Evaluation and management of patients with propionic acidemia undergoing liver transplantation: a comprehensive review

Survival of propionic acidemia patients with liver transplant

Propionic acidemia (PA) is a rare metabolic disorder affecting amino acid metabolism. Liver transplantation improves some outcomes, but the impact on long-term survival remains unclear. A systematic literature review and survival analysis, identifying 94 PA patients who underwent transplantation, revealed a survival probability of 62% at age 33; while median survival was estimated at 40 years. These findings highlight a substantial survival deficit of PA patients compared to the general population despite liver transplantation.

A Review of Disparities and Unmet Newborn Screening Needs over 33 Years in a Cohort of Mexican Patients with Inborn Errors of Intermediary Metabolism

Advances in an early diagnosis by expanded newborn screening (NBS) have been achieved mainly in developed countries, while populations of middle- and low-income countries have poor access, leading to disparities. Expanded NBS in Mexico is not mandatory. Herein, we present an overview of the differences and unmet NBS needs of a group of Mexican patients with inborn errors of intermediary metabolism (IEiM), emphasizing the odyssey experienced to reach a diagnosis. We conducted a retrospective observational study of a historical cohort of patients with IEiM from a national reference center. A total of 924 patients with IEiM were included. Although 72.5% of the diseases identified are detectable by expanded NBS, only 35.4% of the patients were screened. The mortality in the unscreened group was almost two-fold higher than that in the screened group. Patients experienced a median diagnostic delay of 4 months, which is unacceptably long considering that to prevent disability and death, these disorders must be treated in the first days of life. Patients had to travel long distances to our reference center, contributing to their unacceptable diagnostic odyssey. This study highlights the urgent need to have an updated, expanded NBS program with adequate follow up in Mexico and promote the creation of regional medical care centers. We also provide compelling evidence that could prove valuable to decision makers overseeing public health initiatives for individuals impacted by IEiM from middle- and low-income countries.

Systemic gene therapy using an AAV44.9 vector rescues a neonatal lethal mouse model of propionic acidemia

Propionic acidemia (PA) is rare autosomal recessive metabolic disorder caused by defects in the mitochondrially localized enzyme propionyl-coenzyme A (CoA) carboxylase. Patients with PA can suffer from lethal metabolic decompensation and cardiomyopathy despite current medical management, which has led to the pursuit of gene therapy as a new treatment option for patients. Here we assess the therapeutic efficacy of a recently described adeno-associated virus (AAV) capsid, AAV44.9, to deliver a therapeutic PCCA transgene in a new mouse model of propionyl-CoA carboxylase α (PCCA) deficiency generated by genome editing. Pcca-/- mice recapitulate the severe neonatal presentation of PA and manifest uniform neonatal lethality, absent PCCA expression, and increased 2-methylcitrate. A single injection of the AAV44.9 PCCA vector in the immediate newborn period, systemically delivered at a dose of 1e11 vector genome (vg)/pup but not 1e10 vg/pup, increased survival, reduced plasma methylcitrate, and resulted in high levels of transgene expression in the liver and heart in treated Pcca-/- mice. Our studies not only establish a versatile and accurate new mouse model of PA but further demonstrate that the AAV44.9 vectors may be suitable for treatment of many metabolic disorders where hepato-cardiac transduction following systemic delivery is desired, such as PA, and, by extension, fatty acid oxidation defects and glycogen storage disorders.

Prevalence of propionic acidemia in China

Propionic acidemia (PA) is a rare autosomal recessive congenital disease caused by mutations in the PCCA or PCCB genes. Elevated propionylcarnitine, 2-methylcitric acid (2MCA), propionylglycine, glycine and 3-hydroxypropionate can be used to diagnose PA. Early-onset PA can lead to acute deterioration, metabolic acidosis, and hyperammonemia shortly after birth, which can result in high mortality and disability. Late-onset cases of PA have a more heterogeneous clinical spectra, including growth retardation, intellectual disability, seizures, basal ganglia lesions, pancreatitis, cardiomyopathy, arrhythmias, adaptive immune defects, rhabdomyolysis, optic atrophy, hearing loss, premature ovarian failure, and chronic kidney disease. Timely and accurate diagnosis and appropriate treatment are crucial to saving patients' lives and improving their prognosis. Recently, the number of reported PA cases in China has increased due to advanced diagnostic techniques and increased research attention. However, an overview of PA prevalence in China is lacking. Therefore, this review provides an overview of recent advances in the pathogenesis, diagnostic strategies, and treatment of PA, including epidemiological data on PA in China. The most frequent variants among Chinese PA patients are c.2002G > A in PCCA and c.1301C > T in PCCB, which are often associated with severe clinical symptoms. At present, liver transplantation from a living (heterozygous parental) donor is a better option for treating PA in China, especially for those exhibiting a severe metabolic phenotype and/or end-organ dysfunction. However, a comprehensive risk-benefit analysis should be conducted as an integral part of the decision-making process. This review will provide valuable information for the medical care of Chinese patients with PA.

Pathophysiological mechanisms of complications associated with propionic acidemia

Propionic acidemia (PA) is a genetic metabolic disorder caused by mutations in the mitochondrial enzyme, propionyl-CoA carboxylase (PCC), which is responsible for converting propionyl-CoA to methylmalonyl-CoA for further metabolism in the tricarboxylic acid cycle. When this process is disrupted, propionyl-CoA and its metabolites accumulate, leading to a variety of complications including life-threatening cardiac diseases and other metabolic strokes. While the clinical symptoms and diagnosis of PA are well established, the underlying pathophysiological mechanisms of PA-induced diseases are not fully understood. As a result, there are currently few effective therapies for PA beyond dietary restriction. This review focuses on the pathophysiological mechanisms of the various complications associated with PA, drawing on extensive research and clinical reports. Most research suggests that propionyl-CoA and its metabolites can impair mitochondrial energy metabolism and cause cellular damage by inducing oxidative stress. However, direct evidence from in vivo studies is still lacking. Additionally, elevated levels of ammonia can be toxic, although not all PA patients develop hyperammonemia. The discovery of pathophysiological mechanisms underlying various complications associated with PA can aid in the development of more effective therapeutic treatments. The consequences of elevated odd-chain fatty acids in lipid metabolism and potential gene expression changes mediated by histone propionylation also warrant further investigation.

Challenges and strategies for clinical trials in propionic and methylmalonic acidemias

Clinical trial development in rare diseases poses significant study design and methodology challenges, such as disease heterogeneity and appropriate patient selection, identification and selection of key endpoints, decisions on study duration, choice of control groups, selection of appropriate statistical analyses, and patient recruitment. Therapeutic development in organic acidemias (OAs) shares many challenges with other inborn errors of metabolism, such as incomplete understanding of natural history, heterogenous disease presentations, requirement for sensitive outcome measures and difficulties recruiting a small sample of participants. Here, we review strategies for the successful development of a clinical trial to evaluate treatment response in propionic and methylmalonic acidemias. Specifically, we discuss crucial decisions that may significantly impact success of the study, including patient selection, identification and selection of endpoints, determination of the study duration, consideration of control groups including natural history controls, and selection of appropriate statistical analyses. The significant challenges associated with designing a clinical trial in rare disease can sometimes be successfully met through strategic engagement with experts in the rare disease, seeking regulatory and biostatistical guidance, and early involvement of patients and families.

Propionic acidemia in mice: Liver acyl-CoA levels and clinical course

Propionic acidemia (PA) is a severe autosomal recessive metabolic disease caused by deficiency of propionyl-CoA carboxylase (PCC). We studied PA transgenic (Pat) mice that lack endogenous PCC but express a hypoactive human PCCA cDNA, permitting their survival. Pat cohorts followed from 3 to 20 weeks of age showed growth failure and lethal crises of lethargy and hyperammonemia, commoner in males (27/50, 54%) than in females (11/52, 21%) and occurring mainly in Pat mice with the most severe growth deficiency. Groups of Pat mice were studied under basal conditions (P-Ba mice) and during acute crises (P-Ac). Plasma acylcarnitines in P-Ba mice, compared to controls, showed markedly elevated C3- and low C2-carnitine, with a further decrease in C2-carnitine in P-Ac mice. These clinical and biochemical findings resemble those of human PA patients. Liver acyl-CoA measurements showed that propionyl-CoA was a minor species in controls (propionyl-CoA/acetyl-CoA ratio, 0.09). In contrast, in P-Ba liver the ratio was 1.4 and in P-Ac liver, 13, with concurrent reductions of the levels of acetyl-CoA and other acyl-CoAs. Plasma ammonia levels in control, P-Ba and P-Ac mice were 109 ± 10, 311 ± 48 and 551 ± 61 μmol/L respectively. Four-week administration to Pat mice, of carglumate (N-carbamyl-L-glutamic acid), an analogue of N-carbamylglutamate, the product of the only acyl-CoA-requiring reaction directly related to the urea cycle, was associated with increased food consumption, improved growth and absence of fatal crises. Pat mice showed many similarities to human PA patients and provide a useful model for studying tissue pathophysiology and treatment outcomes.

Liver transplantation for pediatric inherited metabolic liver diseases

Liver transplantation (LT) remains the gold standard treatment for end stage liver disease in the pediatric population. For liver based metabolic disorders (LBMDs), the decision for LT is predicated on a different set of paradigms. With improved outcomes post-transplantation, LT is no longer merely life saving, but has the potential to also significantly improve quality of life. This review summarizes the clinical presentation, medical treatment and indications for LT for some of the common LBMDs. We also provide a practical update on the dilemmas and controversies surrounding the indications for transplantation, surgical considerations and prognosis and long terms outcomes for pediatric LT in LBMDs. Important progress has been made in understanding these diseases in recent years and with that we outline some of the new therapies that have emerged.

Pantothenate kinase activation relieves coenzyme A sequestration and improves mitochondrial function in mice with propionic acidemia

[Figure: see text].

Comparative assessment of reported symptoms of influenza, respiratory syncytial virus, and human metapneumovirus infection during hospitalization and post-discharge assessed by Respiratory Intensity and Impact Questionnaire

Background

The hospitalized acute respiratory tract infection (HARTI) study used the Respiratory Intensity and Impact Questionnaire (RiiQ™) Symptom Scale, derived from FluiiQ™, to assess and compare the burden of respiratory infection symptoms for patients with influenza, respiratory syncytial virus (RSV), and human metapneumovirus (hMPV) infection, with or without core risk factors (CRF) (age ≥65; chronic heart, renal, obstructive pulmonary disease; asthma).

Methods

This was a prospective cohort study in adult patients hospitalized with acute respiratory tract infection (40 centers, 12 countries) during two consecutive influenza/RSV/hMPV seasons (2017–2019). The RiiQ™ Symptom Scale and EuroQol 5‐Dimensions 5‐Levels (EQ‐5D‐5L) were assessed by interview at two timepoints during hospitalization and at 1, 2, and 3 months post‐discharge.

Results

Mean lower respiratory tract (LRT) symptom scores were higher for RSV and hMPV participants compared to influenza at 48 h after enrollment/early discharge (p = 0.001) and 3 months post‐discharge (p = 0.007). This was driven by LRT symptoms, including shortness of breath (SOB) (p < 0.01) and wheezing (p < 0.01) during hospitalization, and SOB (p < 0.05) and cough (p < 0.05) post‐discharge. Participants with CRF reported more moderate‐to‐severe SOB (p < 0.05) and wheezing (p < 0.05) compared to CRF(−) participants post‐discharge. EQ‐5D‐5L scores were moderately associated with RiiQ™ LRT and systemic symptoms domains.

Conclusions

Results from the HARTI study suggest that in the study population, LRT symptoms were more severe for RSV and hMPV groups and for patients with CRF. RiiQ™ Symptom Scale scores shows a moderate association with EQ‐5D‐5L indicating that the RiiQ™ may provide useful insights and offer advantages over other measures for use in interventional RSV adult clinical studies.

Anesthetic Management for Pediatric Liver Transplantation in a Patient With Propionic Acidemia: A Case Report

Propionic acidemia is an inborn error of metabolism characterized by accumulation of propionic acid due to deficiency of propionyl-CoA carboxylase. Main stay of treatment focuses on reducing dietary protein. However, orthotropic liver transplantation decreases the frequency of metabolic decompensations and improves life expectancy. We report a case of a 4-year-old boy undergoing orthotropic liver transplantation to treat propionic acidemia. This case highlights the use of intraoperative monitoring of metabolic markers like urine ketones, arterial ammonia, and lactate levels as these patients are at risk for hyperammonemia and metabolic acidosis. Also, the relevance in outcomes when performing early extubation in fast-tracking recovery.

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

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.

Fatal metabolic stroke in a child with propionic acidemia 11 years post liver transplant

Propionic acidemia is a rare autosomal recessive inborn error of metabolism caused by a deficiency of propionyl CoA carboxylase which often manifests with frequent metabolic decompensations and risk of neurological injury. Outcomes with medical therapy remain suboptimal. Liver transplantation has been shown to be a therapeutic option for patients and results in a milder phenotype of the disease and partial correction of the enzyme defect. Liver transplantation has been increasingly reported over the last decade and experience in managing these patients is improving. Long-term outcomes are generally good; however, the risk of complications still exists despite transplantation. We report a child who presented with a fatal metabolic stroke 11 years post liver transplant without any biochemical evidence of decompensation. We highlight the need to closely monitor these patients lifelong despite liver transplantation and maintain multidisciplinary working between hepatology and metabolic clinicians.

The re-occurrence of cardiomyopathy in propionic acidemia after liver transplantation

Cardiomyopathy is a frequent complication of propionic acidemia (PA). It is often fatal, and its occurrence is largely independent of classic metabolic treatment modalities. Liver transplantation (LT) is a treatment option for severe PA as the liver plays a vital role in metabolism of the precursors that accumulate in patients with PA. LT in PA is now considered to be a long-lasting and valid treatment to prevent cardiac disease. The subject of this report had severe cardiomyopathy that largely disappeared prior to undergoing a LT. Three years following the transplant, there was recurrence of cardiomyopathy following a surgery that was complicated with a postoperative aspiration pneumonia. On his last hospital admission, he was presented with pulmonary edema and heart failure. He continued with episodes of intractable hypotension, despite maximum inotropic and diuretic support. He died following redirection of care. We conclude that lethal cardiomyopathy may develop several years after successful LT in patients with PA.

Domino Liver Transplantation: Where are we Now?

BACKGROUND

Domino transplant occurs when a recipient explanted graft is used for a second recipient.

INTRODUCTION

The first experience came from thoracic surgery by the observation that many patients during heart-lung transplantation actually showed a functional heart that could be employed in other subjects with a good result.

RESULTS

This concept was then extended to the field of liver transplantation. At present, some patients transplanted for an inborn metabolic disease may be considered as excellent domino liver donors.

CONCLUSION

The results, limitations, clinical challenges and the donor and recipient features of domino liver transplantation are discussed in this manuscript.

Post-transplantation Outcomes in Patients with PA or MMA: A Review of the Literature

Introduction

Liver transplantation is recognised as a treatment option for patients with propionic acidemia (PA) and those with methylmalonic acidemia (MMA) without renal impairment. In patients with MMA and moderate-to-severe renal impairment, combined liver–kidney transplantation is indicated. However, clinical experience of these transplantation options in patients with PA and MMA remains limited and fragmented. We undertook an overview of post-transplantation outcomes in patients with PA and MMA using the current available evidence.

Methods

A literature search identified publications on the use of transplantation in patients with PA and MMA. Publications were considered if they presented adequate demographic and outcome data from patients with PA or MMA. Publications that did not report any specific outcomes for patients or provided insufficient data were excluded.

Results

Seventy publications were identified of which 38 were full papers. A total of 373 patients underwent liver/kidney/combined liver–kidney transplantation for PA or MMA. The most typical reason for transplantation was recurrent metabolic decompensation. A total of 27 post-transplant deaths were reported in patients with PA [14.0% (27/194)]. For patients with MMA, 18 post-transplant deaths were reported [11% (18/167)]. A total of 62 complications were reported in 115 patients with PA (54%) with cardiomyopathy (n = 12), hepatic arterial thrombosis (HAT; n = 14) and viral infections (n = 12) being the most commonly reported. A total of 52 complications were reported in 106 patients with MMA (49%) with viral infections (n = 14) and renal failure/impairment (n = 10) being the most commonly reported.

Conclusions

Liver transplantation and combined liver–kidney transplantation appears to benefit some patients with PA or MMA, respectively, but this approach does not provide complete correction of the metabolic defect and some patients remain at risk from disease-related and transplantation-related complications, including death. Thus, all treatment avenues should be exhausted before consideration of organ transplantation and the benefits of this approach must be weighed against the risk of perioperative complications on an individual basis.

Liver Transplantation in Children With Propionic Acidemia: Medium-Term Outcomes

Liver transplantation (LT) for patients with propionic acidemia (PA) is an emerging therapeutic option. We present a retrospective review of patients with PA who underwent LT at a tertiary liver center between 1995 and 2015. A total of 14 children were identified (8 males) with median age at initial presentation of 3 days (range, 0-77 days). Pretransplant median protein restriction was 1 g/kg/day (range, 0.63-1.75 g/kg/day), 71% required supportive feeding, and 86% had developmental delay. Frequent metabolic decompensations (MDs) were the main indication for LT with a median age at transplantation of 2.4 years (range, 0.8-7.1 years). Only 1 graft was from a living donor, and 13 were from deceased donors (4 auxiliary). The 2-year patient survival was 86%, and overall study and graft survival was 79% and 69%, respectively. Three patients died after LT: at 43 days (biliary peritonitis), 225 days (acute-on-chronic rejection with multiorgan failure), and 13.5 years (posttransplant lymphoproliferative disease). Plasma glycine and propionylcarnitine remained elevated but reduced after transplant. Of 11 survivors, 5 had at least 1 episode of acute cellular rejection, 2 sustained a metabolic stroke (with full recovery), and 3 developed mild cardiomyopathy after LT. All have liberalized protein intake, and 9 had no further MDs: median episodes before transplant, 4 (range, 1-30); and median episodes after transplant, 0 (range, 0-5). All survivors made some developmental progress after LT, and none worsened at a median follow-up of 5.8 years (range, 2-23 years). LT in PA significantly reduces the frequency of MDs, can liberalize protein intake and improve quality of life, and should continue to be considered in selected cases.

Liver Transplantation for Propionic Acidemia: A Multicenter-linked Database Analysis

OBJECTIVES

Propionic acidemia (PA) is a rare inborn error of metabolism resulting from deficiency in the enzyme necessary for catabolism of branched-chain amino acids, some odd chain fatty acids and cholesterol. Despite optimal medical management, PA often leads to acute and progressive neurological injury. Reports on liver transplantation (LT) as a cellular therapy are limited and varied. The objective of this study was to examine the largest collection of patients who underwent LT for PA.

METHODS

Examining the Scientific Registry of Transplant Recipients and the Pediatric Health Information System administrative billing databases, we performed a multicenter, retrospective analysis of LT over a 16-year period. During this period, 4849 pediatric LT were performed out of which 23 were done for PA at 10 different centers.

RESULTS

The majority of recipients were 5 years of age or younger and had status 1b exception points at the time of transplant. The 1-, 3-, and 5-year graft survival for PA LT recipients was 84.6% and the 1-, 3, and 5-year patient survival was 89.5%. There was no significant difference in graft or patient survival between PA and non-PA LT recipients. Despite historical data to the contrary, we did not find an increased incidence of hepatic arterial thrombosis in patients undergoing LT for PA. Patients in the PA LT group, however, had a significantly higher postoperative rate of readmission compared with the non-PA LT group (90.5% vs 72.8%, P = 0.021).

CONCLUSION

LT for children with PA is a viable treatment option with acceptable outcomes.

Liver transplantation in propionic and methylmalonic acidemia: A single center study with literature review

BACKGROUND

Organic acidemias, especially propionic acidemia (PA) and methylmalonic acidemia (MMA), may manifest clinically within the first few hours to days of life. The classic presentation in the newborn period includes metabolic acidosis, hyperlactatemia, and hyperammonemia that is precipitated by unrestricted protein intake. Implementation of newborn screening to diagnose and initiate early treatment has facilitated a reduction in neonatal mortality and improved survival. Despite early diagnosis and appropriate management, these individuals are prone to have recurrent episodes of metabolic acidosis and hyperammonemia resulting in frequent hospitalizations. Liver transplantation (LT) has been proposed as a treatment modality to reduce metabolic decompensations which are not controlled by medical management. Published reports on the outcome of LT show heterogeneous results regarding clinical and biochemical features in the post transplantation period. As a result, we evaluated the outcomes of LT in our institution and compared it to the previously published data.

STUDY DESIGN/METHODS

We performed a retrospective chart review of nine individuals with PA or MMA who underwent LT and two individuals with MMA who underwent LT and kidney transplantation (KT). Data including number of hospitalizations, laboratory measures, cardiac and neurological outcomes, dietary protein intake, and growth parameters were collected.

RESULTS

The median age of transplantation for subjects with MMA was 7.2 years with a median follow up of 4.3 years. The median age of transplantation for subjects with PA was 1.9 years with a median follow up of 5.4 years. The survival rate at 1 year and 5 years post-LT was 100%. Most of our subjects did not have any episodes of hyperammonemia or pancreatitis post-LT. There was significant reduction in plasma glycine post-LT. One subject developed mild elevation in ammonia post-LT on an unrestricted protein diet, suggesting that protein restriction may be indicated even after LT.

CONCLUSION

In a large single center study of LT in MMA and PA, we show that LT may reduce the incidence of metabolic decompensation. Moreover, our data suggest that LT may be associated with reduced number of hospitalizations and improved linear growth in individuals with PA and MMA.

Kidney disease and organ transplantation in methylmalonic acidaemia

OBJECTIVES

MMA is associated with chronic tubulointerstitial nephritis and a progressive decline in GFR. Optimal management of these children is uncertain. Our objectives were to document the pre-, peri-, and post-transplant course of all children with MMA who underwent liver or combined liver-kidney transplant in our centers.

DESIGN AND METHODS

Retrospective chart review of all cases of MMA who underwent organ transplantation over the last 10 years.

RESULTS

Five children with MMA underwent liver transplant (4/5) and combined liver-kidney transplant (1/5). Three were Mut⁰ and two had a cobalamin B disorder. Four of five were transplanted between ages 3 and 5 years. Renal dysfunction prior to transplant was seen in 2/5 patients. Post-transplant (one liver transplant and one combined transplant) renal function improved slightly when using creatinine-based GFR formula. We noticed in 2 patients a big discrepancy between creatinine- and cystatin C-based GFR calculations. One patient with no renal disease developed renal failure post-liver transplantation. Serum MMA levels have decreased in all to <300 μmol/L. Four patients remain on low protein diet, carnitine, coenzyme Q, and vitamin E post-transplant.

CONCLUSIONS

MMA is a complex metabolic disorder. Renal disease can continue to progress post-liver transplant and close follow-up is warranted. More research is needed to clarify best screening GFR method in patients with MMA. Whether liver transplant alone, continued protein restriction, or the addition of antioxidants post-transplant can halt the progression of renal disease remains unclear.

The Role of Liver Transplantation in Propionic Acidemia

Despite optimal medical treatment and strict low-protein diet, the prognosis of propionic acidemia (PA) patients is generally poor. We aim to report our experience with liver transplantation (LT) in the management of PA patients. Six patients with PA received a LT at a mean age of 5.2 years (1.3-7.5 years). The indications for LT were frequent metabolic decompensations in the first 4 patients and preventative in the last 2 patients. Two patients presented hepatic artery thromboses that were solved through an interventional radiologist approach. These patients showed a very high procoagulant state that was observed by thromboelastography. Arterial vasospasm without thrombus was observed in 2 patients during the LT surgery. In order to avoid hepatic artery thrombosis, an arterial conduit from the recipient aorta to the hepatic artery of the donor was used in the fifth patient. After LT, patients presented improvement in propionyl byproducts without complete normalization, but no decompensations have been observed. In conclusion, LT could be a good therapeutic option to improve the metabolic control and the quality of life of PA patients. Improved surgical strategies along with new techniques of interventional radiology allow us to perform the LT minimizing the complications derived from the higher risk of hepatic artery thrombosis.

Organic acidurias in adults: late complications and management

Organic acidurias (synonym, organic acid disorders, OADs) are a heterogenous group of inherited metabolic diseases delineated with the implementation of gas chromatography/mass spectrometry in metabolic laboratories starting in the 1960s and 1970s. Biochemically, OADs are characterized by accumulation of mono-, di- and/or tricarboxylic acids ("organic acids") and corresponding coenzyme A, carnitine and/or glycine esters, some of which are considered toxic at high concentrations. Clinically, disease onset is variable, however, affected individuals may already present during the newborn period with life-threatening acute metabolic crises and acute multi-organ failure. Tandem mass spectrometry-based newborn screening programmes, in particular for isovaleric aciduria and glutaric aciduria type 1, have significantly reduced diagnostic delay. Dietary treatment with low protein intake or reduced intake of the precursor amino acid(s), carnitine supplementation, cofactor treatment (in responsive patients) and nonadsorbable antibiotics is commonly used for maintenance treatment. Emergency treatment options with high carbohydrate/glucose intake, pharmacological and extracorporeal detoxification of accumulating toxic metabolites for intensified therapy during threatening episodes exist. Diagnostic and therapeutic measures have improved survival and overall outcome in individuals with OADs. However, it has become increasingly evident that the manifestation of late disease complications cannot be reliably predicted and prevented. Conventional metabolic treatment often fails to prevent irreversible organ dysfunction with increasing age, even if patients are considered to be "metabolically stable". This has challenged our understanding of OADs and has elicited the discussion on optimized therapy, including (early) organ transplantation, and long-term care.

Domino Liver Transplantation from a Child with Propionic Acidemia to a Child with Idiopathic Fulminant Hepatic Failure

Domino liver transplant has emerged as a viable strategy to increase the number of grafts available for transplantation. In the domino transplant organs explanted from one patient are transplanted into another patient. The first successful domino liver transplant was performed in Portugal in 1995. Since then this innovative concept has been applied to several genetic or biochemical disorders that are treated by liver transplantation. An important consideration during this operation is that such livers can pose a risk of the de novo development of the disease in the recipient. That is why this surgical procedure requires careful planning, proper selection of the patients, and informed consent of both donor and recipient.

Current strategies for the treatment of inborn errors of metabolism

Inborn errors of metabolism (IEMs) are a large group of inherited disorders characterized by disruption of metabolic pathways due to deficient enzymes, cofactors, or transporters. The rapid advances in the understanding of the molecular pathophysiology of many IEMs, have led to significant progress in the development of many new treatments. The institution and continued expansion of newborn screening provide the opportunity for early treatment, leading to reduced morbidity and mortality. This review provides an overview of the diverse therapeutic approaches and recent advances in the treatment of IEMs that focus on the basic principles of reducing substrate accumulation, replacing or enhancing absent or reduced enzyme or cofactor, and supplementing product deficiency. In addition, the challenges and obstacles of current treatment modalities and future treatment perspectives are reviewed and discussed.

Methylmalonic and propionic acidemias: clinical management update

PURPOSE OF REVIEW

Recent clinical studies and management guidelines for the treatment of the organic acidopathies methylmalonic acidemia (MMA) and propionic acidemia address the scope of interventions to maximize health and quality of life. Unfortunately, these disorders continue to cause significant morbidity and mortality due to acute and chronic systemic and end-organ injury.

RECENT FINDINGS

Dietary management with medical foods has been a mainstay of therapy for decades, yet well controlled patients can manifest growth, development, cardiac, ophthalmological, renal, and neurological complications. Patients with organic acidopathies suffer metabolic brain injury that targets specific regions of the basal ganglia in a distinctive pattern, and these injuries may occur even with optimal management during metabolic stress. Liver transplantation has improved quality of life and metabolic stability, yet transplantation in this population does not entirely prevent brain injury or the development of optic neuropathy and cardiac disease.

SUMMARY

Management guidelines should identify necessary screening for patients with methylmalonic acidemia and propionic acidemia, and improve anticipatory management of progressive end-organ disease. Liver transplantation improves overall metabolic control, but injury to nonregenerative tissues may not be mitigated. Continued use of medical foods in these patients requires prospective studies to demonstrate evidence of benefit in a controlled manner.

Disorders of branched chain amino acid metabolism

The three essential branched-chain amino acids (BCAAs), leucine, isoleucine and valine, share the first enzymatic steps in their metabolic pathways, including a reversible transamination followed by an irreversible oxidative decarboxylation to coenzyme-A derivatives. The respective oxidative pathways subsequently diverge and at the final steps yield acetyl- and/or propionyl-CoA that enter the Krebs cycle. Many disorders in these pathways are diagnosed through expanded newborn screening by tandem mass spectrometry. Maple syrup urine disease (MSUD) is the only disorder of the group that is associated with elevated body fluid levels of the BCAAs. Due to the irreversible oxidative decarboxylation step distal enzymatic blocks in the pathways do not result in the accumulation of amino acids, but rather to CoA-activated small carboxylic acids identified by gas chromatography mass spectrometry analysis of urine and are therefore classified as organic acidurias. Disorders in these pathways can present with a neonatal onset severe-, or chronic intermittent- or progressive forms. Metabolic instability and increased morbidity and mortality are shared between inborn errors in the BCAA pathways, while treatment options remain limited, comprised mainly of dietary management and in some cases solid organ transplantation.

Antibody-mediated rejection after ABO-incompatible pediatric living donor liver transplantation for propionic acidemia: A case report

We herein present the case of a four-yr-old boy with PA who developed AMR after ABO-incompatible LDLT despite undergoing B cell desensitization using rituximab. Although the CD19+ lymphocyte count decreased to 0.1% nine days after the administration of rituximab, he developed a high fever which was accompanied by arthralgia due to a streptococcal infection 13 days after rituximab prophylaxis. After the clearance of the infection, he underwent ABO-incompatible LDLT 36 days after the administration of rituximab. The CD19+ lymphocyte count just prior to LDLT was 1.2%. He developed AMR five days after LDLT, and the antidonor-type IgM and IgG antibody titers increased to 1:1024 and 1:1024, respectively. He was treated by plasma exchange, IVIG, steroid pulse therapy, and rituximab re-administration; however, his liver dysfunction continued. Despite intensive treatment, he died due to complicated abdominal hernia, acute renal failure, and ARDS. This case suggests that a streptococcal infection may induce the activation of innate immune responses; thus, additional desensitization therapy should be considered prior to ABO-incompatible LDLT if B cell reactivation is suspected.

Liver transplantation for pediatric inherited metabolic disorders: Considerations for indications, complications, and perioperative management

LT is an effective therapeutic option for a variety of IEM. This approach can significantly improve the quality of life of patients who suffer from severe disease manifestations and/or life-threatening metabolic decompensations despite medical/dietary management. Due to the significant risks for systemic complications from surgical stressors, careful perioperative management is vital. Even after LT, some disorders require long-term dietary restriction, medical management, and monitoring of metabolites. Successful liver transplant for these complex disorders can be achieved with disease- and patient-specific strategies using a multidisciplinary approach. In this article, we review indications, complications, perioperative management, and long-term follow-up recommendations for IEM that are treatable with LT.

Anaesthetic considerations for liver transplantation in propionic acidemia

Propionic acidemia (PA) is an autosomal recessive disorder of metabolism due to deficiency of the enzyme propionyl-CoA carboxylase (PCC) that converts propionyl-CoA to methylmalonyl-CoA with the help of the cofactor biotin inside the mitochondria. The resultant accumulation of propionyl-CoA causes severe hyperammonaemia and life-threatening metabolic acidosis. Based on the positive outcomes, liver transplantation is now recommended for individuals with recurrent episodes of hyperammonaemia or acidosis that is not adequately controlled with appropriate medical therapies. We report anaesthetic management of two children with PA for liver transplantation at our institution. It is essential for the anaesthesiologist, caring for these individuals to be familiar with the manifestations of the disease, the triggers for decompensation and management of an acute episode.

Long-term sex-biased correction of circulating propionic acidemia disease markers by adeno-associated virus vectors

Propionic academia (PA) occurs because of mutations in the PCCA or PCCB genes encoding the two subunits of propionyl-CoA carboxylase, a pivotal enzyme in the breakdown of certain amino acids and odd-chain fatty acids. There is no cure for PA, but dietary protein restriction and liver transplantation can attenuate its symptoms. We show here that a single intravenous injection of adeno-associated virus 2/8 (AAV8) or AAVrh10 expressing PCCA into PA hypomorphic mice decreased systemic propionylcarnitine and methyl citrate for up to 1.5 years. However, long-term phenotypic correction was always better in male mice. AAV-mediated PCCA expression was similar in most tissues in males and females at early time points and differed only in the liver. Over 1.5 years, luciferase and PCCA expression remained elevated in cardiac tissue for both sexes. In contrast, transgene expression in the liver and skeletal muscles of female, but not male, mice waned—suggesting that these tissues were major sinks for systemic phenotypic correction. These data indicate that single systemic intravenous therapy by AAV vectors can mediate long-term phenotype correction for PA. However, tissue-specific loss of expression in females reduces efficacy when compared with males. Whether similar sex-biased AAV effects occur in human gene therapy remains to be determined.

Reversal of cardiomyopathy in propionic acidemia after liver transplantation: a 10-year follow-up

Cardiomyopathy is a frequent complication in propionic acidemia. It is mostly rapidly fatal and independent of the metabolic control or medical intervention. Here, we present the reversal of a severe cardiomyopathy after liver transplantation in a patient with propionic acidemia and the long-term stability after ten years. Liver transplantation in patients with propionic acidemia may be considered a valid and long-lasting treatment when cardiomyopathy is progressive and unresponsive to medical therapy.

Early and late complications after liver transplantation for propionic acidemia in children: a two centers study

Propionic acidemia (PA) is a severe metabolic disorder with cardiac and neurologic complications and a poor quality of life. Liver transplantation (LT) was thus proposed in PA to increase enzyme activity. We studied retrospectively LT in PA in two European centers. Twelve patients underwent 17 LTs between 1991 and 2013. They developed severe, unusual and unexpected complications, with high mortality (58%). When present, the cardiomyopathy resolved and no acute metabolic decompensation occurred allowing dietary relaxation. Renal failure was present in half of the patients before LT and worsened in all of them. We suggest that cardiac and renal functions should be assessed before LT and monitored closely afterward. A renal sparing immunosuppression should be used. We speculate that some complications may be related to accumulated toxicity of the disease and that earlier LT could prevent some of these consequences. As kidney transplantation has been performed successfully in methylmalonic acidemia, a metabolic disease in the same biochemical pathway, the choice of the organ to transplant could be further discussed.

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.

Effects of adeno-associated virus serotype and tissue-specific expression on circulating biomarkers of propionic acidemia

Propionic acidemia (PA) is an autosomal recessive inborn error of metabolism caused by deficiency of propionyl-CoA carboxylase (PCC). This enzyme is composed of six PCCA and six PCCB subunits and mediates a critical step in catabolism of odd chain fatty acids and certain amino acids. Current treatment options for PA are limited to stringent dietary restriction of protein consumption and some patients undergo elective liver transplantation. We previously generated a hypomorphic model of PA, designated Pcca(-/-)(A138T), with 2% of wild-type enzyme activity that mimics many aspects of the human disease. In this study, we used the differing tissue tropisms of adeno-associated virus (AAV) to probe the ability of liver or muscle-directed gene therapy to treat systemic aspects of this disease that affects many cell types. Systemic therapy with muscle-biased AAV1, liver-biased AAV8, and broadly tropic AAVrh10 mediated significant biochemical corrections in circulating propionylcarnitine (C3) and methyl citrate by all vectors. The innate tissue bias of AAV1 and AAV8 gene expression was made more specific by the use of muscle-specific muscle creatine kinase (specifically MCK6) and hepatocyte-specific transthyretin (TTR) promoters, respectively. Under these targeted conditions, both vectors mediated significant long-term correction of circulating metabolites, demonstrating that correction of muscle and likely other tissue types in addition to liver is necessary to fully correct pathology caused by PA. Liver-specific AAV8-TTR-PCCA mediated better correction than AAV1-MCK-PCCA. These data suggest that targeted gene therapy may be a viable alternative to liver transplantation for PA. They also demonstrate the effects of tissue-specific and broad gene therapy on a cell autonomous systemic genetic disease.

Liver transplantation for pediatric metabolic disease

Liver transplantation (LTx) was initially developed as a therapy for liver diseases known to be associated with a high risk of near-term mortality but is based upon a different set of paradigms for inborn metabolic diseases. As overall outcomes for the procedure have improved, LTx has evolved into an attractive approach for a growing number of metabolic diseases in a variety of clinical situations. No longer simply life-saving, the procedure can lead to a better quality of life even if not all symptoms of the primary disorder are eliminated. Juggling the risk-benefit ratio thus has become more complicated as the list of potential disorders amenable to treatment with LTx has increased. This review summarizes presentations from a recent conference on metabolic liver transplantation held at the Children's Hospital of Pittsburgh of UPMC on the role of liver or hepatocyte transplantation in the treatment of metabolic liver disease.

Intractable metabolic acidosis in a child with propionic acidemia undergoing liver transplantation -a case report-

Propionic acidemia (PA) is a rare autosomal recessive disorder of metabolism caused by deficient activity of the mitochondrial enzyme propionyl-CoA carboxylase. The clinical manifestations are metabolic acidosis, poor feeding, lethargy, vomiting, osteoporosis, neurological dysfunction, pancytopenia, developmental retardation and cardiomyopathy. Liver transplantation has recently been considered as one of the treatment options for patients with PA. This case report describes several anesthetic considerations for patients with PA undergoing liver transplantation. Understanding the patient's status and avoiding events that may precipitate metabolic acidosis are important for anesthetic management of patients with PA. In conclusion, anesthesia should be focused on minimizing the severity of metabolic acidosis with following considerations: (1) maintaining optimal tissue perfusion by avoiding hypotension, (2) preventing hypoglycemia, and (3) providing bicarbonate to compensate for the acidosis.

Monogenic diseases that can be cured by liver transplantation

While the prevalence of most diseases caused by single-gene mutations is low and defines them as rare conditions, all together, monogenic diseases account for approximately 10 in every 1000 births according to the World Health Organisation. Orthotopic liver transplantation (LT) could offer a therapeutic option in monogenic diseases in two ways: by substituting for an injured liver or by supplying a tissue that can replace a mutant protein. In this respect, LT may be regarded as the correction of a disease at the level of the dysfunctional protein. Monogenic diseases that involve the liver represent a heterogeneous group of disorders. In conditions associated with predominant liver parenchymal damage (i.e., genetic cholestatic disorders, Wilson's disease, hereditary hemochromatosis, tyrosinemia, α1 antitrypsin deficiency), hepatic complications are the major source of morbidity and LT not only replaces a dysfunctional liver but also corrects the genetic defect and effectively cures the disease. A second group includes liver-based genetic disorders characterised by an architecturally near-normal liver (urea cycle disorders, Crigler-Najjar syndrome, familial amyloid polyneuropathy, primary hyperoxaluria type 1, atypical haemolytic uremic syndrome-1). In these defects, extrahepatic complications are the main source of morbidity and mortality while liver function is relatively preserved. Combined transplantation of other organs may be required, and other surgical techniques, such as domino and auxiliary liver transplantation, have been attempted. In a third group of monogenic diseases, the underlying genetic defect is expressed at a systemic level and liver involvement is just one of the clinical manifestations. In these conditions, LT might only be partially curative since the abnormal phenotype is maintained by extrahepatic synthesis of the toxic metabolites (i.e., methylmalonic acidemia, propionic acidemia). This review focuses on principles of diagnosis, management and LT results in both paediatric and adult populations of selected liver-based monogenic diseases, which represent examples of different transplantation strategies, driven by the understanding of the expression of the underlying genetic defect.

Generation of a hypomorphic model of propionic acidemia amenable to gene therapy testing

Propionic acidemia (PA) is a recessive genetic disease that results in an inability to metabolize certain amino acids and odd-chain fatty acids. Current treatment involves restricting consumption of these substrates or liver transplantation. Deletion of the Pcca gene in mice mimics the most severe forms of the human disease. Pcca(-) mice die within 36 hours of birth, making it difficult to test intravenous systemic therapies in them. We generated an adult hypomorphic model of PA in Pcca(-) mice using a transgene bearing an A138T mutant of the human PCCA protein. Pcca(-/-)(A138T) mice have 2% of wild-type PCC activity, survive to adulthood, and have elevations in propionyl-carnitine, methylcitrate, glycine, alanine, lysine, ammonia, and markers associated with cardiomyopathy similar to those in patients with PA. This adult model allowed gene therapy testing by intravenous injection with adenovirus serotype 5 (Ad5) and adeno-associated virus 2/8 (AAV8) vectors. Ad5-mediated more rapid increases in PCCA protein and propionyl-CoA carboxylase (PCC) activity in the liver than AAV8 and both vectors reduced propionylcarnitine and methylcitrate levels. Phenotypic correction was transient with first generation Ad whereas AAV8-mediated long-lasting effects. These data suggest that this PA model may be a useful platform for optimizing systemic intravenous therapies for PA.

Genetics and metabolic cardiomyopathies

Metabolic disorders encompass a heterogeneous group of conditions that commonly affect the heart and contribute adversely to cardiovascular outcomes. As the heart is a metabolically active organ, inborn errors in metabolism (IEMs) often present with cardiac manifestations such as cardiomyopathy, arrhythmia, and valvular dysfunction. More than 40 IEMs are reported to cause cardiomyopathy, including fatty acid oxidation defects, glycogen, lysosomal and perioxisome storage diseases, mitochondrial cardiomyopathies, organic acidaemias, aminoacidopathies and congenital disorders of glycosylation. Studies suggest that IEM account for only 5% of cardiomyopathies; however, their diagnosis is imperative to enable the effective institution of disease-specific management strategies. This review describes the more common genetic defects that affect metabolic pathways and give rise to heart muscle disease.

Improved neurologic prognosis for a patient with propionic acidemia who received early living donor liver transplantation

Despite medical therapy, patients with propionic academia (PA) still display a tendency to develop epilepsy. Patients with neonatal-onset PA who have received early living donor liver transplantation (LDLT) are limited in number, and the effect on neurologic prognosis, including epilepsy, is not clear. We report a patient with PA whose EEG findings improved dramatically after undergoing LDLT at age 7 months. The patient's neurologic development and brain MRI findings were quite satisfactory at age 2 years and 3 months. LDLT is effective not only in preventing metabolic decompensation, but also in improving neurologic function to ensure better quality of life.

Living-donor liver transplantation for propionic acidemia

Propionic acidemia is a rare autosomal recessive disorder affecting the catabolism of branched-chain amino acids because of a genetic defect in PCC. Despite the improvements in medical treatment with protein restriction, sufficient caloric intake, supplementation of l-carnitine, and metronidazole, patients with the severe form of propionic acidemia have life-threatening metabolic acidosis, hyperammonemia, and cardiomyopathy, which results in serious neurologic sequelae and sometimes death. This study retrospectively reviewed three children with neonatal-onset propionic acidemia who received LDLT. Between November 2005 and December 2010, 148 children underwent LDLT, with an overall patient survival of 90.5%, in our center. Three patients were indicated for transplantation because of propionic acidemia. All recipients achieved a resolution of metabolic derangement and better quality of life with protein restriction and medication, although urine methylcitrate and serum propionylcarnitine levels did not decrease markedly. LT can reduce the magnitude of progressive cardiac/neurologic disability as a result of poor metabolic control. Further evaluation is therefore required to determine the long-term suitability of this treatment modality.

Chronic management and health supervision of individuals with propionic acidemia

Propionic acidemia is a relatively rare inborn error of metabolism. Individuals with propionic acidemia often have life-threatening episodes of hyperammonemia and metabolic acidosis, as well as intellectual disability. There are many reports of additional problems, including poor growth, stroke-like episodes of the basal ganglia, seizures, cardiomyopathy, long QTc syndrome, immune defects, pancreatitis and optic neuropathy; however, there is little information about the incidence of these problems in this rare disease. Additionally, there are no clear guidelines for medical or surgical management of individuals with propionic acidemia. Through a comprehensive and systematic review of the current medical literature and survey of expert opinion, we have developed practice guidelines for the chronic management of individuals with propionic acidemia, including dietary therapy, use of medications, laboratory monitoring, chronic health supervision, use of gastrostomy tubes and liver transplantation.