Democratic presidential candidate Hillary Clinton takes a question during a town hall campaign event Sunday in Derry, N.H. (Steven Senne/ AP)

DES MOINES, Iowa -- Hillary Clinton released details of a new proposal Tuesday to increase early screening, treatment and funding for autism research, and focus greater attention on services for the estimated more than 3 million people with some form of the disability.

The proposal is one of several in recent weeks -- including a plan to dramatically increase funding for Alzheimer's research -- that have been focused on health issues. Like Alzheimer's disease, autism can be a costly, complex diagnosis that affects families struggling to provide care and navigate insurance, social services and other systems.

Autism, which has large and sometimes competing advocacy groups, is increasingly also a political issue, as advocates ask candidates to address controversies over the cause and prevalence of autism and its practical consequences in education, social services and the workplace. Some people contend that there is a link between autism and childhood vaccinations, but that possibility has been thoroughly debunked by scientific research.

"It's so hard," Clinton said of the "emotional, physical, and financial burden" of caring for those with Alzheimer's or autism. "I want to help families do the work they are already doing, but is so difficult."

"A  lot of those families are just at their wits end trying to figure out how to get services how to get the insurance companies to pay for those services," she said of those dealing with autism.

She spoke at a town hall-style event in Sioux City later Tuesday.

Ari Ne’eman, president of the Autistic Self Advocacy Network, said he welcomes Clinton's plan, especially its focus on solving problems faced by adults with autism.

Those with autism are less concerned on a daily basis with research on its cause, and more concerned with questions such as "can I get and hold a job," Ne'eman said during a conference call arranged by the Clinton campaign. His organization does not make political endorsements.

Two major advocacy groups for people with autism praised Clinton for raising the issue during the campaign and urged other presidential candidates to do the same.

“We commend the [Clinton] campaign because it’s putting an issue on the table that has not been talked about” by others seeking the nomination, said Scott Badesch, president and CEO of the Autism Society of America. Badesch said Clinton’s campaign consulted his organization in preparing the policies released Tuesday.

Autism Speaks, the world’s largest advocacy group for people on the autism spectrum, released a statement that also called for greater discussion of the issue by candidates. “A national plan should be built around enhanced state and federal advocacy, groundbreaking advances in science and research, and a full discussion of” housing, transition and employment needs of people with autism, the statement said.

Autism is now considered a spectrum of brain disorders characterized by difficulties in verbal and nonverbal communication and social interaction, as well as repetitive behaviors.  Children with the most extreme forms are withdrawn, speak little and avoid eye contact. Milder forms, such as Asperger's syndrome, are now included along the autism spectrum. In the past, children with Asperger's, for example, might have been considered abnormal but not truly plagued by a disorder.

In 2014, the Centers for Disease Control and Prevention reported that one in 68 U.S. children has autism, a 30 percent increase over the agency’s estimate just two years earlier. Estimates of adults with autism are much more difficult to come by.

Badesch said he was especially gratified that Clinton called for enacting laws that ban the use of certain kinds of restraints in schools, which, he said, are still used on children with autism and other disabilities. He also cited her plan to beef up programs that help transition students with autism into employment and her proposal to determine the prevalence of autism among adults, as well as their needs.

Not included in the Clinton proposal, he said, is a needed plan to fix the problem of people with autism who lose their benefits and join long waiting lists for services when they move from one state to another.

Clinton would, according to the proposal, push states to require insurance companies to cover behavioral and developmental autism services.

The plan also calls for a "nationwide early screening outreach campaign" to diagnose the disorder earlier in children. And it addresses a slew of other issues, including bullying and mistreatment at schools, transitional programs for adults with autism and enforcing mental health parity.

On Sunday, in response to a question from the mother of a teenager with autism, Clinton noted that the increase in the number of children diagnosed with autism is a problem that should be taken seriously.

I think we have to take seriously what seems to be an increasing diagnosis of autism," Clinton said at a Derry, N.H. town hall meeting. "And we have to do much more research about what is causing it. We’ve got to do what we can to prevent it. And then when it is diagnosed, intensive treatment … that can really help that person be as successful as possible."

Abby Phillip contributed to this report from Manchester, N.H.