Frequently Asked Questions

Photos: We thank photographer Bruce Hall for permission to use his beautiful artwork on this website. Learn more about Bruce and Valerie Hall and their book,  Immersed: Our Experience with Autism ,  here .

Photos: We thank photographer Bruce Hall for permission to use his beautiful artwork on this website. Learn more about Bruce and Valerie Hall and their book, Immersed: Our Experience with Autism, here.

How does NCSA define severe autism?

As with many issues in autism, there is no scientifically precise definition for what constitutes “severe.” For the purposes of NCSA, however, we consider this term to encompass those who satisfy the diagnostic criteria of the DSM-5, and who, by virtue of any combination of cognitive and functional impairments, require continuous or near-continuous, lifelong services, supports, and supervision. Individuals in this category are often nonverbal or have limited use of language, have intellectual impairment, and, in a subset, exhibit challenging behaviors, such as aggression, self-injury, and/or property destruction that interfere with safety and well-being.

How many Americans are affected by severe forms of autism?

It is difficult to put a precise number on this population, but national research and state data provide several indications. According to the U.S. Centers for Disease Control, approximately 1 in 59 children (1.7%) now have autism spectrum disorders. Of that population, 31% were found to have intellectual disability (IQ ≤ 70), 25% to have borderline intellectual disability (IQ 71-85), and 44% to have IQs above 85. (Baio et al. 2018). Therefore nearly one-third (31%) of U.S. children with autism exhibit significant intellectual disability, and more than half (56%) of U.S. children with autism have significant or borderline intellectual disability. According to most studies, severely disabling autism, using co-occurring intellectual disability as a proxy, seems to affect 30-50% of the autism population, depending on how autism is defined. Looking from the angle of the population that is minimally verbal, it is estimated that 30% of youth with autism fall into that category (Tager-Flusberg and Kasari 2013). Core autism and related symptoms are typically more severe in these minimally verbal individuals, and they often exhibit challenging behaviors (Tager-Flusberg et al. 2017).

Based on data from California, the most populous state, California Department of Developmental Services (Cal DDS) identified 3,902 persons with autism in 1987 (Cal DDS 1999), a figure has risen to about 108,000 today (Cal DDS CDER 2018). This surge occurred despite the state enacting more stringent requirements for entry into the developmental disability system in 2003, requiring that individuals exhibit “substantial disability” involving the existence of significant functional limitations in at least three, instead of two, areas of major life activity. (Cal Welf & Inst Code sec 4512). Based on Cal DDS data, the population of adults (22+) with developmental disability type autism is poised to grow nearly five-fold over the next 20 years (see, eg, Cal DDS Fact Book 2017 p. 43, showing 76,489 cases through age 21 [not counting cases not yet entered into the system, typically in ages 0-4], compared to just 19,050 ages 22+, meaning the adult autism population will likely grow from about 19,000 in 2017 to about 94,000 in year 2037, assuming deaths in upper two age brackets.

But weren't people with severe forms of autism routinely mis-labeled in the past as having other conditions such as schizophrenia or mental retardation?

There is evidence of some diagnostic drift over the decades between the 1950s and today. For example, some people diagnosed with childhood schizophrenia or mental retardation (now called intellectual disability) in the past would today receive a primary diagnosis of autism. However, no study has found that these shifts can fully explain the tremendous surge in the incidence of severe, or developmental disability-type, autism witnessed over the past three decades. It is a partial but incomplete explanation.

What causes autism?

Though much remains unknown about causation, research suggests that the neurodevelopmental impairments that result in the clinical manifestations of autism have a variety of different biological underpinnings. In rare cases, the cause lies in recessive mutations inherited from the parents. More commonly, it results from a de novo mutation occurring in a gamete or early embryo that was the progenitor of the affected individual. From a clinical perspective, today about 10% of autism cases can be attributed to a genetic cause. Additional genomic and epigenomic (referring to heritable factors that influence gene expression) will likely be uncovered. In addition, perinatal complications such as prematurity, and certain prenatal exposures, such as anticonvulsant drugs, have also been associated with increased risk for autism.

However, the vast majority of autism cases today are still considered “idiopathic,” in other words, having no identified cause. There is no evidence linking the rising prevalence of autism to childhood vaccines, or vaccines given in any other developmental window. We encourage parents to ensure their children are fully vaccinated in accordance with the recommendations of the American Academy of Pediatrics. Infections resulting from failure to vaccinate can cause serious harm to a child, including brain damage and death.

What does NCSA mean by “related disorders”?

The word autism generally refers to a cluster of neurobehavioral impairments of varying character and intensity seen across a wide variety of underlying disorders. “Autism” is a diagnosis often given by clinicians when the underlying etiology (cause) of the abnormal clinical presentation is unknown but where significant social communication impairments and repetitive behaviors are observed. See DSM-5 definition here. When the etiology is known, for example with genetic disorders such as Fragile X or tuberous sclerosis, or with an environmentally induced disorder such as fetal anticonvulsant syndrome, “autism” is often not a primary diagnosis, but instead is used to signify a certain clinical presentation involving significant social communication impairments and repetitive behaviors. NCSA is more concerned with practical realities and actual characteristics of adaptive functioning than with any diagnostic label, and therefore devotes its efforts not just to those with severe forms of diagnosed autism, but also to those with diagnoses featuring a related clinical and adaptive presentation.

What are the primary challenges facing individuals and families affected by severe autism?

The challenges facing affected individuals and families are enormous, and growing. While every family is different, the challenges often include:

  • Access to appropriate educational interventions and settings

  • Access to appropriate medical care, crisis care, and treatment, including treatment for co-morbidities and underlying health problems

  • Access to appropriate adult services, including residential day and vocational settings

  • Access to supported housing

  • Access to recreational and leisure activities

  • Financial stress

  • Emotional stress and social isolation

  • Physical stress and injury

How will the NCSA promote solutions for affected individuals, families and caregivers?

NCSA will raise awareness about the realities and rising prevalence of severe forms of autism, fight for better research to understand, treat and prevent these debilitating neurodevelopmental disorders, suggest innovative policies to expand options for those who are disabled and dependent, and work to empower families and organizations that provide essential daily support services for this vulnerable population. 

What are NCSA’s positions on important issues facing our population?

Please see NCSA Position Statements on this website. Additional Position Statements will be posted from time to time.

Does the NCSA contend that people with milder forms of autism (such as Asperger syndrome) are not disabled?

Absolutely not. By definition, every form of autism is a serious disorder involving significant deficits in areas of basic mental and behavioral functioning. See DSM-5 definition here. Many people with higher functioning forms of autism (e.g., possessing functional language and basic living skills) have severe disabilities owing to many factors including but not limited to social isolation, depression, inability to obtain or hold a job, and poor self-care and self-advocacy skills. Their disabilities can be extremely serious and all affected are deserving of the greatest societal concern and support. However, from a qualitative point of view, their clinical presentation and needs can vary dramatically from those with severe forms of autism who may lack tools of basic language and cognition, or who may engage in dangerous and disruptive behaviors. It is a matter of qualitative difference, not simply of degree. 

By supporting research into causes and prevention, is NCSA promoting eugenics?

Eugenics refers to the practice of a government or other authority limiting or otherwise directing reproductive rights to fulfill an ideological agenda. We stand firm in opposition to any such practices. Promotion of public health is obviously not equivalent to eugenics, and we support efforts to identify risks to the public health, including neurodevelopmental health. This is the norm across societies, to which end considerable resources are invested, for example, by educating pregnant women to refrain from drinking during pregnancy, by adding iodine to salt to prevent thyroid malfunction-associated cretinism, by prescribing prenatal folate to prevent neural tube defects, by regulating lead in paint, air, and water, by regulating medications that can cause harm to developing brains, by raising awareness of acts that cause brain damage such as shaken baby syndrome, and by monitoring and preventing dangerous infectious such as rubella and Zika. If other avenues for prevention of neurodevelopmental impairment are available, those should be identified and put into practice.

Is NCSA duplicating the work of other autism advocacy organizations?

NCSA has no intention to duplicate the vitally important work of established autism advocacy organizations. We will complement, not supplant, other efforts in our community to improve the lives of those disabled with autism.

Does NCSA provide individualized advice or consultation?

NCSA does not have the resources to provide individualized consultation at this time. Please see our Resources section for a list of organizations that may be able to assist you.

Can I contribute a blog piece to NCSA?

NCSA welcomes blog submissions relating to the following topics, among others: personal stories of living with severe autism; federal and/or state policy addressing long-term care needs and housing; perspectives of professionals and providers serving individuals with severe autism; treatments for autism and co-morbidities; the various subtypes of autisms; autism research; abuse and prevention of abuse; epidemiology; criminal justice reform; and autism acceptance. Please email your submission to

With the exception of official letters and statements written by the NCSA and reproduced herein, the opinions and assertions stated in our blog are solely those of the individual authors, and may not reflect the opinions or beliefs of NCSA or any of its officers, directors, or advisors. Unless otherwise stated, copyright is retained by the original authors.

How can I support NCSA?

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These FAQs are subject to revision at any time.