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What is Developmental regression and explain in detail?
Developmental regression is when a child who has reached a certain developmental stage begins to lose previously acquired milestones. It differs from developmental delay in that a child experiencing developmental delay is either not reaching developmental milestones or not progressing to new developmental milestones, while a child experiencing developmental regression will lose milestones and skills after acquiring them. Developmental regression is associated with diagnoses of autism spectrum disorder, childhood disintegrative disorder, Rett syndrome, Landau-Kleffner syndrome, and neuro-degenerative diseases. The loss of motor, language, and social skills can be treated with occupational therapy, physical therapy, and speech therapy.

Associated Diagnoses
Developmental regression is typically a symptom of neurological disorder.

Autism Spectrum Disorder
Autism spectrum disorder is a developmental disorder in which a childs communication and social skills are affected. Children with autism spectrum disorder can experience a loss of their previously acquired language and social skills. This is often reported by the childs parents. Children can experience loss of vocabulary and language understanding, as well as no longer make eye contact or play social and imitative games when they previously had. They can also experience a loss of motor and basic skills like toileting or feeding themselves. In autism spectrum disorder, this regression occurs in the first few years of development.

Childhood Disintegrative Disorder
Childhood disintegrative disorder (CDD) is a developmental disorder in which children experience a regression of social language, and motor functioning skills. CDD was merged with autism spectrum disorder in the DSM-V in 2013. Children with CDD can experience a loss of expressive and receptive language skills, social and self-care skills, play skills, and/or motor skills. Regression commonly occurs at around 3 or 4 years old, but after at least two years of normal development and before age 10.

Rett Syndrome
Rett syndrome is a neurodevelopmental disorder caused by a genetic mutation. It occurs almost exclusively in girls. A child with Rett syndrome experiences a loss of previously had intentional hand skills, and can experience a loss of language skills. Children can also experience a loss of social skills and autism-like symptoms. The regression typically occurs between 1–4 years of age.

Landau-Kleffner Syndrome
Landau-Kleffner syndrome is a form of epilepsy associated with a loss of language skills. Those with LKS lose their ability to understand spoken language and to verbally express themselves. LKS typically has an onset of between the ages of 2 and 8 years old.

Neuro-degenerative diseases
Neuro-degenerative diseases (disorders like Batten disease) can result in a child losing previously acquired motor, language, and speech skills.

Signs and symptoms
Children with developmental regression lose developmental milestones they have previously gained. These can be motor, social, or language skills. The loss of motor skills could include loss of the ability to purposefully use hands, loss of the ability to feed oneself, loss of the ability to walk, loss of the ability to bathe oneself, and loss of the ability to dress oneself. The loss of social skills could include loss of the ability/desire to play, loss of the ability to make appropriate eye contact, and loss of interest in playing social games