At age 2, Wendell Sherman-Strand still can’t sit up, walk or talk. The curly-haired Minneapolis boy doesn’t have the muscle control to grab a rattle or stand on his own.

And nobody knows exactly why.

So far, every test his doctors have run to find a diagnosis has come up empty. Now, his specialists at the University of Minnesota want to comb through his DNA for an answer.

They’re sending a teaspoon of his blood to a lab in Texas to sequence his genetic makeup.

Wendell is one of the first patients at the university to undergo the newest generation of genetic testing, known as “whole exome sequencing.”

In effect, it allows scientists to go on a fishing expedition through the human genome in search of troublesome mutations.

“Instead of testing one gene at a time, we’re testing really all known genes simultaneously,” said Dr. Christine Eng, senior director of the Medical Genetics lab at Baylor College of Medicine in Houston, where the test is being conducted.

The test is still a rarity — it’s only been widely available for about 18 months. And the state of the art is still so primitive, relatively speaking, that there’s no guarantee it will find a definitive answer.

But for Wendell’s parents, Katie Sherman and John Strand, it’s a chance to solve a medical mystery that has baffled the experts from the start.

A medical netherworld

Wendell’s face lights up with a megawatt smile as he arrives for physical therapy at the university’s Amplatz Children’s Hospital. His bright blue eyes wander randomly — an effect of his nameless condition — but he understands more than he can express, his mother says.

He squeals with glee as Katie Larson, his therapist, balances him on a giant therapy ball. “Come on up,” she says, coaxing him to lift his head. “Go go, fight fight, go go go. You did it! Good job.”

Then she props him up while his mother reads him a book, and he visibly struggles to lift his hand to turn the page. “Another book?” Larson asks. Wendell clasps his fingers to signal the word “more.”

“He does make progress,” his mother says. “It’s just at a really glacial pace.”

Sherman said she’d always assumed that doctors “had a label for everything.” But that was before Wendell, her second son, was born in April 2011.

At first, Sherman and her husband, a high school teacher in Minneapolis, saw no reason to worry. Wendell was a hefty newborn, weighing in at more than 10 pounds.

The couple had no hesitation taking him and his older brother, Bjorn, for summer break to a one-room cabin with no running water near Silver Bay. “We were kind of removed from everything,” she said.

Then, at a family reunion when Wendell was 2 months old, they saw a baby boy who was just a month older.

“I remember thinking, ‘Wow, what a difference one month makes,’ ” Sherman said. The other baby reached out his arms and kicked his legs, while Wendell curled up in a fetal position. “There were moments up there when I was like, well, shouldn’t he be grabbing things? He just didn’t have the strength to hold anything.”

By his six-month checkup, her fears were confirmed. Wendell couldn’t hold his head up when he was pulled to a sitting position. The doctor referred him to a specialist, who referred him to a neurologist. At that point, Sherman said, “I just broke down crying.”

A battery of tests, from MRIs of his brain and spine to a biopsy of his thigh muscle, turned up nothing.

For the family, there were only more questions. Would he grow out of it? Learn to talk? Learn to walk?

“Nobody knew,” his mother said. “You’re in this netherworld of just not knowing how to think.”

That isn’t unusual when it comes to children with developmental delays, said Dr. Peter Karachunski, Wendell’s physician and a pediatric neurologist at the university. “Sometimes it’s easy to answer the question, and sometimes it’s quite difficult.”

Wendell’s case turned out to be particularly challenging, he said. Unlike some conditions that can be traced to a single genetic defect, the little boy’s symptoms could be caused by many. “So we’re kind of stuck right now,” Karachunski said.

That’s why he suggested the gene sequencing test.

Detective work

The test concentrates on about 3 percent of the human genome where “most genetic diseases and most mutations tend to fall,” says Matt Bower, a genetic counselor at the university. That area is known as the exome, he said. “It’s the most likely place to find mutations.”

The test relies on massive computer power to winnow down the suspects, combing through millions of snippets of DNA. “It’s like when you’re looking for a murder suspect,” Bower said, “you’re looking at people with a criminal history vs. just going door to door.”

The whole process takes about 15 weeks and costs about $7,000, said Eng, who oversees Baylor’s medical genetics lab. One reason it takes so long, she said, is that there’s a lot of interpretation. The results are rarely clear-cut — they may turn up genetic variations that have nothing to do with Wendell’s condition. “We have to determine which results are clinically relevant and which ones are not,” she said. “It becomes almost like a puzzle.”

So far, Baylor has run about 1,100 of these tests, with a success rate of 26 percent, she said, meaning only one in four cases comes up with a likely diagnosis.

Even then, the answer only rarely the points the way to a new treatment, she said. More often, it just puts a name to the condition. But that, she said, “is very important to families, and it’s important for physicians, too.” So far, only about a dozen patients at the University of Minnesota have had the test, according to Bower.

Wendell’s parents know there’s a good chance they still won’t have an answer when the test is done. In some ways, Sherman said, “it really doesn’t matter.” Her son is getting therapy to strengthen his muscles and help him communicate, and the family is adapting: they’ve started an online fundraiser, called “Wheels for Wendell,” to buy a handicapped-accessible van.

“In an ideal world, I guess I would love an ultimate prognosis,” Sherman said. “To be honest, I’m not expecting answers,” she added. “Whatever they do find, if they find anything, will be very rare.”