Monosomit

Monosomit, commonly called monosomy in English, is a chromosomal abnormality in which a cell has only one copy of a particular chromosome instead of the usual two. It is a form of aneuploidy and most autosomal monosomies are not compatible with life. Monosomy typically arises from errors in meiosis or mitosis, such as nondisjunction or chromosome loss, leading to gametes or early embryos missing a chromosome.

In humans, the only widely viable monosomy is monosomy X, which results in Turner syndrome. Individuals with Turner syndrome have one complete X chromosome and lack a second sex chromosome. Other autosomal monosomies are generally lethal before birth. Rare cases of mosaicism can occur, where some cells are monosomic and others are normal or trisomic, and these may be observed in certain sex chromosome configurations or in mosaic Turner syndrome.

Clinical features vary depending on which chromosome is affected and whether the monosomy is complete or mosaic. Turner syndrome, the most studied example, is associated with short stature, gonadal dysgenesis, and cardiovascular anomalies, among other features, and often involves infertility. Mosaic monosomies can present with milder or more variable phenotypes. Diagnosis is typically made by karyotyping or other chromosomal analyses, either prenatally (via amniocentesis or chorionic villus sampling) or after birth. Non-invasive prenatal testing can also raise suspicion.

Management is tailored to the chromosome involved and the individual’s symptoms, including growth hormone therapy for Turner syndrome, cardiovascular monitoring, fertility and endocrine counseling, and educational and psychological support. Autosomal monosomies are usually not viable, making the condition largely defined by the well-documented sex chromosome cases and their clinical implications.