About 1 of every 40 American kids — or about 1.5 million youths ages 3 to 17 — have autism spectrum disorder (ASD), an umbrella diagnosis covering a range of neurological and developmental disorders that include autism and Asperger’s syndrome. Symptoms and severity vary dramatically from one person to another, but they typically affect communication and socializing abilities. The findings on prevalence, published last week, were based on a nationally representative sample of 50,212 children. The research also found that parents of kids with ASD are 44 percent more likely to report problems getting mental-health treatment for their children than are parents of children with other emotional, behavioral or developmental disorders. They are also 24 percent less likely to get help with care coordination. ASD has no cure, but children on the spectrum can grow and flourish if they have adequate support and training — often including educational and behavioral interventions and, sometimes, medication — to address their developmental challenges. Children of all racial and ethnic groups and all socioeconomic levels have ASD, although boys more often than girls. Medical researchers generally believe that genetics and possibly environmental factors play a role in the development of ASD. Rates have increased in recent decades, but no one knows why.