Sam Kean has a variety of science-related toys in his D.C. apartment. His book “The Violinist’s Thumb” focuses on DNA. (Bill O'Leary/WASHINGTON POST)

Ehlers-Danlos syndrome is a rare conglomeration of connective-tissue disorders. Symptoms include migraines, easily bruised skin, resistance to anesthetics and, most markedly, hyper-flexible joints that bend in ways bordering on the grotesque. I know all of this because I have become convinced — in the obsessive, giddy way of hypochondriacs — that I have Ehlers-Danlos syndrome. I have become convinced of this because I have just finished reading “The Violinist’s Thumb.”

“All right,” Sam Kean says, settling into a small booth at a Panera in the District. “Show me what you can do.”

I can bend my wrist down to my forearm. I can wrench my fingers backward until they rest on my hand. A hitchhiker’s thumb might arc into a 90-degree angle; mine will go to 135.

Kean appraises my impromptu circus freak show. “Hmm,” he says. “Hmm.”

Kean is 33, slightly built, shaggy-haired. He is the author of “The Violinist’s Thumb,” a freshly published romp through the history of genetic science and the double helixes that make up our personhood. Like Kean’s 2010 bestseller “The Disappearing Spoon,” which was a mash note to the periodic table of elements, “The Violinist’s Thumb” is a loosely jointed collection of true stories. [Loose joints: Also a symptom of Ehlers-Danlos syndrome!]

Kean was raised in South Dakota before moving to Washington. He has that Midwestern matter-of-factness to the way he speaks, tinged with nerd-boy excitement when the topic is genetics. (Bill O'Leary/WASHINGTON POST)

We have come to this Panera to have a loosely jointed conversation about DNA, which is really a conversation about who we are — which is really a conversation about how obsessed we are with who we are. Witness the popularity of NBC’s celebrity genealogy show “Who Do You Think You Are?” or the rampaging success of “The Immortal Life of Henrietta Lacks.” (If we’re splitting hairs — and since we’re splitting cells, we might as well — we’d note that that book wasn’t about immortal life so much as it was about immortal cell lines.)

In Kean’s book, one encounters the debonair Fly Boys, whose grody work — they bred fruit flies — informed our understandings of genetic heredity. One encounters 19th-century violinist Niccolo Paganini, whose extraordinarily bendy thumbs gave Kean’s book its title. His flexibility made him a virtuoso, but it might have been a symptom of Ehlers-Danlos, the genetic abnormality that hastened his death.

“I’m kind of a sucker for the retro-diagnoses,” Kean says.

Take, for example, King Tut. Through DNA, we’ve learned that the boy king had a cleft palate, a club foot and a truckload of other medical anomalies. His parents, it turns out, were brother and sister.

Or take King Tut’s incestuous father. For a long time, archaeologists wondered if Akhenaten, too, had some kind of illness. “You look at drawings of Akhenaten, and he looks very strange,” Kean says. “He has this elongated head and enormous lips. Sometimes, he has huge buttocks or a potbelly.”

Maybe he was just ugly? I ask.

“No — not just a little off, but very off.” So scientists did a CT scan and some genetic tests. It turns out Akhenaten looked completely normal.

”The Violinist's Thumb” by Sam Kean. (Little, Brown and Company)

The big butt, the stretchy head — all of it was an artistic costume designed to give the pharaoh some of the physical qualities commonly attributed to gods. The weird body was propaganda; the scientific speculation had been just guesswork.

What’s remarkable in reading “The Violinist’s Thumb” is how much of scientific progress has been just that — experiments conducted in bathrooms-cum-laboratories by nuns-turned-biologists. Many of the stories in Kean’s book take place before scientists realized what DNA is.

“They thought that proteins were what controlled inheritance — partly because DNA has only four letters: A, C, G and T. That just seemed like such a limited alphabet. Imagine trying to speak a sentence with only four letters. Whereas with proteins, we have 20 different amino acids,” Kean says.

Kean was raised in South Dakota before moving to Washington. He has that Midwestern matter-of-factness to the way he speaks, tinged with nerd-boy excitement when the topic is genetics. His parents’ names are Gene. And Jean. Gene and Jean Kean. He gets why this is funny. He gets why science is funny, why our bumbling toward discovery makes us almost more human than the discovery itself. He writes with a humor and humanity that make him poised to become the next Brian Greene, maybe, or Oliver Sacks — explaining small corners of the universe one case study at a time.

As part of his research for “The Violinist’s Thumb,” Kean sent off a vial of his saliva to be analyzed by one of those mail-order genetic-testing companies. “I just did it sort of on a lark — I thought I’d find something funny or unusual that I could use in the book.”

But in scrolling through the diseases that the company could test for, he was stopped by Parkinson’s. His grandfather had the illness; Kean was plagued by memories of his suffering. He ended up blacking out the disease, effectively saying that if he had the genes, he didn’t want to know.

Only after finishing the book did Kean summon the nerve to request the Parkinson’s analysis. “That was when I felt like I’d gotten enough of an understanding of how genes worked, so that I could face it.”

When he finally peeked at his test results, “it was kind of a switcheroo.” The test first said he didn’t have an increased risk, but later he received an update saying that he might after all. “But, by that point, I was able to face it. It’s a pretty small risk, and I’m not going to live in fear of it.”

Genes are mysterious things, still unpredictable after all of our research, flecks of humanity that can destroy lives but, just as often, can teach us to appreciate the strange wonder of our existence.

“Our evolution could have gone in different directions a lot of times,” Kean says. “We could have gone extinct at some points. We might not have gotten our big brains, or Neanderthals might have made it while we did not. If you look at the big picture, it gives you an appreciation for how lucky our history is — and a little bit of pride for our species. We really have had an amazing journey.”

Sam Kean reads from “The Violinist’s Thumb” on Wednesday at 7 p.m. at Politics and Prose, 5015 Connecticut Ave. NW, and Aug. 2 at 7 p.m. at One More Page, 2200 N. Westmoreland St., Arlington.