ANEUPLOIDY presumably occurs in about 1 out of 40 zygotes and is found in only one of 200 live births. Chromosomal analysis of fetal material obtained from spontaneous abortions reveals various chromosomal aberrations in more than 25% of them. These include monosomies, polyploidies, and trisomies of larger and even of smaller autosomes.1 It appears that of all zygotes with an autosomal chromosomal aberration, only some instances of trisomy D′, E, and G, perhaps less than one half of them, reach the end of gestation and are compatible with postnatal life. While patients with sex chromosomal tetrasomies and pentasomies are found occasionally, individuals with autosomal tetrasomies are very rare.2,3 Double autosomal trisomies likewise are exceedingly rare, while double trisomies consisting of an autosomal trisomy (particularly trisomy G) associated with a sex chromosomal trisomy are encountered with slightly greater frequency.
Mosaicism with various clones showing three, four, and even five
Zellweger H, Abbo G. Double Trisomy and Double Trisomic Mosaicism. Am J Dis Child. 1967;113(3):329-337. doi:10.1001/archpedi.1967.02090180089007