TUESDAY, May 5 (HealthDay News) -- Though dyslexia and attention-deficit disorder are better known, another learning disability -- the inability to write properly -- strikes a significant number of children, a new study suggests.

So-called written-language disorder is a "forgotten learning disability," said Dr. Slavica K. Katusic, an epidemiologist at the Mayo Clinic and lead author of the study in the May issue of Pediatrics.

The ability to write is "a critical skill that they [children] need to have for academic success and social well-being," Katusic said. "They are at risk for long-term personal and economic consequences."

Education specialists define written-language disorder as the inability to write near the level expected based on a person's age, intelligence and education. People who suffer from the condition may have problems with such skills as grammar, spelling, paragraph organization and handwriting, Katusic said.

For the new study, Katusic and her colleagues looked at the school and medical records of 5,718 students in Rochester, Minn. The researchers found that between 6.9 percent and 14.7 percent of the children had the condition, depending on the formula used. Boys were two to three times more likely to have the condition than girls.

Other studies have also suggested a high rate of the disability among children, resulting in what Katusic called "an enormous cost for society" because they grow up to be adults who can't write.

But specialists "are just writing and talking about reading and math disorders and not about written-language disorder," Katusic said.

The causes of the disorder aren't clear, she said, although it's possible that genetic, environmental and socioeconomic factors play a role.

Karen R. Harris, a professor of special education and literacy at Vanderbilt University, said the findings may not offer a complete picture of the problem. The study relied partly on diagnoses by school employees and others, and they can often miss learning disabilities in girls, she said.

"One hypothesis for this is because boys tend to have more acting out behavioral problems than girls do, and thus draw more attention in the assessment process," Harris said.

She also noted that the study was limited because it looked at one city with a largely white, middle-class population.

Katusic said that tutoring can help children learn how to write but that adults need to realize that writing is just as important as reading and math skills.

Michael Siegal, a learning disorder specialist, said that more research needs to be done to place written-language disorder in the large picture of learning disabilities, such as dyslexia.

More awareness of the condition "might focus the attention of parents and teachers on underlying language disorders that have to do with recognizing patterns in how words are spelled and how these are articulated in speech to improve written composition and punctuation," said Siegal, a psychology professor at the University of Trieste in Italy.

More information

The Learning Disabilities Association of America has more on learning disabilities.