This is the kind of movie that congratulates itself for casting a comedienne in a dramatic role and a straight male comic as a gay guy. Maggie and Milo are fraternal twins who are estranged (for 10 years), living on opposite coasts, and seriously depressed for reasons that seem dissimilar but boil down to past family trauma. That Maggie and Milo are played by Kristen Wiig and Bill Hader will get this mediocre dramedy more attention than it deserves. That their performances are good oughtn’t be surprising (the two SNL pros have plenty of experience with the comedy of awkwardness). That their script is so tonally sad-happy yet familiar, one has to attribute to the inexperienced writers. At NYU film school, Mark Heyman and Craig Johnson started scripting something about a student/teacher sex scandal, then shelved the project for years. After Heyman co-wrote Black Swan and Johnson directed True Adolescents here in Washington state (he being a Bellingham native and UW grad), they reconceived the project to focus on the damage wrought on Maggie and Milo many years later, as adults.

And from that, God help us, come healing and forgiveness and confronting the unpleasant past. What Skeleton Twins attempts, but fails, to bring to this sentimental game is against-the-grain novelty. You see, Maggie and Milo are catty, sardonic misanthropes, angry at the world because they haven’t lived up to their youthful potential. (When Milo says “We’re both fuck-ups,” it’s a badge of honor, really.) A failed actor, he returns home to New Jersey, where she’s a dental hygienist married to a doofus (Luke Wilson) whom she treats with gentle contempt (as does the film). Milo seems to have been jilted by some guy back in L.A., but the real problem (Ty Burrell of Modern Family) is waiting in his hometown. Why’d he come back? Perhaps Milo has a misguided notion of love—as opposed to Maggie’s inability to love. (Drunken bathroom sex with strangers is a different matter.)

Skeleton Twins tries very hard, too hard, to leaven the pathos in the Dean family’s past with Maggie and Milo’s insular humor. Still, the snark bogs down in melodrama, and no amount of ’80s pop montages can really change the film’s trajectory. (When even the bitter Maggie can declare “We’re supposed to be there for each other,” you know the cause is lost.) If the jokes were there, a spirit of wrist-slitting dark comedy might emerge. But Heyman and Johnson aren’t from the SNL or Apatow combines. Nor does Skeleton Twins compare well with straight sibling dramas like The Savages or You Can Count on Me. Perhaps the lesson to this heartfelt misfire is that mixing genres is very, very difficult. And if you don’t get the balance right, it’s like kissing your sister. Opens Fri., Sept 19. at Harvard Exit. Rated R. 91 minutes.

bmiller@seattleweekly.com