A gene that increases the risk of developing Alzheimer's has been identified by researchers in the US.
Scientists at University of California, Los Angeles say they have identified a genetic risk factor that could be used to diagnose the disease decades before its onset.
They looked at 336 young people between the ages of 20 and 29 from 223 families. The researchers then analysed the DNA using advanced scanning technology.
Findings showed that the gene SPON1 had weaker connections between the areas of the brain that control reasoning and emotion. This gene also affected how Amyliod plaques, which are a hallmark of Alzheimer's, build in the brain.
One in three people over the age of 65 will develop dementia and at present, 800,000 people in the UK are living with some form of the disease. Over half of these suffer from Alzheimer's.
By 2051, the number of people living with dementia in the UK will have increased to 1.7 million.
Alzheimer's erodes connections in the brain and at present there is no cure.
By identifying a genetic risk factor, researchers think they could switch off this gene and stop the disorder in its tracks, or delay its onset by many years.
Lead author Paul Thompson said: "We found a change in our genetic code that boosts our risk for Alzheimer's disease. If you have this variant in your DNA, your brain connections are weaker. As you get older, faulty brain connections increase your risk of dementia.
"Much of your risk for disease is written in your DNA, so the genome is a good place to look for new drug targets."
"If we scan your brain and DNA today, we can discover dangerous genes that will undermine your ability to think and plan and will make you ill in the future. If we find these genes now, there is a better chance of new drugs that can switch them off before you or your family get ill."
Clive Ballard, scientific advisor at the Alzheimer's Society, said: "This relatively small study uses cutting edge technology to identify a gene that potentially affects a person's risk of Alzheimer's disease.
"However, we know that Alzheimer's development is likely to involve a combination of many genes and the risk associated to this particular gene is small. Therefore it would not be advisable to start screening people for its presence to determine the likelihood of them developing Alzheimer's disease.
"These findings do however provide an important new target for drug development. Less than half of people with dementia ever receiving a diagnosis and there are currently no treatments available that tackle the underlying changes of the condition.
"More research is urgently needed if we are to help people with dementia live well today and find a cure for tomorrow."