Plans to genetically screen newborns for rare diseases are problematic

Rare diseases are often hard to spot. They can evade detection until irreversible organ damage or disability has already set in. Last month, in the hope of preventing just this type of harm, the UK’s health secretary, Wes Streeting, announced a 10-year plan to make genetic testing for hundreds of rare conditions part of standard newborn screening in England. The world is likely to follow, with numerous feasibility programmes already under way, including in the US and Australia. Streeting’s plan is to “leapfrog” disease before it becomes symptomatic. But how scientifically sound is this, exactly?

The genome is a list of letters that feels as if it could be read like a book, but it is a book in a language so new that only a small number of words have been deciphered. And, like any language, even those deciphered words could have multiple meanings. What is known of the risks associated with some gene variants is drawn from decades of studying families at high risk of certain conditions. But we have little experience in population-based genetic testing in...