THE less sperm a man produces, the greater the risk that his sperm will contain genomic imprinting errors.
A team led by Mario Sousa of the University of Porto in Portugal looked at a gene called H19 in sperm samples from around 100 men. This gene should be turned off in sperm by the addition of methyl groups to the DNA, a phenomenon called imprinting. But in almost 30 per cent of men with very low sperm counts, the gene was found to be incompletely methylated in many sperm (The Lancet, vol 363, p 1702).
There is no evidence…
