Monday, June 11, 2007
Alzheimer's disease (AD) afflicts about 10% of persons over 65 and almost half of those over 85.
When Jim Watson had his genome sequenced he asked not to have his ApoE4 status revealed. Why??
Dr Watson did not want to know his genotype status because although twin studies suggest that there are several susceptibility genes which, along with the APOE 4 allele, contribute to up to 80% of LOAD (Late Onset Alzheimer's Disease) cases, the story is nowhere near being finished. Not everyone with APOE4 gets Alzheimer's. In fact, the majority do not......
But the picture for those predisposed is getting clearer.
This last week a study was released by the team at TGen (Translational Genomics) in the journal Neuron. According to the study:
"...suggests that the gene - called GAB2 - modifies an individual's risk when associated with other genes, including APOE4. The study results appear in the June 7 issue of the prestigious peer-reviewed journal, Neuron."
"The team screened the DNA from 1,400 individuals who had been clinically assessed with Alzheimer's prior death, and simultaneously examined more than 500,000 SNPs or genetic variations to characterize and confirm additional LOAD susceptibility genes. The search revealed GAB2."
The polymoprhism is known as SNP rs2373115 . It interacts with APO epsilon 4 to prevent neurofibrillary tangles. This protein is over expressed normally in APOE4 afflicted brain cells.
So what does this mean? GAB2 normally acts like your mother. Remember when you made a mess of your room? If you were lucky, your mother cleaned up the mess. You kept making more of a mess and she kept cleaning up. If your mother didn't clean up, then your room was a constant mess. Even worse, you couldn't find anything in your room that you needed. Much like the way an Alzheimers patient can't find their memories.
In the end a Non-cleaning mother and a really messy kid led to a very dirty room. Just like the combination of GAB2's SNP and APOE4 lead to an odds risk of 4.06 a 400% increased risk.
The Sherpa Says: I agree with Jim. ApoE4 testing can often be uninformative with only 25% of those with the gene polymorphisms going on to get Alzheimers. I think family history will have to lead the way. At least until we have a GAB2/ApoE-4/new gene panel that puts together the picture much more clearly.