Terry G. J. Derks

Efficacy and safety of cyclic pyranopterin monophosphate substitution in severe molybdenum cofactor deficiency type A: a prospective cohort study

BACKGROUND Molybdenum cofactor deficiency (MoCD) is characterised by early, rapidly progressive postnatal encephalopathy and intractable seizures, leading to severe disability and early death. Previous treatment attempts have been unsuccessful. After a pioneering single treatment we now report the outcome of the complete first cohort of patients receiving substitution treatment with cyclic pyranopterin monophosphate (cPMP), a biosynthetic precursor of the cofactor. METHODS In this observational prospective cohort study, newborn babies with clinical and biochemical evidence of MoCD were admitted to a compassionate-use programme at the request of their treating physicians. Intravenous cPMP (80-320 μg/kg per day) was started in neonates diagnosed with MoCD (type A and type B) following a standardised protocol. We prospectively monitored safety and efficacy in all patients exposed to cPMP. FINDINGS Between June 6, 2008, and Jan 9, 2013, intravenous cPMP was started in 16 neonates diagnosed with MoCD (11 type A and five type B) and continued in eight type A patients for up to 5 years. We observed no drug-related serious adverse events after more than 6000 doses. The disease biomarkers urinary S-sulphocysteine, xanthine, and urate returned to almost normal concentrations in all type A patients within 2 days, and remained normal for up to 5 years on continued cPMP substitution. Eight patients with type A disease rapidly improved under treatment and convulsions were either completely suppressed or substantially reduced. Three patients treated early remain seizure free and show near-normal long-term development. We detected no biochemical or clinical response in patients with type B disease. INTERPRETATION cPMP substitution is the first effective therapy for patients with MoCD type A and has a favourable safety profile. Restoration of molybdenum cofactor-dependent enzyme activities results in a greatly improved neurodevelopmental outcome when started sufficiently early. The possibility of MoCD type A needs to be urgently explored in every encephalopathic neonate to avoid any delay in appropriate cPMP substitution, and to maximise treatment benefit. FUNDING German Ministry of Education and Research; Orphatec/Colbourne Pharmaceuticals.

Mutations in RARS Cause Hypomyelination

Hypomyelinating disorders of the central nervous system are still a diagnostic challenge, as many patients remain without genetic diagnosis. Using magnetic resonance imaging (MRI) pattern recognition and whole exome sequencing, we could ascertain compound heterozygous mutations in RARS in 4 patients with hypomyelination. Clinical features included severe spasticity and nystagmus. RARS encodes the cytoplasmic arginyl‐tRNA synthetase, an enzyme essential for RNA translation. This protein is among the subunits of the multisynthetase complex, which emerges as a key player in myelination. Ann Neurol 2014;76:134–139

Disturbed hepatic carbohydrate management during high metabolic demand in medium-chain acyl-CoA dehydrogenase (MCAD)-deficient mice

Medium‐chain acyl–coenzyme A (CoA) dehydrogenase (MCAD) catalyzes crucial steps in mitochondrial fatty acid oxidation, a process that is of key relevance for maintenance of energy homeostasis, especially during high metabolic demand. To gain insight into the metabolic consequences of MCAD deficiency under these conditions, we compared hepatic carbohydrate metabolism in vivo in wild‐type and MCAD−/− mice during fasting and during a lipopolysaccharide (LPS)‐induced acute phase response (APR). MCAD−/− mice did not become more hypoglycemic on fasting or during the APR than wild‐type mice did. Nevertheless, microarray analyses revealed increased hepatic peroxisome proliferator‐activated receptor gamma coactivator‐1α (Pgc‐1α) and decreased peroxisome proliferator‐activated receptor alpha (Ppar α) and pyruvate dehydrogenase kinase 4 (Pdk4) expression in MCAD−/− mice in both conditions, suggesting altered control of hepatic glucose metabolism. Quantitative flux measurements revealed that the de novo synthesis of glucose‐6‐phosphate (G6P) was not affected on fasting in MCAD−/− mice. During the APR, however, this flux was significantly decreased (−20%) in MCAD−/− mice compared with wild‐type mice. Remarkably, newly formed G6P was preferentially directed toward glycogen in MCAD−/− mice under both conditions. Together with diminished de novo synthesis of G6P, this led to a decreased hepatic glucose output during the APR in MCAD−/− mice; de novo synthesis of G6P and hepatic glucose output were maintained in wild‐type mice under both conditions. APR‐associated hypoglycemia, which was observed in wild‐type mice as well as MCAD−/− mice, was mainly due to enhanced peripheral glucose uptake. Conclusion: Our data demonstrate that MCAD deficiency in mice leads to specific changes in hepatic carbohydrate management on exposure to metabolic stress. This deficiency, however, does not lead to reduced de novo synthesis of G6P during fasting alone, which may be due to the existence of compensatory mechanisms or limited rate control of MCAD in murine mitochondrial fatty acid oxidation. (HEPATOLOGY 2008.)

The difference between observed and expected prevalence of MCAD deficiency in The Netherlands: a genetic epidemiological study

Medium chain acyl coenzyme A dehydrogenase (MCAD) deficiency is assumed to be the most common inherited disorder of mitochondrial fatty acid oxidation. Few reports mention the difference between the expected and observed prevalence of MCAD deficiency on the basis of the carrier frequency in the population. We performed a population-wide retrospective analysis of all known MCAD-deficient patients in The Netherlands. In this study, the observed prevalence of MCAD deficiency in The Netherlands was 1/27 400 (95% confidence interval (CI) 1/23 000–1/33 900), significantly different from the expected prevalence of 1/12 100 (95% CI 1/8450–1/18 500). The observed prevalence of MCAD deficiency showed a remarkable north–south trend within the country. From the patients in this cohort, it can be observed that underdiagnosis contributes to a larger extent to the difference between the expected and observed prevalences of MCAD deficiency in our country, than reduced penetrance. We determined estimates of the segregation proportion in a cohort of 73 families under the assumption of complete ascertainment (pLM=0.41, 95% CI 0.31–0.51) and single ascertainment (pD=0.28, 95% CI 0.19–0.37). With the expectation–maximization algorithm, a third estimate was obtained (pEM=0.28, 95% CI 0.20–0.37). The agreement between the latter two estimates supports incomplete selection and the segregation proportions were in agreement with normal mendelian autosomal recessive inheritance.

Inhibition of mitochondrial fatty acid oxidation in vivo only slightly suppresses gluconeogenesis but enhances clearance of glucose in mice

Mitochondrial fatty acid oxidation (mFAO) is considered to be essential for driving gluconeogenesis (GNG) during fasting. However, quantitative in vivo data on de novo synthesis of glucose‐6‐phosphate upon acute inhibition of mFAO are lacking. We assessed hepatic glucose metabolism in vivo after acute inhibition of mFAO by 30 mg kg−1 2‐tetradecylglycidic acid (TDGA) in hypoketotic hypoglycemic male C57BL/6J mice by the infusion of [U‐13C]glucose, [2‐13C]glycerol, [1‐2H]galactose, and paracetamol for 6 hours, which was followed by mass isotopomer distribution analysis in blood glucose and urinary paracetamol‐glucuronide. During TDGA treatment, endogenous glucose production was unaffected (127 ± 10 versus 118 ± 7 μmol kg−1 minute−1, control versus TDGA, not significant), but the metabolic clearance rate of glucose was significantly enhanced (15.9 ± 0.9 versus 26.3 ± 1.1 mL kg−1 minute−1, control versus TDGA,P < 0.05). In comparison with control mice, de novo synthesis of glucose‐6‐phosphate (G6P) was slightly decreased in TDGA‐treated mice (108 ± 19 versus 85 ± 6 μmol kg−1 minute−1, control versus TDGA, P < 0.05). Recycling of glucose was decreased upon TDGA treatment (26 ± 14 versus 12 ± 4 μmol kg−1 minute−1, control versus TDGA, P < 0.05). Hepatic messenger RNA (mRNA) levels of genes encoding enzymes involved in de novo G6P synthesis were unaltered, whereas glucose‐6‐phosphate hydrolase mRNA expressions were increased in TDGA‐treated mice. Glucokinase and pyruvate kinase mRNA levels were significantly decreased, whereas pyruvate dehydrogenase kinase isozyme 4 expression was increased 30‐fold; this suggested decreased glycolytic activity. Conclusion: Acute pharmacological inhibition of mFAO using TDGA had no effect on endogenous glucose production and only a marginal effect on de novo G6P synthesis. Hence, fully active mFAO is not essential for maintenance of hepatic GNG in vivo in fasted mice.(HEPATOLOGY 2008.)

Dietary management in glycogen storage disease type III: what is the evidence?

In childhood, GSD type III causes relatively severe fasting intolerance, classically associated with ketotic hypoglycaemia. During follow up, history of (documented) hypoglycaemia, clinical parameters (growth, liver size, motor development, neuromuscular parameters), laboratory parameters (glucose, lactate, ALAT, cholesterol, triglycerides, creatine kinase and ketones) and cardiac parameters all need to be integrated in order to titrate dietary management, for which age-dependent requirements need to be taken into account. Evidence from case studies and small cohort studies in both children and adults with GSD III demonstrate that prevention of hypoglycaemia and maintenance of euglycemia is not sufficient to prevent complications. Moreover, over-treatment with carbohydrates may even be harmful. The ageing cohort of GSD III patients, including the non-traditional clinical presentations in adulthood, raises ‬‬‬new questions.

Risk stratification by residual enzyme activity after newborn screening for medium-chain acyl-CoA dehyrogenase deficiency: data from a cohort study

BackgroundSince the introduction of medium-chain acyl coenzyme A dehydrogenase (MCAD) deficiency in population newborn bloodspot screening (NBS) programs, subjects have been identified with variant ACADM (gene encoding MCAD enzyme) genotypes that have never been identified in clinically ascertained patients. It could be hypothesised that residual MCAD enzyme activity can contribute in risk stratification of subjects with variant ACADM genotypes.MethodsWe performed a retrospective cohort study of all patients identified upon population NBS for MCAD deficiency in the Netherlands between 2007–2010. Clinical, molecular, and enzymatic data were integrated.ResultsEighty-four patients from 76 families were identified. Twenty-two percent of the subjects had a variant ACADM genotype. In patients with classical ACADM genotypes, residual MCAD enzyme activity was significantly lower (median 0%, range 0-8%) when compared to subjects with variant ACADM genotypes (range 0-63%; 4 cases with 0%, remainder 20-63%). Patients with (fatal) neonatal presentations before diagnosis displayed residual MCAD enzyme activities <1%. After diagnosis and initiation of treatment, residual MCAD enzyme activities <10% were associated with an increased risk of hypoglycaemia and carnitine supplementation. The prevalence of MCAD deficiency upon screening was 1/8,750 (95% CI 1/7,210–1/11,130).ConclusionsDetermination of residual MCAD enzyme activity improves our understanding of variant ACADM genotypes and may contribute to risk stratification. Subjects with variant ACADM genotypes and residual MCAD enzyme activities <10% should be considered to have the same risks as patients with classical ACADM genotypes. Parental instructions and an emergency regimen will remain principles of the treatment in any type of MCAD deficiency, as the effect of intercurrent illness on residual MCAD enzyme activity remains uncertain. There are, however, arguments in favour of abandoning the general advice to avoid prolonged fasting in subjects with variant ACADM genotypes and >10% residual MCAD enzyme activity.

Lipids in hepatic glycogen storage diseases: pathophysiology, monitoring of dietary management and future directions

Hepatic glycogen storage diseases (GSD) underscore the intimate relationship between carbohydrate and lipid metabolism. The hyperlipidemias in hepatic GSD reflect perturbed intracellular metabolism, providing biomarkers in blood to monitor dietary management. In different types of GSD, hyperlipidemias are of a different origin. Hypertriglyceridemia is most prominent in GSD type Ia and associated with long-term outcome morbidity, like pancreatitis and hepatic adenomas. In the ketotic subtypes of GSD, hypertriglyceridemia reflects the age-dependent fasting intolerance, secondary lipolysis and increased mitochondrial fatty acid oxidation. The role of high protein diets is established for ketotic types of GSD, but non-traditional dietary interventions (like medium-chain triglycerides and the ketogenic diet) in hepatic GSD are still controversial and necessitate further studies. Patients with these rare inherited disorders of carbohydrate metabolism meet several criteria of the metabolic syndrome, therefore close monitoring for cardiovascular diseases in ageing GSD patients may be justified.

BH4 treatment in BH4-responsive PKU patients: preliminary data on blood prolactin concentrations suggest increased cerebral dopamine concentrations.

In phenylketonuria (PKU), cerebral neurotransmitter deficiencies have been suggested to contribute to brain dysfunction. Present treatment aims to reduce blood phenylalanine concentrations by a phenylalanine-restricted diet, while in some patients blood phenylalanine concentrations also respond to cofactor treatment with tetrahydrobiopterin (BH4). Recently, a repurposing approach of BH4 was suggested to increase cerebral neurotransmitter synthesis. To investigate whether BH4 may improve cerebral dopamine concentrations in PKU patients beyond its effect through lowering blood phenylalanine concentrations, we investigated blood prolactin concentrations-as a parameter of brain dopamine availability. We retrospectively compared blood prolactin in relation to blood phenylalanine concentrations of nine (male) BH4-responsive PKU patients, when being treated without and with BH4. Blood prolactin concentrations positively correlated to blood phenylalanine concentrations (p=0.002), being significantly lower with than without BH4 treatment (p=0.047). In addition, even in this small number of male patients, blood prolactin concentrations tended to be lower at increasing BH4 dose (p=0.054), while taking blood phenylalanine concentrations into account (p=0.002). In individual BH4-responsive patients, median blood prolactin concentrations were significantly lower while using BH4 than before using BH4 treatment (p=0.024), whereas median blood phenylalanine concentrations tended to be lower, but this did not reach statistical significance (p=0.107). Therefore, these data show that high blood phenylalanine in BH4-responsive PKU male patients seems to be associated with increased blood prolactin concentrations, suggesting reduced cerebral dopamine availability. Moreover, these data suggest that BH4 treatment in itself could decrease blood prolactin concentrations in a dose-responsive way, independent of blood phenylalanine concentrations. We conclude that these preliminary data indicate that BH4 treatment may improve cerebral dopamine concentrations in PKU patients beyond its effect through lowering blood phenylalanine concentrations, possibly in a dose-dependent manner, but further research would be warranted.

Single amino acid supplementation in aminoacidopathies: a systematic review

Aminoacidopathies are a group of rare and diverse disorders, caused by the deficiency of an enzyme or transporter involved in amino acid metabolism. For most aminoacidopathies, dietary management is the mainstay of treatment. Such treatment includes severe natural protein restriction, combined with protein substitution with all amino acids except the amino acids prior to the metabolic block and enriched with the amino acid that has become essential by the enzymatic defect. For some aminoacidopathies, supplementation of one or two amino acids, that have not become essential by the enzymatic defect, has been suggested. This so-called single amino acid supplementation can serve different treatment objectives, but evidence is limited. The aim of the present article is to provide a systematic review on the reasons for applications of single amino acid supplementation in aminoacidopathies treated with natural protein restriction and synthetic amino acid mixtures.