CRISPR, a method for editing genes, is stunning technology. Scientists from Oregon Health and Science University, with colleagues in California, China and South Korea, have managed to edit genes in human embryos that cause heart failure in apparently healthy people – sometimes in quite high profile ways, such as Fabrice Muamba, the Bolton Wanderers star who collapsed during an FA Cup tie with West Ham. This has led to warning that the era of designer babies is upon us, but such predictions are built on a misunderstanding.

When the human genome project was completed, the then US President Bill Clinton said: "Today we are learning the language in which god created life…with this profound new knowledge, humankind is on the verge of gaining immense, new power, to heal.”

That was around 17 years ago, so far, no miracles. Maybe Mr Clinton’s prediction will come true one day, but for the time being there is one big snag. It is not genes that make us who we are, it is how they form a network – an enormously complex web of billions of interconnected genes.

CRISPR can edit one gene – and so far it has proven to be fairly inaccurate at doing that.

CRISPR, or to give it a fuller title: CRISPR–Cas9 is not new – it is just new to scientific knowledge. Francisco Mojica, a scientist at the University of Alicante in Spain discovered it.

It forms part of the natural defence mechanism for bacteria – used to fend off attacks by hostile viruses and other foreign bodies, by editing the DNA of a foreign invader.

Scientists have been attempting to find new applications of CRISPR – the most high profile idea has been to edit the DNA of mosquitos so that they can no longer carry the malaria virus.

There is a snag – it is not always that accurate, and can sometimes erroneously edit genes too, leading to all kinds apocalyptic predictions – as gene editing unintentionally creates some kind of deadly mutation.

But if CRISPR is applied to an embryo at a very early stage – no more than a few days old – it has been shown to be a lot more accurate, at least this was the idea the underpinned the work of the researchers behind this latest high profile breakthrough.

It is indeed good news, especially for the likes of Fabrice Muamba, and others suffering from a very rare mutation that can cause sudden heart attacks. The condition can be removed from a foetus just by changing a single piece of code in the DNA – meaning that people who have this condition can be sure it is not passed onto their children – once the technology has been honed.

Looking further forward, the technology may be applied to other more common conditions such as cystic fibrosis and forms of breast cancer. For generations to come this is wonderful news.

But the lesson of the human genome project is that the DNA that gives us the characteristics that make us who we are – tall, short, fast, strong, blessed with symmetrical faces and maybe intelligent, are incredibly complex. It is not one piece of code that can determine this, and often the code that confers certain characteristics, in combination with other code, can have other functions, too.

As this piece in the Atlantic explained: “Complex traits like height and intelligence are the work of hundreds or thousands of genes, each of which have a tiny effect. The prospect of editing them all is implausible. And since genes are so thoroughly interconnected, it may be impossible to edit one particular trait without also affecting many others.”

CRISPR is fantastic technology that may wipe out certain diseases – but the age of designer babies may still be an age that belongs solely to science fiction books.