The diagnostic challenge in very‐long chain acyl‐CoA dehydrogenase deficiency (VLCADD)

Abstract

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.

Performance of Expanded Newborn Screening in Norway Supported by Post-Analytical Bioinformatics Tools and Rapid Second-Tier DNA Analyses

“…VLCADD is another important disorder in terms of the increased incidence of milder phenotypes that emerges through screening [ 38 , 39 , 40 , 41 ]. Enzyme analysis in lymphocytes for residual activity was used as a valuable tool to recognize carriers and biochemical phenotypes with variants of uncertain significance (VUS) alleles but also to guide treatment intensity [ 42 , 43 ]. That is, for the milder phenotypes with 10–20% residual enzyme activity, both diet and fasting hours were relaxed when healthy.…”

Post-Analytical Tools for the Triage of Newborn Screening Results in Follow-up Can Reduce Confirmatory Testing and Guide Performance Improvement

“…The utilization of post-analytical tools for VLCAD deficiency is a two stage process due to the presence of abnormal biochemical profiles in heterozygous individuals and a robust DSP to discriminate between these conditions. [13] Of the 69 screens reported out as abnormal for VLCAD, one was confirmed to be abnormal, resulting in a PPV for VLCAD deficiency of 1.5% in isolated screens. The single TP case was assigned a medium risk score and proceeded to confirmatory testing after a second screen was abnormal for VLCAD deficiency.…”

False positive cases of elevated tetradecenoyl carnitine in newborn mass screening showed significant loss of body weight

“…NBS for VLCAD deficiency is challenging because the levels of long-chain acylcarnitines can be affected by several conditions, resulting in the misdiagnosis or overdiagnosis of VLCADD. False negatives are often associated with medical treatment, such as glucose infusions, which could normalize plasma acylcarnitine levels in subjects with VLCADD [ 3 ], while false positives have been identified in heterozygous carriers of VLCADD, and even in healthy individuals, under catabolic situations like prolonged fasting between maternal feeding [ 11 , 13 , 14 , 17 ]. Under prolonged fasting, as a physiological response to lipolysis, a large amount of stored fatty acids are transported into the mitochondria and undergo beta-oxidation, which elevates the amount of long-chain acylcarnitines, including C14:1 acylcarnitines, even in healthy individuals [ 18 ].…”