A common genetic cause of male infertility can be overcome using a technique that creates healthy sperm in the laboratory, scientists have shown.
The research, demonstrated in mice, raises the future prospect of hope for men who cannot father children because they have three instead of two sex chromosomes.
But such a treatment, even if shown to be safe, would not be allowed in places such as the UK without a change in the law that bans the use of artificially produced sperm to make babies.
An estimated one in 500 boys are born with an extra X or Y sex chromosome that can disrupt the formation of mature sperm, leading to infertility.
Scientists at London's Francis Crick Institute, working with Japanese colleagues, used a stem cell technique to produce sperm from small pieces of connective tissue taken from the ears of infertile male mice affected the same way.
The mice either had an extra female X or male Y chromosome in addition to the usual XX or XY pairing.
During the process of transforming the fibroblast connective tissue cells into multi-purpose stem cells, some of the unwanted extra chromosomes were lost.
The researchers selected those stem cells lacking the extra chromosome and used chemical signals to coax their development into immature sperm cells.
Once injected into the testes of a host mouse, the cells matured to become healthy and properly functioning sperm. These were then used to fertilise eggs and produce healthy fertile offspring.
Lead scientist Dr Takayuki Hirota, from the Frances Crick Institute, said: "Our approach allowed us to create offspring from sterile XXY and XYY mice.
"It would be interesting to see whether the same approach could one day be used as a fertility treatment for men with three sex chromosomes."
