Incorporating second-tier genetic screening for multiple acyl-CoA dehydrogenase deficiency.

• The incidence of MADD was approximately 1:26,670. • Half of the MADD patients would not be detected under conventional screening protocols. • A novel MALDI-TOF MS assay targeting 23 ETFDH variants in the Chinese population was developed. • Incorporating second-tier genetic screening into the current NBS could improve the performance of MADD NBS. Newborn screening (NBS) for multiple acyl-CoA dehydrogenase deficiency (MADD) has poor sensitivity. This study aimed to evaluate the feasibility of incorporating second-tier genetic screening for MADD. A total of 453,390 newborns were screened for inherited metabolic disorders using tandem mass spectrometry from January 2017 to May 2022. A matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) assay was developed to identify 23 common ETFDH variants and used for second-tier screening of MADD. Overall, 185 newborns with suspected MADD received second-tier genetic screening. Thirty-three (17.8 %) newborns with positive results, of which 7 were homozygotes, 5 were compound heterozygotes, 21 were heterozygotes. Further genetic analysis revealed that 6 of the 21 newborns had a second ETFDH variant. Therefore, 18 patients were finally diagnosed with MADD, with a positive predictive value of 9.73 %. The detection rate and diagnostic rate of MALDI-TOF MS assay were 83.33 % and 66.67 %, respectively. Thus the incidence of MADD in our population was estimated at 1:25,188. Nine different ETFDH variants were identified in MADD patients. The most common ETFDH variant being c.250G > A with an allelic frequency of 47.22 %, followed by c.524G > A (13.89 %) and c.998A > G (13.89 %). All patients had elevation of multiple acylcarnitines at NBS. However, seven patients had normal acylcarnitine levels and two patients showed mild elevation of only two acylcarnitines during the recall review. We have established a high throughput MALDI-TOF MS assay for MADD screening. Half of the MADD patients would not be detected under conventional screening protocols. Incorporating second-tier genetic screening into the current NBS could improve the performance of MADD NBS. [ABSTRACT FROM AUTHOR]