Focal changes in the globi pallidi associated with neurological dysfunction in methylmalonic acidaemia

Follow-up study of neuropsychological scores of infant patients with cobalamin C defects and influencing factors of cerebral magnetic resonance imaging characteristics

Purpose

The purpose of this study was to investigate whether baseline cerebral magnetic resonance imaging (MRI) characteristics could predict therapeutic responsiveness in patients with cobalamin C (cblC) defects.

Materials and methods

The cerebral MRI results of 40 patients with cblC defects were evaluated by a neuroradiologist. Neuropsychological scores and imaging data were collected. Neuropsychological tests were performed before and after standardized treatment.

Results

Thirty-eight patients initially underwent neuropsychological testing [developmental quotient (DQ)]. CblC defects with cerebellar atrophy, corpus callosum thinning and ventricular dilation had significantly lower DQs than those without (P < 0.05). Through a multivariate linear stepwise regression equation after univariate analysis, ventricular dilation was the most valuable predictor of lower DQs. Thirty-six patients (94.7%) underwent follow-up neuropsychological testing. The pre- and post-treatment DQ values were not significantly different (Z = -1.611, P = 0.107). The post-treatment DQ classification (normal, moderately low, or extremely low) showed nearly no change compared to the pretreatment DQ classification (k = 0.790, P < 0.001).

Conclusion

Ventricular dilation, cerebral atrophy and corpus callosum thinning are the main MRI abnormalities of cblC defects, and these manifestations are significantly correlated with delayed development in children. MRI findings can be considered an important tool for determining the severity of cblC defects.

Mitochondrial disease, mitophagy, and cellular distress in methylmalonic acidemia

Mitochondria—the intracellular powerhouse in which nutrients are converted into energy in the form of ATP or heat—are highly dynamic, double-membraned organelles that harness a plethora of cellular functions that sustain energy metabolism and homeostasis. Exciting new discoveries now indicate that the maintenance of this ever changing and functionally pleiotropic organelle is particularly relevant in terminally differentiated cells that are highly dependent on aerobic metabolism. Given the central role in maintaining metabolic and physiological homeostasis, dysregulation of the mitochondrial network might therefore confer a potentially devastating vulnerability to high-energy requiring cell types, contributing to a broad variety of hereditary and acquired diseases. In this Review, we highlight the biological functions of mitochondria-localized enzymes from the perspective of understanding—and potentially reversing—the pathophysiology of inherited disorders affecting the homeostasis of the mitochondrial network and cellular metabolism. Using methylmalonic acidemia as a paradigm of complex mitochondrial dysfunction, we discuss how mitochondrial directed-signaling circuitries govern the homeostasis and physiology of specialized cell types and how these may be disturbed in disease. This Review also provides a critical analysis of affected tissues, potential molecular mechanisms, and novel cellular and animal models of methylmalonic acidemia which are being used to develop new therapeutic options for this disease. These insights might ultimately lead to new therapeutics, not only for methylmalonic acidemia, but also for other currently intractable mitochondrial diseases, potentially transforming our ability to regulate homeostasis and health.

Brain MRI features of methylmalonic acidemia in children: the relationship between neuropsychological scores and MRI findings

Methylmalonic acidemia (MMA) is a severe, heterogeneous disorder of methylmalonate and cobalamin (cbl; vitamin B12) metabolism with a poor prognosis that can cause brain damage. Identifying the magnetic resonance imaging (MRI) findings of MMA might help to make accurate diagnoses earlier in the disease course and exploring the relationship between neuropsychological scores and MRI findings, when therapy is more effective and to improve therapeutic efficacy. Cerebral MRI studies from 37 children with MMA were evaluated by a neuroradiologist. Clinical and imaging data were collected from each patient. All tests were performed during routine investigations and in accordance with the ethical principles of the Declaration of Helsinki. Informed consent was obtained from the guardians of all patients for inclusion in the study. The most common and significant findings were periventricular white matter changes (78.4%), ventricular dilation (29.7%) and cerebral atrophy (40.5%). According to the developmental quotient, the 37 patients were divided into the normal intelligence subgroup (NI, developmental quotient ≥ 85) and the low intelligence subgroup (LI, developmental quotient < 85). The incidence of corpus callosal thinning, cortical atrophy, subcortical white matter changes, and ventricular dilation (grades 0-3) was significantly higher in the LI subgroup than in the NI subgroup (P < 0.05). The incidence of no-mild and moderate-severe ventricular dilation was significantly higher in the LI subgroup than in the NI subgroup (P < 0.05). Ventricular dilatation, cerebral atrophy, white matter changes, and corpus callosal thinning are the main MRI abnormalities in MMA patients, and these manifestations are significantly correlated with delayed development in children.

The correlation between the evolution of bilateral basal ganglia hemorrhage using MR imaging and neurological damage recovery in an infant with methylmalonic aciduria

PURPOSE

We report on one patient with methylmalonic acidemia (MMA) who presented with symmetrical hemorrhage of the caudate nucleus accompanied by severe ventricular dilatation, follow-up magnetic resonance imaging (MRI) findings from one year later, and the clinical manifestations, neuropsychological scores, genetic test results, urine and blood laboratory results and evolution of the disorder.

MATERIALS AND METHODS

This study describes the recent and remote neuropathologic findings, reviews the literature, and discusses the possible pathogenetic mechanisms of these central nervous system lesions.

RESULTS

Patients with MMA may have signs of basal ganglia hemorrhage during acute onset, and the hemorrhage may disappear after treatment. During the treatment, both laboratory examination indexes and neuropsychological scores improved. There was a correlation between the evolution of bilateral basal ganglia hemorrhage using MRI(magnetic resonance imaging) and neurological damage recovery in this infant with MMA.

CONCLUSION

There was a correlation between the evolution of the bilateral basal ganglia hemorrhage using MR imaging and neurological damage recovery in an infant with MMA. We recommend performing conventional MR and diffusion-weighted imaging (DWI) examinations in patients with MMA who present with neurological symptoms.

Novel imaging technologies for genetic diagnoses in the inborn errors of metabolism

Many inborn errors of metabolism and genetic disorders affect the brain. The brain biochemistry may differ from that in the periphery and is not accessible by simple blood and urine sampling. Therefore, neuroimaging has proven to be a valuable tool to not only evaluate the brain structure, but also biochemistry, blood flow and function. Neuroimaging in patients with inborn errors of metabolism can include additional sequences in addition to T1 and T2-weighted imaging because in early stages, there may be no significant findings on the routine sequnces due to the lack of sensitivity or the evolution of abnormalities lags behind the ability of the imaging to detect it. In addition, findings on T1 and T2-weighted imaging of several inborn errors of metabolism may be non-specific and be seen in other non-genetic conditions. Therefore, additional neuroimaging modalities that have been employed including diffusion tensor imaging (DTI), magnetic resonance spectroscopy, functional MRI (fMRI), functional near infrared spectroscopy (fNIRS), or positron emission tomography (PET) imaging may further inform underlying changes in myelination, biochemistry, and functional connectivity. The use of Magnetic Resonance Spectroscopy in certain disorders may add a level of specificity depending upon the metabolite levels that are abnormal, as well as provide information about the process of brain injury (i.e., white matter, gray matter, energy deficiency, toxic buildup or depletion of key metabolites). It is even more challenging to understand how genetic or metabolic disorders contribute to short and/or long term changes in cognition which represent the downstream effects of IEMs. In order to image “cognition” or the downstream effects of a metabolic disorder on domains of brain function, more advanced techniques are required to analyze underlying fiber tracts or alternatively, methods such as fMRI enable generation of brain activation maps after both task based and resting state conditions. DTI can be used to look at changes in white matter tracks. Each imaging modality can explore an important aspect of the anatomy, physiology or biochemisty of the central nervous system. Their properties, pros and cons are discussed in this article. These imaging modalities will be discussed in the context of several inborn errors of metabolism including Galactosemia, Phenylketonruia, Maple syrup urine disease, Methylmalonic acidemia, Niemann-Pick Disease, type C1, Krabbe Disease, Ornithine transcarbamylase deficiency, Sjogren Larsson syndrome, Pelizeaus-Merzbacher disease, Pyruvate dehydrogenase deficiency, Nonketotic Hyperglycinemia and Fabry disease. Space constraints do not allow mention of all the disorders in which one of these modalities has been investigated, or where it would add value to diagnosis or disease progression.

Shunt surgery for early-onset severe hydrocephalus in methylmalonic acidemia: report on two cases and review of the literature

OBJECT

Methylmalonic acidemia (MMA) with early-onset severe hydrocephalus is rare. In this paper, we described two cases of MMA with hydrocephalus and review the literature to elucidate the clinical features of the disease, treatment options, and follow-up results.

METHODS

The PubMed and Embase databases were searched for clinical reports on MMA with severe hydrocephalus, and two unreported cases were presented to illustrate the clinical spectrum.

RESULTS

Six cases of MMA with severe hydrocephalus were observed in the previous literature. Our two patients with severe hydrocephalus but not bulging fontanelle received a ventriculo-peritoneal shunt, and intracranial hypertension was confirmed in both cases during the operation. These patients' clinical symptoms significantly improved after the operation.

CONCLUSIONS

Intracranial hypertension can exist in early-onset severe hydrocephalus in MMA, even if the bulging anterior fontanelle is not apparent. These patients could benefit from a ventriculo-peritoneal shunt.

Evidence of Oxidative Stress and Secondary Mitochondrial Dysfunction in Metabolic and Non-Metabolic Disorders

Mitochondrial dysfunction and oxidative stress have been implicated in the pathogenesis of a number of diseases and conditions. Oxidative stress occurs once the antioxidant defenses of the body become overwhelmed and are no longer able to detoxify reactive oxygen species (ROS). The ROS can then go unchallenged and are able to cause oxidative damage to cellular lipids, DNA and proteins, which will eventually result in cellular and organ dysfunction. Although not always the primary cause of disease, mitochondrial dysfunction as a secondary consequence disease of pathophysiology can result in increased ROS generation together with an impairment in cellular energy status. Mitochondrial dysfunction may result from either free radical-induced oxidative damage or direct impairment by the toxic metabolites which accumulate in certain metabolic diseases. In view of the importance of cellular antioxidant status, a number of therapeutic strategies have been employed in disorders associated with oxidative stress with a view to neutralising the ROS and reactive nitrogen species implicated in disease pathophysiology. Although successful in some cases, these adjunct therapies have yet to be incorporated into the clinical management of patients. The purpose of this review is to highlight the emerging evidence of oxidative stress, secondary mitochondrial dysfunction and antioxidant treatment efficacy in metabolic and non-metabolic diseases in which there is a current interest in these parameters.

MRI characteristics of globus pallidus infarcts in isolated methylmalonic acidemia

BACKGROUND

Bilateral infarcts confined to the globus pallidus are unusual and occur in conjunction with only a few disorders, including isolated methylmalonic acidemia, a heterogeneous inborn error of metabolism. On the basis of neuroradiographic features of metabolic strokes observed in a large cohort of patients with methylmalonic acidemia, we have devised a staging system for methylmalonic acidemia-related globus pallidus infarcts.

MATERIALS AND METHODS

Forty patients with isolated methylmalonic acidemia and neurologic symptoms underwent clinical brain MR imaging studies, which included 3D-T1WI. Infarcted globus pallidus segments were neuroanatomically characterized, and infarct volumes were measured.

RESULTS

Globus pallidus infarcts were present in 19 patients; all were bilateral, and most were left-dominant. A neuroanatomic scoring system based on the infarct patterns was devised; this revealed a 5-stage hierarchical susceptibility to metabolic infarct, with the posterior portion of the globus pallidus externa being the most vulnerable. Globus pallidus infarct prevalence by methylmalonic acidemia class was the following: cblA (5/7, 71%), cblB (3/7, 43%), mut(o) (10/22, 45%), and mut- (1/4, 25%). Tiny lacunar infarcts in the pars reticulata of the substantia nigra, previously unrecognized in methylmalonic acidemia, were found in 17 patients, 13 of whom also had a globus pallidus infarct.

CONCLUSIONS

The staged pattern of globus pallidus infarcts in isolated methylmalonic acidemia suggests a nonuniform, regionally specific cellular susceptibility to metabolic injury, even for patients having milder biochemical phenotypes. In support of this hypothesis, the delineation of lacunar infarcts in the pars reticulata of the substantia nigra, a tissue functionally and histologically identical to the globus pallidus interna, supports the concept of cell-specific pathology.

Methylmalonic acidemia: brain imaging findings in 52 children and a review of the literature

BACKGROUND

Methylmalonic acidemia (MMA) is an autosomal-recessive inborn error of metabolism.

OBJECTIVE

To recognize the CT and MR brain sectional imaging findings in children with MMA.

MATERIALS AND METHODS

Brain imaging studies (47 MR and 5 CT studies) from 52 children were reviewed and reported by a neuroradiologist. The clinical data were collected for each patient.

RESULTS

The most common findings were ventricular dilation (17 studies), cortical atrophy (15), periventricular white matter abnormality (12), thinning of the corpus callosum (8), subcortical white matter abnormality (6), cerebellar atrophy (4), basal ganglionic calcification (3), and myelination delay (3). The brain images in 14 patients were normal.

CONCLUSION

Radiological findings of MMA are nonspecific. A constellation of common clinical and radiological findings should raise the suspicion of MMA.

Looking beyond the basal ganglia: the spectrum of MRI changes in methylmalonic acidaemia

We report imaging abnormalities from 5 brain MR examinations in 4 children with methylmalonic acidaemia between the ages of 20 days and 31 months. In addition to bilateral basal ganglia lesions (pallidum) observed in 3 of 4 children, we found signs of delayed brain maturation (myelination delay, immature gyral pattern, incomplete opercularization) in all children and signs of a white matter disorder in the 3 older children. Unexpectedly, brainstem and cerebellar changes were present in all children. Reviewing the brain imaging changes reported for methylmalonic acidaemia, we discuss the findings and patterns observed in our patients. We postulate that delayed myelination and signs of a white matter disorder as well as brainstem and cerebellar involvement are common findings and may be due to a chronic neurotoxic effect on the developing and ageing brain.

Renal transplant in methylmalonic acidemia: could it be the best option? Report on a case at 10 years and review of the literature

Methylmalonic acidemia (MMA) is an inborn error of organic acid metabolism. Patients with severe disease develop many complications despite treatment; often, the disease progresses to severe damage of the central nervous system or to end-stage renal disease (ESRD). When medical treatment is ineffective, liver, kidney, or combined liver and kidney transplantation is advocated. At present, there are no definite guidelines as for the organ to be transplanted, and results are inconsistent. We report on a 27-year-old woman with MMA MUT0. The clinical symptoms developed at age 4 months. She progressed to ESRD and received a kidney transplant in November 1996 at age 17 years. One hundred and twenty months after transplant, renal function is normal; although urinary levels of methylmalonic acid are above normal limits, no episodes of metabolic decompensation have been observed after transplantation. Although liver is the major site of methylmalonyl-CoA mutase activity, this case and similar ones in the literature suggest that the smaller mutase activity present in the transplanted kidney may be sufficient to ensure partial correction of the metabolism of organic acids sufficient to prevent the onset of episodes of metabolic decompensation. It is worth investigating whether kidney transplant can be a safer and more satisfactory alternative to liver transplantation in cases of MMA unresponsive to medical treatment although urine MMA excretion remains significantly elevated.

Differential inhibitory effects of methylmalonic acid on respiratory chain complex activities in rat tissues

Methylmalonic acidemia is an inherited metabolic disorder biochemically characterized by tissue accumulation of methylmalonic acid (MMA) and clinically by progressive neurological deterioration and kidney failure, whose pathophysiology is so far poorly established. Previous studies have shown that MMA inhibits complex II of the respiratory chain in rat cerebral cortex, although no inhibition of complexes I-V was found in bovine heart. Therefore, in the present study we investigated the in vitro effect of 2.5mM MMA on the activity of complexes I-III, II, II-III and IV in striatum, hippocampus, heart, liver and kidney homogenates from young rats. We observed that MMA caused a significant inhibition of complex II activity in striatum and hippocampus (15-20%) at low concentrations of succinate in the medium, but not in the peripheral tissues. We also verified that the inhibitory property of MMA only occurred after exposing brain homogenates for at least 10 min with the acid, suggesting that this inhibition was mediated by indirect mechanisms. Simultaneous preincubation with the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) and catalase (CAT) plus superoxide dismutase (SOD) did not prevent MMA-induced inhibition of complex II, suggesting that common reactive oxygen (superoxide, hydrogen peroxide and hydroxyl radical) and nitric (nitric oxide) species were not involved in this effect. In addition, complex II-III (20-35%) was also inhibited by MMA in all tissues tested, and complex I-III only in the kidney (53%) and liver (38%). In contrast, complex IV activity was not changed by MMA in all tissues studied. These results indicate that MMA differentially affects the activity of the respiratory chain pending on the tissues studied, being striatum and hippocampus more vulnerable to its effect. In case our in vitro data are confirmed in vivo in tissues from methylmalonic acidemic patients, it is feasible that that the present findings may be related to the pathophysiology of the tissue damage characteristic of these patients.

Evaluation of the effect of chronic administration of drugs on rat behavior in the water maze task

Tissue accumulation of intermediates of the metabolism occurs in various inherited neurodegenerative disorders, including methylmalonic acidemia (MA). Animal cognition is usually tested by measuring learning/memory of rats in behavioral tasks. A procedure in which rats are chronically injected with the metabolites accumulating in the neurometabolic disorder methylmalonic acidemia from the 5th to the 28th day of life is described. The animals were allowed to recover for approximately 30 days, after which they were submitted to the Morris water maze task. This behavioral task consisted of two steps. The first one is called the acquisition phase, where rats were trained for 5 consecutive days performing four trials per day to find the submerged platform. On each trial, the rat was placed in the water in one of four start locations (N, S, W and E). The animal was then allowed to search for the platform for 60 s. Once the rat located the platform, it was permitted to remain on it for 10 s. The acquisition phase was followed by the probe trial 24 h later, in which the platform is not present. The time spent in the quadrant of the former platform position and the correct annulus crossings were obtained as a measure for spatial memory. The next step was the reversal learning (reversal phase) performed 2 weeks later. Animals were trained for 4 days (four trials per day) to find the hidden platform, which had now been moved to a position diagonally opposite (reversed) from its location in the acquisition phase. On the next day, all animals were submitted to a second probe trial, similar to the first one. We observed that rats chronically injected with methylmalonic acid (MA), although presenting no alterations in the acquisition phase, showed a long lasting reversal learning impairment. Moreover, motor activity, evaluated by the swim speed in the maze, was not altered by MA administration. These results are consistent with perseverative behavior.

Ascorbic acid prevents water maze behavioral deficits caused by early postnatal methylmalonic acid administration in the rat

Methylmalonic acidemia consists of a group of inherited neurometabolic disorders biochemically characterized by accumulation of methylmalonic acid (MA) and clinically by progressive neurological deterioration whose pathophysiology is not yet fully established. In the present study we investigated the effect of chronic administration (from the 5th to the 28th day of life) of methylmalonic acid (MA) on the performance of adult rats in the Morris water maze task. MA doses ranged from 0.72 to 1.67 micromol/g of body weight as a function of animal age; control rats were treated with the same volume of saline. Chronic postnatal MA treatment had no effect on body weight and in the acquisition of adult rats in the water maze task. However, administration of MA provoked long lasting reversal learning impairment in this task. Motor activity, evaluated by the swim speed in the maze, was not altered by MA administration, indicating no deficit of locomotor activity in rats injected with the metabolite. We also determined the effect of ascorbic acid administered alone or combined with MA on the same behavioral parameters in order to test whether free radicals might be responsible for the behavioral changes observed in MA-treated animals. Ascorbic acid was able to prevent the behavioral alterations provoked by MA. Moreover, the in vitro exposure of hippocampal and striatal preparations to MA revealed that the acid significantly reduced total radical-trapping antioxidant potential (TRAP) and total antioxidant reactivity (TAR) in the striatum, but not in the hippocampus. Furthermore, MA increased the thiobarbituric acid-reactive substances (TBA-RS) measurement in both structures. These data indicate that oxidative stress might be involved in the neuropathology of methylmalonic acidemia and that early MA administration induces long-lasting behavioral deficits, which are possibly caused by oxygen reactive species generation.

Effect of propionic and methylmalonic acids on the high molecular weight neurofilament subunit (NF-H) in rat cerebral cortex

Propionic and methylmalonic acidemias are inherited neurometabolic disorders biochemically characterized by tissue accumulation of propionic (PA) and methylmalonic (MMA) acids, respectively. Neurofilaments (NF) are important cytoskeletal proteins and phosphorylation/dephosphorylation of NF is important to stabilize the cytoskeleton. We investigated the effects of PA and MMA on the high molecular weight neurofilament subunit associated with the cytoskeletal fraction of rat cerebral cortex along development. Cortical slices from 9- to 60-day-old rats were incubated with 2.5 mM PA or MMA. The cytoskeletal fraction was extracted and the immunoreactivity for phosphorylated or total NF-H was analyzed by immunoblotting using specific antibodies. Results showed that treatment of tissue slices with the acids induced an increased Triton-insoluble phosphorylated NF-H immunoreactivity in up to 17-day-old rats. Furthermore, treatments significantly increased the total amount of NF-H in 12-day-old rats. These findings indicate that PA and MMA alter the dynamic regulation of NF-H assembly in the cytoskeletal fraction.

Inhibition of the mitochondrial respiratory chain complex activities in rat cerebral cortex by methylmalonic acid

Propionic and methylmalonic acidemic patients have severe neurologic symptoms whose etiopathogeny is still obscure. Since increase of lactic acid is detected in the urine of these patients, especially during metabolic decompensation when high concentrations of methylmalonate (MMA) and propionate (PA) are produced, it is possible that cellular respiration may be impaired in these individuals. Therefore, we investigated the effects of MMA and PA (1, 2.5 and 5mM), the principal metabolites which accumulate in these conditions, on the mitochondrial respiratory chain complex activities succinate: 2,6-dichloroindophenol (DCIP) oxireductase (complex II); succinate: cytochrome c oxireductase (complexII+CoQ+III); NADH: cytochrome c oxireductase (complex I+CoQ+complex III); and cytochrome c oxidase (COX) (complex IV) from cerebral cortex homogenates of young rats. The effect of MMA on ubiquinol: cytochrome c oxireductase (complex III) and NADH: ubiquinone oxireductase (complex I) activities was also tested. Control groups did not contain MMA and PA in the incubation medium. MMA significantly inhibited complex I+III (32-46%), complex I (61-72%), and complex II+III (15-26%), without affecting significantly the activities of complexes II, III and IV. However, by using 1mM succinate in the assay instead of the usual 16mM concentration, MMA was able to significantly inhibit complex II activity in the brain homogenates. In contrast, PA did not affect any of these mitochondrial enzyme activities. The effect of MMA and PA on succinate: phenazine oxireductase (soluble succinate dehydrogenase (SDH)) was also measured in mitochondrial preparations. The results showed significant inhibition of the soluble SDH activity by MMA (11-27%) in purified mitochondrial fractions. Thus, if the in vitro inhibition of the oxidative phosphorylation system is also expressed under in vivo conditions, a deficit of brain energy production might explain some of the neurological abnormalities found in patients with methylmalonic acidemia (MMAemia) and be responsible for the lactic acidemia/aciduria identified in some of them.

Ganglioside alterations in the central nervous system of rats chronically injected with methylmalonic and propionic acids

Neurological dysfunction and structural cerebral abnormalities are commonly found in patients with methylmalonic and propionic acidemia. However, the mechanisms underlying the neuropathology of these disorders are poorly understood. We have previously demonstrated that methylmalonic and propionic acids induce a significant reduction of ganglioside N-acetylneuraminic acid in the brain of rats subjected to chronic administration of these metabolites. In the present study, we investigated the in vivo effects of chronic administration of methylmalonic (MMA) and propionic (PA) acids (from the 6th to the 28th day of life) on the distribution and composition of gangliosides in the cerebellum and cerebral cortex of rats. Control rats were treated with the same volumes of saline. It was first verified that MMA and PA treatment did not modify body, cerebellum, or cortical weight, nor the ganglioside concentration in the cerebral cortex of the animals. In contrast, a significant reduction in total ganglioside content in the cerebellum of approximately 20-30% and 50% of control levels occurred in rats injected with MMA and PA, respectively. Moreover, chronic MMA and PA administration did not interfere with the ganglioside pattern in the cerebral cortex, whereas the distribution of individual gangliosides was altered in the cerebellum of MMA- and PA-treated animals. Rats injected with MMA demonstrated a marked decrease in GM1 and GD3, whereas chronic PA treatment provoked a significant reduction of all ganglioside species, with the exception of an increase in GM2. Since gangliosides are closely related to the dendritic surface and other neural membranes, indirectly reflecting synaptogenesis, these ganglioside abnormalities may be associated with the brain damage found in methylmalonic and propionic acidemias.

Metabolic stroke in methylmalonic acidemia five years after liver transplantation

It is believed that liver transplantation may improve the outcome of early onset methylmalonic acidemia. We report a case of methylmalonic acidemia in which successful liver transplantation in infancy failed to prevent neurologic damage caused by a metabolic stroke.

Effects of methylmalonic and propionic acids on glutamate uptake by synaptosomes and synaptic vesicles and on glutamate release by synaptosomes from cerebral cortex of rats

Neurological dysfunction is common in patients with methylmalonic and propionic acidemias. However, the mechanisms underlying the neuropathology of these disorders are far from understood. In the present study we investigated the in vitro effects of methylmalonic (MMA) and propionic (PA) acids at various concentrations (1 microM-5 mM) on three parameters of the glutamatergic system, namely the basal and potassium-induced release of L-[3H]glutamate by synaptosomes, Na+-dependent L-[3H]glutamate uptake by synaptosomes and Na+-independent L-[3H]glutamate uptake by synaptic vesicles from cerebral cortex of male adult Wistar rats. The results showed that MMA significantly increased potassium-induced but not basal L-[3H]glutamate release from synaptosomes with no alteration in synaptosomal L-[3H]glutamate uptake. A significant reduction of L-[3H]glutamate incorporation into vesicles caused by MMA was also detected. In contrast, PA had no effect on these parameters. These findings indicate that MMA alters the glutamatergic system. Although additional studies are necessary to evaluate the importance of these observations for the neuropathology of methylmalonic acidemia, it is possible that the effects elicited by MMA may lead to excessive glutamate concentrations at the synaptic cleft, a fact that may explain previous in vivo and in vitro findings associating MMA with excitotoxicity.

Progressive neurological deterioration and MRI changes in cblC methylmalonic acidaemia treated with hydroxocobalamin

Cobalamin C (cblC) defects result in decreased activity of both methylmalonyl-CoA mutase and N5-methyltetrahydrofolate:homocysteine methyltransferase (methionine synthase), with subsequent methylmalonic acid-uria and homocystinuria. Patients typically show failure to thrive, developmental delay and megaloblastic anaemia. Vitamin B12 therapy has been beneficial in some cases. We report a now 4-year-old Hispanic girl with cblC disease documented by complementation analysis, with progressive neurological deterioration and worsening head MRI changes while on intramuscular hydroxocobalamin begun at age 3 weeks. Oral carnitine and folic acid were added at age 1 year. Blood levels of methylmalonic acid were reduced to treatment ranges. In the absence of acute metabolic crises, she developed microcephaly, progressive hypotonia and decreased interactiveness. Funduscopic examination was normal at age 13 months. At age 19 months, she developed nystagmus, and darkly pigmented fundi and sclerotic retinal vessels were observed on examination. Her neonatal head MRI was normal. By age 1 year, the MRI showed diffuse white-matter loss with secondary third and lateral ventricle enlargement, a thin corpus callosum, and normal basal ganglia. At age 15 months, progression of the white-matter loss, as well as hyperintense globi pallidi, were present. Interval progression of both grey- and white-matter loss was seen at age 27 months. We therefore caution that progressive neurological deterioration and head MRI abnormalities may still occur in cblC disease, despite early initiation of hydroxocobalamin therapy and improvement in toxic metabolite concentrations in physiological fluids.

Propionic and methylmalonic acids inhibit the in vitro phosphorylation of a 85 kDa cytoskeletal protein from cerebral cortex of rats

In this study we examine the action of methylmalonic (MMA) and propionic (PA) acids, metabolites which accumulate in methylmalonic and propionic acidemias respectively, on the endogenous phosphorylating system associated with the cytoskeletal fraction of cerebral cortex of young rats. Chronic treatment with PA and treatment of tissue slices with MMA or PA are effective in decreasing the in vitro phosphorylation into a 85 kDa cytoskeletal associated protein. We tested the effect of the acids on the endogenous kinase activities by using specific kinase activators and inhibitors. Results demonstrated that the acids interfere with the endogenous cAMP-dependent and Ca2+/calmodulin-dependent kinase activities. Furthermore, in vitro dephosphorylation of the 85 kDa protein was totally inhibited in brain slices treated with the acids. Considering the importance of protein phosphorylation to cellular function, we speculate that alteration in the phosphorylating level of cytoskeletal associated phosphoproteins induced by MMA and PA treatments may somehow be involved in steps leading to brain damage.

Methylmalonate toxicity in primary neuronal cultures

Several inhibitors of mitochondrial complex II cause neuronal death in vivo and in vitro. The goal of the present work was to characterize in vitro the effects of malonate (a competitive blocker of the complex) which induces neuronal death in a pattern similar to that seen in striatum in Huntington's disease. Exposure of striatal and cortical cultures from embryonic rat brain for 24 h to methylmalonate, a compound which produces malonate intracellularly, led to a dose-dependent cell death. Methylmalonate (10 mM) caused >90% mortality of neurons although cortical cells were unexpectedly more vulnerable. Cell death was attenuated in a medium containing antioxidants. Further characterization revealed that DNA laddering could be detected after 3 h of treatment. Morphological observations (videomicroscopy and Hoechst staining) showed that both necrotic and apoptotic cell death occurred in parallel; apoptosis was more prevalent. A decrease in the ATP/ADP ratio was observed after 3 h of treatment with 10 mM methylmalonate. In striatal cultures it occurred concomitantly with a decline in GABA and a rise in aspartate content and the aspartate/glutamate ratio. Changes in ion concentrations were measured in similar cortical cultures from mouse brain. Neuronal [Na+]i increased while [K+]i and membrane potential decreased after 20 min of continuous incubation in 10 mM methylmalonate. These changes progressed with time, and a rise in [Ca2+]i was also observed after 1 h. The results demonstrate that malonate collapses cellular ion gradients, restoration of which imposes an additional load on the already compromised ATP-generation machinery. An early elevation in [Ca2+]i may trigger an increase in activity of proteases, lipases and endonucleases and production of free radicals and DNA damage which, ultimately, leads to cells death. The data also suggest that maturational and/or extrinsic factors are likely to be critical for the increased vulnerability of striatal neurons to mitochondrial inhibition in vivo.

Methylmalonic acidaemia with bilateral globus pallidus involvement: a neuropathological study

A 16-month-old boy was hospitalized because of a 1-day history of severe ketoacidosis with lethargy, hypotonia, vomiting, and important dyspnoea. Organic acid assay by gas chromatography-mass spectrometry confirmed the diagnosis of methylmalonic acidaemia (MMA). On the sixteenth day, he developed an acute extrapyramidal disorder. The CT scan of the brain disclosed bilaterally symmetric lucency of basal ganglia. He died at 17 months of age. Post-mortem neuropathological examination, showed severe necrosis with spongiosis, cystic cavitation and numerous lipid-laden macrophages of the globi pallidi, and mild spongiosis of subthalamic nuclei, mammillary bodies, portion of internal capsule adjacent to globus pallidus, superior cerebellar peduncles and tegmentum of brainstem. Pallidal infarction, a focal ischaemic lesion, demonstrates that ischaemia/energy depletion may be important in the etiology of the neuropathology of MMA.

Neurological outcome of methylmalonic acidaemia

OBJECTIVE

To assess the long term outcome of patients with methylmalonic acidaemia in a cross sectional study.

PATIENTS

All 35 patients with methylmalonic acidaemia seen at Great Ormond Street Hospital for Children in London, UK between 1970 and 1996 were studied. They were divided into cobalamin responsive (n = 6) and non-responsive (n = 29), and early and late onset groups.

RESULTS

There was a significant difference between cobalamin responsive and non-responsive groups in severity, survival, and incidence of neurological sequelae. Cobalamin responsive patients had mild disease, irrespective of age at presentation, their neurological complications were less severe, and they are all alive. The cobalamin non-responsive group comprised 19 early and nine late onset patients. The early onset patients had more severe disease at presentation and 14 have died; all late onset patients are alive. There was no significant difference in abnormal neurological signs, although early onset patients had a significantly reduced full scale intelligence quotient and poor cognitive outcome. In both groups, abnormal neurological signs continue to increase with age.

CONCLUSIONS

Cobalamin responsive patients have a better long term outcome. The outcome in the non-responsive patients, particularly the early onset group, remains poor and alternative treatments should therefore be considered early in this group.

Neurological dysfunction in methylmalonic acidaemia is probably related to the inhibitory effect of methylmalonate on brain energy production

Methylmalonic acidaemia is an inherited metabolic disorder caused by a severe deficiency of the activity of the enzyme L-methylmalonyl-CoA mutase or its cofactor 5'-deoxyadenosylcobalamin, resulting in tissue accumulation of large quantities of methylmalonic acid. Among the various clinical features, neurological symptoms are frequently observed. Patients may present cerebral atrophy and basal ganglia abnormalities are common. In the present report, we update the current knowledge on the influence of methylmalonic acid on brain metabolism in the hope of better understanding the neurological dysfunction characteristic of methylmalonic acidaemia. We present evidence showing that the metabolite inhibits brain energy production by various mechanisms and propose that a fall in cellular ATP generation leading to excitotoxicity is crucial for the occurrence of the neurological damage observed in these patients.

Use of human somatotrophin in the treatment of a patient with methylmalonic aciduria

Growth hormone (GH) insufficiency was demonstrated in a patient with methylmalonic aciduria. GH administration at 14-21 U/m2 per week accelerated linear growth, stimulated lipolysis, and produced clinical improvement and reduced urinary methylmalonate excretion. The clinical and metabolic benefits were lost as the dose of GH was increased to 28 U/m2 per week. CONCLUSION. The use of GH in other patients with methylmalonic aciduria (and other disorders of intermediary metabolism demonstrating similar clinical and metabolic features) warrants further study.

Atypical methylmalonic aciduria with progressive encephalopathy, microcephaly and cataract in two siblings--a new recessive syndrome?

Two siblings with atypical methylmalonic aciduria and progressive encephalopathy are reported. Initial symptoms were failure to thrive and growth retardation from the first year of life, progressing to severe mental retardation, microcephaly, dystonia, spasticity and cataracts. The amount of methylmalonic acid excreted in the urine was substantially lower than in classical methylmalonic acidemia and was not reduced by vitamin B12 therapy. The activity of methylmalonyl-CoA mutase and the overall assay of propionic acid metabolism in cultured fibroblasts were normal. The primary defect in this probably new autosomal recessive disorder associated with methylmalonic aciduria is currently not known.

Pancreatitis in patients with organic acidemias

STUDY OBJECTIVE

The discovery of pancreatitis in two children with methylmalonic acidemia led us to review the experience with pancreatitis in a large number of patients with organic acidemias to determine whether pancreatitis is an important complication of these disorders.

DESIGN

Case series.

SETTING

Pediatric metabolism services at five tertiary care centers.

PATIENTS

Records of all patients with organic acidemias followed at the five institutions during the past 10 years were reviewed. Pancreatitis was recognized by symptoms and laboratory findings and confirmed by imaging studies, surgery, or autopsy. At three institutions all cases of pancreatitis in children younger than 10 years were reviewed.

MEASUREMENTS AND RESULTS

Nine children with pancreatitis (seven with acute and two with chronic cases) were identified among 108 children with branched-chain organic acidemias. They ranged in age from 13 months to 9 years. Five had methylmalonic acidemia, three had isovaleric acidemia, and one had maple syrup urine disease. There were three deaths; acute hemorrhagic pancreatitis occurred in two children, and chronic pancreatitis was found at autopsy in a third. All three patients with isovaleric acidemia and pancreatitis were identified after the occurrence of pancreatitis. The survey of pancreatitis at three institutions found 57 other patients (none with an inborn error) in addition to three patients with inborn errors included in this study.

CONCLUSIONS

Acute or chronic pancreatitis may complicate branched-chain organic acidemias and must be considered in the assessment of patients with these disorders who have acute clinical deterioration and vomiting, abdominal pain, encephalopathy or shock, or milder symptoms. Conversely, an inborn error of organic acid metabolism should be considered in children with pancreatitis of unknown origin.

Inhibition of succinate dehydrogenase and beta-hydroxybutyrate dehydrogenase activities by methylmalonate in brain and liver of developing rats

The effects of methylmalonate (MMA) on succinate dehydrogenase (SDH) and beta-hydroxybutyrate dehydrogenase (HBDH) activities in brain and liver of 15-day-old rats were studied. The apparent Km of SDH for succinate was 0.45 mmol/L in brain and 0.34 mmol/L in liver. MMA inhibited the enzyme activity in both tissues with Ki values of 4.5 mmol/L and 2.3 mmol/L in brain and liver, respectively, and the inhibition was of the reversible competitive type. The calculated Km for HBDH with beta-hydroxybutyrate as substrate was 1.26 mmol/L in brain and 0.36 mmol/L in liver. MMA inhibited the enzyme with a Ki value of 0.015 mmol/L in brain and 0.275 mmol/L in liver. These results are probably relevant to our understanding of cerebral metabolism in methylmalonic acidaemic children, especially during ketoacidotic and hypoglycaemic crises, and may be related to the pathogenesis of cerebral dysfunction of methylmalonic acidaemia.

Neurologic outcome of propionic acidemia

Twenty patients with propionic acidemia were reviewed retrospectively. Two groups were identified: those who presented in the first week of life (11 patients) or after the neonatal period (9 patients). The early onset of disease had a much higher death rate (hazard ratio: 7.52) and all patients in this group were mentally retarded (IQ < or = 60). Movement disorder was common in both groups. Of the early-onset group, 3 patients had mild chorea or dystonia. Four in the late-onset group had a severe movement disorder. In the late onset group, cranial computed tomography disclosed transient basal ganglia lucencies following an episode of metabolic decompensation; however, no disturbance in amine neurotransmitter metabolite concentrations were found in the cerebrospinal fluid.

CT and MRI of the brain in inherited neurometabolic disorders

The incidence of many autosomal recessive neurometabolic disorders is very high in Saudi Arabia, probably as a result of the frequency of consanguineous marriages. Because our hospital is the main referral center for the entire Kingdom, we examine a large number of patients who have a wide spectrum of neurometabolic disorders. We add our experience and review the world literature. Though a specific diagnosis is radiologically possible in a few disorders, the diagnosis must always be verified biochemically. When the patient is referred from a pediatric neurologist with the diagnosis of neurometabolic disorder, the aim of the neuroradiologist is to determine the amount of brain damage present and to follow the response to given therapy. When the patient is referred with a nonspecific diagnosis, such as delayed development, the aim is to suggest the possibility of a neurometabolic disorder and to initiate further evaluation including possible therapy and genetic counseling.