Reporting from Ilsan, South Korea, and Los Angeles — Some simply viewed their children as late bloomers. Others refused to discuss or accept the diagnosis.
But many of the affected parents in Ilsan seemed to at least have an inkling when they were told for the first time that their son or daughter had a disorder that in South Korea had long been seen as shameful.
"They knew from the bottom of their hearts that their children were suffering, struggling," said Dr. Young Shin Kim, a Yale psychiatrist who led a groundbreaking six-year study of autism among children in the middle-class suburb of Seoul. "It was hard for them to hear it."
A team of U.S. and Korean researchers recently announced that it had uncovered here the highest rate of autism ever recorded in a general population.
Autism had been recognized in South Korea only in its most severe forms; the condition was considered so rare that the government barely made an effort to track it. But the outside researchers estimated that 2.64% of the city's children have some form of autism, ranging from relatively mild Asperger's syndrome to more debilitating conditions involving intelligence deficits.
The researchers did not suggest that autism was more prevalent here than anywhere else. Instead, they said their study was more thorough than those producing estimates of about 1% in the United States and Europe and that the same methods could result in similar numbers elsewhere.
But in South Korea, the report's most immediate effect has been on families that participated and have been left to struggle in private to accept the presence of a disorder many didn't even know existed.
"It was so shocking," said one mother. "I felt huge guilt, which is natural for a parent, then pain and hopelessness."
"He never eagerly participated in his class," the mother recalled. "He didn't bother anyone, but he wasn't interested."
Like other parents the researchers made available for interviews with The Times, she agreed to talk on condition that her name not be used. She said she worried that it would raise questions about her family's genes and ruin her daughter's marriage prospects.
The boy, now 12, was found to have Asperger's syndrome. Until his diagnosis by the researchers, his mother had considered him a "late bloomer" who walked and talked later than most children and couldn't measure up to his sister in school.
In those respects, his case was typical. The study, published last month in the American Journal of Psychiatry, concluded that milder varieties of autism, without intelligence deficits, were most common in Ilsan and that two-thirds of the total were children who had never been diagnosed with any developmental disability or mental disorder and who got by in ordinary classrooms.
How such children went undetected provides a lesson in how the concept of illness can vary from one culture to another.
In South Korea, autism is still viewed much as it was in the United States a few decades ago, before its definition was broadened to include "high-functioning" cases, its stigma faded and parent-activists made it a powerful political cause.
Before they could start their work, the researchers had to introduce the idea of a less severe autism to Ilsan, a city of 488,590. The researchers visited dozens of elementary schools to seek the cooperation of parents, teachers and administrators.
Roy Richard Grinker, an anthropologist at the George Washington University and study co-author, told them that children with pronounced problems were not difficult to find. Many already had diagnoses. The researchers, he explained, were interested in "finding kids that have issues but don't get recognized or get help."
The goal was to screen all 55,266 residents ages 7 to 12, by having their parents and teachers answer questionnaires about their behavior, communication and social interactions; 33 of 44 schools participated, and the researchers collected questionnaires on 23,337 children.
Of those whose questionnaires suggested autism, 286 were assessed in detail, resulting in 201 autism diagnoses.
The researchers met with each family to explain the results.
"The majority were upset but understood," said Dr. Kim, who led the study. But "some did not accept it and thought we were nuts."
Only three families were willing to talk with a reporter. Kim said several mothers had agreed to participate but their husbands would not let them, refusing to accept that anything was wrong with their children.
One mother said her son was a little weak on social skills but otherwise normal. "I believe that in Korean society, boys are often misunderstood," she said. "So it's harder for them to socialize." The researchers said the boy's diagnosis was Asperger's.