In vitro probe acylcarnitine profiling assay using cultured fibroblasts and electrospray ionization tandem mass spectrometry predicts severity of patients with glutaric aciduria type 2

Prediction of disease severity in multiple acyl-CoA dehydrogenase deficiency: A retrospective and laboratory cohort study

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an ultra-rare inborn error of mitochondrial fatty acid oxidation (FAO) and amino acid metabolism. Individual phenotypes and treatment response can vary markedly. We aimed to identify markers that predict MADD phenotypes. We performed a retrospective nationwide cohort study; then developed an MADD-disease severity scoring system (MADD-DS3) based on signs and symptoms with weighed expert opinions; and finally correlated phenotypes and MADD-DS3 scores to FAO flux (oleate and myristate oxidation rates) and acylcarnitine profiles after palmitate loading in fibroblasts. Eighteen patients, diagnosed between 1989 and 2014, were identified. The MADD-DS3 entails enumeration of eight domain scores, which are calculated by averaging the relevant symptom scores. Lifetime MADD-DS3 scores of patients in our cohort ranged from 0 to 29. FAO flux and [U-¹³ C]C2-, C5-, and [U-¹³ C]C16-acylcarnitines were identified as key variables that discriminated neonatal from later onset patients (all P < .05) and strongly correlated to MADD-DS3 scores (oleate: r = -.86; myristate: r = -.91; [U-¹³ C]C2-acylcarnitine: r = -.96; C5-acylcarnitine: r = .97; [U-¹³ C]C16-acylcarnitine: r = .98, all P < .01). Functional studies in fibroblasts were found to differentiate between neonatal and later onset MADD-patients and were correlated to MADD-DS3 scores. Our data may improve early prediction of disease severity in order to start (preventive) and follow-up treatment appropriately. This is especially relevant in view of the inclusion of MADD in population newborn screening programs.

Management and diagnosis of mitochondrial fatty acid oxidation disorders: focus on very-long-chain acyl-CoA dehydrogenase deficiency

Mitochondrial fatty acid oxidation disorders (FAODs) are caused by defects in β-oxidation enzymes, including very long-chain acyl-CoA dehydrogenase (VLCAD), trifunctional protein (TFP), carnitine palmitoyltransferase-2 (CPT2), carnitine-acylcarnitine translocase (CACT) and others. During prolonged fasting, infection, or exercise, patients with FAODs present with hypoglycemia, rhabdomyolysis, cardiomyopathy, liver dysfunction, and occasionally sudden death. This article describes the diagnosis, newborn screening, and treatment of long-chain FAODs with a focus on VLCAD deficiency. VLCAD deficiency is generally classified into three phenotypes based on onset time, but the classification should be comprehensively determined based on genotype, residual enzyme activity, and clinical course, due to a lack of apparent genotype-phenotype correlation. With the expansion of newborn screening for FAODs, several issues have arisen, such as missed detection, overdiagnosis (including detection of benign/asymptomatic type), and poor prognosis of the neonatal-onset form. Meanwhile, dietary management and restriction of exercise have been unnecessary for patients with the benign/asymptomatic type of VLCAD deficiency with a high fatty acid oxidation flux score. Although L-carnitine therapy for VLCAD/TFP deficiency has been controversial, supplementation with L-carnitine may be accepted for CPT2/CACT and multiple acyl-CoA dehydrogenase deficiencies. Recently, a double-blind, randomized controlled trial of triheptanoin (seven-carbon fatty acid triglyceride) versus trioctanoin (regular medium-chain triglyceride) was conducted and demonstrated improvement of cardiac functions on triheptanoin. Additionally, although the clinical efficacy of bezafibrate remains controversial, a recent open-label clinical trial showed efficacy of this drug in improving quality of life. These drugs may be promising for the treatment of FAODs, though further studies are required.

Efficacy of bezafibrate on fibroblasts of glutaric acidemia type II patients evaluated using an in vitro probe acylcarnitine assay

INTRODUCTION

We evaluated the effects of bezafibrate (BEZ) on β-oxidation in fibroblasts obtained from patients with glutaric acidemia type II (GA2) of various clinical severities using an in vitro probe (IVP) assay.

METHODS

Cultured fibroblasts from 12 patients with GA2, including cases of the neonatal-onset type both with and without congenital anomalies (the prenatal- and neonatal-onset forms, respectively), the infantile-onset, and the myopathic forms, were studied. The IVP assay was performed by measuring acylcarnitines (ACs) in the cell culture medium of fibroblasts incubated with palmitic acid for 96h in the presence of 0-800μM BEZ using tandem mass spectrometry.

RESULTS

The IVP assay showed that 100μM BEZ markedly reduced the level of palmitoylcarnitine (C16) in the neonatal-onset, infantile-onset, and myopathic forms of GA2, either increasing or maintaining a high level of acetylcarnitine (C2), which serves as an index of energy production via β-oxidation. In the prenatal-onset form, although a small reduction of C16 was also observed in the presence of 100μM BEZ, the level of C2 remained low. At concentrations higher than 100μM, BEZ further decreased the level of ACs including C16, but a concentration over 400μM decreased the level of C2 in most cases.

DISCUSSION

BEZ at 100μM was effective for all GA2 phenotypes except for the prenatal-onset form, as a reduction of C16 without deterioration of C2 is considered to indicate improvement of β-oxidation. The effects of higher doses BEZ could not be estimated by the IVP assay but might be small or nonexistent.

Clinical, biochemical and molecular investigation of adult-onset glutaric acidemia type II: Characteristics in comparison with pediatric cases

INTRODUCTION

An increasing number of adult patients have been diagnosed with fatty acid β-oxidation disorders with the rising use of diagnostic technologies. In this study, clinical, biochemical, and molecular characteristics of 2 Japanese patients with adult-onset glutaric acidemia type II (GA2) were investigated and compared with those of pediatric cases.

METHODS

The patients were a 58-year-old male and a 31-year-old male. In both cases, episodes of myopathic symptoms, including myalgia, muscle weakness, and liver dysfunction of unknown cause, had been noted for the past several years. Muscle biopsy, urinary organic acid analysis (OA), acylcarnitine (AC) analysis in dried blood spots (DBS) and serum, immunoblotting, genetic analysis, and an in vitro probe acylcarnitine (IVP) assay were used for diagnosis and investigation.

RESULTS

In both cases, there was no obvious abnormality of AC in DBS or urinary OA, although there was a increase in medium- and long-chain ACs in serum; also, fat deposits were observed in the muscle biopsy. Immunoblotting and gene analysis revealed that both patients had GA2 due to a defect in electron transfer flavoprotein dehydrogenase (ETFDH). The IVP assay indicated no special abnormalities in either case.

CONCLUSION

Late-onset GA2 is separated into the intermediate and myopathic forms. In the myopathic form, episodic muscular symptoms or liver dysfunction are primarily exhibited after later childhood. Muscle biopsy and serum (or plasma) AC analysis allow accurate diagnosis in contrast with other biochemical tests, such as analysis of AC in DBS, urinary OA, or the IVP assay, which show fewer abnormalities in the myopathic form compared to intermediate form.

Favorable outcome after physiologic dose of sodium-D,L-3-hydroxybutyrate in severe MADD

Multiple acyl coenzyme A dehydrogenase deficiency (MADD) is a severe inborn error of metabolism. Experiences with sodium-D,L-3-hydroxybutyrate (3-HB) treatment are limited although positive; however, the general view on outcome of severely affected patients with MADD is relatively pessimistic. Here we present an infant with MADD in whom the previously reported dose of 3-HB did not prevent the acute, severe, metabolic decompensation or progressive cardiomyopathy in the subsequent months. Only after a physiologic dose of 2600 mg/kg of 3-HB per day were ketone bodies detected in blood associated with improvement of the clinical course, N-terminal prohormone of brain natriuretic peptide and echocardiographic parameters. Long-term studies are warranted on 3-HB treatment in patients with MADD.