Mosaic trisomy 7 syndrome

Mosaic trisomy 7 syndrome (Orphanet code 1747) is an extremely rare chromosomal disorder in which some cells in the body contain three copies of chromosome 7 instead of the usual two, while other cells have the normal two copies. This mosaic pattern arises from a postzygotic (after fertilization) error in cell division, meaning it is not typically inherited. The clinical presentation is highly variable and depends on the proportion and distribution of trisomic cells across different tissues. Because of this mosaicism, the severity of symptoms can range widely from mild to more significant developmental concerns. Reported clinical features in the limited number of documented cases may include intrauterine growth restriction, low birth weight, developmental delay, intellectual disability, facial dysmorphism (such as a broad nasal bridge or low-set ears), pigmentary skin anomalies (including areas of hypopigmentation or hyperpigmentation following the lines of Blaschko), and asymmetric growth of the body or limbs. Some patients may also present with renal anomalies or other organ involvement. The phenotype is not consistent across all reported cases, reflecting the variable tissue distribution of the trisomic cell line. There is no specific cure or targeted therapy for mosaic trisomy 7 syndrome. Management is supportive and symptom-based, involving a multidisciplinary team that may include pediatricians, geneticists, developmental specialists, and other subspecialists depending on the organs affected. Early intervention programs for developmental delays, physical therapy, and regular monitoring of growth and organ function are important components of care. Genetic counseling is recommended for affected families, though recurrence risk is generally considered very low since the condition arises sporadically.

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