While agreeing with Fr Jack Mahoney (“Where’s the harm?”, 7 February) that there is a need to seek treatments for complex medical problems, his endorsement of mitochondrial transfer, even in the limited circumstances of maternal spindle transfer (MST), fails to address three key moral issues.First, the gift of a new human life should arise from an act of love through sexual intercourse in which parents give themselves to each other in a fully human way and should not become the result of technological manipulation. Only in this way do we show due reverence to the mystery of life.Second, the impact of this procedure on the woman who donates the egg needs greater moral consideration. She is not just donating any tissue: her donation is inextricably linked with the creation