The new musical “The Bedwetter,” based on comedian Sarah Silverman’s memoir, is not as tight as a fitted sheet.

Potential abounds in the tangled show, which opened Tuesday night off-Broadway at the Atlantic Theater Company, especially in its central idea: that, to the mile-a-minute mind of a 10-year-old, waking up wearing wet pajamas can feel as emotionally traumatic as an adult dealing with divorce or depression. Life already sucks, even at 10.

“The Bedwetter” uses little Sarah’s nighttime problem as an insightful window into the struggles of the eccentric grown-ups in her family. 

That smart framework screams out for a bold and moving musical. So why does it come off so slight and tentative?

Holding the show back the most is an understandable flaw, considering the piece is about a famous person: There is way too much Sarah in it.

At the start, the exuberant and proudly weird girl (Zoe Glick) shows up for her first day at a new school in Bedford, New Hampshire, and introduces her family in peppy song.

Her pop (Darren Goldstein, perfectly cast) owns Crazy Donny’s Factory Outlet, a discount women’s clothing store; her old-Hollywood-obsessed mom, Beth Ann (Caissie Levy), spends most of her days in bed reeling from a tragedy; her teenage sister Laura (Emily Zimmerman) is too ashamed to so much as make eye contact with Sarah; and Nana (Bebe Neuwirth, miscast) is an acerbic alcoholic who has her granddaughter whip up Manhattans. Sarah grins and bears it, says “f–k” a lot and makes fart noises.

Comparisons to “Fun Home,” another autobiographical musical about similarly aged kid with an unusual family dynamic, are unavoidable. However, while that show went deep into the stormy lives of Alison Bechdel’s parents, “Bedwetter” is mostly a light, young-adult-style tale about Sarah. We don’t delve into her family nearly enough, and when we do, it’s casual and fleeting.

The humor also isn’t so sidesplitting as to make up for giving other characters the cold shoulder.

In the musical’s book, by Silverman and Joshua Harmon, nothing is as hilarious as her stand-up or the fabulous “Sarah Silverman Program.” And the jingle-like tunes by Adam Schlesinger, the “Crazy Ex-Girlfriend” songwriter who sadly died of COVID in 2020, don’t get laughs like “I’m F–king Matt Damon” from “Jimmy Kimmel Live” or “Nobody’s Perfect” from Silverman’s music-heavy special “Jesus Is Magic.”

Most of the funny is front-loaded into Act 1 (the booze gags are grating). Then in the second half, after Sarah’s friends (Charlotte MacLeod, Charlotte Elizabeth Curtis and Margot Weintraub) discover her bedwetting secret and a careless doctor prescribes Xanax for her outbursts, she becomes a shell of herself. A ghost. Noticing her grief, Nana and Beth Ann elaborate on the difficult roads they’ve also walked. Finally the show begins to be about something — but it’s too late.

Steeper hills to climb than the script are Anne Kauffman’s clueless direction and Laura Jellinek’s threadbare designs. The Silverman house, Nana’s abode, the school and a hospital room are all identical save for a bed here and a desk there. Bland walls rotate to reveal blander walls with a single sad shelf holding a few trophies or a TV set. For the theater that has housed Best Musical Tony winners like “Spring Awakening” and “The Band’s Visit,” plus the upcoming “Kimberly Akimbo” on Broadway, this set is surprisingly dowdy and devoid of character.

Kauffman, a pro at ushering new plays to the stage, lacks musical theater chops. The numbers (choreography is by Byron Easley) feel as if they were improvised at the last minute. And when characters speak, they are often propped against a wall on the side of the stage, half visible, not landing jokes because the jokes haven’t been visually set up or properly paced.

The most poignant and attention-grabbing scenes belong to Levy, in part because of her open-hearted portrayal of a person experiencing immense pain, but also because the bed she sits in is center stage. We can fully see her.

There are three superb comic performances: Goldstein bopping his head during a cheesy ’80s commercial for Crazy Donny’s is a scream; Rick Crom plays some wacko doctors and does a spot-on Johnny Carson; and Ashley Blanchet is campy as the fantastical Miss New Hampshire.

But they are all stymied by a production that is barely half-finished. The neglected “Bedwetter” needs some Pampers. Er, sorry — pampering.