In the last decade, regression-like symptoms in adolescents and young adults with Down syndrome have become a major issue. Previous studies illustrated the symptoms as deterioration in daily living skills, social relationships, mental health status, and motor functioning, which included various symptoms, such as anxiety, depression, loss of skills, withdrawal, motor slowness, insomnia, mutism, obsessive-compulsive behavior, and catatonia. [1][2][3][4][5] This syndrome, observed in young adults with Down syndrome, has been described using several terminologies, such as regression, catatonia, rapid clinical deterioration, acute regression, regression of social and communication skills in Down syndrome, and unexplained regression in Down syndrome (URDS). 2,3,[5][6][7] The cause of URDS has not been determined, although studies have suggested potential causes, such as Alzheimer's disease, disruption in routine and environmental support, psychosocial distress, catatonia, and autoimmunity. 1,4,5,8 Santoro et al. suggested that there were core and common features of the condition: The core features included regression in adaptive functioning, cognitive function, and motor control and the common features included behavioral issues (internalizing and externalizing symptoms) and mental health problems (e.g., mood and sleep problems). 5 They also found that co-occurring medical conditions were likely not the sole explanation for URDS. In addition, psychological stressors were more prevalent in those with URDS, which suggested that psychological factors could also be related to the exacerbation of the condition. 5 Prior case studies reported the possible effectiveness of a low dosage of neuroleptics, donepezil, or electroconvulsive therapy. 1,9,10 A retrospective study reported that