, a recent study in monozygotic twins has shown that the epigenetic ‘‘code’’ displays alterations, which increase with aging and depend on the amount of time that the twins spent together (Fraga et al., 2005). For example, in 35% (14 of 40)of the investigated twin pairs both genomic 5-methyl-C content and the acetylation levels of H3 and H4 were significantly different in each twin. Moreover, Fraga and colleagues found a direct association between these epigenetic differences and theage of the MZ twins, i.e. the younger pairs were epigenetically similar, whereas the older pairs were most distinct. In recent years, it has become increasingly clear that, besides stochastic changes in the epigenome that occur throughout life, environmental factors such as nutrition, diet, drugs, hormones, and infections modulate a person’s phenotype via epigenetic mechanisms (Abdolmaleky et al., 2004; Liu et al., 2008; Poulsen et al., 2007).

[Chouliaras L, Rutten BP, Kenis G, Peerbooms O, et al. Epigenetic regulation in the pathophysiology of Alzheimer’s disease. Prog Neurobiol. (In Press)]

Alzheimer’s disease is a well-studied example of environment affecting cognition, though exact epigenetic mechanisms are not yet known. Racial differences in prevalence of AD appear to exist. According to the Alzheimer’s Association:

Alzheimer’s disease is more prevalent among African-Americans than among whites — with estimates ranging from 14% to almost 100% higher

The epsilon 4 allele of the APOE gene is believed to be associated with Alzheimer’s and other cognitive impairments. The allele is held by 23.1% of African Americans and 14.9% of whites and it appears to be associated with cognitive decline in people as young as 45. But the most significant role in cognitive decline is not the allele itself the gene-environment interaction of the E4 allele with high cholesterol and diabetes. Just look at this chart, which shows the decline in a subject’s mental acuity over 6 years.

[Blair CK, Folsom AR, Knopman DS, Bray MS, et al. APOE genotype and cognitive decline in a middle-aged cohort. Neurology. 2005;64(2):268-76.]

The African-American cohort in that study was too heterogeneous to make draw any statistically significant conclusions from, however they found that

In African Americans, 4 carriers had greater ultrasound-assessed carotid intima–media thickness than noncarriers.

Which suggests that cognitive decline in that group could’ve happened well before 45.

2 Comments leave one →
  1. 2 Yr Old 156 IQ permalink
    March 21, 2010 3:49 am

    Here’s a baby with a 156 IQ

  2. March 23, 2010 12:30 am

    You can’t reliably measure a 2 year old’s IQ. Correlations with adult IQ are weak at that age. Mensa pussed out by buying into that hype train.

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