developmental regression
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.
loss of developmental skills, as manifested by loss of developmental milestones
medical finding developmental disorder