Largest ever Parkinson’s study shows how symptoms differ between men and women

Parkinson’s disease is the fastest growing neurological disorder, with over 10 million cases worldwide. Up to 150,000 Australians currently live with the disease and 50 new cases are diagnosed each day.

The number of people living with Parkison’s is projected to more than triple between 2020 and 2050.

Yet despite the immense impact on those living with Parkinson’s and their loved ones, and the staggering cost to our economy – at least A$10 billion a year – there is still a lot we don’t know about how this disease presents and progresses.

A recent large-scale study of nearly 11,000 Australians living with Parkinson’s disease provides some critical insights into symptoms, risk factors and how these affect men and women differently. Let’s take a look.

First, what is Parkinson’s disease?

Parkinson’s is a progressive disease in which cells that produce the chemical messenger dopamine in a part of the brain called the “substantia nigra” begin to die. This is accompanied by multiple other brain changes.

It is usually considered a movement disorder. Common motor symptoms include a resting tremor, slowed movement (bradykinesia), muscle stiffness and balance issues.

But Parkinson’s also involves a variety of lesser known non-motor symptoms. These may include:

• mood changes
• difficulties with memory and cognition (including slower thinking, challenges with planning or multitasking and difficulty paying attention or concentrating)
• sleep disturbances
• autonomic dysfunction (such as constipation, low blood pressure and urinary problems).

While these are sometimes referred to as the “invisible” symptoms of Parkinson’s, they often have a greater negative impact on quality of life than motor symptoms.

So, what does the new research tell us?

The study used data collected as part of the Australian Parkinson’s Genetics Study led by the QIMR Berghofer Medical Research Institute. After a pilot study in 2020, it was launched as an ongoing, nationwide research project in 2022.

Some 10,929 Australians with Parkinson’s were surveyed and provided saliva samples for genetic analysis. This is the largest Parkinson’s cohort studied in Australia and the largest active cohort worldwide.

There were several key initial findings.

1. Non-motor symptoms are common

The study reinforced how common non-motor symptoms are, with loss of smell (52%), changes in memory (65%), pain (66%) and dizziness (66%) all commonly reported.

Notably, 96% of participants experienced sleep disturbances, such as insomnia and daytime sleepiness.

2. A better picture of risk factors

The study also provided insights into what can influence Parkinson’s risk.

This is important because we don’t completely understand what causes the dopamine producing cells in the substantia nigra to die in the first place.

Age is the primary risk factor for Parkinson’s. The new study found the average age for symptom onset was 64, and for diagnosis, 68.

3. Genes and environment both play a role

In the recent study, one in four people (25%) had a family history of Parkinson’s. But only 10–15% of Parkinson’s cases are caused by – or strongly linked to – mutations in specific genes.

It’s important to remember that families don’t only share genes but often their environment.

Multiple environmental factors, such as pesticide exposure and traumatic brain injury, also increase risk of Parkinson’s.

The majority (85–90%) of cases of Parkinson’s are likely due to complex interaction between genetic and environmental risk factors, and advancing age.

The study showed environmental exposures linked to Parkinson’s risk were common:

• 36% of people reported pesticide exposure
• 16% had a prior history of traumatic brain injury
• 33% had worked in high-risk occupations (such as agriculture, or petrochemicals or metal processing).

These exposures were significantly higher in men than in women.

4. Differences between the sexes

The disease is 1.5 times more common in men. In the new study, 63% of those surveyed were male.

Parkinson’s also presents and progresses differently in males and females.

The study found women were younger than men at time of symptom onset (63.7 versus 64.4 years) and diagnosis (67.6 versus 68.1 years), and more likely than men to experience pain (70% versus 63%) and falls (45% versus 41%).

Men experienced more memory changes than women (67% versus 61%) and impulsive behaviours, particularly sexual behaviour (56% versus 19%) – although most participants exhibited no or only mild impulsivity.

What we still don’t know

The large-scale study and its comprehensive survey shed valuable light on people living with Parkinson’s in Australia.

But it’s still only a sliver of the population. More than 186,000 people with Parkinson’s were invited to participate and just under 11,000 took part – a less than 6% response rate.

Of these participants, 93% had European ancestry. So this sample may not be fully representative of Parkinson’s disease.

The information we have about symptoms also relied on self-reports by the study’s participants, which are subjective and can be biased or less reliable than objective measurements of function. To address this, the researchers are planning to use smartphones and wearable devices to collect more comprehensive data.

Finally, while this provides a snapshot of the current cohort, it’s not clear how participants compare to people of a similar age without Parkinson’s, or how their symptoms may change over time.

These are important areas of future research for this ongoing study.

What all this means

Studies like this provide crucial insights into risk factors linked to Parkinson’s. They also help us better understand the symptoms people experience.

This is important because the way Parkinson’s presents varies from person to person. Not everyone will experience the same symptoms to the same extent.

Similarly, the way the disease progresses over time differs between people.

A better understanding of the factors that influence this can lead to earlier identification of who’s at risk and more personalised ways of managing this disease.