Monica & David, a stirring, eye-opening documentary about two people with Down syndrome who fall in love, begins where you would expect it to end: with the couple's wedding ceremony in March 2005.

The lavish, festive affair is a highly emotional experience for Monica and David's parents and relatives, whose faces register a combination of joy and worry. Yes, everyone is thrilled that the couple -- born with a genetic disorder that affects roughly one in 800 babies -- has defied the odds and found romance and happiness. But once they're married, then what?

Monica & David, which premieres on HBO at 8 p.m. Thursday after almost a year of racking up awards on the film-festival circuit (including Best Documentary at Tribeca), follows its protagonists as they embark on their life journey. Their disability prevents them from being completely independent: They rely on help from Monica's mother and stepfather, Maria Elena and Bob Walters, with whom they live.

LACK OF ACCEPTANCE

But at what point does that need for assistance become an impediment? That question initially intrigued Alexandra "Ali'' Codina, Monica's cousin, when she noticed the nervous mood surrounding her family in the weeks before the wedding.

"There was still a lack of acceptance within the family as this being a marriage between two adults," Codina, 32, says. "They were still being seen as if they were children. The lack of acceptance was unspoken, but it was there. Not just within the family but also at large. People who heard Monica and David were getting married would always say ‘Isn't that cute?'

‘‘Being a family member, I had a specific level of understanding about this problem, and I had volunteered for many years for programs for adults with disabilities that Monica and David later attended. I felt like I had the privilege of understanding in a very different way who Monica and David were and what their love and life were about."

So Codina, then a programmer for the Miami International Film Festival, took three weeks off, obtained a digital video camera "through a friend of a friend'' and began filming the preparations for the wedding -- Monica's bridal-gown fitting, the rehearsal dinner -- and finally the ceremony. She amassed 30 hours of footage, then returned to her post at the festival, periodically dropping in on Monica and David with her camera.

MAKING CONTACTS

Two years later, she quit her job to concentrate full time on her film. Using savings, Codina hired an editor to help her carve out a nine-minute development trailer that would show potential distributors and financiers the movie she had in mind. She applied to and was accepted by an initiative of the Tribeca Film Festival that allows unknown and first-time filmmakers to pitch their projects to industry executives.

Through the program, Codina landed a meeting with HBO executives, with whom she had already established contact. She had sent a copy of the trailer to Nancy Abraham, senior vice president of the cable network's documentary division.

"We had our first face to face at the festival, and a few months later they made a first-look offer," Codina says. "That basically gives them first dibs to the movie when it's finished. It's basically a very tiny grant, but it's something that helps a lot when you apply for larger grants from other institutions."