There is not such thing as a normal genome

Genome sequencing studies indicate that all humans carry many genetic variants predicted to cause loss of function (LoF) of protein-coding genes, suggesting unexpected redundancy in the human genome. In the study of 2,951 putative LoF variants obtained from 185 human genomes it was estimated that human genomes typically contain ~100 genuine LoF variants with ~20 genes completely inactivated. The study describes functional and evolutionary differences between LoF- tolerant and recessive disease genes, and a method for using these differences to prioritize candidate genes found in clinical sequencing studies. Science Vol. 335 no. 6070 pp. 823-828