Aneuploides

Aneuploides, commonly referred to as aneuploidy, is a chromosomal abnormality in which cells contain an abnormal number of chromosomes that is not an exact multiple of the haploid set. In humans, the typical somatic chromosome count is 46 (23 pairs). Aneuploidies arise from errors in cell division, most often nondisjunction during meiosis or, less frequently, during mitosis, leading to gametes or cells with extra or missing chromosomes. Aneuploidy can be present in a mosaic form, where some cells are euploid and others are aneuploid.

Some aneuploidies are compatible with life, particularly certain sex chromosome abnormalities and a few autosomal trisomies. Examples of liveborn conditions include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome), monosomy X (Turner syndrome), and sex chromosome trisomies such as Klinefelter syndrome (XXY), Triple X (XXX), and XYY syndrome. Most autosomal aneuploidies are lethal in utero or shortly after birth.

Risk factors include advanced maternal age, which increases the likelihood of nondisjunction events, though most cases occur without identifiable parents' age. Aneuploidy is typically detected through prenatal screening and diagnostic testing, such as karyotyping, fluorescence in situ hybridization (FISH), and microarray analysis, as well as noninvasive prenatal testing (NIPT).

Impact ranges from mild to severe and depends on which chromosome is affected and whether the condition is mosaic. Clinical features often include growth restriction, congenital anomalies, and varying degrees of intellectual disability. There is no cure for aneuploidy; management focuses on supportive care, early intervention, and treatment of associated medical issues.