Urea cycle disorders (UCDs) comprise a group of recessive and one X-linked inherited errors of protein metabolism that, due to insufficient detoxification of excess nitrogen, can lead to severe neurological disease. The key feature, but at the same time only a surrogate marker of UCDs, is the resulting mild to severe hyperammonemia. Biochemical analysis is needed to strengthen the suspicion of any underlying UCD but remains for the majority of cases rather indicative than diagnostic due to the

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... ack of definite markers. Thus, in order to confirm a specific UCD, mutation analysis or enzyme assays are the methods of choice. Because of the drastic clinical complications of severe hyperammonemia, an early diagnosis before onset of symptoms would be desirable. The best way to achieve this would be to implement a general newborn screening for these disorders. However, there are several challenges that need to be overcome before newborn screening for UCDs can be introduced. This review will briefly describe the technical and clinical challenges involved in newborn screening for UCDs and will then discuss current experiences with this approach.