The enzymology of mitochondrial fatty acid beta‐oxidation and its application to follow‐up analysis of positive neonatal screening results

Abstract

Oxidation of fatty acids in mitochondria is a key physiological process in higher eukaryotes including humans. The importance of the mitochondrial beta-oxidation system in humans is exemplified by the existence of a group of genetic diseases in man caused by an impairment in the mitochondrial oxidation of fatty acids. Identification of patients with a defect in mitochondrial beta-oxidation has long remained notoriously difficult, but the introduction of tandem-mass spectrometry in laboratories for genetic metabolic diseases has revolutionalized the field by allowing the rapid and sensitive analysis of acylcarnitines. Equally important is that much progress has been made with respect to the development of specific enzyme assays to identify the enzyme defect in patients subsequently followed by genetic analysis. In this review, we will describe the current state of knowledge in the field of fatty acid oxidation enzymology and its application to the follow-up analysis of positive neonatal screening results.

Fatty acid oxidation flux predicts the clinical severity of VLCAD deficiency

“…MCAD, ACAD9, and/or peroxisomal fatty acid oxidation may likely be responsible for this activity. 15,16,29,30 In addition to measuring LC-FAO flux at 37 °C, we also studied flux in cultured fibroblasts at different temperatures, which revealed that cell lines from some patients show a significant decrease in LC-FAO flux when cultured at 40 °C. Indeed, in patients with a LC-FAO flux of more than 6%, a 40% decrease in LC-FAO flux was observed at 40 °C (PID 6, 7, and 11).…”

“…These studies show that nonsense mutations in the encoding gene (ACADVL) result in a severe and early presentation of cardiomyopathy, [12][13][14] but the more frequent missense mutations are associated with both severe or attenuated presentations. 10 Functional tests, including determination of the residual activity of the VLCAD enzyme, 10,15 have been used to test the effects of various mutations on LC-FAO activity. VLCAD enzyme activity measurement as the sole functional readout is disadvantageous because it is not well suited to estimating the influence of genetic variations in potential compensatory enzymes (e.g., MCAD 15 or ACAD9 (ref.…”

“…10 Functional tests, including determination of the residual activity of the VLCAD enzyme, 10,15 have been used to test the effects of various mutations on LC-FAO activity. VLCAD enzyme activity measurement as the sole functional readout is disadvantageous because it is not well suited to estimating the influence of genetic variations in potential compensatory enzymes (e.g., MCAD 15 or ACAD9 (ref. 16)).…”

“…In addition, we performed acylcarnitine profiling after loading cultured skin fibroblasts with labeled palmitate (in vitro probe assay). 15,[17][18][19][20][21] To identify potential predictors of disease severity in VLCADD, we studied clinical severity in 13 patients by applying a new VLCADD clinical severity score (CSS). Patients identified by NBS were excluded because starting treatment early affects the natural history and masks the clinical severity prediction.…”

Necrotizing Enterocolitis and Respiratory Distress Syndrome as First Clinical Presentation of Mitochondrial Trifunctional Protein Deficiency

“…However, discrimination between isolated general MTP deficiency, LCHAD deficiency, isolated LCKAT deficiency (LCKAT deficiency) or isolated LCEH deficiency (LCEH deficiency; not identified yet) cannot be made on the basis of the acylcarnitine profile, but requires specific enzyme testing in lymphocytes or fibroblasts. Furthermore measurement of 3-keto-C18:1-carnitine and 3-keto-C18:2-carnitine, which accumulate in case of LCKAT deficiency but not LCHAD deficiency, might also be helpful (Wanders et al 2010).…”