(NEXSTAR) – Robert F. Kennedy, Jr., who testified before the Senate Wednesday, has struggled for decades with a rare disorder affecting his speech. The nominee to lead Health and Human Services has spasmodic dysphonia, which causes his voice to sound strained and raspy when he speaks.

Spasmodic dysphonia is a neurological disorder that causes muscle spasms in the voice box or larynx, according to the NIH. How severe the spasms are can range greatly. For some, they may find speech strained for a few words every several sentences. In more severe cases, people can have difficulties speaking at all.

Spasmodic dysphonia is more likely to affect women, according to Johns Hopkins Medicine, and symptoms typically surface between age 30 and 50. Kennedy developed the disorder in his 40s, he told NewsNation.

Research into what causes the spams is ongoing, but the NIH reports it’s believed to be related to a problem with part of the brain called the basal ganglia, which helps coordinate muscle movements throughout the body.

There is no cure for spasmodic dysphonia, but there are treatments available. Botulinum toxin (or Botox) can be injected into the affected muscles to reduce spasms.

Kennedy has expressed self-consciousness about the disorder in the past. He said in a town hall on NewsNation, “I cannot listen to myself on TV.”

President Donald Trump nominated Kennedy as his pick for Health and Human Services secretary. As a vaccine skeptic, he’s a controversial figure when it comes to health and health care, leading to a contentious confirmation hearing on Wednesday.