What does Mosaic or Mosaicism mean?
Mosaicism denotes the presence of two populations of cells in one
patient, where usually one of the two is affected by a genetic
disorder. Although most forms of trisomy are due to problems in meiosis
and affect all cells of the zygote, there are cases where the trisomy
only occurs in a selection of the cells. Generally this leads to a
milder phenotype than in non-mosaic patients with the same disorder.
Post-zygote event: a mutational event or abnormally in chromosome
replication/segregation that occurs after fertilization of the ovum by
the sperm, often leading to mosaicism. Germline mosaicism denotes two
or more genetic or cytogenetic cell lines confined to the precursor
(germline) cells of the egg, or sperm; formally called gonadal
mosaicism. Somatic mosaicism denotes two or more genetic or cytogenetic
cell lines within the cell of the body (may or may not include the
germline cells). Isolated: an abnormality that occurs in the absence of
other systemic involvement.
Milewicz, D. M., Witz, A. M., Smith, A. C. M., Manchester, D. K., Waldstein, G., Byers, P. H. Parental somatic and germ-line mosaicism for a multiexon deletion with unusual endpoints in a type III collagen (COL3A1) allele produces Ehlers-Danlos syndrome type IV in the heterozygous offspring. Am. J. Hum. Genet. 53: 62-70, 1993. [PubMed: 8317500, related citations]