One of the UK's leading Alzheimer's experts believes there will be a treatment for the most common forms of the disease within 20 years.

Prof Julie Williams' team at Cardiff University has identified 92 genes that significantly increase the risk of having the progressive condition.

They knew of just three genes when their research began in 2009.

"Things are speeding up and improving all the time," said Prof Williams, who has studied Alzheimer's for 30 years.

"I've learnt more in the last seven years than I did in the previous 20," said the Merthyr Tydfil-born academic, who was appointed a CBE for her research.

Alzheimer's disease affects the brain and is the most common cause of dementia - one of the UK's biggest killers of the over-50s.

Prof Williams, centre director at the UK Dementia Research Institute at Cardiff University, said gene therapy, along with an improved understanding from international studies, was telling researchers more every day.

"Once you know where to start looking then you can study the effects which genes have on specific brain activity," she said.

"Tests which cost millions in the '90s can now be carried out for around £30.

"For example we now know that defective genes changing the way immune cells called microglia work.

"These are the bin lorries of the brain clearing away what they see as rubbish. They may be less efficient at clearing genuine rubbish and mistakenly kill off healthy brain cells, including synapses.

"Of course synapses are the connections between neurons, so if they get eliminated when they shouldn't then you lose connections, you lose thought, you lose memories."

She said her study of thousands of cases made her realise there will never be one smoking gun, instead, the disease must been seen more like heart disease or stroke where many factors contribute and several therapies will help delay or prevent it.

"By 2040 I think we'll be in the position to offer a range of treatment and we might not know exactly why, but one of them will be able to act on the huge range of causes," she said.

Some of the drugs have already been cleared for use in other conditions she added, and could be in clinical use inside five years.

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