As a neurological disorder that causes chronic attacks of drowsiness among other symptoms, narcolepsy might seem very different from a disease like rheumatoid arthritis (RA), which causes severe joint pain and disability.

But these two seemingly disparate health conditions may have more in common than you might imagine. For example, it might surprise you to learn that your immune system is involved in both conditions, and they may even share a genetic link.

Narcolepsy is a chronic neurological disorder that makes you sleepy. But it’s more than that. This disorder causes people to develop what experts sometimes call “excessive daytime sleepiness,” episodes that may last anywhere from a few seconds to a few minutes.

Many people with narcolepsy also develop sudden extreme muscle weakness, or cataplexy, right before falling asleep or when awakening. Some experience brief bouts of paralysis when they wake up. Fragmented or disrupted nighttime sleep is also common if you have narcolepsy.

Narcolepsy affects about 1 in every 2,000 people in the United States, although some speculate that it could be more common because it may go undiagnosed. It’s thought to be caused by environmental factors and genetic factors, although most of the time, family history doesn’t seem to play much of a role in narcolepsy.

But a growing body of evidence suggests that it may also be an autoimmune condition—adding to the growing roster of more than 80 different kinds of autoimmune diseases that have been identified. With an autoimmune condition, your body’s immune system attacks healthy cells because it mistakenly thinks they’re dangerous.

Narcolepsy and the immune system

Here’s why narcolepsy may have an autoimmune component. Research suggests that in people with narcolepsy type 1 (which is the most common kind of narcolepsy), the T cells, which are a type of immune system cell, seem to target hypocretin-producing neurons in the brain. Hypocretin, also known as orexin, is a neurotransmitter (a chemical messenger in your body that tells your body how to function) that regulates your wakefulness and arousal. If your immune system cells target the cells that produce this chemical, it interferes with your brain’s ability to regulate your sleep.

Research also shows that environmental exposure to certain viruses or bacteria may trigger your immune system, leading to the onset of narcolepsy. For example, a 2021 study noted a rise in people with narcolepsy in response to the H1N1 influenza (swine flu) pandemic of 2009. And research also found a link between a monovalent H1N1 influenza vaccine given in Europe in response to the H1N1 pandemic.

RA is an autoimmune disease that develops when your immune system attacks the healthy cells in your body, causing painful inflammation in your joints. Although the specific cause is yet to be determined, certain factors do seem to raise your person’s risk, according to the Centers for Disease Control and Prevention (CDC).

These include:

  • Age. Your risk goes up as you get older.
  • Sex. You’re much more likely to develop RA if you’re a person assigned female at birth than if you’re a person assigned male at birth.
  • Genetics. You’re more likely to develop RA if you have human leukocyte antigen (HLA) class II genotype genes.
  • Smoking tobacco. A history of smoking or a history of your birthing parent smoking seems to be associated with a higher likelihood of developing RA.
  • Obesity. Being overweight or obese may raise your risk.

Let’s look closer at the genetic issue. As it turns out, narcolepsy and RA have a similar genetic link. A 2017 study noted that 90 percent of people with narcolepsy have the HLA gene too and that the presence of HLA significantly increases a person’s risk of developing narcolepsy.

Some research suggests that if you have one autoimmune condition, you may be more likely to develop another one. For example, a 2017 study noted that people with RA seem to have higher rates of other concurrent autoimmune diseases than people with osteoarthritis, which isn’t considered an autoimmune disease.

If you have a gene that predisposes you to narcolepsy, then you have a gene that may predispose you to developing another autoimmune condition, such as RA. The HLA gene variant affects your T cells, which are involved in how your body targets its immune responses.

As scientists learn more about the possible autoimmune etiology of narcolepsy, it could shape the treatments that are offered to people with this condition. Some of the existing treatments for RA are immunomodulators, but some research suggests that immunotherapy could be a promising treatment avenue for narcolepsy in the future. More research is needed to learn more about the possibility.

Anytime you develop new symptoms, pay attention, even if you don’t think they’re a big deal.

For example, you might be tempted to brush off the early symptoms of RA, which start off as pain, swelling, and stiffness in one or more of your joints. But over time, the inflammation can cause permanent damage to your joints—and even some deformities—if not treated before it can progress.

But it can be easy to mistake the symptoms of RA for symptoms of other conditions, so it’s important to see a doctor or healthcare professional and get the right diagnosis so you can begin treatment right away.

Consider contacting a doctor if you begin to experience symptoms of narcolepsy, especially if they begin to take a significant toll on our life and your ability to carry out your normal activities of daily living.

Watch for attacks of extreme sleepiness, especially if you develop other symptoms of narcolepsy like cataplexy or hallucinations right before or after waking up.

If you already know that you have RA and begin to suspect you’re developing symptoms of narcolepsy, let a doctor know right way. The same goes for if you have narcolepsy but begin experiencing some pain or stiffness in your joints. A doctor can examine you, take a medical history, and run tests to learn more.

If you’ve received a diagnosis of an autoimmune condition like RA or narcolepsy, it’s important to know that you may be at higher risk of developing another type of autoimmune condition. If you notice any new symptoms developing, let a doctor know what you’ve been experiencing.