An AJHG paper that is already resting some longer time on my desk says that
Nonsense SNPs introduce premature termination codons into genes and can result in the absence of a gene product … As such, we might expect the disrupted allele to be rare and, in healthy people, observed only in a heterozygous state … we have carried out a large-scale experimental survey of nonsense SNPs in the human genome by genotyping 805 of them … in 1,151 individuals … We identified 169 genes containing nonsense SNPs that were variable in our samples, of which 99 were found with both copies inactivated in at least one individual.
It seems that it doesn’ t even matter if you have lost some genes as there is an enormous plasticity of the human genome where obviously other genes can easily take over, where we have many more examples, yea, yea.