Describe and evaluate the results of the expansion of the Dutch neonatal screening programme for metabolic disorders from 1 to 14 disorders.

Prospective study.

Data were collected on all newborns with an abnormal result in the investigation into metabolic disorders carried out during the period 1 January 2007 to 31 December 2008. The prevalence of diagnosed metabolic diseases was compared to retrospective data from the Dutch diagnosis registry for metabolic diseases.

In 2007 and 2008 abnormal results were detected in 469 and 259 newborns respectively (0.26% and 0.14% of all newborns). In 75 and 102 (0.04% and 0.05% of all newborns) the diagnosis was a true positive (ratio of true to false positives 1:6.4 and 1:2.6 in 2007 and 2008 respectively).

The number of patients diagnosed in both 2007 and 2008 was higher than predicted on the basis of retrospective data. This was largely due to detection of milder forms of enzyme deficiencies, which are not yet known with certainty to lead to clinical symptoms. Initially there was an unacceptable number of false positive results for detection of galactosaemia due to the wrong choice of screening method. In addition, screening for tyrosinaemia type 1 had to be stopped temporarily because it became clear that there was a high risk of false negative results. Finally, the implementation plan was not properly developed, resulting in the absence of structural financial backing for registration and long-term follow-up. Nonetheless, it is obvious that the expansion of the screening programme has lead to considerable health benefits as a result of early detection.