Fatal familial insomnia (FFI) is a very rare sleep disorder that runs in families. It affects the thalamus. This brain structure controls many important things, including emotional expression and sleep. While the main symptom is insomnia, FFI can also cause a range of other symptoms, such as speech problems and dementia.

There’s an even rarer variant called sporadic fatal insomnia. However, there have only been 24 documented cases as of 2016. Researchers know very little about sporadic fatal insomnia, except that it doesn’t seem to be genetic.

FFI gets its name partly from the fact that it often causes death within a year of two of symptoms starting. However, this timeline can vary from person to person.

It’s part of a family of conditions known as prion diseases. These are rare conditions that cause a loss of nerve cells in the brain. Other prion diseases include kuru and Creutzfeldt-Jakob disease. There are only about 300 reported cases of prion diseases each year in the United States, according to Johns Hopkins Medicine. FFI is considered one of the rarest prion diseases.

The symptoms of FFI vary from person to person. They tend to show up between the ages of 32 and 62. However, it’s possible for them to start at a younger or older age.

Possible symptoms of early stage FFI include:

  • trouble falling asleep
  • trouble staying asleep
  • muscle twitching and spasms
  • muscle stiffness
  • movement and kicking when sleeping
  • loss of appetite
  • rapidly progressing dementia

Symptoms of more advanced FFI include:

  • inability to sleep
  • deteriorating cognitive and mental function
  • loss of coordination, or ataxia
  • increased blood pressure and heart rate
  • excessive sweating
  • trouble speaking or swallowing
  • unexplained weight loss
  • fever

FFI is caused by a mutation of the PRNP gene. This mutation causes an attack on the thalamus, which controls your sleep cycles and allows different parts of your brain to communicate with each other.

It’s considered a progressive neurodegenerative disease. This means it causes your thalamus to gradually lose nerve cells. It’s this loss of cells that lead to FFI’s range of symptoms.

The genetic mutation responsible for FFI is passed down through families. A parent with the mutation has a 50 percent chance of passing on the mutation to their child.

If you think you might have FFI, your doctor will likely start by asking you to keep detailed notes about your sleeping habits for a period of time. They might also have you do a sleep study. This involves sleeping in a hospital or sleep center while your doctor records data about things such as your brain activity and heart rate. This can also help rule out any other causes of your sleep problems, such as sleep apnea or narcolepsy.

Next, you may need a PET scan. This type of imaging test will give your doctor a better idea about how well your thalamus is functioning.

Genetic testing can also help your doctor confirm a diagnosis. However, in the United States, you must have a family history of FFI or be able to show that previous tests strongly suggest FFI in order to do this. If you have a confirmed case of FFI in your family, you’re also eligible for prenatal genetic testing.

There’s no cure for FFI. Few treatments can effectively help manage symptoms. Sleep medications, for example, may provide temporary relief for some people, but they don’t work long term.

However, researchers are actively working toward effective treatments and preventive measures. A 2016 animal study suggests that immunotherapy may help, but additional research, including human studies, are needed. There’s also an ongoing human study involving the use of doxycycline, an antibiotic. Researches think it may be an effective way to prevent FFI in people who carry the genetic mutation that causes it.

Many people with rare diseases find it helpful to connect with others who are in a similar situation, either online or in a local support group. The Creutzfeldt-Jakob Disease Foundation is one example. It’s a nonprofit that provides several resources about prion diseases.

It can be years before the symptoms of FFI start to appear. However, once they start, they tend to get rapidly worse over the course of a year or two. While there’s ongoing research about potential cures, there’s no known treatment for FFI, though sleep aids may provide temporary relief.