NZ scientists push closer to revealing gene's role in Parkinson's disease

Despite decades of research, and its impact on one in 500 New Zealanders and millions more around the world, Parkinson's disease remains a medical mystery. Photo / 123RF

Kiwi scientists are pushing closer to revealing one gene's critical role in the development of Parkinson's disease.

A just-launched study comes after New Zealand research, backed by Hollywood star Michael J Fox's world-renowned charity, shed more light on the gene's intriguing link with the notorious neurodegenerative condition.

Parkinson's is a progressive neurodegenerative condition caused by a lack of dopamine in the brain, resulting in slow and awkward movement.

Despite decades of research, and its impact on one in 500 New Zealanders and millions more around the world, the disease remains a medical mystery.

Doctors don't yet know why most people develop it and for those diagnosed, there's no cure.

Associate Professor Justin O'Sullivan of the University of Auckland's Liggins Institute is leading the research team. Photo / Supplied

Over recent years, scientists have been pursuing a promising new lead in a genetic mutation that poses one of the biggest risk factors for the disease.

The specific gene involved is called glucocerebrosidase beta acid, or GBA.

Studies have already shown how GBA mutations hamper an enzyme that helps clean out degraded or excess cell parts, before they can build up to cause the damage seen in Parkinson's disease.

Last August, a team led by Associate Professor Justin O'Sullivan, of the University of Auckland-based Liggins Institute, published findings that pinpointed the specific components of GBA which play a big part in regulating and delaying the disease's onset.

In GBA's "non-coding" areas - once thought of as "junk" DNA with no purpose - the team screened 128 sites to find that, where the gene happened to have a specific combination of three short non-coding DNA sequences, the onset of Parkinson's could be delayed by five years.

They also identified six other non-coding regions that act as switches to control how the GBA gene was turned on or off in the movement and cognitive centres of the brain.

The scientists - who were partly funded by the Michael J Fox Foundation for Parkinson's Research - also created a map showing how such switches affect other genes – in addition to GBA - throughout the human body.

In the new study, supported by New Zealand's Marsden Fund, O'Sullivan will team up with Otago University geneticist Professor Martin Kennedy to look further at the GBA puzzle.

Kennedy said the project proved a "fortuitous merging" of what was initially separate research.

A major charity founded by high-profile Parkinson's sufferer Michael J Fox is putting money behind the New Zealand study. Photo / Wikimedia

While O'Sullivan had been focused on how gene expression was regulated in different cells, Kennedy and PhD student Oscar Graham had been developing a new DNA sequencing method to examine mutations in the GBA gene.

When O'Sullivan and Kennedy sat down together at a Queenstown conference to share their work, they realised what they could learn by combining it.

"When brought together, the two sets of data suggested that not only overt mutations in GBA, but also the natural patterns of subtle variation in the GBA gene, appeared to impact on Parkinson's disease," Kennedy said.

Moreover, it likely did this through changing the expression of perhaps 20 to 30 other genes.

Their joint study, also involving the NZ Brain Research Institute's renowned clinical director, Professor Tim Anderson, ultimately sought to confirm that subtle genetic changes in GBA did indeed affect the onset age of Parkinson's.

But they also wanted to know why many people who carried GBA mutations didn't develop the disease.

Further, they aimed to build simpler ways for detecting the variation so it could be tested in larger studies, along with sophisticated new models exploring its effect in cell biology.

The team planned to import specific stem cells drawn from Parkinson's patients, which would be modified in the lab using the latest gene-editing methods to provide cells with different forms of the GBA gene.

"These cells can be differentiated in the lab into different cell types, such as certain brain cells, then we can look at differences in gene expression due to the presence of different forms of the GBA gene," Kennedy explained.

"Then we will set up experiments to better understand the biological impacts of any gene expression differences, both in the cultured cell models, as well as ultimately in human beings."

Kennedy expected the pioneering research to come with challenges - especially around modifying the gene in cell lines, but also in understanding just what those differences in gene expression caused by various forms of GBA actually meant.

"Until we find those changes and start to think about the functions of the genes, we won't be able to plan precise experiments to answer the key questions of this study."

But if successful, their study may prove crucial to ongoing efforts to understand and prevent Parkinson's.

"GBA is the single biggest genetic factor we know of that underlies Parkinson's, and yet we don't really understand how it exerts its effects," Kennedy said.

"Furthermore, drugs are being developed and trialled that target GBA and the pathway in which it operates, so it is increasingly important to understand all the hows and whys of GBA's role.

"We believe our genetics work will lead to better ability to predict risk of Parkinson's - and perhaps allow targeting of treatment, or even prevention for people at high genetic risk who do not yet have it."