"Males typically present with developmental and language delay, autistic-like behavior, hyperactivity, and varying degrees of learning disabilities and mental retardation," Dills said. "Females will present with a milder presentation -- anxiety, depression, shyness and poor social skills."
Around 20 percent of males with Fragile X meet all the criteria for autism; the remaining may show some signs of autism, but tend to be mostly social.
Deborah Kwan, programs coordinator for the National Fragile X Foundation in San Francisco, said those with Fragile X also have difficulty processing sensory information.
"Many individuals with Fragile X are simply overwhelmed with sensory input," Kwan said, adding that an environment as seemingly routine as a shopping mall can often lead to too many distractions, causing confusion and anxiety.
"Things that we could block out -- a fan, a lawn mower down the street -- these guys can't habituate that. They can't concentrate as easily."
Despite the physical and behavioral complications, most children with Fragile X are able to live well into adulthood.
"There are minimal serious medical problems, and generally they'll have a normal lifespan," said Dills.
Screening for Fragile X involves a simple blood test, which can accurately diagnose the syndrome 99 percent of the time. Kwan said testing for the condition is reaching younger and younger aged children, allowing them to reap the full benefit of care. And in recent decades, researchers have developed treatment strategies, including special education and medication regimens, to help with behavioral problems.
Unfortunately, a cure for the syndrome is proving much more elusive.
"There is no cure for Fragile X at this time," Kwan said. "There is a lot more research to be done."
While researchers study the disorder in a lab setting, for the Heymans, confronting the disorder took a much more personal tone.
"Another challenge was learning how to feel included in our community without having to apologize for his behavior," Gail Heyman said. "We had to figure out how to fit into society without the unwanted stares, without having to explain his unwanted behavior."
Heyman said it was also difficult not to blame herself for her son's condition.
"When you're dealing with a genetic disorder, it is not something that you did," she said. "Learning to accept that was hard."
But she said despite the challenges, her son's Fragile X syndrome "is not a bad thing."
"Our kid is a great kid, and he brings us lots of joy," she said. "We've taken the negative -- it was a negative at first -- and turned it into a positive.
"It is not a reason for murder, but it is a disorder."
For more information, visit The National Fragile X Foundation website.