Mosaicism: the presence of two or more populations of cells within an organism, each with a different genetic composition
Somatic mosaicism affects the cells forming the body, causing disease manifestations to develop in affected individuals. 45,X/46,XX is the most commonly diagnosed mosaicism affecting sex chromosomes. These patients typically have a milder form of Turner syndrome or can be asymptomatic, depending on the ratio of abnormal to normal cells.
Germline mosaicism affects the cells that give rise to gametes, allowing the affected genes to pass to the offspring. The chance of a child being affected depends on the proportion of gametes that carry the mutation. When mosaicism is limited to the germline, the affected parent does not develop clinical manifestations.
