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Chromosome 9, trisomy MeSH Supplementary Concept Data 2025
A chromosomal disorder characterized by the presence of a third copy of chromosome 9. Complete trisomy 9, where all cells have an extra copy, usually results in miscarriage or death in the neonatal period. Thus, most viable individuals have partial trisomy 9, where only certain portions of the chromosome are duplicated, or mosaic trisomy 9p, where there is an extra copy only in certain tissues. Such individuals may have craniofacial and growth abnormalities, congenital heart defects, and intellectual disability. The severity of these symptoms depends on which genes are duplicated and which cell populations are affected.