Mosaic trisomy 15 syndrome

Mosaic trisomy 15 syndrome (also known as trisomy 15 mosaicism) is a rare chromosomal disorder in which some cells in the body contain three copies of chromosome 15 instead of the usual two, while other cells have the normal two copies. Full (non-mosaic) trisomy 15 is typically lethal and results in early pregnancy loss; however, when the trisomy is present in mosaic form, affected individuals may survive to birth and beyond, with a highly variable clinical presentation depending on the proportion and distribution of trisomic cells throughout the body. The syndrome can affect multiple body systems. Key clinical features commonly reported include intrauterine growth restriction, prenatal and postnatal growth retardation, craniofacial dysmorphism (such as a broad nasal bridge, low-set ears, and micrognathia), congenital heart defects, skeletal anomalies, and variable degrees of intellectual disability or developmental delay. Skin pigmentary anomalies following the lines of Blaschko may also be observed, reflecting the mosaic distribution of abnormal cells. Additional features can include renal malformations, limb asymmetry, and café-au-lait spots. The severity of the condition varies widely among affected individuals, largely depending on the percentage of cells carrying the extra chromosome and which tissues are involved. There is no cure or specific targeted therapy for mosaic trisomy 15 syndrome. Management is supportive and symptom-based, involving a multidisciplinary team that may include cardiologists, orthopedic specialists, developmental pediatricians, and geneticists. Early intervention programs for developmental delays, surgical correction of congenital heart defects or other structural anomalies, and ongoing monitoring of growth and development are important components of care. Genetic counseling is recommended for affected families.

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