Childhood Disintegrative Disorder is an extremely rare form of autism. It is also known as CDD, dementia infantalis, disintegrative psychosis or Heller's syndrome.
Children with CDD appear to develop normally until the age of two. After that they go backwards, losing many of the skills they had before, such as the ability to walk or talk.
The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, published in 2013, eliminates childhood disintegrative disorder as a formal diagnosis by dissolving it and other subtypes of autism into one diagnosis called autism spectrum disorder.
The 10th edition of the International Classification of Diseases and Related Health Problems, published in 2010, states that 'other childhood disintegrative disorder' is
'A type of pervasive developmental disorder that is defined by a period of entirely normal development before the onset of the disorder, followed by a definite loss of previously acquired skills in several areas of development over the course of a few months. Typically, this is accompanied by a general loss of interest in the environment, by stereotyped, repetitive motor mannerisms, and by autistic-like abnormalities in social interaction and communication. In some cases the disorder can be shown to be due to some associated encephalopathy but the diagnosis should be made on the behavioural features.'
Please see our detailed entry on Childhood Disintegrative Disorder