Aneuploid

Aneuploidy refers to a deviation from the normal chromosome number in a cell or organism. In humans, the typical euploid state is diploid with 46 chromosomes. An aneuploid cell has either an extra chromosome (trisomy) or a missing chromosome (monosomy). Aneuploidy can be present in a single cell (mosaicism) or throughout the body.

Common examples in humans include trisomies such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome), as well as sex chromosome aneuploidies like monosomy X (Turner syndrome), 47,XXY (Klinefelter syndrome), 47,XXX (Triple X), and 47,XYY. The severity and viability of aneuploid conditions vary widely depending on which chromosome is affected and the degree of imbalance.

Aneuploidy arises primarily from errors in chromosome segregation during cell division. The most frequent causes are nondisjunction in meiosis I or II, mitotic spindle defects, or lagging chromosomes during anaphase. Advanced parental age is a known risk factor for some aneuploidies. While many aneuploid conceptions are not viable, some result in live births with developmental and health challenges, and others are compatible with life but accompanied by distinct phenotypes.

In cancer, somatic aneuploidy is common, with tumor cells often showing multiple gains and losses of chromosomes that can influence growth and treatment response. Detection methods for aneuploidy include karyotyping, fluorescence in situ hybridization (FISH), array comparative genomic hybridization (array CGH), and sequencing-based approaches. There is no cure for aneuploidy itself; management depends on the specific condition or cancer subtype.