Throughout the majority of Parade Productions’ “The Last Schwartz,” at Mizner Park Cultural Arts Center, the character of Simon (Mark Della Ventura) sits slumped on a stool on stage left, his forehead resting on his telescope, gazing into the vast nothingness of space that only comes alive in his imagination. He’s almost 100 percent blind, he shirks at the slightest gesture of physical contact with another person, he’s clearly on the severe end of the autism spectrum, and he doesn’t talk much; when he does, it’s usually about doomsday theory. He’s dressed in a blindingly white getup tailored for his sensitive skin, but the way he sits, it looks like a straitjacket.

Which wouldn’t be inappropriate attire in this madhouse of a play, written by Deborah Zoe Laufer, about a dysfunctional family (is there any other kind in the American theater?) meeting to honor the first anniversary of their patriarch’s death. His four siblings have gathered in their ancestral home to perform this traditional Jewish rite; there’s Norma (Candace Caplin), the eldest and most obstinate member of the tribe; Herb (Ken Clement), who seems content with his newspaper and his feet up but who may be living a life a quiet desperation; Gene (Matt Stabile), a video director who has strayed from his heritage; and the ever-present Simon.

Most of the drama, though—and the comedy, for that matter—revolves around two of the siblings’ other halves, with Kim Ostrenko as Herb’s wife Bonnie and Betsy Graver as Gene’s latest plaything Kia. Both act as the wrenches thrown into the familial machine, whose actions will derail the intended proceedings.

As she elucidates Bonnie’s dark backstory—namely a history of miscarriages, a misguided affair and a repressed family secret—with believable tears and anxiety, we watch Ostrenko’s veneer of marital normalcy chip away until she’s largely an open wound. It’s a vulnerable and devastating performance. Graver likewise excels as another hot, ditzy, plastic blonde who confuses astronomy for astrology and seems to possess no social decorum. For years, she’s become typecast in these parts for a good reason—she can play them with unguarded effortlessness and an actorly intelligence that belies the character’s dim wit.

Caplin, Clement and Stabile are fine, blending into the ensemble without showing us anything particularly exceptional (Caplin isn’t the first actor to sound unconvincing when reciting the Kiddush in Hebrew before a meal, and she won’t be the last). Director Kim St. Leon moves the play at an agreeably liquid pace, finding a tone that hews perhaps too closely to farce at times. The scene where Gene tries to ward off Bonnie is right out of a Jack Lemmon comedy from the ‘50s, all nervous glances and emasculated rapprochement. It feels archer than its surrounding scenes, but it works anyway.

My eyes often drifted back to Simon, though, who in some ways is the play’s most important character and its most tangential. His presence is a constant reminder of the family’s neglect of his condition, but he never comes across as a piteous creature; St. Leon and Della Ventura go a long way toward finding the real person beneath the staggered speech and facial tics. We get real Method-style immersion from Della Ventura, who disappears into this part better than he ever has before; it’s a testament to his abilities that even though he does very little onstage, we miss him the moment he leaves it.

Ironically, he may end up being the most enviable character in the show. When surrounded by so much crazy contention, staring off into nothingness sounds pretty appealing.

“The Last Schwartz” runs through Feb. 23 at the Studio Theatre at Mizner Park Cultural Arts Center, 201 Plaza Real, Boca Raton. Tickets cost $35 to $40. Call the box office at 866/811-4111 or visit paradeproductions.org.