In both cases, he said, "This may all be a timing issue. We may just not be starting our interventions anywhere near early enough."
Rudy Tanzi of Boston's Massachusetts General Hospital, noted that several smaller genetic studies -- including one in which he was involved -- have found genes associated with Alzheimer's.
That said, the large scale of these two studies and the fact that they had similar findings suggests the new genes "will likely hold up as real Alzheimer's genes."
But he said they appear to have limited effects on risk and are likely to be "bit players in a cast of hundreds" of genes that interact to increase the chance of developing the disease.