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.

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

Branched-chain organic acidurias.

Methylmalonic and propionic aciduria (PA) are the most frequent forms of branched-chain organic acidurias. These autosomal recessive disorders result from deficient activity of methylmalonyl-CoA mutase and propionyl-CoA carboxylase, respectively. Clinically, acute or chronic neurologic signs are caused by the accumulation of toxic compounds proximal to the metabolic block. Phenotype varies from severe neonatal-onset forms with high mortality and poor outcome to milder forms with a later onset. In both cases the clinical course is dominated by the risk of relapses of life-threatening episodes of metabolic decompensation and of severe organ failure. Despite improvement of treatment, the overall outcome remains disappointing with no major differences between the two diseases. The diagnosis is based on the presence of characteristic compounds in body fluids as detected by organic acid analysis in urine and acylcarnitine profile in blood. Therapy is based on low-protein high-energy diet, carnitine supplementation, and metronidazole. Some patients with methylmalonic aciduria (MMA) respond to pharmacological doses of vitamin B12. Given the poor long-term prognosis, liver transplantation has been recently attempted as an alternative therapy to conventional medical treatment to cure the underlying metabolic defect. Nevertheless, the overall experience to date does not clearly demonstrate its effectiveness in preventing further deterioration or improving survival and quality of life. The recent implementation of neonatal screening by electrospray tandem mass spectrometry has decreased early mortality and improved the short-term outcome, without changing the detection rate of both diseases in the screening population compared to clinically detected cases. However, the limited number of patients and the short duration of their follow-up do not yet permit drawing final conclusions on its effect on the long-term outcome of methylmalonic and propionic acidemia. © 2006 Wiley-Liss, Inc.

Methylmalonic and propionic aciduria.

Propionic acidemia is an inherited disorder caused by deficiency of propionyl-CoA carboxylase. Although it is one of the most frequent organic acidurias, information on the outcome of affected individuals is still limited. Clinical and outcome data of 55 patients with propionic acidemia from 16 European metabolic centers were evaluated retrospectively. 35 patients were diagnosed by selective metabolic screening while 20 patients were identified by newborn screening. Endocrine parameters and bone age were evaluated. In addition, IQ testing was performed and the patients’ and their families’ quality of life was assessed. The vast majority of patients (>85%) presented with metabolic decompensation in the neonatal period. Asymptomatic individuals were the exception. About three quarters of the study population was mentally retarded, median IQ was 55. Apart from neurologic symptoms, complications comprised hematologic abnormalities, cardiac diseases, feeding problems and impaired growth. Most patients considered their quality of life high. However, according to the parents’ point of view psychic problems were four times more common in propionic acidemia patients than in healthy controls. Our data show that the outcome of propionic acidemia is still unfavourable, in spite of improved clinical management. Many patients develop long-term complications affecting different organ systems. Impairment of neurocognitive development is of special concern. Nevertheless, self-assessment of quality of life of the patients and their parents yielded rather positive results.

/pdf/propionic-acidemia-clinical-course-and-outcome-in-55-28ikr7bzyw.pdf

Propionic acidemia: clinical course and outcome in 55 pediatric and adolescent patients

Isolated methylmalonic acidaemia (MMA) and propionic acidaemia (PA) are rare inherited metabolic diseases. Six years ago, a detailed evaluation of the available evidence on diagnosis and management of these disorders has been published for the first time. The article received considerable attention, illustrating the importance of an expert panel to evaluate and compile recommendations to guide rare disease patient care. Since that time, a growing body of evidence on transplant outcomes in MMA and PA patients and use of precursor free amino acid mixtures allows for updates of the guidelines. In this article we aim to incorporate this newly published knowledge and provide a revised version of the guidelines. The analysis was performed by a panel of multidisciplinary health care experts, who followed an updated guideline development methodology (GRADE). Hence, the full body of evidence up until autumn 2019 was re-evaluated, analysed, and graded. As a result, 21 updated recommendations were compiled in a more concise paper with a focus on the existing evidence to enable well informed decisions in the context of MMA and PA patient care. This article is protected by copyright. All rights reserved.

Guidelines for the diagnosis and management of methylmalonic acidaemia and propionic acidaemia: First revision.

A retrospective study was performed on the clinical outcome and long-term treatment of 17 patients with propionic acidaemia diagnosed during the last 20 years in our hospital. The study group consisted of 12 patients with early onset type of disease and 5 patients with late onset. Seven (41%) patients died, five with early onset and two with late onset. The deceased early onset patients had a median survival of 0.4 years while the deceased late onset patients died at the age of 2.8 and 4 years respectively. Median age of the living early onset patients was 5.2 (1–9.25) years, the late onset patients were 4,7 and 23 years old. Patients were all treated with natural protein restriction and in most cases carnitine and metronidazole were added. The early onset patients were almost all treated with daily home tube feeding. The mean natural protein intake of early onset patients (6.3±1.5 g/day) was significantly lower than the natural protein intake of late onset patients (17.6±5.3 g/day). Supplemental protein intake was higher in early onset patients. The general neurological outcome of our study group was satisfactory with a better outcome for early onset patients. As to growth, many patients showed a failure to thrive, this was particularly for height. The strong protein restriction during the first years of life probably contributed to this.

Clinical outcome and long-term management of 17 patients with propionic acidaemia.

This article describes the metabolic investigations to be applied in any clinical situation consistent with a late acute form of inborn error of metabolism: unexplained coma with or without focal neurological manifestations, recurrent vomiting with lethargy, episodes of ataxia with or without behaviour disorder, fits of psychiatric troubles. In each of these situations, careful medical history is of major importance searching for previous clinical manifestations such as episodes of coma, ataxia or vomiting, anorexia, failure to thrive, developmental delay, all very suggestive of metabolic disorder. The association of neurological symptoms and abnormal hepatic tests is also of great value and must not lead to the diagnosis of Reye's syndrome without considering a metabolic defect of fatty acid oxidation, urea cycle, respiratory chain, or Wilson's disease. When looking for an etiological origin, it is mandatory to collect all the biological information at the same time, also knowing that metabolic abnormalities may be mild and transitory, and that many of them are non specific (metabolic acidosis, hyperlactacidemia, hyperammonemia, hepatic tests disturbances) being encountered in collapsus, shock and multiple organ failure syndrome.

Diagnosis of metabolic coma in children

Clinical presentations of inherited mitochondrial fatty acid oxidation disorders: An update

The authors describe a laboratory investigations protocol to be used by pediatricians facing conditions suggestive of inherited metabolic disorders. This protocol includes: 1) an emergency screening to be systematically performed during the acute clinical phase; 2) samplings to be kept frozen for possible secondary specific investigations according to the results of the emergency screening. In addition a perimortem protocol is also presented, to be applied in every lethal situations in which an inherited metabolic disorder is suspected. The equipment required in order for the clinician to properly perform the different investigations is also described.

Protocol of metabolic investigations in hereditary metabolic diseases

Management and Long Term Follow-up of Organic Acidemias : Criteria for Therapeutic Decisions

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