If you or a loved one is living with Parkinson’s disease (PD), you’ve probably spent a lot of time researching the condition and trying to understand the most essential information about its causes, symptoms, and progression. But even the most detail-oriented researchers may not know every fact about PD, because the disease has so many variables from one person to the next.

By getting to know five essential facts about Parkinson’s, you can deepen your understanding of the condition. Ultimately, more knowledge can empower you to self-advocate as you travel along your PD journey.

Fact 1: Not Everyone With PD Experiences Tremor

Many people think of tremor, or involuntary shaking, as the key symptom of Parkinson’s disease. Although it’s often true that tremor is what initially prompts people to seek a PD diagnosis, not everyone with Parkinson’s experiences tremor.

About 70 percent of people who have Parkinson’s disease will have tremor symptoms during the course of the disease, according to the Parkinson’s Foundation. In some cases, tremor occurs internally, meaning that someone with the condition may feel a shaking sensation inside of their body (often in the limbs, chest, or abdomen) that isn’t visible to outsiders.

Fact 2: Loss of Smell Can Be an Early Symptom of PD

One early sign of Parkinson’s disease that can often be overlooked is a reduced sense of smell. Although not everyone with PD will lose the ability to smell things, this symptom (known as hyposmia) can impact people long before other symptoms develop — sometimes up to a decade beforehand.

A changing sense of smell is a common topic on MyParkinsonsTeam. “Lost any decent sense of smell a while ago,” one member said. Another noted, “Sometimes I can't smell anything — or everything smells the same.”

People who lose their sense of smell with no other cause appear to have an approximately 50 percent chance of developing PD in the subsequent five to 10 years.

Fact 3: Parkinson’s Can Affect Younger People

Although aging is considered the main risk factor for developing Parkinson’s, the disease can affect people who are younger than 40 years old in certain cases. The average age at diagnosis for PD is 60, and anyone diagnosed with the condition who is below the age of 50 is classified as having young-onset Parkinson’s disease (YOPD). YOPD comprises about 10 percent to 20 percent of all PD cases.

YOPD typically progresses more slowly than typical Parkinson’s cases do, and the presenting symptoms can be different. Dystonia (cramping or stiffness) is often an early symptom of PD in younger people, as is dyskinesia (involuntary movements of the body). However, cognitive issues, such as memory loss, confusion, and trouble with balance, tend to be less common in younger people with the disease.

Fact 4: PD Is More Prevalent in Males

Men are 1.5 times more likely than women to develop Parkinson’s disease. In addition, the disease tends to impact men and women differently. In women, early symptoms often include tremor, pain, and recurring falls. In men, however, posture problems and worsening cognitive abilities are common.

Researchers continue to study the potential reasons why PD affects men more often than women, including whether hormones, lifestyle, or other factors may play a role.

Fact 5: Inheriting Parkinson’s Is Rare

Although some people with PD have a family history of the condition, that’s not the case in most instances of the disease. Parkinson’s disease is attributed to inherited genes in about 10 percent to 15 percent of cases. Scientists believe PD is caused by a combination of genetic and environmental factors, although researchers have not yet pinpointed a direct cause of the condition.

The topic of inheriting PD is a common theme of discussion on MyParkinsonsTeam. “I have a sister, two cousins, and a trio of aunts who had PD,” one member wrote. Another said, “My husband and his brother both developed it at the same time. He hasn't had genetic testing to see if that was the cause or not, but it seems like a possibility.”

You can undergo genetic testing to see if you have a mutation in a gene associated with PD, but even if your test results come out positive, your chances of developing Parkinson’s are still low. Researchers continue to study the specific role genes play in the development of PD.

Talk With Others Who Understand

MyParkinsonsTeam is the social network for people with Parkinson’s disease and their loved ones. On MyParkinsonsTeam, more than 76,000 members come together to ask questions, give advice, and share their stories with others who understand life with Parkinson’s.

What Parkinson’s facts do you find the most compelling? Share your experience in the comments below, or start a conversation by posting on your Activities page.