Genetic, biochemical, and clinical spectrum of patients with mitochondrial trifunctional protein deficiency identified after the introduction of newborn screening in the Netherlands.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is included in many newborn screening (NBS) programs. Acylcarnitine-based NBS for LCHADD not only identifies LCHADD, but also the other deficiencies of the mitochondrial trifunctional protein (MTP), a multi-enzyme complex involved in long-chain fatty acid ß-oxidation. Besides LCHAD, MTP harbors two additional enzyme activities: long-chain enoyl-CoA hydratase (LCEH) and long-chain ketoacyl-CoA thiolase (LCKAT). Deficiency of one or more MTP activities causes generalized MTP deficiency (MTPD), LCHADD, LCEH deficiency (not yet reported), or LCKAT deficiency (LCKATD). To gain insight in the outcomes of MTP-deficient patients diagnosed after the introduction of NBS for LCHADD in the Netherlands, a retrospective evaluation of genetic, biochemical, and clinical characteristics of MTP-deficient patients, identified since 2007, was carried out. Thirteen patients were identified: seven with LCHADD, five with MTPD, and one with LCKATD. All LCHADD patients (one missed by NBS, clinical diagnosis) and one MTPD patient (clinical diagnosis) were alive. Four MTPD patients and one LCKATD patient developed cardiomyopathy and died within 1 month and 13 months of life, respectively. Surviving patients did not develop symptomatic hypoglycemia, but experienced reversible cardiomyopathy and rhabdomyolysis. Five LCHADD patients developed subclinical neuropathy and/or retinopathy. In conclusion, patient outcomes were highly variable, stressing the need for accurate classification of and discrimination between the MTP deficiencies to improve insight in the yield of NBS for LCHADD. NBS allowed the prevention of symptomatic hypoglycemia, but current treatment options failed to treat cardiomyopathy and prevent long-term complications. Moreover, milder patients, who might benefit from NBS, were missed due to normal acylcarnitine profiles.

Sensory neuronopathy as a major clinical feature of mitochondrial trifunctional protein deficiency in adults.

INTRODUCTION: Mitochondrial trifunctional protein deficiency (MTPD) is a long-chain fatty acid oxidation disorder characterized by co-existence of rhabdomyolysis episodes and peripheral neuropathy. Two phenotypes are described: generalized mitochondrial trifunctional protein deficiency (gMTPD) and isolated long-chain-3-hydroxyacyl-CoA dehydrogenase deficiency (iLCHADD) that is always associated with the c.1528G>C mutation. Peripheral neuropathy of MTPD is commonly described in children as axonal, length-dependent and sensorimotor. OBJECTIVES: To report clinical and electrophysiological features of four independent adult MTPD patients with peripheral neuropathy. RESULTS: Onset of the disease was characterized in all patients by rhabdomyolysis episodes occurring during childhood preceded by severe hypoglycemic episodes in three patients. Peripheral nerve involvement manifesting as sensory ataxia appeared later, during adolescence or adulthood. In all cases, electroneuromyogram showed no length-dependent sensory potentials decrease characteristic of sensory neuronopathy ("ganglionopathy"). All patients harbored at least one c.1528G>C mutation. DISCUSSION: We describe MTPD as a newly hereditary etiology of sensory neuronopathy in adults, specifically in patients with c.1528G>C mutation. MTPD should be screened for by performing plasma acylcarnitines in patients with chronic sensory neuronopathy and additional suggestive features such as exercise intolerance or retinopathy.

Mutations in HADHB, which encodes the ß-subunit of mitochondrial trifunctional protein, cause infantile onset hypoparathyroidism and peripheral polyneuropathy.

Mitochondrial trifunctional protein (MTP) is a hetero-octamer composed of four α- and four ß-subunits that catalyzes the final three steps of mitochondrial ß-oxidation of long chain fatty acids. HADHA and HADHB encode the α-subunit and the ß-subunit of MTP, respectively. To date, only two cases with MTP deficiency have been reported to be associated with hypoparathyroidism and peripheral polyneuropathy. Here, we report on two siblings with autosomal recessive infantile onset hypoparathyroidism, peripheral polyneuropathy, and rhabdomyolysis. Sequence analysis of HADHA and HADHB in both siblings shows that they were homozygous for a mutation in exon 14 of HADHB (c.1175C>T, [p.A392V]) and the parents were heterozygous for the mutation. Biochemical analysis revealed that the patients had MTP deficiency. Structural analysis indicated that the A392V mutation identified in this study and the N389D mutation previously reported to be associated with hypoparathyroidism are both located near the active site of MTP and affect the conformation of the ß-subunit. Thus, the present patients are the second and third cases of MTP deficiency associated with missense HADHB mutation and infantile onset hypoparathyroidism. Since MTP deficiency is a treatable disease, MTP deficiency should be considered when patients have hypoparathyroidism as the initial presenting feature in infancy.

Impact of newborn screening for fatty acid oxidation disorders on neurological outcome: A Belgian retrospective and multicentric study.

Fatty acid oxidation (FAO) disorders are autosomal recessive genetic disorders affecting either the transport or the oxidation of fatty acids. Acute symptoms arise during prolonged fasting, intercurrent infections, or intense physical activity. Metabolic crises are characterized by alteration of consciousness, hypoglycemic coma, hepatomegaly, cardiomegaly, arrhythmias, rhabdomyolysis, and can lead to death. In this retrospective and multicentric study, the data of 54 patients with FAO disorders were collected. Overall, 35 patients (64.8%) were diagnosed after newborn screening (NBS), 17 patients on clinical presentation (31.5%), and two patients after family screening (3.7%). Deficiencies identified included medium-chain acyl-CoA dehydrogenase (MCAD) deficiency (75.9%), very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency (11.1%), long-chain hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency (3.7%), mitochondrial trifunctional protein (MTP) deficiency (1.8%), and carnitine palmitoyltransferase 2 (CPT 2) deficiency (7.4%). The NBS results of 25 patients were reviewed and the neurological outcome of this population was compared with that of the patients who were diagnosed on clinical presentation. This article sought to provide a comprehensive overview of how NBS implementation in Southern Belgium has dramatically improved the neurological outcome of patients with FAO disorders by preventing metabolic crises and death. Further investigations are needed to better understand the physiopathology of long-term complications in order to improve the quality of life of patients and to ensure optimal management.

Case report: Mitochondrial trifunctional protein deficiency caused by HADHB gene mutation (c.1175C>T) characterized by higher brain dysfunction followed by neuropathy, presented gadolinium enhancement on brain imaging in an adult patient.

Mitochondrial trifunctional protein (MTP) deficiency is an autosomal recessive disorder caused by impaired metabolism of long-chain fatty acids (LCFAs). Childhood and late-onset MTP deficiency is characterized by myopathy/rhabdomyolysis and peripheral neuropathy; however, the features are unclear. A 44-year-old woman was clinically diagnosed with Charcot-Marie-Tooth disease at 3 years of age due to gait disturbance. Her activity and voluntary speech gradually decreased in her 40s. Cognitive function was evaluated and brain imaging tests were performed. The Mini-Mental State Examination and frontal assessment battery scores were 25/30 and 10/18, respectively, suggesting higher brain dysfunction. Peripheral nerve conduction studies revealed axonal impairments. Brain computed tomography showed significant calcification. Magnetic resonance imaging revealed an increased gadolinium contrast-enhanced signal in the white matter, suggesting demyelination of the central nervous system (CNS) due to LCFAs. The diagnosis of MTP deficiency was confirmed through genetic examination. Administration of L-carnitine and a medium-chain fatty triglyceride diet was initiated, and the progression of higher brain dysfunction was retarded within 1 year. This patient's presentation was suggestive of CNS demyelination. The presence of brain calcification, higher brain dysfunction, or gadolinium enhancement in the white matter in patients with peripheral neuropathy may be suggestive of MTP deficiency.

Newborn Screening for Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase and Mitochondrial Trifunctional Protein Deficiencies Using Acylcarnitines Measurement in Dried Blood Spots-A Systematic Review of Test Accuracy.

Background: Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies are rare autosomal recessive fatty acid ß-oxidation disorders. Their clinical presentations are variable, and premature death is common. They are included in newborn blood spot screening programs in many countries around the world. The current process of screening, through the measurement of acylcarnitines (a metabolic by-product) in dried blood spots with tandem mass spectrometry, is subject to uncertainty regarding test accuracy. Methods: We conducted a systematic review of literature published up to 19th June 2018. We included studies that investigated newborn screening for LCHAD or MTP deficiencies by tandem mass spectrometry of acylcarnitines in dried blood spots. The reference standards were urine organic acids, blood acylcarnitine profiles, enzyme analysis in cultured fibroblasts or lymphocytes, mutation analysis, or at least 10-year follow-up. The outcomes of interest were sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). Assessment of titles, abstracts, and full-text papers and quality appraisal were carried out independently by two reviewers. One reviewer extracted study data. This was checked by a second reviewer. Results: Ten studies provided data on test accuracy. LCHAD or MTP deficiencies were identified in 23 babies. No cases of LCHAD/MTP deficiencies were identified in four studies. PPV ranged from 0% (zero true positives and 28 false positives from 276,565 babies screened) to 100% (13 true positives and zero false positives from 2,037,824 babies screened). Sensitivity, specificity, and NPV could not be calculated as there was no systematic follow-up of babies who screened negative. Conclusions: Test accuracy estimates of screening for LCHAD and MTP deficiencies with tandem mass spectrometry measurement of acylcarnitines in dried blood were variable in terms of PPVs. Screening methods (including markers and thresholds) varied between studies, and sensitivity, specificity, and NPVs are unknown.

Peripheral Neuropathy, Episodic Rhabdomyolysis, and Hypoparathyroidism in a Patient with Mitochondrial Trifunctional Protein Deficiency.

A combination of unexplained peripheral neuropathy, hypoparathyroidism, and the inability to cope with metabolic stress could point to a rare inborn error of metabolism, such as mitochondrial trifunctional protein (MTP) deficiency.Here, we describe a 20-year-old woman who was known since childhood with axonal motor sensory polyneuropathy of unknown origin. She presented with progressive dyspnoea, and increased muscle weakness, preceded by 6 days of fever, vomiting, and diarrhoea. Laboratory testing showed rhabdomyolysis, and hypocalcaemia with low parathyroid levels. The patient was intubated because of respiratory insufficiency and a viral and bacterial pneumonia was diagnosed. She was discharged after 16 days of admission. Metabolic screening, performed at the time of rhabdomyolysis, showed increased concentrations of long-chain 3-hydroxyacyl carnitine species, together with elevated urinary excretion of 3-hydroxy dicarboxylic acids. Decreased activity of long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain 3-ketoacyl-CoA thiolase in peripheral lymphocytes and fibroblasts confirmed a MTP deficiency. Sequence analysis of the HADHB gene showed two heterozygous variants: c.209+1G>C (splicing defect) and c.980T>C (p.Leu327Leu). When the acylcarnitine profile was repeated after the episode of rhabdomyolysis had resolved it showed no abnormalities.Our case illustrates a cluster of peripheral neuropathy, episodic rhabdomyolysis, and hypoparathyroidism in a patient with MTP deficiency caused by mutations in the HADHB gene. It stresses the importance of performing metabolic screening when patients are most symptomatic, as normal results can be found at times when no metabolic stress is present. Screening is relatively easy and timely diagnosis has important implications for treatment.

Mitochondrial trifunctional protein deficiency due to HADHB gene mutation in a Chinese family.

We report an 8-year-old girl with lower limb weakness since birth in whom mitochondrial trifunctional protein (MTP) deficiency, an autosomal recessive fatty acid oxidation disorder caused by HADHA or HADHB mutations, had not been definitively diagnosed before she was referred to our hospital. Repeated blood acylcarnitine analysis revealed slightly increased long-chain 3-OH-acylcarnitine levels; electromyography (EMG) suggested peripheral nerve injury; muscle biopsy confirmed a neurogenic lesion in muscle fibers, as shown by EMG. Analysis of the HADHB, which encodes long-chain 3-ketoacyl-CoA thiolase, one of the enzymes constituting mitochondrial trifunctional protein, identified homozygous missense mutation c.739C > T (p.R247C). Mitochondrial trifunctional protein deficiency is an extremely rare disorder and has not been reported in Chinese people to date. It is likely that neonatal onset, as seen in our patient, has not been reported for the neuromyopathic phenotype of mitochondrial trifunctional protein deficiency.