SACRAMENTO, Calif. — They are both Harvard-educated and in their late 30s — he a cardiologist, she a pediatrician. They have three children, a boy and two girls, with a fourth on the way. They have a spacious home in Sacramento's Pocket neighborhood.

Such a charmed life. Such blessings to count. Such a model family.

What you wouldn't know until you cross the threshold at Howard and Tracey Dinh's home is the stress that colors their existence like dreary wallpaper, the challenge of making it through each day with at least one nerve left unfrayed, the anxiety that takes hold whenever they try to exhale.

The Dinhs are the parents of an autistic child, Austin, 7. They love him dearly, care for him constantly and see cognitive improvement almost daily.

But they know Austin won't live a life like Allie, 4, and Anna, 2. Which means their family life — not to mention their careers — never will be quite what they pictured as a couple starting out, which is fine. They came to terms with that long ago.

That doesn't mean there isn't stress. There's plenty of it. "It's one of those things that's all-consuming," Tracey says.

What you also wouldn't know until you meet with the Dinhs is how lucky they consider themselves, how thankful they are their professional backgrounds provide a buffer against money worries.

"I can't imagine what it's like for families where they don't have the financial means, or even a single parent," Tracey said. "In a lot of ways, we are fortunate."

Yet the Dinhs are not immune to caregiving burdens. Some things transcend class distinctions.

Researchers at the University of Washington Autism Center found parents of autistic children show higher stress than those whose children had other developmental-delay issues.

There are hundreds of thousands of such parents: The Centers for Disease Control and Prevention says autism spectrum disorder affects 1 of every 110 U.S. children.

It's not so much the daily living skills — feeding, dressing — that trigger stress, said Dr. Annette Estes, the lead researcher. It's dealing with the erratic, sometimes violent "problem" behavior.

"Many of the parents I meet may be experiencing internal stress, but they respond incredibly adaptively," Estes said. "They're out there learning neurology and genetics and treatment that's specialized. They are using that stress to provide their kids the most optimal chance.

"They are really a high-functioning group of families. But there are people who just get slammed by this."

A University of Wisconsin study, published last year in the Journal of Autism and Developmental Disorders, reported mothers of autistic children showed abnormally low levels of cortisol, a hormone released as a protective response to stress. Researcher Marsha Mailick Seltzer has compared chronic stress profiles of these mothers with those of combat soldiers.

For parents such as the Dinhs, caring for Austin takes equal parts patience and perseverance, with a healthy sprinkling of humor.

One might think that with their medical training, they would be better suited to deal with an autistic child than other parents.

"No, autism just kind of overwhelmed us," Tracey said. "When we were in training, we were only taught the severe form of it. You rarely saw a child with autism."

So when Austin's development seemed unusually slow as an infant and toddler, the Dinhs said they initially were in denial. They were living in Los Angeles while Howard was doing research at UCLA Medical Center. He said he felt nearly overcome with worry, not sure how to respond. It took a toll on their marriage.

After meeting with several experts, a diagnosis came back. In a way, it was a relief to know, since the couple was feeling increasingly anxious and helpless.

They decided they needed to change cities and career goals. By this time, Allie had been born, and they decided Howard had to relinquish his fulfilling, but less financially rewarding, faculty and research position to join a heart practice. Tracey would sacrifice a full-time pediatric practice to devote most of her time to caring for Austin.

Living in Los Angeles was not feasible because of the cost. They chose Sacramento. Howard often works double shifts and weekends at Regional Cardiology Associates. Tracey works less than half time at Kaiser Permanente in south Sacramento, now that Austin is old enough to be in school.

"There are tiny moments I get a little resentful," Tracey said. "I feel like my career was put on the second burner. But I realized I needed to focus on (Austin)."

The couple have adjusted to the routine. Still, there are tense moments.