mozaiktrisómia

Mozaiktrisómia is a genetic condition in which a person has two or more different cell lines, some of which contain an extra copy of one chromosome (trisomy) while other cells have the normal chromosomal complement. The most frequently involved chromosomes are 21, 18, 13, and 7, but trisomies of any chromosome may occur. The abnormal cell line is usually present only in a subset of tissues, which can lead to a milder or variable clinical presentation compared with full trisomy.

The condition arises from errors in chromosome segregation during early embryonic mitotic divisions. It can result from a mitotic nondisjunction event after fertilization or from a postzygotic error in a single cell. Because the extra chromosome is not present in all cells, the phenotypic spectrum is broad; some individuals may have mild or no apparent symptoms, whereas others may exhibit growth retardation, developmental delay, dysmorphic features, or organ malformations that are characteristic of the underlying trisomy.

Detection of mozaiktrisómia requires sampling cells from multiple tissues. Conventional karyotyping of peripheral blood may miss mosaic patterns if affected cells are not circulating in the blood. Techniques such as fluorescence in situ hybridization (FISH), microarray comparative genomic hybridization (aCGH), or next‑generation sequencing (NGS) of DNA from skin fibroblasts, buccal mucosa, or amniotic fluid can reveal the presence of mosaicism and estimate the proportion of abnormal cells in each tissue.

Prognosis depends on the chromosome involved and the proportion of cells carrying the trisomy. High levels of trisomic cells or involvement of critical tissues (brain, heart, kidneys) generally result in more severe outcomes. Genetic counseling is recommended for families to discuss recurrence risk, which varies depending on whether the mosaicism arose de novo or is present in a parent’s germline.