Table 1.

The Occurrence of Genomic Variations Detectable by Molecular Cytogenetic (Cytogenomic) Techniques in Unaffected Individuals

Type of Genomic Variations	Interindividual Variation	Intercellular Variation	Key References
CNVs	very common1	unreported	[2-7, 14, 19]
Structural chromosome rearrangements detected by molecular cytogenetic techniques	very rare2	unreported	[36, 51]
Structural chromosome rearrangements detected by cytogenetic techniques	rare3	very rare	[25-27, 50]
Variation of heterochromatic regions	common4	unreported	[28, 37, 38, 50]
Euchromatic variants	rare	unreported	[29]
Fragile sites Common Rare	— 5	very common rare6	[30, 31, 39]
Supernumerary marker chromosomes	very rare	rare	[32, 40]
Aneuploidy	unreported	very common7	[10, 12]
Polyploidy	unreported	very common7	[10, 12]

¹almost in all the individuals investigated

²single case-reports or small cohorts investigated

³less than 1 per 1000 individuals

⁴more than 1 per 1000 individuals

⁵fragile sites are usually observed in a proportion of cells (metaphase spreads)

⁶rare fragile are uncommonly observed in healthy individuals

⁷low-level mosaics.