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Developmental regression is the loss of a previously learnt skill or ability. Skills lost may include language or communication skills; social skills; cognitive skills, motor skills, and toileting. The skills which are lost, and when, may vary between and within various disorders. It can occur in metabolic disorders, or in neurodevelopmental disorders such as autism , Rett Syndrome , Childhood Disintegrative Disorder , and Landau-Kleffner Syndrome. The prognosis for treatable conditions is usually dependant on early intervention and the underlying mechanisms will differ depending on the disorder it is present in.

Causes
There are many causes of developmental regression, which vary depending on the condition. The causes and underlying neurobiology of regression in psychological disorders such as autism, Childhood Disintegrative Disorder, Rett Syndrome, and Landau-Kleffner Syndrome are largely unknown. Some cases of developmental regression are caused by inherited metabolic disorders such as a Vitamin B12 deficiency, but could also be caused by CNS (Central Nervous System) tumour, hydrocephalus or meningitis.

Autism
A child who starts showing signs of regression should first be assessed for autism. There is much variability within the field in whether the loss of certain skills should be classified as regressive autism. The skill which is most commonly agreed upon is the loss of language, the second most commonly agreed would be the loss of social skills.

Skills which may be lost include (these vary between definitions) :


 * Language skills
 * Babble
 * Single words
 * Strings of words
 * Social skills
 * Social engagement
 * Eye contact
 * Social smiles
 * Interactive play
 * Motor skills (rare)
 * Self feeding
 * Self dressing
 * Other skills (rare)
 * Toileting

The average age of onset of autistic regression in research is between 19 and 21 months, but some report regression occurring before 1 year of age. Some believe that younger onsets of regressive autism may be misdiagnosed cases of Rett Syndrome. The majority of research shows that onset will occur before the child's third birthday.

Prevalence
Regression is one type of onset in autism (other onsets include early onset and plateau). The majority of research estimates the prevalence of regression to be between 12.5 to 50% ; although some research indicates much higher figures. Differences in these estimates are attributed to different definitions of regression. More strict definitions of regression typically require the loss of language, whereas broader definitions may not necessarily require this for a classification of regressive autism. This allows for children to be diagnosed with regressive autism prior to the development of language. Research showing a high prevalence of regression, has indicated that lower estimates may be due to the difficulty of observing certain skills before they are lost. For example, in very early regression many skills may not yet have developed, but smaller, more subtle skills which are less noticeable may be lost. More research is needed to support this theory. Larger studies generally indicate a lower prevalence of regression.

Development Prior to Regression
Research on development prior to regression is mixed. Some indicate apparently typical social development, and others indicate that this is rare.

Diagnosis and Research
Both diagnosis and research usually depend on either observation of home videos and parental report. However, using home-videos is not always an option, leaving parents to depend on memory. Some research has attempted to diagnose prospectively, by assessing high risk children every 3-6 months, from approximately 6 months of age. To do this they test for various skills at each meeting and use parental reports to see if particular skills are present or absent. .

Causes
There is no known cause for regression in autism and the underlying biology has not yet been determined. Many parents report a trigger event but these reports have not been verified by research. Possible triggers which have been mentioned include :
 * Psychosocial events (such as birth of a sibling or parental absence)
 * Medical events (such as illness, or immunization)

Other possible causes which have been mentioned within research include :
 * Environmental
 * Psychosocial stressors
 * Prenatal and obstetric problems
 * Vaccinations
 * Socioeconomic factors
 * Ethnicity
 * Biological
 * Epilepsy
 * Genetic predisposition
 * Mitochondrial disorders
 * Macrocephaly

Epilepsy/epileptiform activity is the most researched possible cause of regression. One study found that it occurred in 19% of children with regressive autism, where only 10% of children with non-regressive autism had epileptiform activity, while some research has shown there may be connection between autism and immune dysfunction.

Prognosis
Recovery is rare. Research on the outcomes of children with regressive autism in comparison to other onset types of autism vary. Some indicate that those with regressive autism have worse developmental outcomes, including lower verbal and non-verbal IQ, language & social skills. There are no established treatments or prevention methods for regressive autism. Early behavioural intervention is advised to encourage better outcomes, which have shown to help, but outcomes may also be related to initial IQ. Some research has shown that corticosteroid therapy may help.

Childhood Disintegrative Disorder
Also known as CDD, regression in this condition is very similar to that in autism. There is debate as to whether it should be classified as a separate disorder to autism. Children with Childhood Disintegrative Disorder are generally more fearful and are more intellectually impaired than children with autism. CDD is diagnosed when the regression takes place before 10 years of age, but requires normal development up to at least 2 years of age. The onset of regression in CDD is very rapid compared to the onset of symptoms in autism spectrum disorders such as Aspergers, and then stabilises.

Skills and abilities which regress include :
 * Language skills
 * Social skills
 * Play skills
 * Adaptive behaviour
 * Toileting
 * Motor skills

Causes
It is currently unknown what the cause behind the regression in CDD is. Evidence points towards a combination of physiological and psychological factors. It is suspected that it may be due to neurodegenerative processes, and that it may share similar causes as autism. Some cases point towards psychological trauma going towards triggering the onset of the disorder.

Treatment
There are not currently any established treatments or prevention methods for CDD. Behavioural interventions may be possible, but most early intervention programmes for children with ASD take place at age 2 or 3, before the time many children develop CDD. Medications which have been tried include carbamazepine, thioridazine, zuclopenthixol, diazepam and corticosteroid treatment.

Landau-Kleffner Syndrome
Also known as Acquired Epileptiform Aphasia, Landau-Kleffner syndrome involves the loss of language skills along with abnormal EEG changes. Prior to regression motor and language development will appear normal. Onset is usually between 4 and 7 years of age. There is no established cause, but there may be associations with :
 * Low-grade brain tumours
 * Closed-head injury
 * Demyelinating disease
 * Central Nervous System vasculitis
 * Mitochondrial Respiratory Chain Complex 1 Deficiency

It is unknown whether the abnormal EEG causes the language dysfunction or whether both are symptoms of a common cause.

There is some evidence that antiepileptic drugs and corticosteroid therapy may help with the autistic-like symptoms in Landau Kleffner Syndrome.

Rett Syndrome
The Regression which occurs in Rett Syndrome occurs around 1 - 4 years of age and may involve  :
 * Loss of ability to carry out purposeful hand and finger movements
 * Loss of previously learned words or babble
 * General loss of communicative behaviour
 * Loss of social behaviour
 * Play Skills
 * Motor Skills

The cause of the condition in 95-97% of cases is a mutation in the MECP2 gene. However, the reason behind the exact timing of the regression is unknown. Many may have developmental issues prior to regression.

Blindness
The regression that occurs in blind children is due to the development of regressive autism, which occurs in 11-25% of blind children. The occurrence of regressive autism in blind children is most common in children who have CNS (Central Nervous System) related blindness. The skills which are affected the most are language skills and sociability. It usually occurs between 16 and 27 months of age. Parents often report psychosocial or medical trigger events, as is the case in autism.

Vitamin B12 Deficiency
There are several metabolic disorders which can involve a regression of skills. A deficiency of Vitamin B12 usually must be present for several years before symptoms show, but it has been seen in infants. It may be due to a metabolic disorder in the patient, or a lack of intake. In an exclusively breastfed infant, developmental regression can be caused by pernicious anemia or a lack of meat in the mother's diet by causing brain atrophy.

The regression which takes place may include:


 * Loss of smiling
 * They may develop a difficulty in swallowing (dysphagia)
 * Loss of ability to hold up their head
 * Sensory deficits
 * Deep tendon reflexes (loss of)
 * Weakness

It is potentially reversible with early Vitamin B12 therapy.