The two brothers, 9-year-old Abdul Rasheed and 13-year-old Shoaib Ahmed have come to be known as ‘Solar Kids’ and has mystified Pakistani doctors. The two suffer from an affliction so peculiar that there are no other known cases of the condition anywhere in the world.

They are like other children during the day. They’re able to talk, walk, eat, and be physically active. But when the sun goes down, almost as though they’re under the effects of an enchanted curse, they’re deprived of movement or the ability to speak. Once sun goes down, they both become paralyzed – unable to move or talk.

Mohammad Hashim, the father of the two brothers, comes from a village near Quetta, the capital of southwestern Baluchistan province. He and his wife are first cousins and two of their six children died at an early age. Their other two children have not displayed any unusual symptoms.

Doctors remain perplexed by the condition, though they believe it may have something to do with genetics, as the boys’ mother and father are first cousins. “We took this case as a challenge,” said Javed Akram, a professor of medicine at the Pakistan Institute of Medical Sciences.

Akram said the government is providing free medical care to the siblings, who came from an impoverished family.

The pair have been under observation by doctors at a hospital in Islamabad where efforts have been underway to determine exactly what is causing their unique symptoms. One theory – that the sunlight itself is keeping them going – has been ruled out as it was found that the boys are able to function just fine in a pitch black room in the middle of the day.

Researchers are collecting soil and air samples from the family’s home village, and sending the brothers’ blood samples to overseas medical labs for examination.

While temporary paralysis and sleep paralysis — caused by nerve damage or a halting of muscle movement during REM sleep, respectively — are real conditions that can occur in ordinary people, neither of these things appear to be causing the brothers’ syndrome. Doctors hope that, with time, they’ll be able to learn what’s causing the disease, and prevent it from progressing with treatment.

While talking to the brothers, “I will become a teacher,” Shoaib Ahmed told the AP, and his younger brother said he wants to be an Islamic scholar.