Monosomien

Monosomien, or monosomies, are chromosomal conditions in which a cell contains only one copy of a chromosome instead of the usual two. They can involve any chromosome, but in humans most autosomal monosomies are not compatible with life. The best-known viable monosomy is monosomy X, in which only one X chromosome is present (46, X0). This condition is associated with Turner syndrome.

Turner syndrome occurs in about 1 in 2,000 to 2,500 live female births. Typical features include short stature, gonadal dysgenesis, and a range of congenital heart and kidney anomalies, as well as possible learning difficulties and delayed puberty. Management is multidisciplinary and may involve growth hormone therapy, estrogen replacement, and regular monitoring for associated health issues. Some individuals have mosaic Turner syndrome (for example, 45,X/46,XX), which can result in milder or more variable features.

Monosomies arise from errors in cell division, such as nondisjunction during gamete formation or early embryonic mitosis, leading to a zygote missing one chromosome. If the monosomy is present only in some cells (mosaicism), the phenotype depends on the extent and distribution of monosomic cells.

Diagnosis is typically made by karyotyping and supported by molecular tests such as fluorescence in situ hybridization (FISH) or array comparative genomic hybridization (array CGH). Prenatal detection is possible through amniocentesis or chorionic villus sampling.

Other total monosomies are usually lethal before birth and result in severe birth defects or miscarriage. Partial monosomies, which involve deletions of chromosome segments, produce a wide range of phenotypes dependent on the affected region. Monosomies can also occur in cancer cells as somatic alterations during clonal evolution.