Autism

Many studies have looked at whether there is a relationship between vaccines and ASD. To date, the studies continue to show that vaccines are not associated with ASD.

CDC knows some parents and others still have concerns. To address these concerns, CDC is part of the Inter-Agency Autism Coordinating Committee (IACC), which is working with the National Vaccine Advisory Committee (NVAC) on this issue. The job of the NVAC is to advise and make recommendations regarding the National Vaccine Program. Communication between the IACC and the NVAC will allow each group to share skills and knowledge, improve coordination, and promote better use of research resources on vaccine topics.

For more information about vaccines and ASD, see the following sites:

Immunization Safety Office | CDC

• Thimerosal and Vaccines
• Measles, Mumps, Rubella (MMR) Vaccine
• Thimerosal in Flu Vaccine
• Timeline: Thimerosal in Vaccines (1999–2010)

Yes—more children are being identified and diagnosed with autism spectrum disorder (ASD) than in the past, based on ongoing CDC monitoring. Since the CDC began tracking ASD prevalence among 8-year-olds in 2000, estimates have generally increased over time, though they vary across communities.

Importantly, those changes do not automatically mean autism itself is becoming more common. Year-to-year differences and variation across regions likely reflect a combination of factors, including:

• Changes in diagnostic practices and screening

• Greater awareness among families, schools, and clinicians

• Differences in access to evaluation and services

• How consistently children are identified across communities

Because early support can make a meaningful difference, equitable and timely identification remains a public health priority—so children and families can access services they may need.

Yes. Adults can be diagnosed with autism spectrum disorder (ASD). Autism is a lifelong neurodevelopmental condition, and many people are identified later—often after years of coping strategies, “masking,” or being treated for related concerns such as anxiety, depression, or ADHD.

How an adult evaluation typically works
A clinician (often a psychologist, psychiatrist, or specialized team) will usually:

• Review medical, educational, and mental health history

• Ask detailed questions about current functioning (communication, sensory sensitivities, routines, social interaction)

• Gather developmental history when possible (from family members or early records)

• Use standardized interviews and psychological measures to support the assessment

Why adult diagnosis can be more complex
Diagnosing ASD in adulthood can be challenging because early developmental information may be limited, and a long history of other diagnoses or learned coping strategies can make autism traits less obvious.

What help can look like
A diagnosis can guide evidence-based supports, including skills-based and behavioral approaches, therapy for co-occurring conditions, workplace or academic accommodations, and practical strategies tailored to the individual’s needs and strengths.

Mitochondria are small structures inside most of the body’s cells. They act like the cell’s energy centers, turning nutrients (such as sugar) and oxygen into the energy cells need to function.

In mitochondrial disease, the mitochondria don’t produce energy efficiently. When cells can’t make enough energy, organs that require a lot of energy—such as the brain, muscles, heart, eyes, ears, and kidneys—may not work as well.

Mitochondrial diseases include many different conditions, and they can vary widely:

• They may affect one organ system or many

• Symptoms can be mild or severe

• Some people may have few or no noticeable symptoms for a period of time

In forms that commonly affect children, symptoms often appear in the toddler or preschool years, though age of onset can differ depending on the specific disorder.

“Mitochondrial disease” and “mitochondrial disorder” are generally used to mean the same thing.

Yes, there can be a relationship—but it appears to involve a small subset of people.

• Some children with a mitochondrial disorder may also meet criteria for autism spectrum disorder (ASD). Others may show autism-like traits (for example, differences in communication, sensory processing, or behavior) without a formal ASD diagnosis. And many have no autism-related signs at all.

• Most people with ASD do not have a mitochondrial disease. Likewise, having ASD does not automatically suggest a mitochondrial disorder.

When ASD and a mitochondrial disorder occur together, it’s not uncommon for there to be additional neurological or medical concerns, such as:

• Seizures/epilepsy

• Differences in muscle tone (low tone or stiffness)

• Movement disorders

• Broader, multi-system symptoms (for example, significant fatigue, exercise intolerance, or involvement of organs beyond the brain)

Research is still evolving on how often mitochondrial disease and ASD co-occur and why they overlap in some cases. Right now, the co-occurrence appears rare, and more high-quality studies are needed to clarify the connection.

Encephalopathy is a broad medical term that refers to a condition that affects how the brain functions. It often involves changes in thinking, alertness, behavior, or development.

Regression means losing skills that were previously learned—for example, a child who had begun talking, walking, or engaging socially may stop doing those things or do them less consistently.

Regressive encephalopathy describes a situation where a brain-related condition leads to a loss of previously acquired skills.

In some children with mitochondrial disorders, development may appear typical for a period of time, and then regression can occur—often in the toddler or preschool years. The underlying condition may have been present all along, but a stressor can sometimes “set off” a decline, such as:

• a significant illness (including viral infections like the flu)

• high fever

• dehydration

• poor nutrition or reduced food intake

Because regression can have many causes—and may require timely evaluation—new or sudden loss of skills should be discussed with a healthcare professional.

Most people with autism spectrum disorder (ASD) do not have—and have never had—an encephalopathy.

That said, there is a small subset of individuals with ASD who experience regression (a loss of previously acquired skills). In some cases, that regression may be linked to an underlying medical or neurological condition that could be described as a regressive encephalopathy.

A few important clarifications:

• Regression is a pattern of change (losing skills). It can occur in ASD, but it does not automatically mean encephalopathy is present.

• Encephalopathy is a broad medical term for brain dysfunction and can have many causes. When present, it can sometimes mimic or overlap with autism-like features, especially if it affects communication, behavior, attention, or development.

If a child or adult shows new or rapid loss of skills, or a noticeable change in functioning, it’s important to seek clinical evaluation to identify potentially treatable causes and ensure appropriate support.

Different brain regions control different functions—and mitochondrial disease can affect whichever regions have the highest energy demands or are most vulnerable. Because of that, mitochondrial disorders can be linked to a wide range of neurological symptoms, and the pattern can differ from person to person.

Depending on which brain systems are affected, a person may experience:

• Seizures

• Differences in speech, learning, or social communication

• Feeding or swallowing difficulties

• Muscle weakness or low muscle tone

• Coordination, balance, or movement problems

• Fatigue and reduced stamina

• Changes in thinking, attention, or behavior

Some people may have one primary challenge, while others have multiple symptoms across different systems. The severity can also range from mild to significant, and symptoms may fluctuate—especially during illness or other physiological stress.

Current scientific evidence does not show that vaccines cause mitochondrial disease or routinely worsen it.

What we do know is that many infections vaccines prevent—such as influenza—can place major stress on the body. For some people with mitochondrial disorders, that stress can contribute to metabolic decompensation or regression, especially during high fever, dehydration, or poor intake. Preventing serious illness is one reason vaccination is often an important part of care.

Vaccines can cause temporary side effects like fever or fatigue. For individuals with mitochondrial disease, it’s reasonable to plan ahead with their healthcare team about monitoring and fever management, especially if there is a history of sensitivity to illness or prior complications.

Bottom line: for most children, vaccines are a safe and effective way to prevent potentially dangerous infections, and decisions should be made with a clinician who understands the individual’s medical history and risk profile.

No. Children are not routinely tested for mitochondrial diseases—and that includes children with autism and other developmental differences.

Testing for mitochondrial disease is typically considered only when a child’s signs and symptoms raise concern, because evaluation can be complex and may require multiple types of samples and specialized testing. Depending on the situation, this can include blood and other laboratory tests, and in some cases more invasive sampling (such as muscle), along with careful clinical assessment.

Clinicians decide whether testing is appropriate based on the full picture—medical history, physical findings, and symptoms that suggest a possible mitochondrial disorder.

If you’re concerned your child might have a mitochondrial disorder, the best next step is to talk with your child’s pediatrician. Mitochondrial testing is not routine and is usually recommended only when a child’s medical history and symptoms suggest it could be relevant.

When you speak with the doctor, it can help to discuss:

• Any loss of skills (regression) or sudden changes in development

• Seizures, significant fatigue, muscle weakness/low tone, or movement changes

• Symptoms affecting multiple body systems (for example: developmental concerns plus feeding issues, hearing/vision changes, heart or kidney concerns)

• Whether a referral to a specialist (such as neurology, genetics, or metabolic medicine) is appropriate

If your child has new or rapid loss of skills, seizures, or a sudden decline after illness, seek medical evaluation promptly.