MCAD deficiency in Denmark

► Four times more newborns with MCADD are detected by screening than expected. ► Mutation spectrum in the newborns is different from that in patients. ► There is a reduced penetrance of the c.985A>G mutation. ► Frequency of c.985A>G homozygotes is twice that predicted from the carrier frequency. ► Rapid genotyping of initial blood spot is important for diagnosis and counseling.