Globally, autism is estimated to affect 24.8 million people . In the 2000s, the number of people affected was estimated at 1–2 per 1,000 people worldwide. In the developed countries, about 1.5% of children are diagnosed with ASD , from 0.7% in 2000 in the United States. It occurs four-to-five times more often in males than females. The number of people diagnosed has increased dramatically since the 1960s, partly due to changes in diagnostic practice. The question of whether actual rates have increased is unresolved.
Rett syndrome (RTT) is a genetic brain disorder that typically becomes apparent after 6 to 18 months of age in females. Symptoms include problems with language, coordination, and repetitive movements. Often there is slower growth, problems walking, and a smaller head size. Complications can include seizures, scoliosis, and sleeping problems. Those affected, however, may be affected to different degrees.
Rett syndrome is due to a genetic mutation of the MECP2 gene. This gene occurs on the X chromosome. Typically it develops as a new mutation, with less than one percent of cases being inherited from a person's parents. It occurs almost exclusively in girls. Boys who have a similar mutation typically die shortly after birth. Diagnosis is based on symptoms and can be confirmed with genetic testing.
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 severe and sudden 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.
A pervasive developmental disorder not otherwise specified (PDD-NOS) is one of the four autism spectrum disorders (ASD) and also one of the five disorders classified as a pervasive developmental disorder (PDD). According to the DSM-IV, PDD-NOS is a diagnosis that is used for "severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, but the criteria are not met for a specific PDD" or for several other disorders. PDD-NOS is often called atypical autism, because the criteria for autistic disorder are not met, for instance because of late age of onset, atypical symptomatology, or subthreshold symptomatology, or all of these. Even though PDD-NOS is considered milder than typical autism, this is not always true. While some characteristics may be milder, others may be more severe.
...that an autistic savant (historically described as idiot savant) is a person with both autism and Savant syndrome? Savant Syndrome describes a person having both a severe developmental or mental handicap and extraordinary mental abilities not found in most people. The Savant Syndrome skills involve striking feats of memory and often include arithmetic calculation and sometimes unusual abilities in art or music.
There is considerable disagreement over the exact nature of autism; however, it is generally considered to be a neurodevelopmental condition that manifests in markedly abnormal social interaction, communication ability, patterns of interests, and patterns of behavior. It encompasses a wide range of atypical conditions, none of which is well understood. Although there are common and specific physical conditions comorbid to autism spectrum disorders, not all people diagnosed with autism spectrum disorders experience these. The diagnostic criteria, as of 2006, are still generally limited to psychiatric and cognitive evaluation methods with IQ score and a particular patterns of abilities (common to those with autism) featuring strongly in the formal diagnosis of autism and distinguishing it from Asperger syndrome at the time of diagnosis.