Coloured scanning electron micrograph of human sperm cells PDC/SCIENCE PHOTO LIBRARY Infertility isn’t something men like to talk about but it’s very common. Around 1 in 10 couples will have problems with conception, and in half of cases it is wholly or partly to do with sperm. In many cases, existing fertility treatments can’t help – but a US start-up called Paterna Biosciences thinks it can change this. Paterna claims that it can take stem cells from the testes and turn them into sperm cells in the lab. What’s more, the company says this technique could enable almost all the men for whom fertility treatments currently fail to father children of their own. But others in the field think it could be of very limited use for treating male infertility – unless it’s combined with CRISPR gene editing. That’s right, I’m talking about creating gene-edited children. Let’s start at the beginning. There are a huge range of reasons why men may struggle to father a child. They may have a low sperm count, their sperm …