e made the statement before the Filipino community in Russia while poking fun at a singer he had a sung with in a duet earlier in a program.“I have a talent. I can look at you, but my other eye would be moving down,” Duterte said. “Look, the other eye is smaller.

It’s small, right? It moves on its own. Actually it’s myasthenia gravis. It’s a nerve malfunction.

“I got it from my grandfather. He’s also like this. So I believe, really, in genetics.

”Myasthenia gravis is a chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles and usually affects eye and eyelid movement, facial expression, chewing, talking and swallowing.

It has been listed by the National Organization for Rare Disorders or NORD as a rare disease.

Most people with myasthenia have no family history of the disorder.

It appears to occur spontaneously for unknown reasons, according to NORD. However, 3 to 5 percent of patients may have family members with it or other autoimmune disorders.

Its symptoms may include the drooping of one or both eyelids, blurred or double vision, a change in facial expression, difficulty swallowing, shortness of breath and impaired speech

Those with myasthenia gravis may develop tumors in the gland, which are often harmless but may become cancerous.

The disease may also cause respiratory failure, which requires immediate medical care.

A nationwide survey early this year showed that Filipino adults are worried about Duterte’s health, and more of them also believe the President has health problems.

In his previous speeches, Duterte has said he also suffers from migraine, back pain and Buerger’s disease.

He has undergone endoscopy and colonoscopy because he suffers from a gastroesophageal reflux disease called Barret’s esophagus.Duterte also faced a cancer scare last year after his doctors found a growth in his digestive tract.

However, the tests produced negative results.

He also said he was taking sleeping pills.Malacañang has declined to release Duterte’s medical bulletin, invoking the constitutional provision that disclosure is only needed once the President suffers from a case of serious illness.

Concerns about the President’s health have also been triggered by his absence in public events or if he has been out of the public eye for a week.