Lisakromosoomide

Lisakromosoomide, or extra chromosomes, are chromosomal abnormalities in which an individual possesses one or more additional copies of a chromosome beyond the normal human set. The typical human karyotype contains 46 chromosomes (two sex chromosomes and 44 autosomes). Extra chromosomes can be whole chromosomes, creating trisomies, or less commonly arise from duplications that yield partial trisomies or mosaic patterns.

Most cases result from nondisjunction during meiosis in the formation of gametes, producing aneuploid gametes that, upon fertilization, give a zygote with an altered chromosome number. In mosaic cases, the abnormality arises after fertilization and is present in only a proportion of cells. While some trisomies are compatible with life, others lead to miscarriage or severe congenital conditions.

Common trisomies that survive to birth include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Sex chromosome aneuploidies such as Klinefelter syndrome (47,XXY), Triple X syndrome (47,XXX), and XYY syndrome (47,XYY) are examples of extra sex chromosomes and can present with variable features and often milder phenotypes than autosomal trisomies.

Detection and diagnosis rely on genetic testing. Prenatal screening methods include noninvasive tests and ultrasound markers, while diagnostic procedures such as amniocentesis or chorionic villus sampling determine chromosome number. Postnatally, karyotyping or targeted genetic tests confirm the diagnosis.

Clinical impact ranges from mild to severe and depends on which chromosome is involved and the degree of mosaicism. Management is multidisciplinary, with medical care for associated anomalies and developmental support, including early intervention services, education plans, and family counseling. The prognosis varies by condition and overall health.