Sam and John Fetters are identical twins with autism. But Sam is in college, while John still struggles to form sentences. Their experience may shed light on the disorder's mix of nature and nurture.

Having siblings can mean shared family and childhood experiences — and also shared bedrooms and rivalries. A growing body of research shows us that sibling relationships can shape us for life.

Siblings can have a profound effect on us in childhood and over the course of our lives. How have these bonds affected you? Share your story with us.