Further assessment of performance and outcome is needed

Although individually rare, inborn errors of metabolism represent a potentially preventable cause of death and disability. Screening for phenylketonuria (birth prevalence 10 per 100 000) was introduced in the United Kingdom over 30 years ago. It has proved successful in preventing severe mental retardation. The development of tandem mass spectrometry enables a wide variety of additional compounds to be assayed on the dried blood spots routinely collected from newborn infants.1 The combined birth prevalence of disorders, excluding phenylketonuria, which could be detected by screening is about 20 per 100 000. Of these, medium chain acyl CoA dehydrogenase deficiency is one of the most important. However, despite experience of screening over a million infants, many questions about screening for this disorder remain unanswered.

In the United Kingdom between 5 and 11 per 100 000 live born infants have medium chain acyl CoA dehydrogenase deficiency, which is about 35 to 70 children each year.2 This recessively inherited disorder classically presents during infancy and early childhood with a severe illness characterised by encephalopathy and hypoglycaemia. This is usually precipitated by a minor febrile illness, particularly gastroenteritis, and fasting. Of those presenting clinically, up to a quarter will die and about a third of survivors will have irreversible neurological damage. 3 4 In a significant proportion there is a history of previous sudden unexplained death or encephalopathy in a sibling.4 However, the presentation varies widely, with some individuals not presenting until they are adults …