Editor's note: This is the last in a series of CNN stories surrounding National Autism Awareness Month, aimed at highlighting issues linked to the disorder that affects an estimated 1 in 88 U.S. children.
(CNN) -- Matthew Allen's 10 brothers and sisters have grown up helping their parents take care of him.
Ranging in age from 2 to 27, they are his playmates, his protectors, his teachers and his advocates.
They taught him to talk, but they speak for him when he doesn't have the words.
And they all dread the possible phone call bearing the news that something awful has happened to him.
Matt's a middle child; he's 16, and he has autism.
Living with his parents in Woodbridge, Virginia, Matt has limited verbal skills and often wanders away from home and into dangerous situations. He has attempted to climb electric towers and expects cars to stop for him if he steps into the street.
"We are all always worrying about him when we are not at home," said Matt's oldest sister, 27-year-old Sarah Allen. "We also know that one day we will be responsible for him as guardians."
For National Autism Awareness Month, CNN iReport asked families affected by the disorder to tell the world what life is like.
We heard from dozens of people with varying degrees of autism and Asperger's syndrome. Also, parents shared stories about raising children with the disorder. But few people have shared stories about the unique stresses and gifts that autism can bring to sibling relationships.
Matthew was diagnosed with less severe autism initially, but as a toddler and preschooler he presented "some of the most severe symptoms I've seen," said Allen. Now Matthew displays symptoms across a wide spectrum, from high functioning to "more challenged," she said.
For example, Matthew can speak and he has an emotional interest in his family. He has adaptive skills, and he shows substantial cognitive understanding and can make simple logical connections. Like many people with autism, Matthew desires routine and sameness. Matthew also requires moment-by-moment supervision, his sister said, because he sometimes suddenly leaves the house and walks into the street or into neighbors' yards.
Some of these dynamics are portrayed in TV series like NBC's "Parenthood" and films such as 1988's "Rain Man," where autism poses challenges for brothers and sisters.
Sarah Allen, now a special education teacher who works with children on the autism spectrum, recorded a video for iReport featuring Matt and his brothers and sisters. She said she's used to seeing autism awareness stories about higher functioning individuals, but less attention is given to children with more severe behavior problems and limited communication skills.
She wanted to show how her brother has affected the entire family -- and how involved his siblings are in his life.
While they love Matt deeply, having a sibling with severe autism, she said, has put an immense burden on the family. Although organizing family events would pose extra challenges for any family as big as the Allens, Matthew's needs complicate things even more.
"It strains every relationship in the home," Allen said. "Our vacations, weekends, family dinners -- everything has to be structured to be something he can handle. There are many things we just can't do as a family."
Her sister Rebekah -- also a special education teacher -- added, "Things many people take for granted, like attending their child's soccer games, graduations, going out to eat as a family, family vacations and free time on the weekends, are completely centered around Matthew's needs. ... We can count on our hands the number of times we have been able to do these activities."
Sarah and her siblings worry about Matt's options to achieve a secure and fulfilling lifestyle once he reaches adulthood.
As Matt -- who stands well over 6 feet tall and is still prone to meltdowns -- becomes harder to handle at home, the family hopes to find an arrangement "where he can maintain some form of work and leisure while being kept safe," but they know "such situations are typically rare and immensely expensive," said Allen.
How he will be cared for "has been a source of much discussion the past three years. It is very emotional for all of us."
But Matthew, she says, has given his siblings the gifts of empathy, flexibility and patience.
"Matt is one of the most important people in my life," said Allen. "Each of my siblings can say the same."