Neurological outcome of methylmalonic acidaemia

Gene therapy for organic acidemias: Lessons learned from methylmalonic and propionic acidemia

Organic acidemias (OA) are a group of rare autosomal recessive disorders of intermediary metabolism that result in a systemic elevation of organic acid. Despite optimal dietary and cofactor therapy, OA patients still suffer from potentially lethal metabolic instability and experience long-term multisystemic complications. Severely affected patients can benefit from elective liver transplantation, which restores hepatic enzymatic activity, improves metabolic stability, and provides the theoretical basis for the pursuit of gene therapy as a new treatment for patients. Because of the poor outcomes reported in those with OA, especially methylmalonic and propionic acidemia, multiple gene therapy approaches have been explored in relevant animal models. Here, we review the results of gene therapy experiments performed using MMA and PA mouse models to illustrate experimental paradigms that could be applicable for all forms of OA.

Treatment of metabolic disorders using genomic technologies: Lessons from methylmalonic acidemia

Hereditary methylmalonic acidemia (MMA) caused by deficiency of the enzyme methylmalonyl-CoA mutase (MMUT) is a relatively common and severe organic acidemia. The recalcitrant nature of the condition to conventional dietary and medical management has led to the use of elective liver and combined liver-kidney transplantation in some patients. However, liver transplantation is intrinsically limited by organ availability, the risks of surgery, procedural and life-long management costs, transplant comorbidities, and a remaining underlying risk of complications related to MMA despite transplantation. Here, we review pre-clinical studies that present alternative approaches to solid organ transplantation as a treatment for MMUT MMA, including adeno-associated viral gene addition therapy, mRNA therapy, and genome editing, with and without nuclease enhancement.

The Regulation and Characterization of Mitochondrial-Derived Methylmalonic Acid in Mitochondrial Dysfunction and Oxidative Stress: From Basic Research to Clinical Practice

Methylmalonic acid (MMA) can act as a diagnosis of hereditary methylmalonic acidemia and assess the status of vitamin B12. Moreover, as a new potential biomarker, it has been widely reported to be associated with the progression and prognosis of chronic diseases such as cardiovascular events, renal insufficiency, cognitive impairment, and cancer. MMA accumulation may cause oxidative stress and impair mitochondrial function, disrupt cellular energy metabolism, and trigger cell death. This review primarily focuses on the mechanisms and epidemiology or progression in the clinical study on MMA.

Review of neuropsychological outcomes in isolated methylmalonic acidemia: recommendations for assessing impact of treatments

Methylmalonic acidemia (MMA) due to methylmalonyl-CoA mutase deficiency (OMIM #251,000) is an autosomal recessive disorder of organic acid metabolism associated with life-threatening acute metabolic decompensations and significant neuropsychological deficits. "Isolated" MMA refers to the presence of excess methylmalonic acid without homocysteine elevation. Belonging to this class of disorders are those that involve complete deficiency (mut⁰) and partial deficiency (mut^-) of the methylmalonyl-CoA mutase enzyme and other disorders causing excess methylmalonic acid excretion. These other disorders include enzymatic subtypes related to cobalamin A defect (cblA) (OMIM #25,110), cobalamin B defect (cblB) (OMIM #251,110) and related conditions. Neuropsychological attributes associated with isolated MMA have become more relevant as survival rates increased following improved diagnostic and treatment strategies. Children with this disorder still are at risk for developmental delay, cognitive difficulties and progressive declines in functioning. Mean IQ for all types apart from cblA defect enzymatic subtype is rarely above 85 and much lower for mut⁰ enzymatic subtype. Identifying psychological domains responsive to improvements in biochemical status is important. This review suggests that processing speed, working memory, language, attention, and quality of life may be sensitive to fluctuations in metabolite levels while IQ and motor skills may be less amenable to change. Due to slower developmental trajectories, Growth Scale Values, Projected Retained Ability Scores and other indices of change need to be incorporated into clinical trial study protocols. Neuropsychologists are uniquely qualified to provide a differentiated picture of cognitive, behavioral and emotional consequences of MMA and analyze benefits or shortcomings of novel treatments.

Efficacy of Living Donor Liver Transplantation in Patients with Methylmalonic Acidemia

PURPOSE

Despite aggressive medical and nutritional management, patients with methylmalonic acidemia (MMA) often suffer from multi-organ damage. Early deceased donor liver transplantation (DDLT) has emerged as an intervention to prevent disease progression. We investigated the efficacy of living donor LT (LDLT) with a potential carrier of MMA and a small volume of graft in patients with MMA as an alternative to DDLT.

METHODS

Of five patients (three male, two female; median age 5.7 years; range, 1.3-13.7 years), four underwent carrier LDLT, while one underwent non-carrier auxiliary LDLT. All patients received pre- and post-LT continuous renal replacement therapy and were provided with minimal restriction diet according to serum MMA level after LT. MMA levels in the serum and urine, the incidence of metabolic crisis, and clinical findings before and after LT were compared.

RESULTS

The survival rate was 100% during 2.2 years of follow up period after LT. In all five cases, MMA titer in the serum after transplantation decreased with less restrictive diet. Metabolic crisis was not observed during the follow-up period. In addition, no patient showed progression of severe renal impairment requiring hemodialysis. Progression of delayed cognitive development was not observed. Social functioning with improved neuropsychiatric development was observed.

CONCLUSION

This study showed that LDLT achieved improved quality of life with less restrictive diet, therefore it could be a feasible alternative option to DDLT for the treatment of patients with MMA, even with an auxiliary LT.

An expanding spectrum of complications in isolated methylmalonic aciduria

Isolated methylmalonic acidurias represent a heterogeneous genetic group of inborn errors of propionate metabolism with the common biochemical hallmark of elevated methylmalonic acid present in tissues and body fluids. It was first described in the 1960s and over the years better understanding of the disease and its presentation, earlier diagnosis, and most importantly advances in treatment have resulted in extended survival of patients. With that an expanding spectrum of complications is emerging which requires attention and regular monitoring to facilitate early intervention and reduce disease burden.

Movement Disorders and Renal Diseases

Movement disorders often emerge from the interplay of complex pathophysiological processes involving the kidneys and the nervous system. Tremor, myoclonus, ataxia, chorea, and parkinsonism can occur in the context of renal dysfunction (azotemia and electrolyte abnormalities) or they can be part of complications of its management (dialysis and renal transplantation). On the other hand, myoglobinuria from rhabdomyolysis in status dystonicus and certain drugs used in the management of movement disorders can cause nephrotoxicity. Distinct from these well-recognized associations, it is important to appreciate that there are several inherited and acquired disorders in which movement abnormalities do not occur as a consequence of renal dysfunction or vice versa but are manifestations of common pathophysiological processes affecting the nervous system and the kidneys. These disorders are the emphasis of this review. Increasing awareness of these conditions among neurologists may help them to identify renal involvement earlier, take timely intervention by anticipating complications and focus on therapies targeting common mechanisms in addition to symptomatic management of movement disorders. Recognition of renal impairment in a patient with complex neurological presentation may narrow down the differentials and aid in reaching a definite diagnosis.

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.

Cognition in childhood dystonia: a systematic review

AIM

Cognitive impairments have been established as part of the non-motor phenomenology of adult dystonia. In childhood dystonia, the extent of cognitive impairments is less clear. This systematic review aims to present an overview of the existing literature to elucidate the cognitive profile of primary and secondary childhood dystonia.

METHOD

Studies focusing on cognition in childhood dystonia were searched in MEDLINE and PsychInfo up to October 2017. We included studies on idiopathic and genetic forms of dystonia as well as dystonia secondary to cerebral palsy and inborn errors of metabolism.

RESULTS

Thirty-four studies of the initial 527 were included. Studies for primary dystonia showed intact cognition and IQ, but mild working memory and processing speed deficits. Studies on secondary dystonia showed more pronounced cognitive deficits and lower IQ scores with frequent intellectual disability. Data are missing for attention, language, and executive functioning.

INTERPRETATION

This systematic review shows possible cognitive impairments in childhood dystonia. The severity of cognitive impairment seems to intensify with increasing neurological abnormalities. However, the available data on cognition in childhood dystonia are very limited and not all domains have been investigated yet. This underlines the need for future research using standardized neuropsychological procedures in this group.

WHAT THIS PAPER ADDS

There is limited data on cognition in childhood dystonia. Primary dystonia showed intact cognition and IQ, but mild working memory and processing speed deficits. Secondary dystonia showed more pronounced deficits and lower IQ, with frequent intellectual disability. There is a strong need for case-control studies assessing cognition using standardized neuropsychological tests.

The proteome of methylmalonic acidemia (MMA): the elucidation of altered pathways in patient livers

Methylmalonic acidemia (MMA) is a heterogeneous and severe autosomal recessive inborn error of metabolism most commonly caused by the deficient activity of the vitamin B12 dependent enzyme, methylmalonyl-CoA mutase (MUT). The main treatment for MMA patients is the dietary restriction of propiogenic amino acids and carnitine supplementation. Despite treatment, the prognosis for vitamin B12 non-responsive patients remains poor and is associated with neonatal lethality, persistent morbidity and decreased life expectancy. While multi-organ pathology is a feature of MMA, the liver is severely impacted by mitochondrial dysfunction which likely underlies the metabolic instability experienced by the patients. Liver and/or combined liver/kidney transplantation is therefore sometimes performed in severely affected patients. Using liver specimens from donors and MMA patients undergoing elective liver transplantation collected under a dedicated natural history protocol (clinicaltrials.gov: NCT00078078), we employed proteomics to characterize the liver pathology and impaired hepatic metabolism observed in the patients. Pathway analysis revealed perturbations of enzymes involved in energy metabolism, gluconeogenesis and Krebs cycle anaplerosis. Our findings identify new pathophysiologic and therapeutic targets that could be valuable for designing alternative therapies to alleviate clinical manifestations seen in this disorder.

Novel Mouse Models of Methylmalonic Aciduria Recapitulate Phenotypic Traits with a Genetic Dosage Effect

Methylmalonic aciduria (MMAuria), caused by deficiency of methylmalonyl-CoA mutase (MUT), usually presents in the newborn period with failure to thrive and metabolic crisis leading to coma or even death. Survivors remain at risk of metabolic decompensations and severe long term complications, notably renal failure and neurological impairment. We generated clinically relevant mouse models of MMAuria using a constitutive Mut knock-in (KI) allele based on the p.Met700Lys patient mutation, used homozygously (KI/KI) or combined with a knockout allele (KO/KI), to study biochemical and clinical MMAuria disease aspects. Transgenic Mut(ki/ki) and Mut(ko/ki) mice survive post-weaning, show failure to thrive, and show increased methylmalonic acid, propionylcarnitine, odd chain fatty acids, and sphingoid bases, a new potential biomarker of MMAuria. Consistent with genetic dosage, Mut(ko/ki) mice have lower Mut activity, are smaller, and show higher metabolite levels than Mut(ki/ki) mice. Further, Mut(ko/ki) mice exhibit manifestations of kidney and brain damage, including increased plasma urea, impaired diuresis, elevated biomarkers, and changes in brain weight. On a high protein diet, mutant mice display disease exacerbation, including elevated blood ammonia, and catastrophic weight loss, which, in Mut(ki/ki) mice, is rescued by hydroxocobalamin treatment. This study expands knowledge of MMAuria, introduces the discovery of new biomarkers, and constitutes the first in vivo proof of principle of cobalamin treatment in mut-type MMAuria.

Mass Spectrometry-Based Metabolomic and Proteomic Strategies in Organic Acidemias

Organic acidemias (OAs) are inherited metabolic disorders caused by deficiency of enzymatic activities in the catabolism of amino acids, carbohydrates, or lipids. These disorders result in the accumulation of mono-, di-, or tricarboxylic acids, generally referred to as organic acids. The OA outcomes can involve different organs and/or systems. Some OA disorders are easily managed if promptly diagnosed and treated, whereas, in others cases, such as propionate metabolism-related OAs (propionic acidemia, PA; methylmalonic acidemia, MMA), neither diet, vitamin therapy, nor liver transplantation appears to prevent multiorgan impairment. Here, we review the recent developments in dissecting molecular bases of OAs by using integration of mass spectrometry- (MS-) based metabolomic and proteomic strategies. MS-based techniques have facilitated the rapid and economical evaluation of a broad spectrum of metabolites in various body fluids, also collected in small samples, like dried blood spots. This approach has enabled the timely diagnosis of OAs, thereby facilitating early therapeutic intervention. Besides providing an overview of MS-based approaches most frequently used to study the molecular mechanisms underlying OA pathophysiology, we discuss the principal challenges of metabolomic and proteomic applications to OAs.

Impact of age at onset and newborn screening on outcome in organic acidurias

BACKGROUND AND AIM

To describe current diagnostic and therapeutic strategies in organic acidurias (OADs) and to evaluate their impact on the disease course allowing harmonisation.

METHODS

Datasets of 567 OAD patients from the E-IMD registry were analysed. The sample includes patients with methylmalonic (MMA, n = 164), propionic (PA, n = 144) and isovaleric aciduria (IVA, n = 83), and glutaric aciduria type 1 (GA1, n = 176). Statistical analysis included description and recursive partitioning of diagnostic and therapeutic strategies, and odds ratios (OR) for health outcome parameters. For some analyses, symptomatic patients were divided into those presenting with first symptoms during (i.e. early onset, EO) or after the newborn period (i.e. late onset, LO).

RESULTS

Patients identified by newborn screening (NBS) had a significantly lower median age of diagnosis (8 days) compared to the LO group (363 days, p < 0.001], but not compared to the EO group. Of all OAD patients 71 % remained asymptomatic until day 8. Patients with cobalamin-nonresponsive MMA (MMA-Cbl(-)) and GA1 identified by NBS were less likely to have movement disorders than those diagnosed by selective screening (MMA-Cbl(-): 10 % versus 39 %, p = 0.002; GA1: 26 % versus 73 %, p < 0.001). For other OADs, the clinical benefit of NBS was less clear. Reported age-adjusted intake of natural protein and calories was significantly higher in LO patients than in EO patients reflecting different disease severities. Variable drug combinations, ranging from 12 in MMA-Cbl(-) to two in isovaleric aciduria, were used for maintenance treatment. The effects of specific metabolic treatment strategies on the health outcomes remain unclear because of the strong influences of age at onset (EO versus LO), diagnostic mode (NBS versus selective screening), and the various treatment combinations used.

CONCLUSIONS

NBS is an effective intervention to reduce time until diagnosis especially for LO patients and to prevent irreversible cerebral damage in GA1 and MMA-Cbl(-). Huge diversity of therapeutic interventions hampers our understanding of optimal treatment.

Hepatoblastoma in a patient with methylmalonic aciduria

Childhood malignant tumors and their treatment are not well described in the natural history of methylmalonic aciduria (MMA). Here we present a case of hepatoblastoma occurring in the native liver of a 19-month-old male with MMA. His tumor was unresectable at diagnosis and he received neoadjuvant chemotherapy with cisplatin, 5-fluorouracil and vincristine. He developed metabolic acidosis and hyperglycemia during chemotherapy. In addition, he developed anemia, thrombocytopenia and febrile neutropenia. He underwent a combined liver-kidney transplant for local control of his tumor and to treat MMA. He remains in remission more than five years after his transplant. In addition, his transplant has cured his MMA and he is able to tolerate a regular diet without developing metabolic crises.

Impaired Health-Related Quality of Life in Children and Families Affected by Methylmalonic Acidemia

An understanding of health related quality of life (HRQoL) in children and families affected by methylmalonic acidemia (MMA) is important in planning counseling and therapeutic intervention. Liver transplantation (LT) is used as a treatment for MMA; however, its risks and benefits continue to be investigated. The purpose of this study was twofold: (1) to measure HRQoL in children and families affected by MMA using the Pediatric Quality of Life Inventory (PedsQL™) parent version, and (2) to assess the impact of LT on HRQoL by comparing LT and non-LT patient scores and free responses. Parents/caregivers reported lower scores on the majority of the PedsQL™ scales as compared to samples of healthy children, children with solid organ transplants for indications other than MMA, and families affected by chronic conditions. Scores for children with MMA were lowest in school and social functioning and scores for families were lowest in worry and activity impairment. There were no significant differences in LT and non-LT patient scores on the PedsQL™ scales. Our results document the negative impact of MMA on HRQoL.

Spectrum of Mutations in 60 Saudi Patients with Mut Methylmalonic Acidemia

Defects in the human gene encoding methylmalonyl-CoA mutase enzyme (MCM) give rise to a rare autosomal recessive inherited disorder of propionate metabolism termed mut methylmalonic acidemia (MMA). Patients with mut MMA have been divided into two subgroups: mut⁰ with complete loss of MCM activity and mut^- with residual activity in the presence of adenosylcobalamin (AdoCbl). The disease typically presents in the first weeks or months of life and is clinically characterized by recurrent vomiting, metabolic acidosis, hyperammonemia, lethargy, poor feeding, failure to thrive and neurological deficit. To better elucidate the spectrum of mutations causing mut MMA in Saudi patients, we screened a cohort of 60 Saudi patients affected by either forms of the disease for mutations in the MUT gene. A total of 13 different mutations, including seven previously reported missense changes and six novel mutations, were detected in a homozygous state except for two compound heterozygous cases. The six novel mutations identified herein consist of three nonsense, two missense and one frameshift, distributed throughout the whole protein. This study describes for the first time the clinical and mutational spectrum of mut MMA in Saudi Arabian patients.

Cost-effectiveness of liver transplantation in methylmalonic and propionic acidemias

Propionic acidemia (PA) and classical methylmalonic acidemia (MMA) are rare inborn errors of metabolism that can cause early mortality and significant morbidity. The mainstay of disease management is lifelong protein restriction. As an alternative, liver transplantation (LT) may improve survival, quality of life, and prevent further neurological deterioration. The aim of our study was to estimate the incremental costs and outcomes of LT versus nutritional support in patients with early-onset MMA or PA. We constructed a Markov model to simulate and compare life expectancies, quality-adjusted life years (QALYs), and lifetime direct and indirect costs for a cohort of newborns with MMA or PA who could either receive LT or be maintained on conventional nutritional support. We conducted a series of 1-way and probabilistic sensitivity analyses. In the base case, LT on average resulted in 1.5 more life years lived, 7.9 more QALYs, and a savings of $582,369 for lifetime societal cost per individual compared to nutritional support. LT remained more effective and less costly in all 1-way sensitivity analyses. In the probabilistic sensitivity analysis, LT was cost-effective at the $100,000/QALY threshold in more than 90% of the simulations and cost-saving in over half of the simulations. LT is likely a dominant treatment strategy compared to nutritional support in newborns with classical MMA or PA.

Valproate therapy exacerbating intermediate phenotype of methylmalonic aciduria

A, 11-year-old male, with delayed milestones after the age of 6 months with recurrent myoclonus and generalized tonic-clonic seizures had clinical worsening after institution of valproate, was detected to have elevated serum lactate level and marked methyl malonic aciduria. Patient had remarkable improvement following withdrawal of valproate and substitution of hydroxocobalamin.

Early Liver Transplantation for Neonatal-Onset Methylmalonic Acidemia

With conventional dietary treatment, the clinical course of methylmalonic acidemia due to cobalamin-unresponsive methylmalonyl-CoA mutase (MCM) deficiency is characterized by the persistent risk of recurrent life-threatening decompensation episodes with metabolic acidosis, hyperammonemia, and coma. Liver transplant has been proposed as an alternative treatment and anecdotally attempted in the last 2 decades with inconsistent results. Most criticisms of this approach have been directed at the continuing risk of neurologic and renal damage after transplant. Here, we report the perioperative and postoperative clinical and biochemical outcomes of 2 patients with severe MCM deficiency who underwent early liver transplant. In both cases, liver transplant allowed prevention of decompensation episodes, normalization of dietary protein intake, and a marked improvement of quality of life. No serious complications have been observed at 12 years' and 2 years' follow-up, respectively, except for mild kidney function impairment in the older patient. On the basis of our experience, we strongly suggest that liver transplant should be offered as a therapeutic option for children with cobalamin-unresponsive MCM deficiency at an early stage of the disease.

Treatment of methylmalonic acidemia by liver or combined liver-kidney transplantation

OBJECTIVE

To assess biochemical, surgical, and long-term outcomes of liver (LT) or liver-kidney transplantation (LKT) for severe, early-onset methylmalonic acidemia/acid (MMA).

STUDY DESIGN

A retrospective chart review (December 1997 to May 2012) of patients with MMA who underwent LT or LKT at Lucile Packard Children's Hospital at Stanford.

RESULTS

Fourteen patients underwent LT (n = 6) or LKT (n = 8) at mean age 8.2 years (range 0.8-20.7). Eleven (79%) were diagnosed during the neonatal period, including 6 by newborn screening. All underwent deceased donor transplantation; 12 (86%) received a whole liver graft. Postoperative survival was 100%. At a mean follow-up of 3.25 ± 4.2 years, patient survival was 100%, liver allograft survival 93%, and kidney allograft survival 100%. One patient underwent liver re-transplantation because of hepatic artery thrombosis. After transplantation, there were no episodes of hyperammonemia, acidosis, or metabolic decompensation. The mean serum MMA at the time of transplantation was 1648 ± 1492 μmol/L (normal <0.3, range 99-4420). By 3 days, post-transplantation levels fell on average by 87% (mean 210 ± 154 μmol/L), and at 4 months, they were 83% below pre-transplantation levels (mean 305 ± 108 μmol/L). Developmental delay was present in 12 patients (86%) before transplantation. All patients maintained neurodevelopmental abilities or exhibited improvements in motor skills, learning abilities, and social functioning.

CONCLUSIONS

LT or LKT for MMA eradicates episodes of hyperammonemia, results in excellent long-term survival, and suggests stabilization of neurocognitive development. Long-term follow-up is underway to evaluate whether patients who undergo early LT need kidney transplantation later in life.

Mutation analysis of methylmalonyl CoA mutase gene exon 2 in Egyptian families: Identification of 25 novel allelic variants

Methylmalonic aciduria (MMA) is an autosomal recessive disorder of methylmalonate and cobalamin (cbl; vitamin B₁₂) metabolism. It is an inborn error of organic acid metabolism which commonly results from a defect in the gene encoding the methylmalonyl-CoA mutase (MCM) apoenzyme. Here we report the results of mutation study of exon 2 of the methylmalonyl CoA mutase (MUT) gene, coding MCM residues from 1 to 128, in ten unrelated Egyptian families affected with methylmalonic aciduria. Patients were presented with a wide-anion gap metabolic acidosis. The diagnosis has established by the measurement of C3 (propionylcarnitine) and C3:C2 (propionylcarnitine/acetylcarnitine) in blood by using liquid chromatography–tandem mass spectrometry (LC/MS–MS) and was confirmed by the detection of an abnormally elevated level of methylmalonic acid in urine by using gas chromatography–mass spectrometry (GC/MS) and isocratic cation exchange high-performance liquid-chromatography (HPLC). Direct sequencing of gDNA of the MUT gene exon 2 has revealed a total of 26 allelic variants: ten of which were intronic, eight were located upstream to the exon 2 coding region, four were novel modifications predicted to affect the splicing region, three were novel mutations within the coding region: c.15G > A (p.K5K), c.165C > A (p.N55K) and c.7del (p.R3EfsX14), as well as the previously reported mutation c.323G > A (p.R108H).

Methylmalonic acidemia: a megamitochondrial disorder affecting the kidney

BACKGROUND

Classical (or isolated) methylmalonic acidemia (MMA) is a heterogeneous inborn error of metabolism most typically caused by mutations in the vitamin B12-dependent enzyme methylmalonyl-CoA mutase (MUT). With the improved survival of individuals with MMA, chronic kidney disease has become recognized as part of the disorder. The precise description of renal pathology in MMA remains uncertain.

METHODS

Light microscopy, histochemical, and ultrastructural studies were performed on the native kidney obtained from a 19-year-old patient with mut MMA who developed end stage renal disease and underwent a combined liver-kidney transplantation.

RESULTS

The light microscopy study of the renal parenchyma in the MMA kidney revealed extensive interstitial fibrosis, chronic inflammation, and tubular atrophy. Intact proximal tubules were distinguished by the widespread formation of large, circular, pale mitochondria with diminished cristae. Histochemical preparations showed a reduction of cytochrome c oxidase and NADH activities, and the electron microscopy analysis demonstrated loss of cytochrome c enzyme activity in these enlarged mitochondria.

CONCLUSIONS

Our results demonstrate that the renal pathology of MMA is characterized by megamitochondria formation in the proximal tubules in concert with electron transport chain dysfunction. Our findings suggest therapies that target mitochondrial function as a treatment for the chronic kidney disease of MMA.

Proposed guidelines for the diagnosis and management of methylmalonic and propionic acidemia

Methylmalonic and propionic acidemia (MMA/PA) are inborn errors of metabolism characterized by accumulation of propionic acid and/or methylmalonic acid due to deficiency of methylmalonyl-CoA mutase (MUT) or propionyl-CoA carboxylase (PCC). MMA has an estimated incidence of ~ 1: 50,000 and PA of ~ 1:100’000 -150,000. Patients present either shortly after birth with acute deterioration, metabolic acidosis and hyperammonemia or later at any age with a more heterogeneous clinical picture, leading to early death or to severe neurological handicap in many survivors. Mental outcome tends to be worse in PA and late complications include chronic kidney disease almost exclusively in MMA and cardiomyopathy mainly in PA. Except for vitamin B₁₂ responsive forms of MMA the outcome remains poor despite the existence of apparently effective therapy with a low protein diet and carnitine. This may be related to under recognition and delayed diagnosis due to nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity.

These guidelines aim to provide a trans-European consensus to guide practitioners, set standards of care and to help to raise awareness. To achieve these goals, the guidelines were developed using the SIGN methodology by having professionals on MMA/PA across twelve European countries and the U.S. gather all the existing evidence, score it according to the SIGN evidence level system and make a series of conclusive statements supported by an associated level of evidence. Although the degree of evidence rarely exceeds level C (evidence from non-analytical studies like case reports and series), the guideline should provide a firm and critical basis to guide practice on both acute and chronic presentations, and to address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Furthermore, these guidelines highlight gaps in knowledge that must be filled by future research. We consider that these guidelines will help to harmonize practice, set common standards and spread good practices, with a positive impact on the outcomes of MMA/PA patients.

Increased susceptibility of brain acetylcholinesterase activity to methylmalonate in young rats with renal failure

Tissue methylmalonic acid (MMA) accumulation is the biochemical hallmark of methylmalonic acidemia. Clinically, the disease is characterized by progressive neurological deterioration and renal failure, whose pathophysiology is still undefined. In the present study we investigated the effect of acute MMA administration on some important parameters of brain neurotransmission in cerebral cortex of rats, namely Na(+), K(+)-ATPase, ouabain-insensitive ATPases and acetylcholinesterase activities, in the presence or absence of kidney injury induced by gentamicin administration. Initially, thirty-day old Wistar rats received one intraperitoneal injection of saline or gentamicin (70 mg/kg). One hour after, the animals received three consecutive subcutaneous injections of MMA (1.67 μmol/g) or saline, with an 11 h interval between each injection. One hour after the last injection the animals were killed and the cerebral cortex isolated. MMA administration by itself was not able to modify Na(+), K(+)-ATPase, ATPases ouabain-insensitive or acetylcholinesterase activities in cerebral cortex of young rats. In rats receiving gentamicin simultaneously with MMA, it was observed an increase in the activity of acetylcholinesterase activity in cerebral cortex, without any alteration in the activity of the other studied enzymes. Therefore, it may be speculated that cholinergic imbalance may play a role in the pathogenesis of the brain damage. Furthermore, the pathophysiology of tissue damage cannot be exclusively attributed to MMA toxicity, and control of kidney function should be considered as a priority in the management of these patients, specifically during episodes of metabolic decompensation when MMA levels are higher.

Renal growth in isolated methylmalonic acidemia

PURPOSE

We sought to predict renal growth based on clinical and metabolic parameters in patients with isolated methylmalonic acidemia, a group of disorders associated with chronic kidney disease.

METHODS

Fifty patients with methylmalonic acidemia, followed from 2004 to 2011, were classified by molecular genetics and studied using a combined cross-sectional and longitudinal design that included renal ultrasound examinations, anthropometric measurements, and metabolic phenotyping. Renal length was compared with that of healthy controls and modeled to other clinical parameters using multiple-regression analyses.

RESULTS

Comparisons with age-matched controls showed that renal length in subjects with methylmalonic acidemia was significantly decreased (P < 0.05). Stepwise regression modeling found that combinations of height, serum cystatin C, and serum methymalonic acid concentrations best predicted kidney size. The regression equations used to generate methylmalonic acidemia kidney nomograms were renal length (cm) = 6.79 + 0.22 × age for the controls and 6.80 + 0.09 × age for the methylmalonic acidemia cohort (P < 0.001; constant and slope).

CONCLUSION

Renal length, reflective of kidney growth, significantly decreased in patients with methylmalonic acidemia over time as compared with controls and was predictable with select clinical parameters. Cystatin C and serum methylmalonic acid concentrations were highly correlated with smaller kidneys and decreased renal function in this patient population.

Acute renal failure potentiates methylmalonate-induced oxidative stress in brain and kidney of rats

Tissue methylmalonic acid (MMA) accumulation is the biochemical hallmark of methylmalonic acidemia. The disease is clinically characterized by progressive neurological deterioration and kidney failure, whose pathophysiology is still unclear. In the present work we investigated the effects of acute MMA administration on various parameters of oxidative stress in cerebral cortex and kidney of young rats, as well as the influence of acute renal failure on MMA-elicited effects on these parameters. Acute renal failure was induced by gentamicin, an aminoglycoside antibiotic whose utilization over prolonged periods causes nephrotoxicity. The administration of gentamicin alone increased carbonyl content and inhibited superoxide dismutase (SOD) activity in cerebral cortex, as well as increased thiobarbituric acid-reactive substances (TBA-RS) and sulfhydryl levels and diminished glutathione peroxidase activity in kidney. On the other hand, MMA administration increased TBA-RS levels in cerebral cortex and decreased SOD activity in kidney. Furthermore, the simultaneous administration of MMA and gentamicin to the rats provoked an augment in TBA-RS levels and superoxide generation in cerebral cortex and in TBA-RS, carbonyl and sulfhydryl levels in kidney, while diminished SOD activity in both studied tissues. Finally, nitrate/nitrite content, reduced glutathione levels, 2',7'-dihydrodichlorofluorescein oxidation and catalase activity were not affected by this animal treatment in either tissue. In conclusion, our present data are in line with the hypothesis that MMA acts as a toxin in brain and kidney of rats and suggest that renal injury potentiates the toxicity of MMA on oxidative stress parameters in brain and peripheral tissues.

Methylmalonic acidemia: diagnosis and neuroimaging findings of this neurometabolic disorder (an Iranian pediatric case series)

OBJECTIVE

Methylmalonic acidemia is one of the inborn errors of metabolism resulting in the accumulation of acylcarnitine in blood and increased urinary methylmalonic acid excretion. This disorder can have symptoms, such as neurological and gastrointestinal manifestations, lethargy, and anorexia.

MATERIALS & METHODS

The patients who were diagnosed as methylmalonic acidemia in the Neurology Department of Mofid Children's Hospital in Tehran, Iran, between 2002 and 2012 were included in our study. The disorder was confirmed by clinical findings, neuroimaging findings, and neurometabolic and genetic assessment in reference laboratory in Germany. We assessed the age, gender, past medical history, developmental status, clinical manifestations, and neuroimaging findings of 20 patients with methylmalonic acidemia.

RESULTS

Eighty percent of the patients were offspring of consanguineous marriages. Half of the patients had Failure to thrive (FTT) due to anorexia; 85% had history of developmental delay or regression, and 20% had refractory seizure, which all of them were controlled. The patients with methylmalonic acidemia were followed for approximately 5 years and the follow-up showed that the patients with early diagnosis had a more favorable clinical response in growth index, refractory seizure, anorexia, and neurodevelopmental delay. Neuroimaging findings included brain atrophy, basal ganglia involvement (often in putamen), and periventricular leukomalacia.

CONCLUSION

According to the results of this study, we suggest that early assessment and diagnosis have an important role in the prevention of disease progression and clinical signs.

Infantile spasms (West syndrome) in children with inborn errors of metabolism: a review of the literature

West syndrome (infantile spasms) is an epileptic encephalopathy that includes psychomotor deterioration. In rare cases, it is due to an inherited, progressive metabolic disease. More than 25 inborn errors of metabolism have been considered etiologic or predisposing factors for infantile spasms. This is a review of the literature on reported cases of children diagnosed with a metabolic disease who developed infantile spasms. This article presents in brief the most frequent inborn errors of metabolism that have been associated with West syndrome and also illustrates the importance of screening for inborn errors of metabolism in infantile spasms.

Clinical and molecular findings in Thai patients with isolated methylmalonic acidemia

Isolated methylmalonic acidemia (MMA) is a genetically heterogeneous organic acid disorder caused by either deficiency of the enzyme methylmalonyl-CoA mutase (MCM), or a defect in the biosynthesis of its cofactor, adenosyl-cobalamin (AdoCbl). Herein, we report and review the genotypes and phenotypes of 14 Thai patients with isolated MMA. Between 1997 and 2011, we identified 6 mut patients, 2 cblA patients, and 6 cblB patients. The mut and cblB patients had relatively severe phenotypes compared to relatively mild phenotypes of the cblA patients. The MUT and MMAB genotypes were also correlated to the severity of the phenotypes. Three mutations in the MUT gene: c.788G>T (p.G263V), c.809_812dupGGGC (p.D272Gfs*2), and c.1426C>T (p.Q476*); one mutation in the MMAA gene: c.292A>G (p.R98G); and three mutations in the MMAB gene: c.682delG (p.A228Pfs*2), c.435delC (p.F145Lfs*69), and c.585-1G>A, have not been previously reported. RT-PCR analysis of a common intron 6 polymorphism (c.520-159C>T) of the MMAB gene revealed that it correlates to deep intronic exonization leading to premature termination of the open reading frame. This could decrease the ATP:cobalamin adenosyltransferase (ATR) activity resulting in abnormal phenotypes if found in a compound heterozygous state with a null mutation. We confirm the genotype-phenotype correlation of isolated MMA in the study population, and identified a new molecular basis of the cblB disorder.

Microarray based mutational analysis of patients with methylmalonic acidemia: identification of 10 novel mutations

Methylmalonic acidemia is an autosomal recessive metabolic disorder affecting the propionate oxidation pathway in the catabolism of several amino acids, odd-chain fatty acids, and cholesterol. Methylmalonic acidemia is characterized by elevated levels of methylmalonic acid in the blood and urine. Mutations in the MUT gene, encoding methylmalonyl-CoA mutase carries out isomerization of L-methylmalonyl-CoA to succinyl-CoA, cause methylmalonic acidemia. In this study, 30 Turkish patients diagnosed with mut methylmalonic acidemia were screened for mutations using custom designed sequencing microarrays. The study resulted in detection of 22 different mutations, 10 of which were novel: p.Q132*, p.A137G, c.753+1T, p.T387I, p.Q514E, p.P615L, p.D625V, c.1962_1963delTC, p.L674F, and c.2115_2116insA. The most common, p.P615T, was identified in 28.0% of patients. These results suggest that microarray based sequencing is a useful tool for the detection of mutations in MUT in patients with mut methylmalonic acidemia.

Neurocognitive phenotype of isolated methylmalonic acidemia

OBJECTIVE

Methylmalonic acidemia (MMA) is a metabolic disorder with a poorly defined long-term neurocognitive phenotype. We studied the neuropsychological outcomes of patients and examined clinical covariates that influenced cognition.

METHODS

A diverse cohort with mut, cblA, or cblB subtypes of isolated MMA (N = 43), ages 2 to 32 years, were evaluated at a single center over a 6-year period. The influence of clinical, laboratory, and metabolic parameters on neuropsychological testing results was determined.

RESULTS

Early-onset mut patients (n = 21) manifested the most severe neurocognitive impairments, with a mean ± SD full-scale IQ (FSIQ) of 71.1 ± 14.75. Late-onset mut patients (n = 6) had a mean FSIQ of 88.5 ± 27.62. cblA (n = 7), cblB (n = 6), and mut patients diagnosed prenatally or by newborn screening (n = 3) obtained mean FSIQs in the average range (100.7 ± 10.95, 96.6 ± 10.92, and 106.7 ± 6.66, respectively). Hyperammonemia at diagnosis and the presence of a seizure disorder were associated with a lower FSIQ (P = .001 and P = .041, respectively), but other clinical variables, including basal ganglia injury and mutation status, did not. FSIQ remained stable over longitudinal testing (n = 10). Decreased scores on processing speed, compared with all other intellectual domains, emerged as a specific neurocognitive manifestation.

CONCLUSIONS

The neurocognitive outcomes seen in isolated MMA are highly variable. An earlier age of disease onset, the presence of hyperammonemia at diagnosis, and a history of seizures were associated with more severe impairment. In all patient subtypes, selective deficits in processing speed were present.

Gene therapy in a murine model of methylmalonic acidemia using rAAV9-mediated gene delivery

Methylmalonic acidemia (MMA), an inherited metabolic disorder caused by deficient activity of methylmalonyl-CoA mutase, carries a poor prognosis for long-term survival. While administration of a recombinant adeno-associated virus serotype 8 vector (rAAV8) can rescue Mut(-/-) mice from neonatal lethality and provide sustained phenotypic correction, translation of gene therapy to human subjects will likely require multiple rounds of systemic administration and, ideally, the use of a vector that transduces the kidney. To examine the effectiveness of alternative rAAVs in the treatment of MMA, a serotype 9 rAAV expressing the Mut cDNA was constructed and delivered to newborn Mut(-/-) mice (n=11). rAAV9 gene therapy directed hepatic transgene expression within 24 h and effectively rescued the Mut(-/-) mice from lethality, conferred long-term survival, markedly improved metabolism and resulted in striking preservation of renal function and histology. Systemic readministration of the vector at a dose similar to that used in human clinical trials (2.5 × 10(9) GC of rAAV9 per gram) to older, treated Mut(-/-) mice (n=5) lowered circulating metabolites, increased in vivo propionate oxidative capacity and produced transgene expression in the kidney and liver. Our data support the use of an rAAV9 vector in the acute and chronic treatment of MMA, and highlight the renal tropism afforded by this novel serotype.

Liver-directed recombinant adeno-associated viral gene delivery rescues a lethal mouse model of methylmalonic acidemia and provides long-term phenotypic correction

Methylmalonic acidemia is a severe metabolic disorder caused by a deficiency of the ubiquitously expressed mitochondrial enzyme, methylmalonyl-CoA mutase (MUT). Liver transplantation has been used to treat a small number of patients with variable success, and whether liver-directed gene therapy might be employed in such a pleiotropic metabolic disorder is uncertain. In this study, we examined the therapeutic effects of hepatocyte-directed delivery of the Mut gene to mice with a severe form of methylmalonic acidemia. We show that a single intrahepatic injection of recombinant adeno-associated virus serotype 8 expressing the Mut gene under the control of the liver-specific thyroxine-binding globulin (TBG) promoter is sufficient to rescue Mut(-/-) mice from neonatal lethality and provide long-term phenotypic correction. Treated Mut(-/-) mice lived beyond 1 year of age, had improved growth, lower plasma methylmalonic acid levels, and an increased capacity to oxidize [1-(13)C]propionate in vivo. The older treated mice showed increased Mut transcription, presumably mediated by upregulation of the TBG promoter during senescence. The results indicate that the stable transduction of a small number of hepatocytes with the Mut gene can be efficacious in the phenotypic correction of an inborn error of organic acid metabolism and support the rapid translation of liver-directed gene therapy vectors already optimized for human subjects to patients with methylmalonic acidemia.

Glutaric aciduria type I and methylmalonic aciduria: simulation of cerebral import and export of accumulating neurotoxic dicarboxylic acids in in vitro models of the blood-brain barrier and the choroid plexus

Intracerebral accumulation of neurotoxic dicarboxylic acids (DCAs) plays an important pathophysiological role in glutaric aciduria type I and methylmalonic aciduria. Therefore, we investigated the transport characteristics of accumulating DCAs - glutaric (GA), 3-hydroxyglutaric (3-OH-GA) and methylmalonic acid (MMA) - across porcine brain capillary endothelial cells (pBCEC) and human choroid plexus epithelial cells (hCPEC) representing in vitro models of the blood-brain barrier (BBB) and the choroid plexus respectively. We identified expression of organic acid transporters 1 (OAT1) and 3 (OAT3) in pBCEC on mRNA and protein level. For DCAs tested, transport from the basolateral to the apical site (i.e. efflux) was higher than influx. Efflux transport of GA, 3-OH-GA, and MMA across pBCEC was Na(+)-dependent, ATP-independent, and was inhibited by the OAT substrates para-aminohippuric acid (PAH), estrone sulfate, and taurocholate, and the OAT inhibitor probenecid. Members of the ATP-binding cassette transporter family or the organic anion transporting polypeptide family, namely MRP2, P-gp, BCRP, and OATP1B3, did not mediate transport of GA, 3-OH-GA or MMA confirming the specificity of efflux transport via OATs. In hCPEC, cellular import of GA was dependent on Na(+)-gradient, inhibited by NaCN, and unaffected by probenecid suggesting a Na(+)-dependent DCA transporter. Specific transport of GA across hCPEC, however, was not found. In conclusion, our results indicate a low but specific efflux transport for GA, 3-OH-GA, and MMA across pBCEC, an in vitro model of the BBB, via OAT1 and OAT3 but not across hCPEC, an in vitro model of the choroid plexus.

Management of West syndrome in a patient with methylmalonic aciduria

Infantile spasms (or West syndrome) occur occasionally in patients with branched-chain organic acidurias. We describe a patient diagnosed with methylmalonic aciduria at 4.5 months of age during an episode of metabolic decompensation. The child was developmentally delayed and hypotonic; his electroencephalography (EEG) showed hypsarrythmia and brain magnetic resonance imaging (MRI) demonstrated moderate abnormalities in the globi pallidi. Following the failure of vigabatrin and lamotrigine to control the spasms, hydrocortisone was introduced. Methylmalonic acid excretion increased at the onset of steroid therapy but was rapidly corrected with transient protein restriction and initiation of metronidazole therapy. Full control of spasms and hypsarrythmia permitted the discontinuation of hydrocortisone therapy a year following its initiation. Tone and development improved although the latter remained delayed. This case illustrates the importance of screening for inborn errors of metabolism in seizure disorders, and that, although challenging, the management of methylmalonic aciduria with concurrent steroid therapy is possible and beneficial.

Cognitive and social profiles in two patients with cobalamin C disease

Cobalamin C (cblC) disease, an inborn error of vitamin B(12) metabolism, results in neurometabolic, neurochemical and neuroanatomical changes. Little is known of the long-term effects of the disorder on cognition and behaviour in children. Here, the complete neuropsychological profiles of two 12-year-old girls with cblC disease are presented. The two girls were tested longitudinally with standardized neuropsychological tests including intellectual ability, attention and memory, as well as executive, adaptive and behavioural function. The results indicate the presence of intellectual dysfunction, attention problems, and concerns with behavioural aspects of executive function. Both patients demonstrated a pattern of decreasing intellectual function over time, which may reflect a growing developmental gap in comparison with their same age peers. These impairments are in contrast to the relatively spared verbal expression and comprehension abilities, as well as strengths in sociability. The findings highlight a pattern of neuropsychological strengths and weaknesses that may distinguish cblC disease from other inborn errors of metabolism. Overt sociability such as observed in these two patients may actually mask underlying cognitive deficits because the patients appear to function at a more advanced level than that reflected by quantitative assessment of intellectual and cognitive functioning. This is of clinical and functional importance and suggests that accurate determination of cognitive, adaptive and social abilities necessitates an in-depth and broad evaluation. The presence of significant intellectual and cognitive deficits also underscores the need to document and monitor cognitive development in children with cblC disease and to consider remediative and adaptive learning strategies.

Long-term rescue of a lethal murine model of methylmalonic acidemia using adeno-associated viral gene therapy

Methylmalonic acidemia (MMA) is an organic acidemia caused by deficient activity of the mitochondrial enzyme methylmalonyl-CoA mutase (MUT). This disorder is associated with lethal metabolic instability and carries a poor prognosis for long-term survival. A murine model of MMA that replicates a severe clinical phenotype was used to examine the efficacy of recombinant adeno-associated virus (rAAV) serotype 8 gene therapy as a treatment for MMA. Lifespan extension, body weight, circulating metabolites, transgene expression, and whole animal propionate oxidation were examined as outcome parameters after gene therapy. One-hundred percent of the untreated Mut^−/− mice (n = 58) died by day of life (DOL) 72, whereas >95% of the adeno-associated virus–treated Mut^−/− mice (n = 27) have survived for ≥1 year. Despite a gradual loss of transgene expression and elevated circulating metabolites in the treated Mut^−/− mice, the animals are indistinguishable from unaffected control littermates in size and activity levels. These experiments provide the first definitive evidence that gene therapy will have clinical utility in the treatment of MMA and support the development of gene therapy for other organic acidemias.

Prediction of outcome in isolated methylmalonic acidurias: combined use of clinical and biochemical parameters

Objectives Isolated methylmalonic acidurias (MMAurias) are caused by deficiency of methylmalonyl-CoA mutase or by defects in the synthesis of its cofactor 5'-deoxyadenosylcobalamin. The aim of this study was to evaluate which parameters best predicted the long-term outcome. Methods Standardized questionnaires were sent to 20 European metabolic centres asking for age at diagnosis, birth decade, diagnostic work-up, cobalamin responsiveness, enzymatic subgroup (mut(0), mut(-), cblA, cblB) and different aspects of long-term outcome. Results 273 patients were included. Neonatal onset of the disease was associated with increased mortality rate, high frequency of developmental delay, and severe handicap. Cobalamin non-responsive patients with neonatal onset born in the 1970s and 1980s had a particularly poor outcome. A more favourable outcome was found in patients with late onset of symptoms, especially when cobalamin responsive or classified as mut(-). Prevention of neonatal crises in pre-symptomatically diagnosed newborns was identified as a protective factor concerning handicap. Chronic renal failure manifested earlier in mut(0) patients than in other enzymatic subgroups. Conclusion Outcome in MMAurias is best predicted by the enzymatic subgroup, cobalamin responsiveness, age at onset and birth decade. The prognosis is still unfavourable in patients with neonatal metabolic crises and non-responsiveness to cobalamin, in particular mut(0) patients.

Growth hormone therapy in neonatal patients with methylmalonic acidemia

BACKGROUND

Information regarding growth hormone (GH) therapy in neonatal patients with methylmalonic academia (MMA) is lacking. We present our experience with GH therapy in neonatal patients with MMA.

METHODS

Four neonatal patients with mut 0 type MMA were identified through newborn screening for elevated propionylcarnitine (C3) levels. GH therapy (0.6 IU/kg/week, subcutaneously) was prescribed for patient 1 after 1 month of admission, and was prescribed for patients 2, 3 and 4 on the 1st day of admission. We evaluated weight, skin erosion, hospital stay, and serum levels of C3 after GH therapy.

RESULTS

All of the neonatal patients with MMA displayed obvious weight gain and distinct improvement in skin erosions after GH therapy. The duration of hospital stay for patients 2, 3 and 4 was reduced compared to that of patient 1. However, the metabolic effects of GH therapy on reducing serum levels of C3 seem to be indeterminate.

CONCLUSION

Our clinical findings suggest that GH therapy has potentially beneficial effects on neonatal patients with MMA.

Evidence for catabolic pathway of propionate metabolism in CNS: expression pattern of methylmalonyl-CoA mutase and propionyl-CoA carboxylase alpha-subunit in developing and adult rat brain

Methylmalonyl-CoA mutase (MCM) and propionyl-CoA carboxylase (PCC) are the key enzymes of the catabolic pathway of propionate metabolism and are mainly expressed in liver, kidney and heart. Deficiency of these enzymes leads to two classical organic acidurias: methylmalonic and propionic aciduria. Patients with these diseases suffer from a whole spectrum of neurological manifestations that are limiting their quality of life. Current treatment does not seem to effectively prevent neurological deterioration and pathophysiological mechanisms are poorly understood. In this article we show evidence for the expression of the catabolic pathway of propionate metabolism in the developing and adult rat CNS. Both, MCM and PCC enzymes are co-expressed in neurons and found in all regions of the CNS. Disease-specific metabolites such as methylmalonate, propionyl-CoA and 2-methylcitrate could thus be formed autonomously in the CNS and contribute to the pathophysiological mechanisms of neurotoxicity. In rat embryos (E15.5 and E18.5), MCM and PCC show a much higher expression level in the entire CNS than in the liver, suggesting a different, but important function of this pathway during brain development.

Long-term needs of adult patients with organic acidaemias: outcome and prognostic factors

BACKGROUND

With improvements in the treatment of children with organic acidaemias (OA), the number surviving to adulthood is increasing. To plan appropriate services for their care it is important to know what their needs are.

OBJECTIVE

To describe the clinical and social problems affecting adult patients with OA.

PATIENTS AND METHODS

We reviewed the medical records of 15 adult patients diagnosed with OA. Social attainment (housing, schooling and occupation) was analysed. Nutritional status was evaluated by body mass index (BMI) and laboratory studies. Neurological and visceral complications were noted. Cognitive outcome was evaluated by psychometric testing and/or educational attainment.

RESULTS

Seven had methylmalonic acidaemia (MMA), 4 isovaleric acidaemia (IVA) and 4 propionic acidaemia (PA). Ten were female, and median age was 23.5 years (range 18-48). All but three had late-onset disease. Two patients became pregnant during follow up. Four patients had obtained university degrees and were working. Three-quarters of the patients required some kind of social support. All had a good nutritional status. Height was normal in IVA and 3 PA patients. Osteoporosis was present in 2 out of 8 patients assessed. A variety of neurocognitive or visceral complications were seen in two-thirds of the patients. Metabolic decompensations were unusual.

CONCLUSIONS

The approach to adult patients with OA has to be multidisciplinary, with the clinician and dietician as the core of the team, but with the collaboration of clinical nurses specialists, social workers and other specialist services and the support of a biochemical and molecular laboratory.

Inherited metabolic disorders and cerebral infarction

The association of genetic factors and cerebral infarction (CI) has long been established. A positive family history alone is a recognized risk factor for CI and vascular events in general. However, there are certain inherited conditions that further increase the risk of stroke. These conditions are generally metabolic and mitochondrial genetic defects that have variable modes of inheritance. This article reviews major inherited metabolic disorders that predispose an individual to CI. Ten main conditions will be discussed: Fabry's disease, cerebrotendinous xanthomatosis, tangier disease, familial hypercholesterolemia, homocystinuria, methylmalonic acidemia, glutaric aciduria type I, propionic acidemia, ornithine transcarbamylase deficiency and mitochondrial encephalopathy, lactic acidosis and stroke-like phenomenon.

Enamel defects and salivary methylmalonate in methylmalonic acidemia

INTRODUCTION AND OBJECTIVE

To characterize enamel defects in patients with methylmalonic acidemia (MMA) and cobalamin (cbl) metabolic disorders and to examine salivary methylmalonate levels in MMA.

SUBJECTS AND METHODS

Teeth from patients (n = 32) were evaluated for enamel defects and compared with age- and gender-matched controls (n = 55). Complementation class (mut, cblA, cblB and cblC) and serum methylmalonate levels were examined. Primary teeth from two patients were examined by light and scanning electron microscopy and salivary methylmalonate levels from two patients were analyzed.

RESULTS

Enamel defects were significantly more prevalent per tooth in the affected group than the control group, across complementation types (P < 0.0001). The mut MMA subgroup had a significantly higher prevalence per individual of severe enamel defects than controls (P = 0.021), and those with enamel defects exhibited higher serum methylmalonate levels than those without (P = 0.017). Salivary methylmalonate levels were extremely elevated and were significantly higher than controls (P = 0.002). Primary teeth were free of enamel defects except for two cblC patients who exhibited severe enamel hypoplasia. One primary tooth from a cblC patient manifested markedly altered crystal microstructure.

CONCLUSION

Enamel anomalies represent a phenotypic manifestation of MMA and cbl metabolic disorders. These findings suggest an association between enamel developmental pathology and disordered metabolism.

Mitochondrial dysfunction in mut methylmalonic acidemia

Methylmalonic acidemia is an autosomal recessive inborn error of metabolism caused by defective activity of methylmalonyl-CoA mutase (MUT) that exhibits multiorgan system pathology. To examine whether mitochondrial dysfunction is a feature of this organic acidemia, a background-modified Mut-knockout mouse model was constructed and used to examine mitochondrial ultrastructure and respiratory chain function in the tissues that manifest pathology in humans. In parallel, the liver from a patient with mut methylmalonic acidemia was studied in a similar fashion. Megamitochondria formed early in life in the hepatocytes of the Mut(-/-) animals and progressively enlarged. Liver extracts prepared from the mutants at multiple time points displayed respiratory chain dysfunction, with diminished cytochrome c oxidase activity and reduced intracellular glutathione compared to control littermates. Over time, the exocrine pancreas and proximal tubules of the kidney also exhibited megamitochondria, and older mutant mice eventually developed tubulointerstitial renal disease. The patient liver displayed similar morphological and enzymatic findings as observed in the murine tissues. These murine and human studies establish that megamitochondria formation with respiratory chain dysfunction occur in a tissue-specific fashion in methylmalonic acidemia and suggest treatment approaches based on improving mitochondrial function and ameliorating the effects of oxidative stress.