Story highlights With North Korea's leader out of public eye, sister's profile increases

A think-tank run by defectors says she may be temporarily leading the government

Kim Yo Jong is in her twenties; she attended private school in Switzerland

The mystery surrounding North Korea's erratic young leader, Kim Jong Un, only deepens by the day.

He has not been seen publicly in more than a month. Rumors are flying that Kim is ill with gout, diabetes, even possible problems with his ankles. Now, a group of defectors say they believe Kim's younger sister, Kim Yo Jong, may be running the country while he recuperates.

The North Korea Intellectuals' Solidarity, a think-tank run by defectors, says Kim Yo Jong may be at least temporarily leading the government. The group has not revealed the source of its information, and CNN cannot independently confirm it. But Kim Yo Jong's star appears to be rising.

Michael Madden, who runs the blog North Korea Leadership Watch, says Kim Yo Jong has been identified in North Korean media as deputy director of the Workers' Party, a very powerful position.

Victor Cha, an analyst with the Center for Strategic and International Studies who previously handled the North Korea account with the National Security Council, says Kim Yo Jong began surfacing publicly earlier this year at party functions.

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"Clearly it's an effort to slow-track her into becoming somebody who is important within the system," Cha says. "I can see how it's possible that she's in some sort of temporary position. It's very difficult for the North Korean system to run without one of the Kim family at least titularly in charge. So, if Kim Jong Un is indisposed, she's really the only available body that's left, in terms of a direct Kim family line."

Who is Kim Yo Jong?

Madden says Kim Yo Jong was born in 1987 or 1988, and attended private school in Switzerland with Kim Jong Un. They both stayed at the North Korean embassy while attending the Swiss school, Madden says, and lived there under assumed names.

Madden says Kim Yo Jong is the youngest of seven siblings their father, Kim Jong Il, had with four women. Many of them are half-siblings, but Kim Jong Un and Kim Yo Jong have the same mother.

Madden says Kim Yo Jong was always close to her father, and after returning from Switzerland, she was appointed to positions of responsibility in the government. She would act as an advance-team leader, inspecting sites before official visits, and had administrative duties as well.

Now, he says, she continues those duties and has taken on more responsibility under her brother's rule: dealing with policy and receiving intelligence briefings. She acts "almost like a White House chief-of-staff would," Madden says.

He says he believes she had a large role in planning the recent trip by three top North Korean officials to South Korea while her brother was absent from the scene.

Ready for prime time?

Given her age and that so little is known about Kim Yo Jong, North Korea-watchers are concerned about her being in the top leadership spot, if only temporarily. The stress and palace intrigue inside the North Korean regime, they say, may be overwhelming.

"If in fact she is running the country -- as someone in their early to mid twenties, to me that is quite alarming," Cha says. "It means there is something seriously wrong with Kim Jong Un and there is some sort of void that they're desperately trying to fill."

All eyes will be on a significant event this Friday, October 10. That's the 69th anniversary of the founding of the ruling Workers' Party. Kim Jong Un attended the anniversary event last year. If he doesn't show up at Friday's ceremonies, concern over his public disappearance will only grow.

If he does attend, intelligence analysts will be looking at his appearance, his body language -- every detail -- very carefully.