Leukodystrophy and CSF purine abnormalities associated with isolated 3-methylcrotonyl-CoA carboxylase deficiency

Intracranial Calcification Associated with 3-Methylcrotonyl-CoA Carboxylase Deficiency

3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency is the most frequent organic aciduria detected in newborn screening programs. It demonstrates a variable heterogeneous clinical phenotype, ranging from neonatal onset with severe neurological disorders to asymptomatic adult forms. Herein, we report the first 2 related cases of 3-MCC deficiency presenting with intracranial calcification in the literature. A girl and a boy aged 3 years, 9 months and 4 years were included in the study. The main clinical manifestations were acquired microcephaly, global developmental delay, intractable seizures, mild feeding difficulty, and intermittent dystonic contractions. On physical and neurological examinations, their weights, heights, and head circumferences were below the 3rd percentile, they had acquired microcephaly, truncal hypotonia, upper and lower limb spasticity, hyperreflexia, positive bilateral Babinski signs, and clonus. The detailed biochemical and metabolic tests were unremarkable, except blood 3-hydroxyisovalerylcarnitine (C5OH) was slightly increased in case 1. Cranial computed tomography demonstrated mild cerebral and cerebellar atrophy as well as bilateral periventricular and thalamic calcifications in both cases. We identified a homozygous mutation of c.1015G>A (p.V339M) in the MCCC2gene, and the mutation was confirmed by Sanger sequencing. To the best of our knowledge, our cases are the first reported describing intracranial calcification in cases with 3-MCC deficiency. This report expands on the underlying causes of intracranial calcifications and suggests that 3-MCC deficiency may have intracranial calcifications on bilateral thalamus and periventricular white matters. If clinical findings show intracranial calcification, 3-MCC deficiency should also be kept in mind.

Targeted cerebrospinal fluid analysis for inborn errors of metabolism on an LC-MS/MS analysis platform

BACKGROUND

Laboratory investigations of cerebrospinal fluid (CSF) are essential when suspecting an inborn error of metabolism (IEM) involving neurological features. Available tests are currently performed on different analytical platforms, requiring a large sample volume and long turnaround time, which often delays timely diagnosis. Therefore, it would be preferable to have an "one-instrument" targeted multi-metabolite approach.

METHOD

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) platform, based on two different methods for analysing 38 metabolites using positive and negative electrospray ionisation modes, was established. To allow for platform extension, both methods were designed to use the same CSF sample preparation procedure and to be run on the same separation column (ACE C18-PFP).

RESULTS

Assessment of the LC-MS/MS platform methods was first made by analytical validation, followed by the establishment of literature-based CSF cut-off values and reference ranges, and by the measurement of available samples obtained from patients with confirmed diagnoses of aromatic l-amino acid decarboxylase deficiency, guanidinoacetate methyltransferase deficiency, ornithine aminotransferase deficiency, cerebral folate deficiency and methylenetetrahydrofolate reductase deficiency.

CONCLUSION

An extendable targeted LC-MS/MS platform was developed for the analysis of multiple metabolites in CSF, thereby distinguishing samples from patients with IEM from non-IEM samples. Reference concentrations for several biomarkers in CSF are provided for the first time. By measurement on a single analytical platform, less sample volume is required (200 μL), diagnostic results are obtained faster, and preanalytical issues are reduced.

SYNOPSIS

LC-MS/MS platform for CSF analysis consisting of two differentially designed methods.

Expanded Newborn Screening for Inborn Errors of Metabolism by Tandem Mass Spectrometry in Suzhou, China: Disease Spectrum, Prevalence, Genetic Characteristics in a Chinese Population

Expanded newborn screening for inborn errors of metabolism (IEMs) by tandem mass spectrometry (MS/MS) could simultaneously analyze more than 40 metabolites and identify about 50 kinds of IEMs. Next generation sequencing (NGS) targeting hundreds of IMEs-associated genes as a follow-up test in expanded newborn screening has been used for genetic analysis of patients. The spectrum, prevalence, and genetic characteristic of IEMs vary dramatically in different populations. To determine the spectrum, prevalence, and gene mutations of IEMs in newborns in Suzhou, China, 401,660 newborns were screened by MS/MS and 138 patients were referred to genetic analysis by NGS. The spectrum of 22 IEMs were observed in Suzhou population of newborns, and the overall incidence (excluding short chain acyl-CoA dehydrogenase deficiency (SCADD) and 3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD)) was 1/3,163. The prevalence of each IEM ranged from 1/401,660 to 1/19,128, while phenylketonuria (PKU) (1/19,128) and Mild hyperphenylalaninemia (M-HPA) (1/19,128) were the most common IEMs, followed by primary carnitine uptake defect (PCUD) (1/26,777), SCADD (1/28,690), hypermethioninemia (H-MET) (1/30,893), 3-MCCD (1/33,412) and methylmalonic acidemia (MMA) (1/40,166). Moreover, 89 reported mutations and 51 novel mutations in 25 IMEs-associated genes were detected in 138 patients with one of 22 IEMs. Some hotspot mutations were observed for ten IEMs, including PAH gene c.728G > A, c.611A > G, and c.721C > T for Phenylketonuria, PAH gene c.158G > A, c.1238G > C, c.728G > A, and c.1315+6T > A for M-HPA, SLC22A5 gene c.1400C > G, c.51C > G, and c.760C > T for PCUD, ACADS gene c.1031A > G, c.164C > T, and c.1130C > T for SCAD deficiency, MAT1A gene c.791G > A for H-MET, MCCC1 gene c.639+2T > A and c.863A > G for 3-MCCD, MMUT gene c.1663G > A for MMA, SLC25A13 gene c.IVS16ins3Kb and c.852_855delTATG for cittrullinemia II, PTS gene c.259C > T and c.166G > A for Tetrahydrobiopterin deficiency, and ACAD8 gene c.1000C > T and c.286C > A for Isobutyryl coa dehydrogenase deficiency. All these hotspot mutations were reported to be pathogenic or likely pathogenic, except a novel mutation of ACAD8 gene c.286C > A. These mutational hotspots could be potential candidates for gene screening and these novel mutations expanded the mutational spectrum of IEMs. Therefore, our findings could be of value for genetic counseling and genetic diagnosis of IEMs.

Neuroimaging Findings of Organic Acidemias and Aminoacidopathies

Although individual cases of inherited metabolic disorders are rare, overall they account for a substantial number of disorders affecting the central nervous system. Organic acidemias and aminoacidopathies include a variety of inborn errors of metabolism that are caused by defects in the intermediary metabolic pathways of carbohydrates, amino acids, and fatty acid oxidation. These defects can lead to the abnormal accumulation of organic acids and amino acids in multiple organs, including the brain. Early diagnosis is mandatory to initiate therapy and prevent permanent long-term neurologic impairments or death. Neuroimaging findings can be nonspecific, and metabolism- and genetics-based laboratory investigations are needed to confirm the diagnosis. However, neuroimaging has a key role in guiding the diagnostic workup. The findings at conventional and advanced magnetic resonance imaging may suggest the correct diagnosis, help narrow the differential diagnosis, and consequently facilitate early initiation of targeted metabolism- and genetics-based laboratory investigations and treatment. Neuroimaging may be especially helpful for distinguishing organic acidemias and aminoacidopathies from other more common diseases with similar manifestations, such as hypoxic-ischemic injury and neonatal sepsis. Therefore, it is important that radiologists, neuroradiologists, pediatric neuroradiologists, and clinicians are familiar with the neuroimaging findings of organic acidemias and aminoacidopathies. ^©RSNA, 2018.

3-Methylcrotonyl-CoA carboxylase deficiency: Mutational spectrum derived from comprehensive newborn screening

The deficiency of 3-methycrotonyl-CoA carboxylase (3-MCC; EC 6.4.1.4) is an autosomal recessive organic aciduria that is included in the newborn screening programs of several countries. This study reports data mainly obtained from the Portuguese newborn screening program collected over a ten-year period. Analysis of the MCCC1 and MCCC2 genes yielded 26 previously unreported mutations and a variant of clinically unknown significance. These mutations are discussed in the context of their likely impact on the function of the 3-MCC enzyme, with a view to exploring whether a phenotype-genotype correlation might be discerned. Further, these mutations were analysed in the context of what is known of the MCCC1 and MCCC2 mutational spectra, information that will be useful in both clinical and laboratory practice.

A 3-methylcrotonyl-CoA carboxylase deficient human skin fibroblast transcriptome reveals underlying mitochondrial dysfunction and oxidative stress

Isolated 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive inherited metabolic disease of leucine catabolism with a highly variable phenotype. Apart from extensive mutation analyses of the MCCC1 and MCCC2 genes encoding 3-methylcrotonyl-CoA carboxylase (EC 6.4.1.4), molecular data on MCC deficiency gene expression studies in human tissues is lacking. For IEMs, unbiased '-omics' approaches are starting to reveal the secondary cellular responses to defects in biochemical pathways. Here we present the first whole genome expression profile of immortalized cultured skin fibroblast cells of two clinically affected MCC deficient patients and two healthy individuals generated using Affymetrix(®)HuExST1.0 arrays. There were 16191 significantly differentially expressed transcript IDs of which 3591 were well annotated and present in the predefined knowledge database of Ingenuity Pathway Analysis software used for downstream functional analyses. The most noticeable feature of this MCCA deficient skin fibroblast transcriptome was the typical genetic hallmark of mitochondrial dysfunction, decreased antioxidant response and disruption of energy homeostasis, which was confirmed by mitochondrial functional analyses. The MCC deficient transcriptome seems to predict oxidative stress that could alter the complex secondary cellular response that involve genes of the glycolysis, the TCA cycle, OXPHOS, gluconeogenesis, β-oxidation and the branched-chain fatty acid metabolism. An important emerging insight from this human MCCA transcriptome in combination with previous reports is that chronic exposure to the primary and secondary metabolites of MCC deficiency and the resulting oxidative stress might impact adversely on the quality of life and energy levels, irrespective of whether MCC deficient individuals are clinically affected or asymptomatic.

Outcomes of cases with 3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency - Report from the Inborn Errors of Metabolism Information System

INTRODUCTION

3-Methyl crotonyl CoA carboxylase (3MCC) deficiency is an inborn error of leucine metabolism whose detection was increased with the advent of expanded newborn screening. While most NBS-identified infants appear clinically normal, prior studies suggest a possible increased risk for developmental or metabolic abnormalities. As yet, no predictive markers are known that can identify children at risk for biochemical or developmental abnormalities.

METHOD

All available 3-MCC cases diagnosed by newborn screening in the Inborn Errors of Metabolism Information System (IBEM-IS) were reviewed for markers that might be predictive of outcome.

RESULTS

A limited number of cases were identified with traditional biochemical symptoms including acidosis, hyperammonemia or lactic acidosis, and 15% of those with available developmental information had recorded developmental disabilities not clearly attributable to other causes. There was no correlation between newborn screening (NBS) C5OH level and presence of metabolic, newborn, later-life or developmental abnormalities in these cases.

DISCUSSION

This sample, obtained from the IBEM-IS database, attempts to avoid some of the ascertainment bias present in retrospective studies. An increase in developmental abnormalities and in traditionally described metabolic symptoms remains apparent, although no specific biochemical markers appear predictive of outcome. The role that prevention of fasting plays in outcome cannot be ascertained. These data suggest that C5OH level found on newborn screening by itself is not sufficient for diagnostic or predictive purposes.

Brain magnetic resonance imaging and proton MR spectroscopic findings after metabolic crisis in 3-methylcrotonylglycinuria

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopic (MRS) findings in 3-methylcrotonylglycinuria presenting with acute metabolic decompensation in a previously healthy 7-year old female are described. The patient was hospitalized with fever, irritability, gastrointestinal problems, drowsiness, signs of upper motor neuron deficit, and rapidly progressive respiratory distress requiring assisted ventilation. Laboratory workup showed severe metabolic acidosis, and the diagnosis of 3-methylcrotonylglycinuria was established by the mass spectrometry analysis of urine sample. Although initial CT imaging workup was found to be gross normal, subsequent MRI of the brain in the early chronic stage of the disease showed symmetrical ill-defined signal abnormalities within medulla oblongata, pons, inferior cerebellar peduncles, and periventricular white matter in cerebral hemispheres. Diffusion-weighted images were unremarkable. Single-voxel proton MRS showed elevated levels of lactate, branched-chain amino acids, as well as glutamine and glutamate. To the best of our knowledge, this is the first reported case of late onset 3-methylcrotonylglycinuria with complete MRI and MRS workup in the early chronic phase after metabolic crisis.

Consanguinity and rare mutations outside of MCCC genes underlie nonspecific phenotypes of MCCD

Purpose

3-Methylcrotonyl-CoA carboxylase deficiency (MCCD) is an autosomal recessive disorder of leucine catabolism that has a highly variable clinical phenotype, ranging from acute metabolic acidosis to nonspecific symptoms such as developmental delay, failure to thrive, hemiparesis, muscular hypotonia, and multiple sclerosis. Implementation of newborn screening for MCCD has resulted in broadening the range of phenotypic expression to include asymptomatic adults. The purpose of this study was to identify factors underlying the varying phenotypes of MCCD.

Methods

We performed exome sequencing on DNA from 33 cases and 108 healthy controls. We examined these data for associations between either MCC mutational status, genetic ancestry, or consanguinity and the absence or presence/specificity of clinical symptoms in MCCD cases.

Results

We determined that individuals with nonspecific clinical phenotypes are highly inbred compared with cases that are asymptomatic and healthy controls. For 5 of these 10 individuals, we discovered a homozygous damaging mutation in a disease gene that is likely to underlie their nonspecific clinical phenotypes previously attributed to MCCD.

Conclusion

Our study shows that nonspecific phenotypes attributed to MCCD are associated with consanguinity and are likely not due to mutations in the MCC enzyme but result from rare homozygous mutations in other disease genes.

3-methylcrotonyl-CoA carboxylase deficiency: clinical, biochemical, enzymatic and molecular studies in 88 individuals

Background

Isolated 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder of leucine metabolism caused by mutations in MCCC1 or MCCC2 encoding the α and β subunit of MCC, respectively. The phenotype is highly variable ranging from acute neonatal onset with fatal outcome to asymptomatic adults.

Methods

We report clinical, biochemical, enzymatic and mutation data of 88 MCC deficient individuals, 53 identified by newborn screening, 26 diagnosed due to clinical symptoms or positive family history and 9 mothers, identified following the positive newborn screening result of their baby.

Results

Fifty-seven percent of patients were asymptomatic while 43% showed clinical symptoms, many of which were probably not related to MCC deficiency but due to ascertainment bias. However, 12 patients (5 of 53 identified by newborn screening) presented with acute metabolic decompensations. We identified 15 novel MCCC1 and 16 novel MCCC2 mutant alleles. Additionally, we report expression studies on 3 MCCC1 and 8 MCCC2 mutations and show an overview of all 132 MCCC1 and MCCC2 variants known to date.

Conclusions

Our data confirm that MCC deficiency, despite low penetrance, may lead to a severe clinical phenotype resembling classical organic acidurias. However, neither the genotype nor the biochemical phenotype is helpful in predicting the clinical course.

3-Methylcrotonylglycine disrupts mitochondrial energy homeostasis and inhibits synaptic Na(+),K (+)-ATPase activity in brain of young rats

Deficiency of 3-methylcrotonyl-CoA carboxylase activity is an inherited metabolic disease biochemically characterized by accumulation and high urinary excretion of 3-methylcrotonylglycine (3MCG), and also of 3-hydroisovalerate in lesser amounts. Affected patients usually have neurologic dysfunction, brain abnormalities and cardiomyopathy, whose pathogenesis is still unknown. The present study investigated the in vitro effects of 3MCG on important parameters of energy metabolism, including CO(2) production from labeled acetate, enzyme activities of the citric acid cycle, as well as of the respiratory chain complexes I-IV (oxidative phosphorylation), creatine kinase (intracellular ATP transfer), and synaptic Na(+),K(+)-ATPase (neurotransmission) in brain cortex of young rats. 3MCG significantly reduced CO(2) production, implying that this compound compromises citric acid cycle activity. Furthermore, 3MCG diminished the activities of complex II-III of the respiratory chain, mitochondrial creatine kinase and synaptic membrane Na(+),K(+)-ATPase. Furthermore, antioxidants were able to attenuate or fully prevent the inhibitory effect of 3MCG on creatine kinase and synaptic membrane Na(+),K(+)-ATPase activities. We also observed that lipid peroxidation was elicited by 3MCG, suggesting the involvement of free radicals on 3MCG-induced effects. Considering the importance of the citric acid cycle and the electron flow through the respiratory chain for brain energy production, creatine kinase for intracellular energy transfer, and Na(+),K(+)-ATPase for the maintenance of the cell membrane potential, the present data indicate that 3MCG potentially impairs mitochondrial brain energy homeostasis and neurotransmission. It is presumed that these pathomechanisms may be involved in the neurological damage found in patients affected by 3-methylcrotonyl-CoA carboxylase deficiency.

The consequences of extended newborn screening programmes: do we know who needs treatment?

The development of an evidence base for newborn screening is especially difficult because of the rarity of disorders now detectable. One consequence of expanded newborn screening is that physicians are being called upon to manage asymptomatic babies with persistent biochemical disturbances that indicate likely enzyme deficiencies. Some of these may be very mild. There is not always agreement as to who should be treated. Particular problems are seen with disorders that were previously thought very rare but are now found frequently by newborn screening. Some of these disorders appear benign or nearly so, and in the present state of knowledge should clearly not be included in routine newborn screening panels.

3-methylcrotonyl-CoA carboxylase deficiency and severe multiple sclerosis

This report describes a female with isolated 3-methylcrotonyl-CoA carboxylase deficiency. She had a mild Reye-like episode, loss of scalp hair, psychomotor retardation, and an attention-deficit hyperactivity disorder. The diagnosis was made at 13 years of age when she developed relapsing remitting multiple sclerosis with a malignant course. Treatment with steroids had initially a good therapeutic effect on the relapses. The response to interferon beta-1a treatment was poor. On mitoxantrone treatment there was a considerable neurologic recovery.

Newborn screening for 3-methylcrotonyl-CoA carboxylase deficiency: population heterogeneity ofMCCA andMCCB mutations and impact on risk assessment

New technology enables expansion of newborn screening (NBS) of inborn errors aimed to prevent adverse outcome. In conditions with a large share of asymptomatic phenotypes, the potential harm created by NBS must carefully be weighed against benefit. Policies vary throughout the United States, Australia, and Europe due to limited data on outcome and treatability of candidate screening conditions. We elaborated the rationale for decision making in 3-methylcrotonyl-coenzyme A (CoA) carboxylase deficiency (MCCD), which afflicts leucine catabolism, with reported outcomes ranging from asymptomatic to death. In Bavaria, we screened 677,852 neonates for 25 conditions, including MCCD, based on elevated concentrations of 3-hydroxyisovalerylcarnitine (3-HIVA-C). Genotypes of MCCA (MCCC1) and MCCB (MCCC2) were assessed in identified newborns, their relatives, and in individuals (n = 17) from other regions, and correlated to biochemical and clinical phenotypes. NBS revealed eight newborns and six relatives with MCCD, suggesting a higher frequency than previously assumed (1:84,700). We found a strikingly heterogeneous spectrum of 22 novel and eight reported mutations. Allelic variants were neither related to biochemical nor anamnestic data of our probands showing all asymptomatic or benign phenotypes. Comparative analysis of case reports with NBS data implied that only few individuals (< 10%) develop symptoms. In addition, none of the symptoms reported so far can clearly be attributed to MCCD. MCCD is a genetic condition with low clinical expressivity and penetrance. It largely represents as nondisease. So far, there are no genetic or biochemical markers that would identify the few individuals potentially at risk for harmful clinical expression. The low ratio of benefit to harm was pivotal to the decision to exclude MCCD from NBS in Germany. MCCD may be regarded as exemplary of the ongoing controversy arising from the inclusion of potentially asymptomatic conditions, which generates a psychological burden for afflicted families and a financial burden for health care systems.

Maternal mutation 677C > T in the methylenetetrahydrofolate reductase gene associated with severe brain injury in offspring

A frequent polymorphism in the gene coding for 5,10-methylenetetrahydrofolate reductase is the substitution 677C > T which produces a thermolabile and inefficient enzyme. Homozygosity for the 677C > T allele is the most important determinant of hyperhomocys-teinemia, when folic acid intake is reduced. Most studies on the relationship between the 677C > T variant in the mother and defects in the offspring have focused on neural-tube defects. This study is a retrospective case-control investigation of hypoxic-ischemic encephalopathy of the newborn (HIEN) with reference to the 677C > T polymorphism as a genetic risk for this condition. The prevalence of the 677C > T allele was studied in 11 children with HIEN, their respective mothers, and 85 healthy individuals. Plasma homocysteine levels after fasting and methionine loading were determined in both mothers and controls. Ten of 11 patients were evaluated using magnetic resonance (MR) imaging, and all showed multicystic encephalomalacia and severe brain vasculopathy. Seven mothers were homozygous and four heterozygous for the 677C > T allele. Five of the children were homozygous and six heterozygous for this polymorphism. The variant allele frequency was higher in the group of mothers with affected children than in the controls and was associated with an increase in plasma homocysteine after methionine loading, in the group of mothers than in controls. The 677C > T mutation in mothers, either in a homozygous or heterozygous state, together with poor nutritional status (probable folate deficiency) may represent a risk factor for irreversible HIEN in the offspring.