Twin study offers hope for Alzheimer’s disease

A recent study revealed that one of the hallmark features of Alzheimer’s disease is only partially connected to genes.

The study, led by Dr Rebecca Koncz at UNSW’s Centre for Healthy Brain Ageing, looked at the brains of identical and non-identical twins.

The aim of the study was to determine the proportion of amyloid accumulation that is determined by genes or the environment.

Amyloid is a protein that accumulates in the brain early in the development of Alzheimer’s disease, sometimes even decades before symptoms appear.

“It’s one of the very early markers of the condition and it is only part of the story…Just because one has amyloid doesn’t mean they have Alzheimer’s disease,” she told Community Care Review.

This means that it is an important marker of the condition but alone does not cause it.

Twins were used for the study because they provide a unique sample, with identical twins sharing 100 per cent of their genetic material and non-identical twins sharing on average about 50 per cent.

Cautious optimism  

The study found that about 40 to 50 per cent of the variation in amyloid load is due to genes, which is considered to be a “moderate” amount, according to Dr Koncz.

She believes these findings provide hope for “cautious optimism”.

“This is interesting because it means the remaining variation in amyloid is susceptible to environmental factors,” she said.

“If only 40 to 50 per cent is attributed to genes, the question we want to address is what are the other factors contributing to the build-up of amyloid?”

Dr Koncz and her team then looked at vascular risk factors, such as high blood pressure, diabetes, being overweight or obese and high cholesterol, to determine if that would explain the amyloid load in the participants.

They did not find a connection, however, Dr Koncz believes there could be several reasons for this, such as the sample size of the participants being too small.

Although vascular risk factors can be partly determined by genes, they are also influenced by lifestyle choices, Dr Koncz said.

“One might have a genetic vulnerability to develop a condition and then might engage in lifestyle factors like smoking or not being physically active,” she said.

“That then has the potential to add to the risk of accumulating either amyloid or developing dementia down the track.”

Environmental factors

These findings suggest that environmental factors play an important role, Dr Koncz said.

“If about 40 to 50 per cent we attribute to the genes then an estimated 50 to 60 per cent then is due to environmental factors,” she said.

The search is still on for what these could be and it’s a matter of working out what is contributing to amyloid specifically.

“At the end of the day, my suspicion is that it’s not just one magic bullet unfortunately, in terms of the prevention and intervention,” Dr Koncz said.

“It’s likely the combination of lots of these potentially modifiable risk factors that contribute to the risk of amyloid accumulation and then the subsequent development of Alzheimer’s disease.”

The next step for Dr Koncz’s research is to move beyond just looking at amyloid the protein and onto determining if a genetic overlap exists between amyloid and cognitive impairment, such as memory problems, difficulties with language and brain processing speed.

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