Phytohemagglutinin stimulation of lymphocytes improves mutation analysis of carbamoylphosphate synthetase 1

► We perform RNA based mutation analysis for CPS1 using stimulated lymphocytes. ► The method described does substantially shorten the time to diagnosis. ► RNA investigations are important to understand the relevance of DNA changes. ► CPS1 transcript variants were found to occur with tissue-specific frequency. ► We describe 7 novel CPS1 mutations.