Background: Medium-Chain Acyl-CoA Dehydrogenase (MCAD) deficiency is a fatty acid oxidation disorder that can have variable clinical severity. There is still limited information on its clinical presentation and longitudinal history by genotype, and effectiveness of newborn screening (NBS).
Methods: Retrospective data were collected from 90 patients (44 female, 46 male) to compare biochemical data with clinical outcomes. The frequency of adverse events (number of hypoglycemia-related ER visits and admissions) was assessed by genotype (homozygosity or not for the common pathogenic variant, p.Lys329Glu, in the ACADM gene), and method of diagnosis (NBS vs. clinical).
Results: MCAD deficiency in Utah was more frequent compared to the United States average (1: 9266 versus 1:17,759 newborns). With age, C8-carnitine did not change significantly whereas C2-carnitine decreased (p < .001), possibly reflecting reduced carnitine supplementation typically seen with age. Children with MCAD deficiency had normal growth. p.Lys329Glu homozygotes had higher NBS C8-carnitine (23.4 ± 19.6 vs. 6.6 ± 3.0 μmol/L) and lifetime plasma C8-carnitine levels (6.2 ± 5 vs. 3.6 ± 1.9 μmol/L) compared to patients with at least one other pathogenic variant (p < .001 for both) and higher transaminases compared to compound heterozygotes (ALT 41.9 ± 6.2 vs. 31.5 ± 3.7 U/L, AST 63.9 ± 5.8 vs. 45.7 ± 1.8 U/L, p < .05 for both). On average, p.Lys329Glu homozygotes had more hypoglycemic events than compound heterozygotes (1.44 versus 0.49 events/patient) as did patients diagnosed clinically compared to those diagnosed by NBS (2.15 versus 0.62 events/patient), though these differences were not statistically significant. Neonatal death was observed before results of newborn screening were available in one patient homozygous for the common p.Lys329Glu pathogenic variant, but severe neonatal complications (hypoglycemia, cardiac arrhythmia) were also seen in patients with other mutations. No irreversible complications were observed after diagnosis in any patient with MCAD deficiency.
Discussion: Homozygosity for the common ACADM p.Lys329Glu pathogenic variant was associated with increased levels of C8-carnitine and transaminases. Newborn screening provides the opportunity to reduce morbidity and post-neonatal mortality in all patients with MCAD deficiency, regardless of genotype.
Keywords: Carnitine; Clinical outcome; Fatty acid oxidation; Medium chain AcylCoA dehydrogenase (MCAD) deficiency; Newborn screening.
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