Autism: what it is, symptoms, spectrum levels, diagnosis and treatment options

What it is, what the symptoms are, how we can classify them, diagnosis, treatments, and more!

From initial identification to actual diagnosis, autism is the focus of numerous stereotypes and misconceptions that can obscure the true experiences of those living with this disorder. 

One of the biggest challenges faced by autistic patients is the difficulty in social understanding and the lack of information about autism spectrum disorder. 

Whether in interpersonal relationships, access to the job market, forming friendships, or inclusion in school, this lack of understanding is a common barrier that often prevents them from fully and equally participating in these spaces. 

In this article, we will explore what autism is, its characteristics, causes, diagnosis, and treatment for Autism Spectrum Disorder (ASD). Enjoy your reading! 

What is Autism?

Autism or Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that affects areas such as communication, social interaction, and repetitive and restrictive behaviors, with early onset that can vary among individuals and in severity, as defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) by the American Psychiatric Association (1) and the World Health Organization (2).

The estimated global prevalence of autism is around 65 per 10,000 individuals; however, this rate can vary according to factors such as male sex, that is one of the most well-established etiological factors for autism (3, 4); sociodemographic status, and race/ethnicity (5).

The incidence rate of ASD has tripled over the last three decades. Due to the broad spectrum of its etiology, a considerable number of autistic children fail to receive appropriate behavioral and pharmacological treatment (6). 

What Causes Autism?

The causes of autism are diverse and not always fully explained. However, autism results from alterations in the development of complex neural networks, secondary to failures in synaptogenesis (the process of forming synapses between neurons).

There is no single cause of autism, but it is known that genetic factors, environmental factors, and epigenetics play an important role in its development (7).

ASD is a complex multifactorial condition in which various alterations in different genes act together and/or are combined with environmental factors (8), making it an unspecific condition resulting from multiple causes of non-linear factors. Several risk factors for its development have been discussed, such as: 

• Genetic factors (gene expression and variants);
• Environmental pollution (accumulation of metal ions, exposure to pesticides);
• Immunological deficiencies;
• Viral infections;
• Parental age;
• Health, mental state, and maternal-fetal interactions;
• Modulations in gut microbiota.

These risk factors can contribute to the development of autism independently or synergistically, leading to a wide spectrum of characteristics observed in autistic patients. The variable quantitative influence of a broad spectrum of risk factors can result in a unique set of characteristics in each patient (6). 

How can autism be classified?

Autism Spectrum Disorder (ASD) can be classified into two main categories: syndromic (or complex) autism and non-syndromic (or essential/idiopathic) autism.

Syndromic autism is associated with identifiable genetic syndromes or medical conditions and is often accompanied by additional clinical features, such as dysmorphisms, malformations, microcephaly, global developmental delay, and comorbidities, including epilepsy and gastrointestinal disorders. It is estimated to account for approximately 20% to 40% of cases (3, 9–11).

Among syndromic autism cases, certain populations show a significantly higher prevalence, particularly those with specific genetic syndromes or medical conditions such as Fragile X syndrome, Down syndrome, tuberous sclerosis, neurofibromatosis type 1, as well as Angelman syndrome and Cornelia de Lange syndrome, among other chromosomal or monogenic alterations.

In these contexts, the prevalence of ASD is higher than in the general population, reaching approximately 30% in Fragile X syndrome, 16% in Down syndrome, and up to 40% in tuberous sclerosis (11–15). 

Additionally, children with intellectual disability or sensory impairments, such as visual or hearing deficits, also show a higher prevalence of syndromic autism (13).

In contrast, non-syndromic (essential or idiopathic) autism refers to cases in which no associated clinical or genetic abnormalities are identified, representing the more isolated phenotype within the spectrum (9,10,16).

Furthermore, so-called multiplex autism describes situations in which there is a positive family history of similarly affected individuals, highlighting the genetic and clinical heterogeneity of ASD. 

Genetic Factors Related to Autism

Despite the recognition of nearly 800 clinically relevant or known susceptibility genes for ASD (17) characterized by numerous etiological studies, it seems that no cohesive model of causality, biomarker (18), or specific mode of transmission for autism development has been strongly identified (19).

Family and heritability studies have shown that genetic factors contribute, with estimates of up to 90% in monogenic conditions, such as tuberous sclerosis, fragile X syndrome, and Rett syndrome; but represent less than 10% of all ASD cases (17, 18).

The main genetic alterations leading to ASD include (19): 

• Copy number variations (CNVs) such as microdeletions and microduplications (e.g., Angelman syndrome and Prader-Willi syndrome, Williams syndrome);
• Chromosomal alterations (e.g., Turner syndrome, Down syndrome);
• Monogenic syndromes (e.g., fragile X syndrome, Rett syndrome, PTEN gene disorders);
• Mitochondrial syndromes. 

What are the signs of autism?

The signs of autism vary according to age but generally involve impairments in social communication and restricted, repetitive patterns of behavior.

In children, signs may include language delay or regression, lack of eye contact, failure to respond to their name, limited use of communicative gestures, repetitive play, absence of pretend play, restricted interests, stereotyped behaviors (such as hand flapping), and unusual sensory responses (3, 13, 20).

In adults, autism is primarily characterized by persistent difficulties in social interaction and communication, including atypical nonverbal communication, difficulty interpreting social norms, and challenges in maintaining relationships. Restricted interests, behavioral rigidity, and difficulties in social and occupational adaptation are also common, impacting functional independence (21).

Moreover, many adults develop “masking” strategies to hide symptoms, which can make diagnosis more challenging, without eliminating vulnerability to emotional difficulties such as anxiety and depression (3, 13, 20, 21). 

Severity and support levels in autism

Although Autism Spectrum Disorder (ASD) is no longer divided into diagnostic subtypes as in the past, terms such as “type of autism” or “high-functioning autism” are still commonly used to describe different profiles within the spectrum.

Currently, this differentiation is based on the level of support required for the individual’s functioning.

According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), published by the American Psychiatric Association, ASD can be classified into three support levels, defined based on impairments in social communication and the presence of restricted and repetitive behaviors (20, 22, 23). 

Classification of support levels

It is important to note that these levels are not static and may change over time depending on therapeutic interventions, social environment, and individual development. 

What Are the Symptoms of Autism?

ASD presents a wide clinical variability, being conceptualized as a behavioral syndrome that can manifest with various clinical presentations in different intensities, such as dysmorphic features, intellectual disability, hyperactivity, gastrointestinal problems, sleep disturbances and epilepsy (1).

In addition to the variable clinical presentation, behavioral and psychiatric comorbidities are common in individuals with ASD and can have a substantial impact on overall health, quality of life, and long-term prognosis.

Approximately 30% of individuals with ASD require psychological and psychiatric treatments, including medication for behavioral changes such as hyperactivity, impulsivity, inattention, aggression, self-harm, mood disorders, and psychotic or tic disorders (26, 27). 

How Is Autism Diagnosed?

The diagnosis of autism is essentially clinical and can be made between 18-24 months of age. It is around this age that characteristic symptoms can be distinguished from typical development and other developmental delays or conditions (5). 

The American Academy of Pediatrics (28) recommends screening all infants and young children to identify early signs of autism at 18 months and again at 24 months of age. Evaluations or assessment scales that have been validated for clinical and research purposes are useful in establishing the diagnosis of autism. 

Tests help to find the cause (in a minority of cases), and understanding the cause helps to better direct treatment. 

What Are the Diagnostic Criteria for Autism?

Since there is no specific clinical test for diagnosing ASD, the diagnosis is currently based on the criteria established by the DSM-5: Diagnostic and Statistical Manual of Mental Disorders (1), which allows for identifying if the patient shows signs of delays in age-specific developmental milestones and initiating early interventions.

The DSM-5 manual allows for specifying if ASD is associated with a known medical or genetic condition or an environmental factor, associated with another neurodevelopmental, mental, or behavioral disorder; specifying the current severity for Criterion A and Criterion B: requiring very substantial support, requiring substantial support, requiring support; and specifying with or without concurrent intellectual impairment, with or without concurrent language impairment, with catatonia. 

The diagnostic criteria are divided into A, B, C, D, and E: 

1. Persistent deficits in social communication and social interaction across multiple contexts, as manifested (limitation in social-emotional reciprocity; limitation in non-verbal communication behaviors; limitation in developing,maintaining, and understanding relationships), currently or byprevious history; 
2. Restricted and repetitive patterns of behavior, interests, or activities, as manifested by at least two of the following (stereotyped or repetitive motor movements, use of objects, or speech; insistence on sameness, inflexible adherence to routines, or ritualized patterns of behavior; highly restricted, fixated interests that are abnormal in intensity or focus; hyper- orhyporeactivityto sensory input), currently or by previous history; 
3. Symptoms must be present early in the developmental period (may not become fullymanifestuntil social demands exceed limited capacities or may be masked by learned strategies later in life); 
4. Symptoms cause clinically significant impairment in social, occupational, or otherimportant areasof current functioning; 
5. These disturbances are not better explained by intellectual disability (intellectual developmental disorder) or global developmental delay.

Signs of autism in children

It is possible to suspect autism spectrum disorder by observing some signs that your child may display, such as: 

• Avoids eye contact;
• Language development appears different;
• Engages in repetitive movements without apparent reason;
• Does not respond when called by name;
• Tends to move their fingers and hands in a peculiar way;
• Often repeats sounds and words out of context;
• Isolates themselves from other children without reason;
• Plays with objects and toys in unusual ways;
• Overreacts to loud noises or physical contact;
• Shows excessive interest in very specific topics;
• Follows rigid routines and gets upset when something changes. 

My child was diagnosed with ASD. What should I do?

Upon receiving an autism diagnosis, one of the most important steps is early intervention. Treatment for autism is individualized since each patient has a unique spectrum of symptoms, so there is no standard treatment. 

Because autism is an extremely complex condition, it requires multidisciplinary approaches aimed at providing effective prognostic and therapeutic strategies (20). 

Autism in adults

Although autism is often diagnosed in childhood, many individuals receive a diagnosis in adulthood. This may occur because symptoms were subtle during childhood or due to the development of social adaptation strategies. 

In adults, ASD may present with characteristics such as: 

• Difficulty understanding implicit social cues
• Preference for structured routines
• Intense interests in specific areas
• Increased sensory sensitivity
• Challenges in social or professional environments with high interaction demands

In recent years, there has been increased recognition of autism in adults, especially following the expansion of diagnostic criteria and greater awareness of the spectrum. 

Treatments and therapies for Autism Spectrum Disorder

Treatment for ASD is primarily based on early and intensive behavioral interventions, considered the first-line approach. The use of medications is generally directed toward managing associated conditions such as anxiety, irritability, and hyperactivity (13). 

Behavioral interventions 

Naturalistic Developmental Behavioral Interventions (NDBI) and Applied Behavior Analysis (ABA) are widely used, with evidence of improvement in language, social communication, and adaptive behavior. Parent-mediated interventions and social skills groups also contribute to social development, while adapted Cognitive Behavioral Therapy (CBT) is recommended for anxiety associated with ASD (3; 13). 

Educational support and complementary therapies 

Management is multidisciplinary and includes structured educational support, speech therapy, and occupational therapy. Strategies such as the TEACCH program and the use of augmentative and alternative communication may be necessary in some cases (13, 20). 

Complementary and alternative therapies 

Evidence for complementary therapies is limited. Physical activity may provide functional benefits, while dietary interventions have not demonstrated consistent effectiveness for core ASD symptoms. Approaches such as chelation and hyperbaric oxygen therapy are not recommended due to lack of benefit and potential risks (28–30). 

What tests does SYNLAB offer for autism investigation?

SYNLAB offers advanced genetic testing for the investigation of Autism Spectrum Disorder (ASD), contributing to the identification of potential genetic causes and supporting clinical decision-making. Key approaches include: 

• CHG-Array: indicated for the detection of copy number variations (CNVs)
• Autism panel using next-generation sequencing (NGS): analyzes more than 100 genes associated with ASD
• Clinical exome focused on intellectual disability: a broader approach that allows evaluation of a large number of genes related to neurodevelopmental conditions, especially in more complex or undiagnosed cases

Learn About the SYNLAB Group, a Leader in Medical Diagnostic Services!

Conducting precise and up-to-date tests is essential for more accurate diagnoses and better treatment guidance. SYNLAB is here to help.

We offer diagnostic solutions with rigorous quality control to the companies, patients, and doctors we serve. We’ve been in Brazil for over 10 years, operate in 36 countries across three continents, and are the leading service provider in Europe.

Get in touch with the SYNLAB team and learn about the tests available.

Frequently Asked Questions about Autism (FAQ)

What is autism (ASD)?

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by differences in communication, social interaction, and the presence of restricted and repetitive behaviors, with early onset and manifestations that vary among individuals. 

What are the main signs of autism?

The signs of autism include difficulties in communication and social interaction, lack of eye contact, language delay, repetitive behaviors, and atypical sensory responses, with variation in severity among individuals. 

Does autism have different types or levels?

Currently, ASD is classified according to the level of support required (mild, moderate, or high), rather than “types of autism,” better reflecting the diversity of the spectrum. 

How is autism diagnosed?

The diagnosis of Autism Spectrum Disorder is clinical, based on DSM-5 criteria, and involves the assessment of development, behavior, and social interaction, and it can be identified in the early years of life. 

Are there tests to investigate autism?

There is no single test for diagnosing ASD; however, genetic testing can be used as a supportive tool in the investigation, helping to identify associated causes and guide clinical management. 

What are the main treatments for ASD?

Treatment is based on behavioral interventions, multidisciplinary support, and, when necessary, the use of medications to manage associated symptoms, with a focus on improving quality of life and functional outcomes. 

References 

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