Mosaic trisomy 14 syndrome

Mosaic trisomy 14 syndrome is a rare chromosomal disorder in which some cells in the body contain three copies of chromosome 14 instead of the usual two, while other cells have the normal two copies. Full (non-mosaic) trisomy 14 is generally lethal and results in early miscarriage, so nearly all liveborn cases are mosaic. The condition is also referred to as trisomy 14 mosaicism. Because the extra chromosome is present in only a proportion of cells, the severity of symptoms can vary widely depending on the percentage and distribution of trisomic cells across different tissues. Mosaic trisomy 14 syndrome affects multiple body systems. Key clinical features include intrauterine growth restriction, intellectual disability of variable degree, craniofacial dysmorphism (such as a broad nose, short philtrum, micrognathia, low-set and abnormally shaped ears, and an abnormally shaped skull), congenital heart defects (including tetralogy of Fallot and ventricular septal defects), and genitourinary anomalies (such as micropenis and cryptorchidism in males). Skeletal abnormalities, including narrow shoulders, asymmetric limb length, and clinodactyly, are also frequently reported. Skin pigmentary anomalies following the lines of Blaschko may be present, reflecting the mosaic distribution of abnormal cells. There is no cure or specific targeted therapy for mosaic trisomy 14 syndrome. Management is supportive and symptomatic, tailored to the individual's specific clinical manifestations. This may include surgical correction of congenital heart defects, early intervention programs for developmental delays, physical and occupational therapy, and ongoing monitoring by a multidisciplinary team including cardiology, urology, orthopedics, and developmental pediatrics. Prognosis is highly variable and depends on the severity of organ involvement and the proportion of trisomic cells.

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