Is Kyron Horman Disappearance Tied to Stepmom's Postpartum Depression?

"Her emotional state was more erratic" after daughter's birth, husband says.

PORTLAND, Oregon, July 10, 2010 — -- There have been new twists and startling accusations in the case of Kyron Horman, the 7-year-old Portland boy who has been missing for more than a month. While his family clings to hope that he's still alive, they are raising new questions about his stepmother.

Kyron's parents, Kaine Horman and Desiree Young, have revealed one of the reasons they say they fear Kyron's stepmother, Terri Horman, is hiding something -- that she changed after the birth of her baby, Kiara, 19 months ago.

"She went through some postpartum depression after the birth, and her emotional state was just more erratic," her husband, Kaine Horman, said.

It's not just the so-called baby blues: Eight out of every 10 new mothers experience postpartum depression, a serious condition affecting many women within a year of giving birth.

But doctors say for a few women, what begins as mild depression can escalate over time to psychosis, impairing judgment, and in rare and tragic cases, it can lead them to kill.

Andrea Yates had a history of postpartum depression when she drowned her five children in her Texas apartment in 2001.

A postpartum psychosis case in Georgia last month ended in a 15-year prison sentence for Joanne Tucker, who beat her infant daughter to death.

While there is no confirmation of their claim, Kyron's parents said they believe postpartum depression could be a factor linking the stepmother Terri Horman to Kyron's disappearance.

"I just really want her to do the right thing," Young said. "I can't say it enough, that Kyron is still out there and he needs to come home."

There are no charges against Terri Horman; both she and her attorney declined to comment for this report.

Louann Brizendine, a neuropsychiatrist and author of "The Female Brain," told "Good Morning America" that for as many as one out of 20 women, the huge change in hormones after giving birth can lead to postpartum depression.

"Another group, one out of 1,000, may develop more severe mental illness called postpartum psychosis, and that is the one that's more associated with women killing their children and fantasizing [about killing their children]," she said, using the Andrea Yates case as an example.

What's the Difference Between Postpartum and Psychosis Depression?

Postpartum depression symptoms are marked by a lot of time spent crying, irritablity, depression or having no energy to care for self or baby, Brizendine said.

"Postpartum psychosis is where the mother actually loses touch with reality, bizarre thinking, strange ideas and may have what seems to be a complete personality change," she said. In the context of losing reality, a mother may think that "somehow the baby is evil and the baby may need to be killed to save it from going to hell."

Typically, the illness can surface three to six weeks after giving birth, but it can last intermittently up to one year or even several years, with "relapses for some time," Brizendine said.

Terri Horman's daughter is 19 months old.

"I have not evaluated this woman myself, but from the data I've heard like you have heard on the media, it sounds as if there's been some kind of evaluation of her that led them to take her daughter away from her for safekeeping," she said.

Data also points to Terri Horman not being suicidal, Brizendine said, otherwise officials would probably put her in a psychiatric hospital.