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

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.

Cardiac RNase Z edited via CRISPR-Cas9 drives heart hypertrophy in Drosophila

Cardiomyopathy (CM) is a group of diseases distinguished by morphological and functional abnormalities in the myocardium. It is etiologically heterogeneous and may develop via cell autonomous and/or non-autonomous mechanisms. One of the most severe forms of CM has been linked to the deficiency of the ubiquitously expressed RNase Z endoribonuclease. RNase Z cleaves off the 3'-trailer of both nuclear and mitochondrial primary tRNA (pre-tRNA) transcripts. Cells mutant for RNase Z accumulate unprocessed pre-tRNA molecules. Patients carrying RNase Z variants with reduced enzymatic activity display a plethora of symptoms including muscular hypotonia, microcephaly and severe heart hypertrophy; still, they die primarily due to acute heart decompensation. Determining whether the underlying mechanism of heart malfunction is cell autonomous or not will provide an opportunity to develop novel strategies of more efficient treatments for these patients. In this study, we used CRISPR-TRiM technology to create Drosophila models that carry cardiomyopathy-linked alleles of RNase Z only in the cardiomyocytes. We found that this modification is sufficient for flies to develop heart hypertrophy and systolic dysfunction. These observations support the idea that the RNase Z linked CM is driven by cell autonomous mechanisms.

Evaluation of Right Ventricular Function in Patients with Propionic Acidemia-A Cross-Sectional Study

(1) Background: In propionic acidemia (PA), myocardial involvement often leads to progressive cardiac dysfunction of the left ventricle (LV). Cardiomyopathy (CM) is an important contributor to mortality. Although known to be of prognostic value in CM, there are no published data on right ventricular (RV) function in PA patients. (2) Methods: In this cross-sectional single-center study, systolic and diastolic RV function of PA patients was assessed by echocardiography, including frequency, onset, and combinations of echocardiographic parameters, as well as correlations to LV size and function. (3) Results: N = 18 patients were enrolled. Tricuspid annulus S' was abnormal in 16.7%, RV-longitudinal strain in 11.1%, tricuspid annular plane systolic excursion (TAPSE) in 11.1%, Tricuspid valve (TV) E/e' in 33.3%, and TV E/A in 16.7%. The most prevalent combinations of pathological parameters were TV E/A + TV E/e' and TAPSE + TV S'. With age, the probability of developing abnormal RV function increases according to age-dependent normative data. There is a significant correlation between TAPSE and mitral annular plane systolic excursion (MAPSE), and RV/LV-longitudinal strain (p ≤ 0.05). N = 5 individuals died 1.94 years (mean) after cardiac evaluation for this study, and all had abnormal RV functional parameters. (4) Conclusions: Signs of diastolic RV dysfunction can be found in up to one third of individuals, and systolic RV dysfunction in 16.7% of individuals in our cohort. RV function is impaired in PA patients with a poor outcome. RV functional parameters should be used to complement clinical and left ventricular echocardiographic findings.

Detection of early cardiac disease manifestation in propionic acidemia - Results of a monocentric cross-sectional study

BACKGROUND

In propionic acidemia (PA) myocardial involvement is common and includes development of cardiomyopathy, life-threatening acute heart failure, and acquired long-QT syndrome. We sought to investigate which echocardiographic parameters of left ventricular systolic and diastolic function indicate early cardiac disease manifestation in PA.

METHODS

This is a prospective observational study (cross-sectional design) in a Tertiary Medical Care Center. Individuals with confirmed PA were enrolled and the following cardiac investigations were performed in all study individuals: echocardiographic measurements of systolic and diastolic left ventricular (LV) function (LV fractional shortening (LV-FS), LV ejection fraction by biplane modified Simpson's (LV-EF), mitral annular plane systolic excursion (MAPSE), LV global longitudinal strain (LV-GLS) by speckle tracking echocardiography (STE), pulsed Doppler analyses of mitral valve (MV) inflow velocities (MV E/A) and MV deceleration time (DT-E), tissue doppler imaging (TDI) of the mitral annulus (MV E/e'), and LV myocardial performance index (LV-MPI)). LV and left atrial (LA) diameters were assessed. 12‑lead electrocardiograms (ECG) were recorded and corrected QT intervals (QTc) calculated. Clinical phenotype and laboratory parameters at the time of cardiac investigation were assessed. Besides descriptive analyses we analyzed frequency, onset, and combinations of echocardiographic and ECG data as well as their correlations with clinical and biochemical findings. The effects of 'age at visit' and LV functional parameters on QTc were analyzed with multiple regression.

RESULTS

A total of 18 patients with confirmed PA were enrolled. Median age at PA onset was 6 days (range 1-357 days). Median age at visit for cardiac evaluation was 13.1 years (range 0.6-28.1 years). LV-GLS was abnormal in 72.2%, LV-EF in 61.1%, MAPSE in 50%, MV E/e' in 44.4%, LV-MPI in 33.3%, LV-FS in 33.3%, and MV E/A in 27.8%. In cases with normal or near normal LV-FS, LV-GLS was pathological in 5/10, LV-EF in 4/10, and MAPSE in 3/10. The probability of developing LV dysfunction - systolic and diastolic - increases with age. LV-MPI is a reliable parameter to indicate systolic LV-dysfunction in combination with a dilated LV, i. e. dilated cardiomyopathy (DCM) in PA. Multiple regression reveals a significant positive association between LV diameters and QTc. Abnormal LV-GLS significantly correlates with reduced muscle strength, muscle tone and/or abnormal gross motor function.

CONCLUSIONS

Our data suggests a high prevalence of cardiac disease manifestation in PA, considerably higher than in previous studies, where only LV-FS was used to assess LV function. Usage of advanced echocardiographic techniques, such as LV-GLS assessment, may allow for early detection of subtle LV dysfunction in PA, and may lead to timely cardiac treatment but also consideration of liver transplantation to prevent development of manifest cardiac complications.

Successful heart transplantation in a patient with adolescent-onset dilated cardiomyopathy secondary to propionic acidaemia: a case report

BACKGROUND

Propionic acidaemia (PA) is an autosomal recessive disorder resulting from deficiency of propionyl-CoA carboxylase, a mitochondrial enzyme that metabolizes propionyl-CoA. Generally, patients with PA develop symptoms in the neonatal period due to protein intake through breastfeeding; however, late-onset PA with atypical symptoms, including cardiomyopathy, has been recently reported.

CASE SUMMARY

We present the case of a 25-year-old male with late-onset PA complicated by advanced heart failure (HF) due to isolated secondary dilated cardiomyopathy, who required left ventricular assist device (LVAD) implantation and finally underwent heart transplantation (HTx). Initially, the patient developed HF at the age of 16 and was diagnosed with mitochondrial cardiomyopathy. Due to refractory HF, he underwent an LVAD implantation and was scheduled for HTx. During the preoperative period for HTx, the patient suffered from sepsis due to the worsening of LVAD driveline exit-site infection complicated by overt metabolic acidosis, finally leading to the diagnosis of late-onset PA. After this diagnosis, adequate nutritional interventions were introduced, and the cardiac function was partially restored enough for him to be weaned-off LVAD; however, the patient became inotrope dependent and underwent HTx. The post-HTx course was uneventful with special nutritional management, and he has experienced no adverse metabolic events in the past 3 years.

DISCUSSION

Late-onset PA can cause isolated adult-onset cardiomyopathy, and LVAD or HTx should be considered when PA is complicated by advanced HF and is unresponsive to conventional medical therapies.

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.

Metabolic perturbations mediated by propionyl-CoA accumulation in organs of mouse model of propionic acidemia

Propionic acidemia (PA) is an autosomal recessive metabolic disorder after gene encoding propionyl-CoA carboxylase, Pcca or Pccb, is mutated. This genetic disorder could develop various complications which are ascribed to dysregulated propionyl-CoA metabolism in organs. However, the effect of attenuated PCC on propionyl-CoA metabolism in different organs remains to be fully understood. We investigated metabolic perturbations in organs of Pcca^-/-(A138T) mice (a mouse model of PA) under chow diet and acute administration of [¹³C₃]propionate to gain insight into pathological mechanisms of PA. With chow diet, the metabolic alteration is organ dependent. l-Carnitine reduction induced by propionylcarnitine accumulation only occurs in lung and liver of Pcca^-/- (A138T) mice. [¹³C₃]Propionate tracing data demonstrated that PCC activity was dramatically reduced in Pcca^-/-(A138T) brain, lung, liver, kidney, and adipose tissues, but not significantly changed in Pcca^-/-(A138T) muscles (heart and skeletal muscles) and pancreas, which was largely supported by PCCA expression data. The largest expansion of propionylcarnitine in Pcca^-/-(A138T) heart after acute administration of propionate indicated the vulnerability of heart to high circulating propionate. The overwhelming propionate in blood also stimulated ketone production from the increased fatty acid oxidation in Pcca^-/-(A138T) liver by lowering malonyl-CoA, which has been observed in cases where metabolic decompensation occurs in PA patients. This work shed light on organ-specific metabolic alternations under varying severities of PA.

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.

Dual mRNA therapy restores metabolic function in long-term studies in mice with propionic acidemia

Propionic acidemia/aciduria (PA) is an ultra-rare, life-threatening, inherited metabolic disorder caused by deficiency of the mitochondrial enzyme, propionyl-CoA carboxylase (PCC) composed of six alpha (PCCA) and six beta (PCCB) subunits. We herein report an enzyme replacement approach to treat PA using a combination of two messenger RNAs (mRNAs) (dual mRNAs) encoding both human PCCA (hPCCA) and PCCB (hPCCB) encapsulated in biodegradable lipid nanoparticles (LNPs) to produce functional PCC enzyme in liver. In patient fibroblasts, dual mRNAs encoded proteins localize in mitochondria and produce higher PCC enzyme activity vs. single (PCCA or PCCB) mRNA alone. In a hypomorphic murine model of PA, dual mRNAs normalize ammonia similarly to carglumic acid, a drug approved in Europe for the treatment of hyperammonemia due to PA. Dual mRNAs additionally restore functional PCC enzyme in liver and thus reduce primary disease-associated toxins in a dose-dependent manner in long-term 3- and 6-month repeat-dose studies in PA mice. Dual mRNAs are well-tolerated in these studies with no adverse findings. These studies demonstrate the potential of mRNA technology to chronically administer multiple mRNAs to produce large complex enzymes, with applicability to other genetic disorders.

Propionic acidemia is a serious pediatric inherited disorder with no effective treatments. Here the authors demonstrate that delivering dual mRNAs as an enzyme replacement approach can be used as an effective therapy in a mouse model of propionic acidemia, with potential applicability to chronically administer multiple mRNAs in other genetic disorders.

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.

Cardiac phenotype in propionic acidemia - Results of an observational monocentric study

BACKGROUND

Propionic acidemia (PA) is an organic aciduria caused by inherited deficiency of propionyl-CoA carboxylase. Left ventricular dysfunction and QT prolongation may lead to life-threatening complications. Systematic analyses of cardiac phenotypes, in particular effects of specific cardiac therapies, are scarce.

METHODS

In this longitudinal observational monocentric study (data from 1989 to 2017) all PA patients treated at our center were included. Echocardiographic parameters (left ventricular end-diastolic diameter: LVEDD, left ventricular shortening fraction, mitral valve Doppler inflow pattern) and 12‑lead electrocardiogram recordings (corrected QT interval: QTc) were analyzed. Symptomatic patients were dichotomized to the group "early-onset" (symptoms within 28 days of life) and "late-onset" (symptoms after 28 days). Associations between cardiac function, LVEDD, QTc and clinical parameters (age at onset, beta-blocker or Angiotensin-converting enzyme inhibitor = ACE-I therapy) were analyzed.

RESULTS

18 patients with PA were enrolled, 17 of them were symptomatic and one asymptomatic, with a median age at diagnosis of 6 days. 14/17 (82%) had early onset disease manifestation. Systolic left ventricular dysfunction (i.e. hypokinetic phenotype of cardiomyopathy) was diagnosed in 7/18 (39%) patients at a median age of 14.4 years, all had early onset. Two patients had a dilated left ventricle and systolic left ventricular dysfunction (i.e. dilated hypokinetic phenotype - dilated cardiomyopathy). Diastolic left ventricular dysfunction was found in 11/18 (61%) individuals, typically preceding systolic left ventricular dysfunction. ACE-I therapy did not improve systolic left ventricular function. Mean QTc was 445 ms (+/- 18.11 ms). Longer QTc was associated with larger LVEDD.

CONCLUSIONS

Systolic left ventricular dysfunction was found in 39% of patients, reflecting high disease severity. Two thirds of all individuals showed signs of diastolic left ventricular dysfunction usually preceding systolic left ventricular dysfunction; it therefore may be considered as an indicator for early cardiac disease manifestation, possibly allowing earlier treatment modification. Unresponsiveness to routine cardiac therapy highlights the need to evaluate further strategies, such as liver transplantation.

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.

Cardiac and Liver Disease in Children: Implications for Management Before and After Liver Transplantation

There is close interaction between the functions of the liver and heart affecting the presentation, diagnosis, and outcome of acute and chronic cardiac and liver disease. Conditions affecting both organ systems should be considered when proposing transplantation because the interaction between cardiac disease and liver disease has implications for diagnosis, management, selection for transplantation, and, ultimately, for longterm outcomes after liver transplantation (LT). The combination of cardiac and liver disease is well recognized in adults but is less appreciated in pediatric patients. The focus of this review is to describe conditions affecting both the liver and heart and how they affect selection and management of LT in the pediatric population.

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.

Disturbance of bioenergetics and calcium homeostasis provoked by metabolites accumulating in propionic acidemia in heart mitochondria of developing rats

Propionic acidemia is caused by lack of propionyl-CoA carboxylase activity. It is biochemically characterized by accumulation of propionic (PA) and 3-hydroxypropionic (3OHPA) acids and clinically by severe encephalopathy and cardiomyopathy. High urinary excretion of maleic acid (MA) and 2-methylcitric acid (2MCA) is also found in the affected patients. Considering that the underlying mechanisms of cardiac disease in propionic acidemia are practically unknown, we investigated the effects of PA, 3OHPA, MA and 2MCA (0.05-5 mM) on important mitochondrial functions in isolated rat heart mitochondria, as well as in crude heart homogenates and cultured cardiomyocytes. MA markedly inhibited state 3 (ADP-stimulated), state 4 (non-phosphorylating) and uncoupled (CCCP-stimulated) respiration in mitochondria supported by pyruvate plus malate or α-ketoglutarate associated with reduced ATP production, whereas PA and 3OHPA provoked less intense inhibitory effects and 2MCA no alterations at all. MA-induced impaired respiration was attenuated by coenzyme A supplementation. In addition, MA significantly inhibited α-ketoglutarate dehydrogenase activity. Similar data were obtained in heart crude homogenates and permeabilized cardiomyocytes. MA, and PA to a lesser degree, also decreased mitochondrial membrane potential (ΔΨm), NAD(P)H content and Ca²⁺ retention capacity, and caused swelling in Ca²⁺-loaded mitochondria. Noteworthy, ΔΨm collapse and mitochondrial swelling were fully prevented or attenuated by cyclosporin A and ADP, indicating the involvement of mitochondrial permeability transition. It is therefore proposed that disturbance of mitochondrial energy and calcium homeostasis caused by MA, as well as by PA and 3OHPA to a lesser extent, may be involved in the cardiomyopathy commonly affecting propionic acidemic patients.

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.

Intracellular calcium mishandling leads to cardiac dysfunction and ventricular arrhythmias in a mouse model of propionic acidemia

Propionic acidemia (PA) is a rare metabolic disease associated with mutations in genes encoding the α and β subunits of the enzyme propionyl-CoA carboxylase. The accumulation of toxic metabolites results in mitochondrial dysfunction, increased reactive oxygen species production and oxidative damage, which have been associated with the disease pathophysiology. Clinical symptoms are heterogeneous and include cardiac complications, mainly cardiac dysfunction and arrhythmias, which are recognized as one of the major life-threatening manifestations in patients. We aimed to investigate the molecular mechanisms underlying the cardiac phenotype using a hypomorphic mouse model (Pcca^-/-(A138T)) that recapitulates some biochemical and clinical characteristics of PA. We demonstrate that Pcca^-/-(A138T) mice present with depressed cardiac function along with impaired cell contractility when compared to the wild-type mice. Cardiac dysfunction in Pcca^-/-(A138T) mice was associated with lower systolic Ca²⁺ release ([Ca²⁺]_i transients), impairment in the sarcoplasmic reticulum (SR) Ca²⁺ load and decreased Ca²⁺ re-uptake by SR-Ca²⁺ ATPase (SERCA2a). These functional changes correlated well with the depressed activity of SERCA2a, the elevated ROS levels and SERCA2a oxidation rate in cardiomyocytes isolated from Pcca^-/-(A138T) mice. In addition, decreased SR-Ca²⁺ load in Pcca^-/-(A138T) cardiomyocytes was associated with increased diastolic Ca²⁺ release. The increase in Ca²⁺ sparks, Ca²⁺ waves and spontaneous [Ca²⁺]_i transients in Pcca^-/-(A138T) cardiomyocytes could be responsible for the induction of ventricular arrhythmias detected in these mice. Overall, our results uncover the role of impaired Ca²⁺ handling in arrhythmias and cardiac dysfunction in PA, and identify new targets for the development of therapeutic approaches for this devastating metabolic disease.

Methylmalonic acidemia/propionic acidemia - the biochemical presentation and comparing the outcome between liver transplantation versus non-liver transplantation groups

Background

Most patients with isolated methylmalonic acidemia (MMA) /propionic acidemia (PA) presenting during the neonatal period with acute metabolic distress are at risk for death and significant neurodevelopmental disability. The nationwide newborn screening for MMA/PA has been in place in Taiwan from January, 2000 and data was collected until December, 2016.

Results

During the study period, 3,155,263 newborns were screened. The overall incidence of MMA mutase type cases was 1/121,356 (n = 26), 1 cobalamin B was detected and that for PA cases (n = 4) was 1/788,816. The time of referral is 8.8 days for MMA patients, and 7.5 days for PA patients. The MMA mutase type patients have higher AST, ALT, and NH₃ values as well as a lower pH value (p < 0.05). The mean age for liver transplantation (LT) is 402 days (range from 0.6–6.7 yr) with 16 out of 20 cases (80.0%) using living donors. The mean admission length shortened from 90.6 days/year (pre-LT) to 5.3 days/year (at 3rd year post-LT) (p < 0.0005). Similarly, the tube feeding ratio decreased from 67.8 to 0.50% (p < 0.00005). The anxiety level of the caregiver was reduced from 33.4 to 27.2 after LT (p = 0.001) and the DQ/IQ performance of the patients was improved after LT from 50 to 60.1 (p = 0.07).

Conclusion

MMA/PA patients with LT do survive and have reduced admission time, reduced tube feeding and the caregiver is less anxious.

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.

Propionyl-CoA carboxylase - A review

Propionyl-CoA carboxylase (PCC) is the enzyme which catalyzes the carboxylation of propionyl-CoA to methylmalonyl-CoA and is encoded by the genes PCCA and PCCB to form a hetero-dodecamer. Dysfunction of PCC leads to the inherited metabolic disorder propionic acidemia, which can result in an affected individual presenting with metabolic acidosis, hyperammonemia, lethargy, vomiting and sometimes coma and death if not treated. Individuals with propionic acidemia also have a number of long term complications resulting from the dysfunction of the PCC enzyme. Here we present an overview of the current knowledge about the structure and function of PCC. We review an updated list of human variants which are published and provide an overview of the disease.

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.