Table 1

Types of mosaicism*

ConditionDNAResultant phenotype
*Does not consider other types such as those found in neoplasms.
Chimeric states such as persistence of fetal cells derived from prior pregnancies are not considered as mosaicism as they do not derive from the same zygote.
Normal developmental differences in different tissues and cell typesNuclear DNA sequence the same in all cells (not true mosaicism)Normal
Mitochondrial heteroplasmyNuclear DNA sequence the same in all cells, mitochondrial DNA can differ from cell to cell due to mutations in the mitochondrial DNA and differential distribution (heteroplasmy)Patient normal or abnormal; may lead to abnormal offspring
Chromosomal mosaicismNuclear DNA differs; usually two different classes due to varying chromosomal complementsPatient normal or abnormal; may lead to abnormal offspring
Germ line mosaicism (resulting from a de novo mutation in a germ cell)Nuclear DNA differs; only in germ line cellsPatient normal; may lead to multiple abnormal offspring
Somatic mosaicism due to de novo mutation (+/− germ line) (resulting from a de novo mutation at a stage during embryogenesis)Nuclear DNA differs in different tissues and number of cells, depending on stage and site of the de novo mutationPatient usually abnormal; disease may be milder than expected
Somatic mosaicism due to reversion (resulting from a mutation that corrects (reverts) a deleterious inherited mutation in some cells)Nuclear DNA differs in different tissues and cells, depending on stage and site of the reversionPatient may be abnormal, possibly milder than expected or occasionally normal