Learn More (germline mosaicism)

Germline mosaicism for a specific genetic condition occurs when an individual has two populations of cells in the gonads (testes or ovaries). One population of cells contains only wild type alleles. The other population of cells contains a pathogenic variant or a chromosome anomaly. Germline mosaicism is the result of sporadic mutation or chromosome alteration in a cell that will give rise to gamete cells. The pathogenic variant or chromosome anomaly is confined to the individual's germline and is not present in other cells of the body.

Germline mosaicism is typically seen in autosomal dominant or X-linked disorders. It becomes evident or suspected when an unaffected parent has two or more children with the same pathogenic variant or chromosome anomaly, which is not present in the leukocyte DNA of either parent.

Molecular genetic testing using blood or tissue samples (other than germline tissue) from an individual with germline mosaicism will not identify the pathogenic variant or chromosome anomaly that is present in the germline.

The recurrence risk for a genetic condition is proportionate to the number of gamete cells that contain the pathogenic variant or chromosome anomaly. Germline mosaicism has been reported in numerous genetic conditions; some genetic conditions are associated with a higher risk for germline mosaicism (e.g., Duchenne muscular dystrophy, osteogenesis imperfecta).

Germline mosaicism for this fully penetrant autosomal dominant condition is suspected in the father because he has two affected children and is not affected himself.

Revised: 4-22-16

Related term: somatic mosaicism