An expert sheds light on this bizarre and mysterious psychological disorder, which is the basis of the HBO show Sharp Objects and the documentary Mommy Dead and Dearest.

Credit: Anne Marie Fox/HBO

Spoilers for HBO’s Sharp Objects below.

In the opening scene of “Falling,” the penultimate episode of HBO’s limited series Sharp Objects, journalist Camille Preaker wakes up in her childhood bedroom to find that her clothes have been changed during the night. She’s hung over after attending a high school party with her younger sister Amma, and their mother Adora stands nearby, urging Camille to take medicine from an unlabeled bottle.

Like she has her whole life, Camille resists her mother’s attempt to care for her. But in the room next door, Amma is more willing. She allows Adora to give her various pills and syrups, and we see what at first appeared to be a hangover worsen throughout the episode—she stumbles around the family’s Victorian mansion sweaty and vomiting.

If you’ve read the Gillian Flynn novel the show is based on, you were probably eagerly expecting this scene, as well as the one that comes after. Richard, a detective working to solve the murders of two young girls, digs up the medical files of Camille and Amma’s sister Marion, who died decades earlier. The nurse who treated Marion tells Richard she suspects Adora has Munchausen by proxy syndrome, a psychological disorder whereby a caretaker, usually a mother, fakes, exaggerates, or causes an illness in a child, typically to gain sympathy and attention.

The syndrome may sound familiar to HBO viewers who watched the network’s 2017 documentary Mommy Dead and Dearest, which investigated the real-life Blanchard case. Gypsy Rose Blanchard had been diagnosed with a slew of diseases—including leukemia, muscular dystrophy, and epilepsy. At least that's what her mother, Dee Dee, told friends and neighbors.

But when Dee Dee was found dead in the Missouri home mother and daughter shared in 2015, a shocking story of deception and abuse unfolded. Turns out that Gypsy, who was 23 when her mother died, hadn't been ill at all. Like the fictional Sharp Objects sisters, Gypsy was a victim of Munchausen by proxy syndrome.

Both shows illustrate an extreme example of a mother who had the disorder; Gypsy ended up killing her mom to escape maltreatment, and while we don’t yet know how Sharp Objects will end (the series finale airs Sunday night at 9 p.m. Eastern), “Falling” implies that Adora was responsible for Marion’s death, and may have more recently had a hand in the murders of the two other girls.

But even less severe cases of Munchausen by proxy are harrowing to hear about and difficult to understand. We talked to an expert who shed more light on this bizarre disorder.

It's a deadly form of child abuse

Approximately 600 new cases are uncovered every year. "While only 9-10% of these published cases lead to death, 25% of the siblings of these victims had also been diagnosed with the same illnesses and have died," Marc Feldman, PhD, a clinical professor of psychiatry and adjunct professor of psychology at the University of Alabama in, Tuscaloosa, Alabama, tells Health. "So we conclude these siblings were mostly cases of Munchausen by proxy that weren't recognized."

The disorder is the most lethal form of child abuse, he says. Examples of the abuse illustrate why. A mother or other caregiver will feign or create illness by injecting the child with bacteria, placing their own blood in the child's feces, giving a child laxatives, or rubbing a child's skin with a caustic substance like oven cleaner.

Denial of these acts is extreme, too. "You can show videotapes from the hospital of the mother hurting the child or injecting bacteria into an IV, and they will deny it," says Feldman. "I never forgot years ago a mother was shown suffocating a child clearly and she said 'oh, I was just tickling her mouth.' They’ll avoid taking any responsibility at all costs."

The lies tend to start in infancy

A mom or caretaker with Munchausen by proxy usually begins faking her child's health when the child is pre-verbal or only beginning to speak, because manipulation is much easier. An infant or toddler may not be able to associate the mother's actions with their illnesses at such a young age. Only years or decades later, when a child develops and pieces the situation together, can he or she try to escape the abuse. In the Blanchard case, it wasn't until Gypsy was in her twenties that she actively tried to run away and later colluded with her boyfriend to kill her mother.

Warning signs can be hard to spot

When a parent says that a child is ill—and the child looks and acts visibly sick as well—it's hard to imagine that the illness could be a lie. But there are clues to look for. One hint: every episode of the illness only happens when the mother is alone with the child. Another warning sign is if other family members have died unexpectedly, says Feldman. And if the mother and child are separated and the child starts to heal or is no longer ill, that could also be a sign of Munchausen by proxy.

Mothers with Munchausen by proxy tend to have similar family situations. "Fathers tend to be absent in these cases, physically or emotionally," says Feldman. "In these cases, there is often a very traditional take on child care as the mother's province. Fathers don't get involved with the children or have jobs that require being away from the family for sometime." The disorder may be intergenerational too. A woman who has it may have had a mother or grandmother who was a hypochondriac or taught her children to turn health issues into dramatic situations.

It's a mental disorder and a form of abuse

Munchausen by Proxy was first considered a form of child abuse in 1977, when a British pediatrician referred to it as such in one of his cases. Before then, the disorder and its effects on victims were rarely discussed, says Feldman.

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In 2013, the Diagnostic and Statistical Manual of Mental Disorders classified the disorder as a mental illness. "The American Psychiatric Association labeled Munchausen by Proxy as an associated mental illness called 'factious disorder imposed on another,' so it's a mental illness and form of abuse," says Feldman. "I personally have a problem with this classification because it tends to exonerate mothers. They can say 'I'm just the victim of this mental disorder.' I prefer to talk about it as a form of mistreatment."