Alzheimer's disease is an incurable disease that slowly destroys the patient's brain’s cells and always ends in death.

Currently, around 4.5 Americans are affected by the disease but scientists report that the incidence is to double over the next 25 years.

They discovered a second gene linked to the late-onset Alzheimer's disease, named SIRL1, and it is believed that this gene discovery will lead to a new drug development and confirm that the scientists are on the right tracks to finding a solution for the disease that causes brain cells’ death and for which there is no known cure.

Scientists have had major problems identifying late-onset genes. The first late-onset Alzheimer's gene, called APOE, was found 14 years ago. There have been found early-onset genes but they accounts for only 10% of all cases.

Although the cause of Alzheimer's is not known, it is believed that the brain cells’ destruction starts with plaque, produced by a protein called amyloid, depositing in the brain. Most of the drugs being produced and undergoing clinical trials are made to target amyloid protein in the brain and block it or remove it.

The newly discovered SORL1 gene was found to play a protective role by recycling amyloid through the brain, preventing it from stalling and turning into toxic plaque. However, when the gene is defective, it fails to prevent amyloid accumulation in the brain.

Having a defect in the SORL1 gene does mean that a patient will necessarily develop Alzheimer's, but it does represent the risk. The search for other genetic variants linked to the disease continues and it is believed that there could be 20 or more.

The importance of the new gene is that it opens new pathways to explore the cause as well as potential targets for treatment of the Alzheimer’s disease-scientists say.