aneuploide

An aneuploide is a cell or organism whose chromosome number is not an exact multiple of a haploid set. In humans, euploid is 46 chromosomes; aneuploide includes trisomies (three copies of a chromosome) or monosomies (one copy). Common viable human aneuploides include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome), and sex chromosome aneuploides such as Turner syndrome (monosomy X), Klinefelter syndrome (47,XXY), Triple X (47,XXX), and XYY syndrome. Most aneuploides are lethal in early development; survivors often have intellectual disability or congenital anomalies.

Causes and mechanisms: primarily nondisjunction during meiosis I or II, producing gametes with an abnormal chromosome number; fertilization yields a zygote with trisomy or monosomy. Mitotic errors after fertilization can cause mosaic aneuploidy. Advanced maternal age is a known risk factor for oocyte nondisjunction. Structural rearrangements such as translocations can also result in unbalanced chromosome complements in offspring.

Detection and diagnosis: prenatal screening includes maternal serum markers and noninvasive cell-free DNA testing, followed by diagnostic procedures such as chorionic villus sampling or amniocentesis with karyotyping or chromosomal microarray. Postnatally, standard karyotyping or molecular methods confirm the diagnosis.

Impact and management: phenotypic outcomes depend on the chromosomes involved; there is no cure for most aneuploides. Management focuses on early intervention, treatment of associated conditions, and supportive services. Aneuploidy is also common in cancer as a feature of chromosomal instability, reflecting somatic alterations.