Other studies of patients who are ApoE4 carriers and non-carriers are under way.

FORBES: Pfizer And J&J Alzheimer's Drug Fails Late-Stage Trial

There are few clinical differences, experts say, between those with APOE4 and those without it once they develop the disease.

FORBES: Magazine Article

The trials include two in patients with APOE4 (an Alzheimer's disease risk factor) and two in patients without the gene.

FORBES: Magazine Article

One big mystery is why hitting amyloid with a drug would benefit people without the APOE4 gene but not those with it.

FORBES: Magazine Article

The best Elan trial results unexpectedly came in the subset of about 35% of patients who lack a gene mutation called APOE4.

FORBES: Magazine Article

Alzheimer's is probably caused by a complex interaction of many genes, and it is possible those with the APOE4 gene are less able to repair their injured brains.

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Roughly half of Alzheimer's patients have the APOE4 gene variant.

FORBES: Hope Mixes With Doubt For Alzheimer's

The researchers, from 15 institutions including the Institute of Neurology in London, analysed the DNA of 1, 411 people and found GAB2 influenced the risk of dementia among those with APOE4.

BBC: NEWS | Health | Scientists find new dementia gene

Late Tuesday afternoon, the companies presented mediocre trial results showing that bapineuzumab (b-mab for short) didn't work overall in an 18-month second stage trial but seemed to help a subset of patients who lack a certain gene mutation, APOE4.

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But a subset of patients who did not have a genetic variant called APOE4, showed statistically significant improvements across four different tests for Alzheimer's symptoms, Wyeth and Elan said, when compared to a control group of patients who did not get the drug.

FORBES: Hope Mixes With Doubt For Alzheimer's