While infection with rubella during pregnancy causes fewer than 1% of cases of autism, vaccination against rubella can prevent many of those cases.

There is no known cure. Children recover occasionally, so that they lose their diagnosis of ASD; this occurs sometimes after intensive treatment and sometimes not. It is not known how often recovery happens; reported rates in unselected samples of children with ASD have ranged from 3% to 25%. Most children with autism acquire language by age five or younger, though a few have developed communication skills in later years. Most children with autism lack social support, meaningful relationships, future employment opportunities or self-determination. Although core difficulties tend to persist, symptoms often become less severe with age.

Few high-quality studies address long-term prognosis. Some adults show modest improvement in communication skills, but a few decline; no study has focused on autism after midlife. Acquiring language before age six, having an IQ above 50, and having a marketable skill all predict better outcomes; independent living is unlikely with severe autism. Most people with autism face significant obstacles in transitioning to adulthood.

All of the causes of childhood disintegrative disorder are still unknown. Sometimes CDD surfaces abruptly within days or weeks, while in other cases it develops over a longer period of time. A Mayo Clinic report indicates: "Comprehensive medical and neurological examinations in children diagnosed with childhood disintegrative disorder seldom uncover an underlying medical or neurological cause. Although the occurrence of epilepsy is higher in children with childhood disintegrative disorder, experts don't know whether epilepsy plays a role in causing the disorder."

CDD, especially in cases of later age of onset, has also been associated with certain other conditions, particularly the following:

- Lipid storage diseases: In this condition, a toxic buildup of excess fats (lipids) takes place in the brain and nervous system.

- Subacute sclerosing panencephalitis: Chronic infection of the brain by a form of the measles virus causes subacute sclerosing panencephalitis. This condition leads to brain inflammation and the death of nerve cells.

- Tuberous sclerosis (TSC): TSC is a genetic disorder. In this disorder, tumors may grow in the brain and other vital organs like kidneys, heart, eyes, lungs, and skin. In this condition, noncancerous (benign) tumors, hamartomas, grow in the brain.

- Leukodystrophy: In this condition, the myelin sheath does not develop in a normal way causing white matter in the brain to disintegrate.

The diagnostic category pervasive developmental disorders (PDD), as opposed to specific developmental disorders (SDD), refers to a group of five disorders characterized by delays in the development of multiple basic functions including socialization and communication. The pervasive developmental disorders are: All autism spectrum disorders and Rett syndrome.

The first four of these disorders are commonly called the autism spectrum disorders; the last disorder is much rarer, and is sometimes placed in the autism spectrum and sometimes not.

The onset of pervasive developmental disorders occurs during infancy, but the condition is usually not identified until the child is around three years old. Parents may begin to question the health of their child when developmental milestones are not met, including age appropriate motor movement and speech production.

There is a division among doctors on the use of the term PDD. Many use the term PDD as a short way of saying PDD-NOS (Pervasive developmental disorder not otherwise specified). Others use the general category label of PDD because they are hesitant to diagnose very young children with a specific type of PDD, such as autism. Both approaches contribute to confusion about the term, because the term PDD actually refers to a category of disorders and is not a diagnostic label.

The childhood disintegrative disorder (CDD), also known as Heller's syndrome and disintegrative psychosis, is a rare condition characterized by late onset of developmental delays—or stunning reversals—in language, social function, and motor skills. Researchers have not been successful in finding a cause for the disorder. CDD has some similarity to autism, and is sometimes considered a low-functioning form of it. In May 2013, the term CDD, along with other types of autism, was fused into a single diagnostic term called "autism spectrum disorder" under the new DSM-5 manual. Therefore, CDD is now also called "regressive autism", being that this term can now refer to any type of autism spectrum disorder that involves regression, including CDD.

CDD was originally described by Austrian educator Theodor Heller (1869–1938) in 1908, 35 years before Leo Kanner and Hans Asperger described autism. Heller had previously used the name "dementia infantilis" for the syndrome.

An apparent period of fairly normal development is often noted before a regression in skills or a series of regressions in skills. The age at which this regression can occur varies, but typically after 3 years of normal development. The regression can be so dramatic that the child may be aware of it, and may in its beginning even ask, vocally, what is happening to them. Some children describe or appear to be reacting to hallucinations, but the most obvious symptom is that skills apparently attained are lost.

Many children are already somewhat delayed when the disorder becomes apparent, but these delays are not always obvious in young children. This has been described by many writers as a devastating condition, affecting both the family and the individual's future. As is the case with all pervasive developmental disorder categories, there is considerable controversy about the right treatment for CDD.

Children with PDD vary widely in abilities, intelligence, and behaviors. Some children do not speak at all, others speak in limited phrases or conversations, and some have relatively normal language development. Repetitive play skills and limited social skills are generally evident as well. Unusual responses to sensory information – loud noises, lights – they also are common.

The prognosis of SCT is unknown. In contrast, much is known about the adolescent and adult outcomes of children having ADHD. Those with SCT symptoms typically show a later onset of their symptoms than do those with ADHD, perhaps by as much as a year or two later on average. They have as much or more difficulty with academic tasks and far fewer social difficulties than do people having ADHD. They do not have the same risks for oppositional defiant disorder, conduct disorder, or social aggression and thus may have different life course outcomes compared to children with ADHD-HI and Combined subtypes who have far higher risks for these other "externalizing" disorders.

However, unlike ADHD, there are no longitudinal studies of children with SCT that can shed light on the developmental course and adolescent or adult outcomes of these individuals.

Unlike ADHD, the general causes of SCT symptoms are almost unknown, though one recent study of twins suggested that the condition appears to be nearly as heritable or genetically influenced in nature as ADHD. That is to say that the majority of differences among individuals in these traits in the population may be due mostly to variation in their genes. The heritability of SCT symptoms in that study was only slightly lower than that for ADHD symptoms with a somewhat greater share of trait variation being due to unique environmental events. For instance, in ADHD, the genetic contribution to individual differences in ADHD traits typically averages between 75 and 80% and may even be as high as 90%+ in some studies. That for SCT may be 50–60%.

Far less is known about SCT yet the symptoms seem to indicate that the posterior attention networks may be more involved in the disorder than the prefrontal cortex region of the brain and difficulties with working memory so prominent in ADHD. This hypothesis gained greater support following a 2015 fMRI-study comparing Inattentive ADHD and SCT-diagnosed patients, which found that the left superior parietal lobule (SPL) showed remarkably decreased activity in SCT-cohorts.

Unlike ADHD in which there exist hundreds of studies on molecular genetics identifying candidate genes that may contribute to the disorder, there are no studies of molecular genetics that specifically evaluated individuals having SCT. Although ADHD appears to be linked to problems with the availability of or sensitivity to dopamine and norepinephrine and the efficiency of the large chemical structures of the specific receptors and re-uptake receptors, the neurotransmitters that may be linked to SCT are unknown.

Recently a study showed a small link between thyroid functioning and SCT symptoms suggesting that thyroid dysfunction is not the cause of SCT. High rates of SCT were observed in children who had suffered prenatal alcohol exposure and in survivors of acute lymphoblastic leukemia, where they were associated with cognitive late effects.

A spectrum disorder is a mental disorder that includes a range of linked conditions, sometimes also extending to include singular symptoms and traits. The different elements of a spectrum either have a similar appearance or are thought to be caused by the same underlying mechanism. In either case, a spectrum approach is taken because there appears to be "not a unitary disorder but rather a syndrome composed of subgroups". The spectrum may represent a range of severity, comprising relatively "severe" mental disorders through to relatively "mild and nonclinical deficits".

In some cases, a spectrum approach joins together conditions that were previously considered separately. A notable example of this trend is the autism spectrum, where conditions on this spectrum may now all be referred to as autism spectrum disorders. In other cases, what was treated as a single disorder comes to be seen (or seen once again) as comprising a range of types, a notable example being the bipolar spectrum. A spectrum approach may also expand the type or the severity of issues which are included, which may lessen the gap with other diagnoses or with what is considered "normal". Proponents of this approach argue that it is in line with evidence of gradations in the type or severity of symptoms in the general population, and helps reduce the stigma associated with a diagnosis. Critics, however, argue that it can take attention and resources away from the most serious conditions associated with the most disability, or on the other hand could unduly medicalize problems which are simply challenges people face in life.

Several types of spectrum are in use in these areas, some of which are being considered in the DSM-5.

A Generalized anxiety spectrum. This spectrum has been defined by duration of symptoms: a type lasting over six months (a DSM-IV criterion), over one month (DSM-III), or lasting two weeks or less (though may recur), and also isolated anxiety symptoms not meeting criteria for any type.

A Social anxiety spectrum. This has been defined to span shyness to social anxiety disorder, including typical and atypical presentations, isolated signs and symptoms, and elements of avoidant personality disorder.

A panic-agoraphobia spectrum. Due to the heterogeneity (diversity) found in individual clinical presentations of panic disorder and agoraphobia, attempts have been made to identify symptom clusters in addition to those included in the DSM diagnoses, including through the development of a dimensional questionnaire measure.

A Post-traumatic stress spectrum or trauma and loss spectrum. Work in this area has sought to go beyond the DSM category and consider in more detail a spectrum of severity of symptoms (rather than just presence or absence for diagnostic purposes), as well as a spectrum in terms of the nature of the stressor (e.g. the traumatic incident) and a spectrum of how people respond to trauma. This identifies a significant amount of symptoms and impairment below threshold for DSM diagnosis but nevertheless important, and potentially also present in other disorders a person might be diagnosed with.

A depersonalization-derealization spectrum. Although the DSM identifies only a chronic and severe form of depersonalization disorder, and the ICD a 'depersonalization-derealization syndrome', a spectrum of severity has long been identified, including short-lasting episodes commonly experienced in the general population and often associated with other disorders.

Among the medical signs are dacryocystitis, seizures, intellectual disability, and paralysis, each of which is a complication resulting from the diminutive foramina. A common sign reported as a result of the disease has been a difference of the size of the eyes.

Craniodiaphyseal dysplasia (also known as CDD or lionitis) is an extremely rare autosomal recessive bone disorder that causes calcium to build up in the skull, disfiguring the facial features and reducing life expectancy.

These calcium deposits decrease the size of cranial foramina, and can also decrease the hole in the cervical spinal canal. In the few cases recorded, most of the sufferers died in childhood.

The underlying genetics are uncertain.