First off, there are no standardized imaging, molecular or genetic tests that can be used to diagnose ASD. Additionally, there is a lot of variety in how ASD affects individuals. The behavioral manifestations of ASD depend on ones developmental stage, age of presentation, current support, and individual variability. Lastly, there are multiple conditions that may present similarly to Autism Spectrum Disorder, including intellectual disability, hearing impairment, a specific language impairment such as Landau–Kleffner syndrome. ADHD, anxiety disorder, and psychotic disorders. Furthermore, the presence of autism can make it harder to diagnose coexisting psychiatric disorders such as depression.Ideally the diagnosis of ASD should be given by a team of clinicians (e.g. pediatricians, child psychiatrists, child neurologists) based on information provided from the affected individual, caregivers, other medical professionals and from direct observation. Evaluation of a child or adult for Autism Spectrum Disorder typically starts with a pediatrician or primary care physician taking a developmental history and performing a physical exam. If warranted, the physician may refer the individual to an ASD specialist who will observe and assess cognitive, communication, family, and other factors using standardized tools, and taking into account any associated medical conditions. A pediatric neuropsychologist is often asked to assess behavior and cognitive skills, both to aid diagnosis and to help recommend educational interventions. Further workup may be performed after someone is diagnosed with ASD. This may include a clinical genetics evaluation particularly when other symptoms already suggest a genetic cause.
They are common among children with ASD; there are no firm data, but studies have reported prevalences ranging from 11% to 84%. Many anxiety disorders have symptoms that are better explained by ASD itself, or are hard to distinguish from ASDs symptoms. Rates of comorbid depression in individuals with an ASD range from 4–58%. The relationship between ASD and schizophrenia remains a controversial subject under continued investigation, and recent meta-analyses have examined genetic, environmental, infectious, and immune risk factors that may be shared between the two conditions. Oxidative stress, DNA damage and DNA repair have been postulated to play a role in the aetiopathology of both ASD and schizophrenia. Deficits in ASD are often linked to behavior problems, such as difficulties following directions, being cooperative, and doing things on other peoples terms. Symptoms similar to those of attention deficit hyperactivity disorder (ADHD) can be part of an ASD diagnosis. Sensory processing disorder is also comorbid with ASD, with comorbidity rates of 42–88%. Starting in adolescence, some people with Asperger syndrome (26% in one sample) fall under the criteria for the similar condition schizoid personality disorder, which is characterized by a lack of interest in social relationships, a tendency towards a solitary or sheltered lifestyle, secretiveness, emotional coldness, detachment and apathy. Asperger syndrome was traditionally called "schizoid disorder of childhood." Genetic disorders - about 10–15% of autism cases have an identifiable Mendelian (single-gene) condition, chromosome abnormality, or other genetic syndromes. Several metabolic defects, such as phenylketonuria, are associated with autistic symptoms.