The Role of Liver Transplantation in Propionic Acidemia

An Early Cost-Utility Model of mRNA-Based Therapies for the Treatment of Methylmalonic and Propionic Acidemia in the United Kingdom

BACKGROUND AND OBJECTIVE

Novel messenger RNA (mRNA)-based therapies, currently in development, are emerging as a promising potential treatment modality for a broad range of life-threatening and life-limiting inherited liver diseases, including methylmalonic acidemia (MMA) and propionic acidemia (PA). However, owing in part to their complexity, they are likely to come at considerable financial cost to healthcare systems. The objective of this research was to synthesize available evidence on the costs and clinical consequences associated with MMA and PA for the purpose of exploratory economic evaluation of novel mRNA-based therapies using an early cost-utility model from the United Kingdom payer perspective.

METHODS

A Markov model was constructed to simulate the costs and outcomes associated with novel mRNA therapies, compared with a combination of dietary management and organ transplantation (standard of care) among hypothetical cohorts of new-born patients with MMA and PA. Key model drivers were identified, and a price threshold analysis was performed to estimate value-based price ranges for future mRNA therapies given willingness-to-pay thresholds for orphan diseases.

RESULTS

mRNA therapy was associated with an additional 5.7 and 1.3 quality-adjusted life-years (QALYs) gained per patient lifetime among patients with MMA and PA, respectively. Key drivers of cost-effectiveness were relative improvement in utility among patients who receive mRNA-based therapy and transplantation, and the cost of mRNA therapy. Assuming a willingness to pay range of £100,000-£300,000 per QALY gained, the model demonstrated mRNA therapy to be cost-effective in MMA and PA at an annual treatment cost of £70,452-£94,575 and £31,313-£36,695, respectively.

CONCLUSIONS

Despite the lack of a strong evidence base in MMA and PA, this model provides a useful tool to estimate the cost-effectiveness, and inform value-based pricing, of new mRNA-based therapies. Our analyses also identified areas for research that will have the greatest value in reducing uncertainty in future health economic evaluations of such treatments.

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.

Relief of CoA sequestration and restoration of mitochondrial function in a mouse model of propionic acidemia

Propionic acidemia (PA, OMIM 606054) is a devastating inborn error of metabolism arising from mutations that reduce the activity of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). The defects in PCC reduce the concentrations of nonesterified coenzyme A (CoASH), thus compromising mitochondrial function and disrupting intermediary metabolism. Here, we use a hypomorphic PA mouse model to test the effectiveness of BBP-671 in correcting the metabolic imbalances in PA. BBP-671 is a high-affinity allosteric pantothenate kinase activator that counteracts feedback inhibition of the enzyme to increase the intracellular concentration of CoA. Liver CoASH and acetyl-CoA are depressed in PA mice and BBP-671 treatment normalizes the cellular concentrations of these two key cofactors. Hepatic propionyl-CoA is also reduced by BBP-671 leading to an improved intracellular C3:C2-CoA ratio. Elevated plasma C3:C2-carnitine ratio and methylcitrate, hallmark biomarkers of PA, are significantly reduced by BBP-671. The large elevations of malate and α-ketoglutarate in the urine of PA mice are biomarkers for compromised tricarboxylic acid cycle activity and BBP-671 therapy reduces the amounts of both metabolites. Furthermore, the low survival of PA mice is restored to normal by BBP-671. These data show that BBP-671 relieves CoA sequestration, improves mitochondrial function, reduces plasma PA biomarkers, and extends the lifespan of PA mice, providing the preclinical foundation for the therapeutic potential of BBP-671.

Therapeutic potential of living donor liver transplantation from heterozygous carrier donors in children with propionic acidemia

Background

Current world experience regarding living donor liver transplantation (LDLT) in the treatment of propionic acidemia (PA) is limited, especially in terms of using obligate heterozygous carriers as donors. This study aimed to evaluate the clinical outcomes of LDLT in children with PA.

Methods

From November 2017 to January 2020, 7 of the 192 children who underwent LDLT at our institution had been diagnosed with PA (median age, 2.1 years; range, 1.1–5.8 years). The primary indication for transplantation was frequent metabolic decompensations in 6 patients and preventative treatment in 1 patient. Of the seven parental living donors, six were genetically proven obligate heterozygous carriers.

Results

During a median follow-up of 23.9 months (range, 13.9–40.2 months), all patients were alive with 100% allograft survival, and no severe transplant-related complications occurred. In the case of liberalized protein intake, they did not suffer metabolic decompensation or disease-related complications and made progress in neurodevelopmental delay and body growth, as well as blood and urinary metabolite levels. In one patient with pre-existing mild dilated cardiomyopathy, her echocardiogram results completely normalized 13.8 months post-transplant. All living donors recovered well after surgery, with no metabolic decompensations or procedure-related complications. Western blotting revealed that the hepatic expressions of PCCA and PCCB in one of the heterozygous donors were comparable to those of the normal healthy control at the protein level.

Conclusions

LDLT using partial liver grafts from asymptomatic obligate heterozygous carrier donors is a viable therapeutic option for selected PA patients, with no negative impact on donors’ and recipients' clinical courses.

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

[Figure: see text].

Liver transplantation in children with inborn errors of metabolism: 30 years experience in NSW, Australia

BACKGROUND

Inborn errors of metabolism (IEM) are a diverse group of genetic disorders that can result in significant morbidity and sometimes death. Metabolic management can be challenging and burdensome for families. Liver transplantation (LT) is increasingly being considered a treatment option for some IEMs. IEMs are now considered the second most common reason for pediatric LT.

AIM

To review the data of all children with an IEM who had LT at The Children's Hospital at Westmead (CHW), NSW, Australia between January 1986 and January 2019.

METHODS

Retrospective data collected from the medical records and genetic files included patient demographics, family history, parental consanguinity, method of diagnosis of IEM, hospital and intensive care unit admissions, age at LT, graft type, clinical outcomes and metabolic management pre and post-LT.

RESULTS

Twenty-four LT were performed for 21 patients. IEM diagnoses were MSUD (n = 4), UCD (n = 8), OA (n = 6), TYR type I (n = 2) and GSD Ia (n = 1). Three patients had repeat transplants due to complications. Median age at transplant was 6.21 years (MSUD), 0.87 years (UCD), 1.64 years (OA) and 2.2 years (TYR I). Two patients died peri-operatively early in the series, one died 3 months after successful LT due to septicemia. Eighteen LTs have been performed since 2008 in comparison to six LT prior to 2008. Dietary management was liberalized post LT for all patients.

CONCLUSIONS

Referral for LT for IEMs has increased over the last 33 years, with the most referrals in the last 10 years. Early LT has resulted in improved clinical outcomes and patient survival.

Pediatric metabolic liver diseases: Evolving role of liver transplantation

Metabolic liver diseases (MLD) are the second most common indication for liver transplantation (LT) in children. This is based on the fact that the majority of enzymes involved in various metabolic pathways are present within the liver and LT can cure or at least control the disease manifestation. LT is also performed in metabolic disorders for end-stage liver disease, its sequelae including hepatocellular cancer. It is also performed for preventing metabolic crisis’, arresting progression of neurological dysfunction with a potential to reverse symptoms in some cases and for preventing damage to end organs like kidneys as in the case of primary hyperoxalosis and methyl malonic acidemia. Pathological findings in explant liver with patients with metabolic disease include unremarkable liver to steatosis, cholestasis, inflammation, variable amount of fibrosis, and cirrhosis. The outcome of LT in metabolic disorders is excellent except for patients with mitochondrial disorders where significant extrahepatic involvement leads to poor outcomes and hence considered a contraindication for LT. A major advantage of LT is that in the post-operative period most patients can discontinue the special formula which they were having prior to the transplant and this increases their well-being and improves growth parameters. Auxiliary partial orthotopic LT has been described for patients with noncirrhotic MLD where a segmental graft is implanted in an orthotopic position after partial resection of the native liver. The retained native liver can be the potential target for future gene therapy when it becomes a clinical reality.

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.

Gene diagnosis and pedigree analysis of two Han ethnicity families with propionic acidemia in Fujian

Propionic acidemia is associated with pathogenic variants in PCCA or PCCB gene. We investigated the potential pathogenic variants in PCCA or PCCB genes in Fujian Han population.Two probands and their families of Han ethnicity containing two generations were subject to newborn screening using tandem mass spectrometry, followed by diagnosis using urine gas chromatography mass spectrometry. Sanger sequencing was used to identify potential mutations in PCCA and PCCB genes.Compound heterozygous variants were identified in PCCB gene in two siblings of the first family, the youngest girl showed a novel missense variant c.1381G>C (p.Ala461Pro) in exon 13 and a heterozygous missense variant c.1301C>T (p.Ala434Val) in exon 13, which were inherited respectively from their parents. The oldest boy is a carrier with a novel missense variant c.1381G>C (p.Ala461Pro) in exon 13 which were inherited from his father. In the second family, c.1535G>A homozygous mutations were identified in the baby girl, which were inherited respectively from their parents. In silico analysis, several different types of bioinformatic software were utilized, which predicted that the novel variant c.1381G>C in PCCB gene was damaged. According to ACMG principle, the missense variant c.1381G>C (p.Ala461Pro) in exon 13 was a Variant of Undetermined Significance (VUS).One novel missense variant and two missense variants in PCCB gene were identified in the study. The novel variant of PCCB gene identified VUS was identified for the first time in the Chinese population, which enriched the mutational spectrum of PCCB gene.

Living Related Liver Transplantation for Metabolic Liver Diseases in Children

ABSTRACT

Metabolic liver diseases (MLDs) are a heterogeneous group of inherited conditions for which liver transplantation can provide definitive treatment. The limited availability of deceased donor organs means some who could benefit from transplant do not have this option. Living related liver transplant (LrLT) using relatives as donors has emerged as one solution to this problem. This technique is established worldwide, especially in Asian countries, with shorter waiting times and patient and graft survival rates equivalent to deceased donor liver transplantation. However, living donors are underutilized for MLDs in many western countries, possibly due to the fear of limited efficacy using heterozygous donors. We have reviewed the published literature and shown that the use of heterozygous donors for liver transplantation is safe for the majority of MLDs with excellent metabolic correction. The use of LrLT should be encouraged to complement deceased donor liver transplantation (DDLT) for treatment of MLDs.

Liver Transplantation for Propionic Acidemia: Evidence from A Systematic Review and Meta-analysis

BACKGROUND

The worldwide experience of liver transplantation (LT) in the treatment of propionic acidemia (PA) remains limited and fragmented. This review aims to provide a comprehensive and quantitative understanding of post-transplant clinical outcomes in PA patients.

METHODS

MEDLINE, Embase and the Cochrane Library databases were searched for studies focusing on PA patients who underwent LT. The pooled estimate rates and 95% confidence intervals (CIs) were calculated using a random-effects model with Freeman-Tukey double arcsine transformation.

RESULTS

Twenty-one studies involving 70 individuals were included. The pooled estimate rates were 0.95 (95% CI, 0.80-1.00) for patient survival and 0.91 (95% CI, 0.72-1.00) for allograft survival. The pooled estimate rates were 0.20 (95% CI, 0.05-0.39) for rejection, 0.08 (95% CI, 0.00-0.21) for hepatic artery thrombosis, 0.14 (95% CI, 0.00-0.37) for cytomegalovirus/Epstein-Barr virus infection and 0.03 (95% CI, 0.00-0.15) for biliary complications. The pooled estimate rates were 0.98 (95% CI, 0.88-1.00) for metabolic stability, 1.00 (95% CI, 0.79-1.00) for reversal of pre-existing cardiomyopathy and 0.97 (95% CI, 0.78-1.00) for improvement of neurodevelopmental delay. A large proportion of patients achieved liberalization of protein intake posttransplant [pooled estimate rate 0.66 (95% CI, 0.35-0.93)].

CONCLUSIONS

Despite the risk of transplant-related complications, LT is a viable therapeutic option in PA patients, with satisfactory survival rates and clinical outcomes. Given the diversity in neurological assessment methods and the inconsistency in achievement of dietary protein liberalization across different studies, consensus on neurological evaluation methods and post-transplant protein intake is necessary. Longer-term clinical outcomes of LT for PA warrants further investigation.

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.

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.

Chronic kidney disease in propionic acidemia

Purpose

Propionic acidemia (PA) is a severe metabolic disorder characterized by multiorgan pathology, including renal disease. The prevalence of chronic kidney disease (CKD) in PA patients and factors associated with CKD in PA are not known.

Methods

Thirty-one subjects diagnosed with PA underwent laboratory and clinical evaluations through a dedicated natural history study at the NIH (ClinicalTrials.gov identifier: NCT02890342).

Results

Cross-sectional analysis of the creatinine-based estimated glomerular filtration rate (eGFR) in subjects with native kidneys revealed an age-dependent decline in renal function (P <0.002). Among adults with PA, 4/8 (50%) had eGFR <60 mL/min/1.73 m². There was a significant discrepancy between eGFRs calculated using estimating equations based on serum creatinine compared to serum cystatin C (P <0.0001). The tubular injury marker, plasma lipocalin-2, and plasma uric acid were strongly associated with CKD (P <0.0001). The measured 24-hour creatinine excretion was below normal, even after adjusting for age, height, and sex.

Conclusions

CKD is common in adults with PA and is associated with age. The poor predictive performance of standard eGFR estimating equations, likely due to reduced creatine synthesis in kidney and liver, could delay the recognition of CKD and management of ensuing complications in this population.