Partial duplication/triplication of chromosome 18 syndrome

Partial duplication/triplication of chromosome 18 syndrome (Orphanet code 262682) refers to a group of rare chromosomal anomalies in which a segment of chromosome 18 is present in extra copies — either duplicated (resulting in three copies of the segment) or triplicated (resulting in four copies). The clinical presentation is highly variable depending on the size and location of the duplicated or triplicated segment, as well as whether the short arm (18p) or long arm (18q) is involved. This condition is also sometimes referred to as partial trisomy 18 or partial tetrasomy 18, depending on the degree of extra chromosomal material. Affected individuals commonly present with developmental delay, intellectual disability, growth abnormalities, and a range of congenital malformations. Craniofacial dysmorphisms are frequently observed and may include microcephaly or macrocephaly, a broad or flat nasal bridge, low-set ears, and micrognathia. Congenital heart defects, skeletal anomalies, and genitourinary malformations may also occur. Hypotonia in infancy is common, and seizures have been reported in some cases. The severity of the phenotype generally correlates with the amount of extra chromosomal material present, with triplications tending to produce more severe manifestations than duplications. There is no specific cure for this condition. Management is supportive and multidisciplinary, tailored to the individual's specific clinical features. This may include early intervention programs, physical and occupational therapy, speech therapy, cardiac monitoring or surgical correction of heart defects, and management of seizures with anticonvulsant medications. Genetic counseling is recommended for affected families, as the duplication or triplication may arise de novo or be inherited from a parent carrying a balanced chromosomal rearrangement.

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