The diagnostic challenge in very-long chain acyl-CoA dehydrogenase deficiency (VLCADD)
Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is the most common defect of mitochondrial β-oxidation of long-chain fatty acids. However, the unambiguous diagnosis of true VLCADD patients may be challenging, and a high rate of false positive individuals identified by newborn screening undergo confirmation diagnostics. In this study, we show the outcome of enzyme testing in lymphocytes as a confirmatory tool in newborns identified by screening, and the correlation with molecular sequencing of the ACADVL gene. From April 2013 to March 2017, in 403 individuals with characteristic acylcarnitine profiles indicative of VLCADD, palmitoyl-CoA oxidation was measured followed by molecular genetic analysis in most of the patients with residual activity (RA) <50%. In almost 50% of the samples (209/403) the RA was >50%, one-third of the individuals (125/403) displayed a RA of 30–50% and 69/403 individuals showed a residual activity of 0–30%. Sequencing of the ACADVL gene revealed that all individuals with activities below 24% were true VLCADD patients, individuals with residual activities between 24 and 27% carried either one or two mutations. Twenty new mutations could be identified and functionally classified based on their effect on enzyme function. Finally, we observed an up-regulation of MCAD-activity in many patients. However, this did not correlate with the degree of VLCAD RA. Although the likely clinical phenotype cannot be fully foreseen by genetic and functional tests as it depends on many factors, our data demonstrate the strength of this functional enzyme test in lymphocytes as a quick and reliable method for confirmation diagnostics of VLCADD.
Fatty acid oxidation disorders
Medium-chain acyl-CoA dehydrogenase
Medium-chain fatty acids
Very long-chain acyl-CoA dehydrogenase
All authors read, drafted and approved the final manuscript. JH conducted the research and drafted the manuscript; ST designed the research, wrote the manuscript and had primary responsibility for final content; CB and SB were responsible for enzyme testing; UM supported the interpretation of the molecular genetics data; US drafting the article and revised it critically for important intellectual content. The study was financially supported by a grant from the Eva-Uth- and Müller-Fahnenberg Foundations given to Sara Tucci.
Compliance with ethical standards
All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2000 (5). The study was approved under study number 78/18 by the ethical review board of Albert-Ludwig University of Freiburg. Informed consent was obtained from all patients for being included in the study.
Conflict of interest
Sara Tucci has received a grant and travel reimbursements by Vitaflo and Dr. Schär unrelated to this study. Julia Hesse, Carina Braun, Sidney Behringer, Uta Matysiak and Ute Spiekerkoetter declare that they have no conflict of interest.
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