Patrick O’Brien was 30 years old when he was diagnosed with Amyotrophic Lateral Sclerosis, or ALS. Commonly referred to as Lou Gehrig’s disease, ALS is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord. What that clinical definition means for O’Brien is laid out in his energetic, jocular and life-affirming film “TransFatty Lives.” O’Brien, a filmmaker, Internet sensation and DJ known as “DJ TransFatty,” made the film as a video love letter to his son, Sean, who was born well after O’Brien’s diagnosis.

The film’s opening sequence shows O’Brien falling down in his apartment and in the process knocking over a stack of 45 rpm records. It’s a heartwrenching and ominous moment for an audience that already knows the inevitable outcome of O’Brien’s illness. Nevertheless, he begins at the beginning, documenting his rapid decline from the very moment his doctor gives him the dire diagnosis and tells him he has two to five years to live. “A lot of people have asked me what it’s like to find out you’re going to die,” says O’Brien in the artificial voice in which he narrates the documentary. “It sucks. It’s strange.” Later in the film he’ll assert that his disease has inspired him to attain “enlightenment by shotgun. In a weird way, it’s exciting.”

Those kinds of dichotomies are ever-present in the film. As he records the months leading up to his son’s birth, O’Brien draws the heartbreaking comparison that his muscles are shrinking while his baby’s are growing. The baby is born and his life-affirming milestones continue to coincide with O’Brien’s downward spiral. As the son begins to walk, the father makes the monumental decision to have a tracheotomy so he can breathe on a ventilator and see his son grow.

Like O’Brien, the film is edgy, raw, irreverent—a pop-culture collage interspersed with the hard, body-centric details of living with a debilitating, terminal disease. The film showcases a bevy of archival materials from O’Brien’s life, as well as black-and-white footage interspersed with color and a number of soundtracks cut by DJ TransFatty himself. “I still have my mind,” says O’Brien. “It’s the only thing I can control.” By the end of the film, O’Brien is communicating with his film crew using eye movements.

Along with O’Brien, the other heroes of the film are the staff at the Leonard Florence Center for Living in Chelsea, Mass. Transferred there from a nursing home in Maryland, O’Brien is reborn in a place that eschews the nursing-home model O’Brien had come to know and dread. It’s the deliberate deinstitutionalization of a terminal illness. There are no nurses’ stations, food trays or pill carts at the Center. The place is very much a home, and to that end O’Brien’s request to have his walls painted hot pink is honored. At the Center he travels for the first time since his diagnosis to see his son in Florida. On another outing he goes to a Nine Inch Nails concert. He sports black nail polish and a colorful mohawk. “I am a freak on wheels,” he says. “I love it.”

“TransFatty Lives” will open the ReelAbilities Film Festival Boston on Sunday, April 3. It comes to the Boston area having won a number of audience awards for best documentary at several film festivals, including the well-known Tribeca Film Festival. The ReelAbilities Film Festival was originally founded in 2007 at Manhattan’s Jewish Community Center. In 2012, ReelAbilities festivals showing films by and about people with disabilities expanded to other cities. Boston’s festival is co-presented with the Boston Jewish Film Festival.

The ReelAbilities Film Festival Boston runs from Sunday, April 3, to Thursday, April 14. For more information and a complete listing of festival films and venues, please click here.