Tetrasomy 18p syndrome

Tetrasomy 18p syndrome, also known as isochromosome 18p syndrome or i(18p) syndrome, is a rare chromosomal disorder caused by the presence of a supernumerary isochromosome composed of two copies of the short arm (p) of chromosome 18. This results in four copies of the 18p genetic material instead of the usual two. The extra genetic material disrupts normal development and affects multiple body systems, including the central nervous system, musculoskeletal system, and craniofacial structures. Key clinical features include intellectual disability of variable severity, developmental delay (particularly in speech and motor milestones), microcephaly, and characteristic facial features such as a flat midface, small mouth, low-set ears, strabismus, and a thin upper lip. Muscle tone abnormalities are common, with neonatal hypotonia often evolving into spasticity or dystonia in childhood. Feeding difficulties are frequently observed in infancy. Seizures occur in a subset of patients. Skeletal anomalies, including scoliosis and joint contractures, may develop over time. Some individuals may have congenital heart defects, renal anomalies, or growth retardation. Tetrasomy 18p typically arises as a de novo event, most often due to errors in maternal meiosis. There is no cure for the condition, and management is supportive and symptomatic. Treatment may include physical therapy, occupational therapy, speech therapy, anti-epileptic medications for seizures, and surgical intervention for orthopedic or cardiac complications. Early intervention programs are recommended to optimize developmental outcomes. Regular monitoring by a multidisciplinary team is important to address the evolving medical and developmental needs of affected individuals.

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