This bizarre road trip gone wrong may be a rare case of the shared psychosis called “folie à deux” in action

Running for safety.
Running for safety.
Image: Reuters/Lucy Nicholson
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How did a family road trip end with a police investigation and two people in psychiatric care?

The ongoing saga of the Tromp family has left Australia stumped. The family of five disappeared over a week ago, leaving behind passports, credit cards, and mobile phones. All five family members would later be found one by one, some clearly traumatized.

Here’s how the road trip unfolded

  • On Aug. 29, Mark Tromp, aged 51, and wife Jacoba, 53, fled their farm in the outskirts of Melbourne, taking their three adult children—Riana, Mitchell, and Ella—and heading north.
  • Thirty miles into the road trip, eldest son Mitchell was made to throw his phone out of the car window. Mitchell, 25, eventually left the family trip on Aug. 30 at Bathurst, New South Wales and made his own way back to Melbourne.
  • Eldest daughter Riana and youngest child Ella would also abandon their parents, leaving at Jenolan Caves. They headed to Goulburn, where the sisters split up.
  • Ella stole a car in Goulburn, New South Wales, and drove it back to Victoria. She was later charged with theft of a motor vehicle. Her sister Riana was found “catatonic” hiding in the back of a man’s car in regional NSW, not knowing her name, nor where she was. She was eventually taken to Goulburn Hospital.
  • On Aug. 31, police found the family car in Victoria’s north-east after they receive a report that it was seen following another car. Police pulled the car over and a man thought to be Mark ran away.
  • Jacoba is found on Sept. 1 by a member of the public and taken to Yass hospital and transferred to Goulburn hospital to be treated alongside Riana.
  • Mark is finally found on Sept. 2 in good health on a street near the Wangaratta airport. He later releases a statement apologizing for the “hurt and concern” caused by the trip. The family would take the time to recover and receive appropriate assistance, including mental health services.

While it still remains unclear why the family went on the road trip, Ella later told reporters: “I think our state of mind wasn’t in the best place.” Quite the understatement.

Mitchell told local media that his parents were fearing for their lives before they decided to flee. While he’d never felt in danger, he went along with his family to see where they were going. He appears to have been the only one who didn’t believe his family was in imminent danger.

Folie à deux

The traumatic road trip has left some wondering whether the family were suffering from a rare shared psychotic disorder known as folie à deux (which is French for ”the madness of two.”) It was first coined in 1877 to describe the transference of delusional beliefs from one person to another who knows them well. Married couples, siblings, and parents and children accounted for over 90% of the cases of folie à deux.

In 2008, Swedish twins Ursula and Sabina Eriksson came to national attention when footage showed them running into oncoming traffic on a busy highway in England, near Liverpool. Both sisters were hit by cars, leaving one sister unconscious for several minutes. They had resisted help from paramedics and officers, with Sabina shouting, “They’re going to steal your organs.” Sabina was arrested for attacking an officer and later released, when she went on to stab a man to death. She admitted to manslaughter on the grounds of diminished responsibility and sentenced to five years.

These delusional beliefs can affect more than two people, which was highlighted in the case of shared psychotic disorder involving three biological sisters in South Carolina—a folie à trois, perhaps. The youngest of the three sisters became convinced there was a problem with the Bible and was chosen by God to make it right. In order to follow God’s commands, the sisters decided they needed to go to a house and demanded to be let in. When the owner refused, they tried to break into the house and attacked the police officers that were called. After they were arrested, the three sisters were put in the same cell in a small local jail, where they prayed, chanted, and sat in a circle while nude.

They plead temporary insanity. All three sisters were discharged and were prevented from visiting each other without supervision.

And then there’s the Slender Man phenomenon. Two 12-year-old girls lured a classmate into the local woods and proceeded to stab her 19 times to please a mythical internet creature known as the Slender Man. The creature, which became a widely popular Internet horror meme, was often depicted as a tall, thin, faceless man in a suit who preyed on children. The two girls told officers that by killing their classmate, they would earn Slender Man’s protection and would be able to live with him in a mansion in the forest.

While the rest of the world speculated on what impact these delusions had on these girls, a Wisconsin court ruled that both girls would be tried as sane adults. The girls’ lawyers insist they both suffer from mental-health problems .

Most of what’s known about folie à deux is is derived from case reports and anecdotes, making it difficult to study in a controlled manner. There’s therefore little known about the prevalence and best treatment. The disorder, though extremely rare, has garnered attention in popular culture, appearing in The X-Files, Law and Order, and Criminal Minds.