Mosaic trisomy 2 syndrome

Mosaic trisomy 2 syndrome (also known as trisomy 2 mosaicism) is an extremely rare chromosomal disorder in which some cells of the body contain three copies of chromosome 2 instead of the usual two, while other cells have the normal chromosomal complement. This mosaic state arises as a postzygotic (after fertilization) error in cell division and is not typically inherited. The clinical presentation is highly variable and depends on the proportion and distribution of trisomic cells across different tissues. Because the abnormality occurs in only a fraction of cells, the severity can range from mild to severe. Key clinical features that have been reported in affected individuals include intrauterine growth restriction (IUGR), developmental delay, intellectual disability, craniofacial dysmorphism (such as a broad or prominent forehead, low-set ears, and micrognathia), congenital heart defects, limb anomalies, and pigmentary skin changes that may follow the lines of Blaschko — reflecting the mosaic distribution of abnormal cells. Renal and genital anomalies have also been described in some cases. The phenotype is extremely variable; some individuals may be only mildly affected while others have significant multi-system involvement. There is no specific cure or targeted therapy for mosaic trisomy 2 syndrome. Management is supportive and symptom-based, involving a multidisciplinary team that may include cardiologists, nephrologists, developmental specialists, 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 the mainstays of care. Genetic counseling is recommended for affected families, though recurrence risk is generally considered to be very low given the sporadic nature of the condition.

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