Within the human body there is a gene called apoE, which encodes a protein called apolipoprotein E, that is considered important for brain function. However, a mutation of this molecule is also a known risk factor for Alzheimer's disease. So what would happen if a person didn't have this gene?

When a 40-year-old man missing the apoE gene walked into Dr. Mary Malloy's clinic, this question was answered. 

Malloy and her colleagues studied the man. He had disfiguring symptoms - protruding pustules on his hands, elbows, ears and feet, welts - and a genetic condition called dysbetalipoproteinemia. His brain, however, was a normal size, had a usual amount of white matter and seemed generally unaffected. They published their findings in JAMA Neurology.

Scientists have wondered whether the absence of the apoE gene produces healthy cognitive function. After running multiple cognitive tests they also found that the man's thinking and memory skills were completely normal.

"This particular case tells us you can actually live without any apoE in the brain," said Dr. Joachim Herz, a scientist at the University of Texas Southwestern Medical Center who was not involved in the study but wrote an editorial about it.

"So if they were to develop anti-apoE therapies for Alzheimer's, we would not have to worry about serious neurological side effects," he added.

ApoE is studied by researchers who think altering it may help prevent Alzheimer's by reducing, eliminating or neutralizing the effects from the mutated form of apoE as long as the brain can still function normally.

Malloy said that apolipoprotein E helps transport cholesterol into the liver and in the brain, it helps transport cholesterol from the neuron to a storage area and then back.

The biggest mutation of apoE that is a risk factor for Alzheimer's is apoE4. People with one copy of the mutated gene are five times more likely to develop Alzheimer's. This mutation affects 20 percent of the general population. The other two risk factors are apoE3 and apoE2.

This development may help scientists and researchers find a new intervention for Alzheimer's.

"Our observations on this patient suggest that this strategy may now be entertained seriously," Malloy said.

But the benefits don't just stop with Alzheimer's. Malloy said this therapy could also help patients with Parkinson's disease and even traumatic brain injuries.