Tetraploidy syndrome

Tetraploidy syndrome is an extremely rare and severe chromosomal disorder in which cells contain four complete sets of chromosomes (92 chromosomes instead of the normal 46). This condition, also referred to as tetraploidy or 92,XXXX/92,XXYY karyotype, arises from errors in cell division during very early embryonic development. Tetraploidy may occur in a complete (pure) form or as a mosaic, where only some cells carry the tetraploid complement while others are normal. Complete tetraploidy is almost invariably lethal, with most affected pregnancies ending in early miscarriage or stillbirth. The rare liveborn infants with complete or mosaic tetraploidy typically present with severe multi-system abnormalities. Key clinical features include profound intrauterine growth restriction, severe intellectual disability, craniofacial anomalies (such as low-set ears, hypertelorism, micrognathia, and cleft palate), congenital heart defects, central nervous system malformations, skeletal anomalies, and genital abnormalities. Hypotonia and feeding difficulties are commonly observed in surviving neonates. Additional features may include renal malformations and limb defects. The phenotype can vary depending on whether the tetraploidy is complete or mosaic, with mosaic forms generally being less severe but still associated with significant developmental delays and congenital anomalies. There is no curative treatment for tetraploidy syndrome. Management is entirely supportive and symptomatic, focusing on addressing individual congenital anomalies such as surgical correction of heart defects or cleft palate, nutritional support, and developmental therapies. Prognosis is extremely poor for complete tetraploidy, with survival beyond the neonatal period being exceptionally rare. Mosaic tetraploidy may allow for somewhat longer survival, though significant morbidity remains. Genetic counseling is recommended for affected families, although the condition is generally considered a sporadic event with a very low recurrence risk.

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