Effects of the copy number of ribosomal genes (genes for rRNA) on viability of subjects with chromosomal abnormalities

The number of active ribosomal genes (AcRG) was evaluated in 172 carriers of chromosomal abnormalities (CA) such as Down's syndrome (DS), Robertsonian translocations (RT), Klinefelter's and Turner's syndromes, trisomy Х, disomy Y, and various structural CA. In controls (n = 318), AcRG dosage varied from 119 to 190 copies with a mean of 151 copies per diploid genome. In CA carriers, except for DS newborns, AcRG dosage was not beyond these limits. As shown previously, only within these limits cellular homeostasis and organism's viability can be supported, while genomes beyond these limits are eliminated by embryonic loss. About 10% of embryos with DS and 50% of embryos with RT die/are aborted exclusively due to a surplus (DS) or a shortage (RT) of AcRG. AcRG dosage also affects the CA carrier's viability after birth, as demonstrated by comparing newborn and aged (10-40 y.o.) DS patients. Sampling range of AcRG dosage becomes considerably narrower with age: DS newborns ranged from 139 to 194 RG copies (σ2 = 3.59), while aged DS patients varied from 152 to 190 copies (σ2 = 1.55) with the same mean. Each CA group showed peculiarities in AcRG dosage distribution. We found that carriers of numerical abnormalities of gonosomes (sex chromosomes) concentrate within the area of medium, most adaptive dosages, whilst carriers of structural CA can only survive with relatively high AcRG number. Our article is the first ever to report an association of CA viability with the genomic number of AcRG.