Newborn screening for inborn errors of metabolism: principles, policies and weighing the evidence

Newborn screening for metabolic disorders has become a contentious issue. The aim of screening is to identify individuals at risk and start treatment before they become ill. To this end newborn screening programmes are well established in many countries and recent technological developments have lead to an expansion of these programmes. These require careful evaluation, both of the process and the outcome. The original Wilson and Jungner criteria for evaluation are still valid but, in this review, three main points are particularly considered. The burden and the natural history of the disease need to be defined. The test should predict accurately those who would develop clinical disease but current screening programmes detect many with ‘mild’ disease, the importance of which is often unclear. This is particularly relevant when assessing any improvement in outcome which should be seen in terms of the advantages and problems for both the individual and the family.