Parents desperate to help children they believe have rare, controversial disorder

“I just kept thinking, ‘What’s going on with my child?'” Vanessa Baier told “20/20” while fighting back tears.

Alexia had been breaking out into erratic, explosive behavior that would appear completely out of left field.

“It was just swings that were very dramatic and uncalled for, for the situation,” her father, Brian Baier, told “20/20.”

Parents desperate to help children they believe have rare, controversial disorder

Baier Family Photo”She had such a fun personality,” Vanessa Baier described her daughter, Alexia.

“There have been times where [her tantrum] was an hour and a half, two hours,” Vanessa Baier said.

Alexia, now 8, wasn’t always so volatile. Her mother, a special-needs teacher; her father, an accountant; and their oldest daughter, Kyla, had all welcomed a very typical baby girl to their loving home outside Chicago.

“She had such a fun personality. She was always laughing, smiling,” Vanessa Baier said.

And as Alexia began attending preschool, her mom said her daughter was excited and loved her new friends and teachers.

“She was on track. She was even advanced in different areas. She was just a typical 4-year-old,” AJ McCree, the school’s principal, told “20/20.”

Parents desperate to help children they believe have rare, controversial disorder

Baier Family PhotoThe Baiers admitted their daughter, Alexia, into a psychiatric ward after she tried to stab her mother in the eye with a mascara wand.

But in the winter of 2014, Alexia got sick. A doctor diagnosed her with strep throat.

“That was the first time she ever had strep throat,” Vanessa Baier said. “No big deal, just run-of-the-mill strep throat.”

Alexia was prescribed a typical course of antibiotics, but as the infection disappeared, her bubbly personality began to change.

“It was less than two days later. It was defiance and OCD [behavior]. She just all of a sudden seemed angry,” her mother said.

“It really came to my attention that something was off when Lexi would start to destroy the classroom,” McCree said, referring to Alexia. “It was a lot of screaming, a lot of hitting and kicking adults.”

(MORE: What is PANDAS, the disorder some doctors say can cause extreme behavioral changes in kids?)

Alarmed teachers isolated Alexia from the other preschoolers and even resorted to using bookshelves as barricades.

“Furniture would get tipped over. Bins of toys were dumped or thrown at people. When we would try and keep her safe in an isolated area, she would continue to elevate and elevate,” McCree said.

“They had to call in the social worker, the psychologist, the principal. I mean, there was a team of teachers involved,” Vanessa Baier said. “It was like a Tasmanian devil running through the classroom.”

Tearfully remembering her daughter’s worsening behavior, Vanessa Baier said she felt “a lot of guilt and personal blame about what am I doing wrong? And how can we help?”

McCree, the school’s principal, said that when a child suddenly acts out, it may indicate trouble at home, but, he said, Alexia was an anomaly, because her home life appeared very stable.

“When somebody switches temperaments, we look to see is something changing at the home? Whether it’s the parents that are separating and any violence that they might be exposed to that way and it just didn’t seem to be the case with this family,” he said.

Parents desperate to help children they believe have rare, controversial disorder

Baier Family Photo”It was like a Tasmanian devil running through the classroom,” said Vanessa Baier.

“We’re trying to team together to try to figure out what’s going on, but at the same time it’s like this just isn’t making sense,” Vanessa Baier said. “I don’t know how to de-escalate my own child.”

This was especially troubling to Vanessa Baier because de-escalating children in crisis is part of her responsibility as a special-needs teacher.

But things became dire when Alexia’s prolonged tantrums turned into threats toward her family and herself.

“Telling my 6-year-old (Kyla), ‘You have to stay in your bedroom because I don’t know what your sister is capable of,’ is heartbreaking. She knew the whole time. She had told me, ‘Something’s wrong with Alexia’s brain.’ She knew,” Vanessa Baier said. “‘Something happened because this is not my sister.'”

Vanessa Baier said Alexia knew something was wrong too.

“She would cry and say, ‘Mommy, why can’t I be good? I just want to be good.’ That broke my heart,” she said.

A trip for milkshakes turns into a scary moment

Vanessa Baier began taping Alexia’s episodes because her husband was often at work when the worst behaviors would occur.

“A lot of times he was discounting it,” Vanessa Baier said. “The psychologist we went to, she told me it was my mom guilt. … I was like, ‘Nobody’s believing me.'”

It took a toll on Vanessa and Brian Baier’s marriage.

“Him not believing me, that hurts, and then the arguing about how to discipline her and what was going on,” Vanessa Baier said.

“At the beginning, I’m at work, working 50, 60 hours a week. I can’t be on the phone with you for an hour talking to you every day or come home every day to help you deal with these situations,” Brian Baier said. “Before I really recognized what it was, that it wasn’t something that she could deal with alone and shouldn’t have to.”

Kyla, Alexia’s older sister, said the tantrums scared her.

“When Alexia starts throwing a tantrum, I kind of get sad,” Kyla told “20/20.”

Parents desperate to help children they believe have rare, controversial disorder

PlayHome videos show young girl throwing unexplainable, volatile tantrums

When she was in the middle of a flare-up, Alexia said, she couldn’t sense that something is happening.

“I just go and try to hurt people,” Alexia told “20/20.”

After three months of relentless emotional anguish, Vanessa Baier said an incident during a simple run for milkshakes became the final straw.

It seemed like a routine trip until Alexia insisted on having some of her mother’s milkshake while Vanessa Baier was driving them home.

Vanessa Baier had told Alexia: “No.”

“Then she (Alexia) said, ‘If you don’t give me your milkshake, I’m going to unbuckle my seatbelt,’ and I didn’t respond,” Vanessa Baier said. ̶