WEST FARGO (AP) - Six-year-old Ariana Kaseman and her 2-year-old brother, Lucas, have been sick their entire lives, and the reason is a mystery.

Their parents, Teresa and Kevin Kaseman, have made trips to doctors in Fargo and to the Mayo Clinic in Rochester, Minn., to try to find the source of the neurological problems and unending bouts of fever and pain their children suffer. Ariana and Lucas are confined to wheelchairs.

"We've checked with everything for them, and we've just not been able to come up with anything," said Dr. Janet Tillisch, a pediatrician at Dakota Clinic in Fargo.

"There's hundreds of diseases these kids could have, and every test has come up normal," Tillisch said. "We know it has to be something genetic because both kids are involved, but we just can't put a finger on it. It's very frustrating."

Insurance pays for some of the family's expense. Teresa Kaseman said that dealing with paperwork fights over what is covered and what is not consumes most of her non-work hours - time she would rather spend with her children.