Risk stratification by residual enzyme activity after newborn screening for medium-chain acyl-CoA dehyrogenase deficiency: data from a cohort study
1 Section of Metabolic Diseases, Beatrix Children’s Hospital, University of Groningen, University Medical Centre of Groningen, PO Box 30 001, CA84, 9700 RB, Groningen, The Netherlands
2 Laboratory of Metabolic Diseases, Department of Laboratory Medicine, University of Groningen, University Medical Centre of Groningen, PO Box 30 001, CA84, 9700 RB, Groningen, The Netherlands
3 Center for Liver, Digestive and Metabolic Diseases, University of Groningen, University Medical Centre of Groningen, PO Box 30 001, CA84, 9700 RB, Groningen, The Netherlands
4 Institiute for Genetic and Metabolic Disease, Department of Paediatrics, Radboud University Medical Centre Nijmegen, Nijmegen, The Netherlands
5 Centre for Lysosomal and Metabolic Diseases, Department of Paediatrics, Erasmus Medical Centre, Rotterdam, The Netherlands
6 Department of Metabolic Diseases, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
7 Department of Metabolic and Endocrine Diseases, Wilhelmina Children’s Hospital, University Medical Centre Utrecht, Utrecht, The Netherlands
8 Section of Metabolic Diseases, Department of Paediatrics, VU University Medical Centre, Amsterdam, The Netherlands
9 Department of Pediatrics and Laboratory of Genetic-Metabolic Diseases, Maastricht University Medical Centre, Maastricht, The Netherlands
10 Laboratory for Infectious Diseases and Perinatal Screening, National institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands
11 Laboratory Genetic Metabolic Diseases, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
Orphanet Journal of Rare Diseases 2012, 7:30 doi:10.1186/1750-1172-7-30Published: 25 May 2012
Since the introduction of medium-chain acyl coenzyme A dehydrogenase (MCAD) deficiency in population newborn bloodspot screening (NBS) programs, subjects have been identified with variant ACADM (gene encoding MCAD enzyme) genotypes that have never been identified in clinically ascertained patients. It could be hypothesised that residual MCAD enzyme activity can contribute in risk stratification of subjects with variant ACADM genotypes.
We performed a retrospective cohort study of all patients identified upon population NBS for MCAD deficiency in the Netherlands between 2007–2010. Clinical, molecular, and enzymatic data were integrated.
Eighty-four patients from 76 families were identified. Twenty-two percent of the subjects had a variant ACADM genotype. In patients with classical ACADM genotypes, residual MCAD enzyme activity was significantly lower (median 0%, range 0-8%) when compared to subjects with variant ACADM genotypes (range 0-63%; 4 cases with 0%, remainder 20-63%). Patients with (fatal) neonatal presentations before diagnosis displayed residual MCAD enzyme activities <1%. After diagnosis and initiation of treatment, residual MCAD enzyme activities <10% were associated with an increased risk of hypoglycaemia and carnitine supplementation. The prevalence of MCAD deficiency upon screening was 1/8,750 (95% CI 1/7,210–1/11,130).
Determination of residual MCAD enzyme activity improves our understanding of variant ACADM genotypes and may contribute to risk stratification. Subjects with variant ACADM genotypes and residual MCAD enzyme activities <10% should be considered to have the same risks as patients with classical ACADM genotypes. Parental instructions and an emergency regimen will remain principles of the treatment in any type of MCAD deficiency, as the effect of intercurrent illness on residual MCAD enzyme activity remains uncertain. There are, however, arguments in favour of abandoning the general advice to avoid prolonged fasting in subjects with variant ACADM genotypes and >10% residual MCAD enzyme activity.