Sperm link to genetic imprinting disorders

Men with low sperm counts have an increased risk of passing on certain rare genetic disorders, say Portuguese researchers. The new study, published in the Lancet, provides another possible explanation for the slightly higher rate of 'imprinting disorders', such as Beckwith-Wiedemann syndrome (BWS), in children conceived using IVF.

Scientists at the University of Porto compared DNA from the sperm of 123 men with normal or low sperm counts. They looked for DNA changes associated with the imprinting process - the 'tagging' of certain genes in the egg and sperm, which marks them as either maternal or paternal in origin. They found that the imprinted genes in the 27 men with normal sperm counts appeared normal, but of the 96 men with low sperm counts, 24 per cent had imprinting abnormalities. This could increase the risk of disorders caused by a failure of the imprinting process, the researchers say.

Previous studies indicate that there is a link between IVF and certain imprinting disorders, such as BWS, which causes overgrowth of various body tissues and an increased risk of particular cancers. Some scientists have suggested that the techniques used in IVF could be the reason for this link, particularly the conditions under which embryos are cultured in the laboratory. But it now seems as though there might be another explanation - that sperm from infertile men are more likely to contain faulty imprinted genes.

Chris Barratt, an IVF expert based at the University of Birmingham, stressed that imprinting disorders are very rare. However, he said the findings were a 'significant issue', and that couples undergoing fertility treatment because the man had a low sperm count should be counselled about the risk of their child being affected. He added that tests to look for imprinting problems in sperm DNA could only be carried out in genetics research centres, and not in IVF clinics.