AUSTIN, Texas (AP) — A family spokesman says Luci Baines Johnson, the youngest daughter of former President Lyndon Johnson, is being treated at the Mayo Clinic for what doctors suspect is a rare autoimmune disorder that affects the nervous system.

Spokesman Tom Johnson says an emergency medical charter flew Johnson to the clinic in Rochester, Minn., on Friday. She was admitted to a hospital in Austin, Texas, on Wednesday after experiencing weakness in her limbs.

The spokesman’s statement says doctors suspect Guillain-Barre syndrome, which affects the nerves that control movement and can cause paralysis. He says the former first daughter was in excellent health before she was taken to the hospital this week.

He says Johnson’s husband and her sister, Lynda Johnson Robb, are among the relatives with her at the hospital.