Trisomiaan

Trisomiaan is a chromosomal condition characterized by the presence of three copies of a chromosome in most cells, rather than the usual two. This extra genetic material can influence development and health to varying degrees.

Most trisomies arise from nondisjunction during the formation of eggs or sperm, which leads to a duplicated chromosome in the embryo. In some cases, trisomy results from a balanced translocation in one parent or from mosaicism, where only a portion of cells carry the extra chromosome. The most common viable trisomies are trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Sex chromosomes can also be involved, producing conditions such as XXX, XXY (Klinefelter), and XYY.

Prenatal detection includes noninvasive prenatal testing (NIPT) using cell-free fetal DNA, ultrasound markers, and maternal serum screening. Diagnostic confirmation is possible with chorionic villus sampling (CVS) or amniocentesis followed by karyotyping. After birth, chromosomal analysis confirms trisomia and guides care.

Clinical features depend on which chromosome is affected and whether the trisomy is full or mosaic. Down syndrome commonly involves intellectual disability, characteristic facial features, and congenital heart defects. Edwards and Patau syndromes are typically associated with multiple anomalies and limited survival. Some individuals with trisomies experience milder symptoms, especially in mosaic or sex-chromosome trisomies.

Management is multidisciplinary, focusing on medical treatment, developmental support, and education. There is currently no way to prevent nondisjunction, but recurrence risk is generally low; however, it is higher if a parent carries a balanced translocation. Genetic counseling helps families understand risks and options.