(Cover) - EN Showbiz - Colin Farrell's son is a "happy" boy despite having a rare congenital disease.

Colin has two sons, James, seven, and 21-month-old Henry. While promoting his new movie Fright Night on Late Show With David Letterman last night, Colin made a poignant revelations about his eldest son's life with Angelman Syndrome.

Colin's son experiences lack of speech, but James is not too adversely affected by the disease. In fact, he was diagnosed by his doctor during a fit of glee.

"[James was diagnosed] actually when a doctor saw how happy he was," said Colin. "[The doctor] was like, Does he always smile this much?'"

Angelman Syndrome is a neurogenic disorder that only affects one in 30,000 children that is often misdiagnosed as cerebral palsy or autism. Characteristics of the disorder consist of seizures, lack of speech, development delay and difficulty walking or balancing.

Since this is such a rare disease, Colin is intent on exposing the condition to the masses. He also wants to support organisations that scientifically research the disease such as Foundation for Angelman Syndrome Therapeutics by asking people to donate their time or money to the cause.

"So there's not that much funding because it doesn't benefit pharmaceutical companies, of course," said Colin, "So cureangelman.org, if you want to go there and throw down a few dollars."

James began walking just shy of his fourth birthday. Colin ensures that his son is in good spirits.

"My boy happens to be highly functioning," said Colin. "I should say my boy's a really happy boy and I've in my life been around some children who are sick or suffering and to be honest my boy's doing really good."

Colin's new movie Fright Night will be in US theatres on August 19. (C) Cover Media