Liver Transplantation for Propionic Acidemia and Methylmalonic Acidemia: Perioperative Management and Clinical Outcomes

Long-term neurodevelopmental outcomes following liver transplantation for metabolic disease-a single centre experience

This study describes the neurodevelopmental outcome of children with urea cycle disorders (UCD) and organic acidemias (OA) preliver transplant (LT), 1-year, and 3-years post-LT. We performed a retrospective chart review of children with OA or UCD transplanted between January 2014 and December 2021. Standardized motor and cognitive assessment scores were collected from children who had ≥1 motor/cognitive assessment at any timepoint. Pre-LT brain magnetic resonance imaging (MRI) was graded. Associations between demographic/medical variables and neurodevelopmental outcomes were explored. Twenty-six children (64% male) underwent LT at a median age of 1.4 (interquartile range 0.71, 3.84) years. Fifteen (58%) had a UCD diagnosis, 14 (54%) required dialysis for hyperammonemia, and 10 (42%) had seizures typically around diagnosis. The proportion of children with gross motor scores >1 standard deviation (SD) below the mean increased across timepoints, and ≥50% demonstrated general intellect scores >2 SD below the mean at each timepoint. The following significant associations were noted: UCD diagnoses with lower general intellect scores (p = 0.019); arginosuccinate lyase deficiency diagnosis with lower visual motor scores at 3-years post-LT (p = 0.035); a history of seizures pre-LT with lower general intellect (>2SD below the mean) at 3-years post-LT (p = 0.020); dialysis pre-LT with lower motor scores (>1 SD below the mean) at 1-year post-LT (p = 0.039); pre-emptive LT with higher general intellect scores at 3-years post-LT (p = 0.001). MRI gradings were not associated with developmental scores. In our single centre study, children with UCD or OA had a higher prevalence of developmental impairment post-LT compared to population norms. Earlier screening, pre-emptive transplant, and rehabilitation may optimize long-term outcomes.

Acquired Diaphragmatic Hernia and Intestinal Obstruction in a Child with Methylmalonic Acidemia Following Pediatric Liver Transplantation

BACKGROUND

An acquired diaphragmatic hernia (ADH) is an uncommon event following pediatric liver transplantation. Pediatric liver transplantation proves effective in prolonging survival and improving quality of life for children with methylmalonic acidemia. Remarkably, there have been no previous reports documenting the occurrence of post-liver transplant ADH in patients diagnosed with methylmalonic acidemia.

METHODS

We present a case of a child with methylmalonic acidemia who underwent pediatric liver transplantation at the age of 19 months, followed by choledochoenterostomy due to bile leakage. Three months later, during a subsequent computed tomography (CT) scan, a focal protrusion of the right diaphragmatic muscle was observed. Subsequently, a severe intestinal obstruction emerged a year later, which was diagnosed as an ADH.

RESULTS

Following an emergency assessment of the right hemithorax, necrotic bowel resection and repair of the diaphragmatic hernia (DH) were conducted. Consequently, the hernia repair procedure was successful, and the child was discharged on the 18th postoperative day.

CONCLUSIONS

The clinical presentation and laboratory tests of ADH resembles metabolic decompensation in methylmalonic acidemia, primarily impacting the gastrointestinal and respiratory systems. It can result in severe complications, including intestinal obstruction, and should be considered a potential late complication.

Clinical Practice Recommendations on Kidney Management in Methylmalonic Acidemia: an Expert Consensus Statement From ERKNet and MetabERN

Methylmalonic acidemias (MMAs) are rare inherited metabolic diseases with multiorgan involvement. Chronic kidney disease (CKD) is a common complication, leading to kidney failure, dialysis, and kidney transplantation (KT). The objective of these guidelines was to develop clinical practice recommendations focusing on specific aspects of the kidney management of this disease. Development of these clinical practice recommendations is an initiative of the European Reference Network for Rare Kidney Diseases in collaboration with the European Reference Network for Hereditary Metabolic Disorders and included pediatric and adult nephrologists, metabolic specialists, as well as liver and kidney transplant specialists. CKD has become a significant clinical issue that requires specific follow-up in both pediatric and adult departments. Creatinine-based formulae significantly overestimate kidney function and the estimation of estimated glomerular filtration rate (eGFR) is more accurate using cystatin C. Besides usual kidney indications, acute dialysis may be required in emergency in case of acute metabolic decompensation to clear metabolic toxins. Long-term dialysis may be initiated for clearance of toxic metabolites. Long hours on hemodialysis (HD) and/or daily dialysis are required. The indications for transplantation in MMA are a high rate of metabolic decompensations, a high burden of disease and difficult metabolic control. Transplantation is also indicated in case of long-term complications. Combined liver-kidney transplantation (LKT) should be preferred in patients with MMA with CKD. Possible calcineurin inhibitors (CNIs) induced neurotoxicity was described in patients with MMA requiring immunosuppressive treatment monitoring and adaptation. Overall, 13 statements were produced to provide guidance on the management of CKD, dialysis, and transplantation in pediatric and adult patients with MMA.

The Impact of Early Indication of Living Donor Liver Transplantation on the Outcomes of Patients With Propionic Acidemia: A Single-Center Experience

BACKGROUND

Liver transplantation has been indicated for propionic acidemia (PA) patients with frequent metabolic decompensation and performed as an enzyme replacement therapy. We retrospectively evaluated the outcomes of patients with PA and analyze the appropriate timing of living donor liver transplantation (LDLT).

METHODS

We reviewed 12 children with PA who underwent LDLT, who were divided into early (period from the first episode of metabolic decompensation to LDLT < 1 year; n = 6) and late (> 1 year; n = 6) indication groups depending on the timing of LDLT.

RESULTS

The patient and graft survival rates were 100% in 12 children with PA, and the median observation period was 61 months (5-193 months). None of the patients experienced any episodes of metabolic decompensation after LDLT. The timing of LDLT did not influence the incidence of surgical complications. Two patients in the late indication group had episodes of cardiac arrest and long QT syndrome before LDLT, and one patient showed prolongation of QT interval after LDLT. Two of the six patients in the late indication group had findings of metabolic stroke of the brain on MRI before LDLT. Although LDLT improved the findings of metabolic stroke, a decrease in development quotient score was shown in the post-LDLT course.

CONCLUSIONS

LDLT may be an effective therapeutic option for improving metabolic control. Early LDLT might be help prevent cardiomyopathy and neurological impairment.

Long-Term Outcomes of Living Donor Liver Transplantation for Methylmalonic Acidemia

BACKGROUND

Despite early diagnosis and medical interventions, patients with methylmalonic acidemia (MMA) suffer from multi-organ damage and recurrent metabolic decompensations.

METHODS

We conducted the largest retrospective multi-center cohort study so far, involving five transplant centers (NCCHD, KUH, KUHP, ATAK, and EMC), and identified all MMA patients (n = 38) undergoing LDLT in the past two decades. Our primary outcome was patient survival, and secondary outcomes included death-censored graft survival and posttransplant complications.

RESULTS

The overall 10-year patient survival and death-censored graft survival rates were 92% and 97%, respectively. Patients who underwent LDLT within 2 years of MMA onset showed significantly higher 10-year patient survival compared to those with an interval more than 2 years (100% vs. 81%, p = 0.038), although the death-censored graft survival were not statistically different (100% vs. 93%, p = 0.22). Over the long-term follow-up, 14 patients (37%) experienced intellectual disability, while two patients developed neurological complications, three patients experienced renal dysfunction, and one patient had biliary anastomotic stricture. The MMA level significantly decreased from 2218.5 mmol/L preoperative to 307.5 mmol/L postoperative (p = 0.038).

CONCLUSIONS

LDLT achieves favorable long-term patient and graft survival outcomes for MMA patients. While not resulting in complete cure, our findings support the consideration of early LDLT within 2 years of disease onset. This approach holds the potential to mitigate recurrent metabolic decompensations, and preserve the long-term renal function.

Long-term clinical outcomes and health-related quality of life in patients with isolated methylmalonic acidemia after liver transplantation: experience from the largest cohort study in China

BACKGROUND

Liver transplantation (LT) has been proposed as a viable treatment option for selected methylmalonic acidemia (MMA) patients. However, there are still controversies regarding the therapeutic value of LT for MMA. The systematic assessment of health-related quality of life (HRQoL)-targeted MMA children before and after LT is also undetermined. This study aimed to comprehensively assess the long-term impact of LT on MMA, including multiorgan sequelae and HRQoL in children and families.

METHODS

We retrospectively evaluated 15 isolated MMA patients undergoing LT at our institution between June 2013 and March 2022. Pre- and post-transplant data were compared, including metabolic profiles, neurologic consequences, growth parameters, and HRQoL. To further assess the characteristics of the HRQoL outcomes in MMA, we compared the results with those of children with biliary atresia (BA).

RESULTS

All patients had early onset MMA, and underwent LT at a mean age of 4.3 years. During 1.3-8.2 years of follow-up, the patient and graft survival rates were 100%. Metabolic stability was achieved in all patients with liberalized dietary protein intake. There was a significant overall improvement in height Z scores (P = 0.0047), and some preexisting neurological complications remained stable or even improved after LT. On the Pediatric Quality of Life Inventory (PedsQL™) generic core scales, the mean total, physical health, and psychosocial health scores improved significantly posttransplant (P < 0.05). In the family impact module, higher mean scores were noted for all subscales post-LT, especially family function and daily activities (P < 0.01). However, the total scores on the generic core scales and transplant module were significantly lower (Cohen's d = 0.57-1.17) when compared with BA recipients. In particular, social and school functioning (Cohen's d = 0.86-1.76), treatment anxiety, and communication (Cohen's d = 0.99-1.81) were far behind, with a large effect size.

CONCLUSIONS

This large single-center study of the mainland of China showed an overall favorable impact of LT on isolated MMA in terms of long-term survival, metabolic control, and HRQoL in children and families. The potential for persistent neurocognitive impairment and inherent metabolic fragility requires long-term special care. Video Abstract (MP4 153780 KB).

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.

Characterizing the mechanism of action for mRNA therapeutics for the treatment of propionic acidemia, methylmalonic acidemia, and phenylketonuria

Messenger RNA (mRNA) therapeutics delivered via lipid nanoparticles hold the potential to treat metabolic diseases caused by protein deficiency, including propionic acidemia (PA), methylmalonic acidemia (MMA), and phenylketonuria (PKU). Herein we report results from multiple independent preclinical studies of mRNA-3927 (an investigational treatment for PA), mRNA-3705 (an investigational treatment for MMA), and mRNA-3210 (an investigational treatment for PKU) in murine models of each disease. All 3 mRNA therapeutics exhibited pharmacokinetic/pharmacodynamic (PK/PD) responses in their respective murine model by driving mRNA, protein, and/or protein activity responses, as well as by decreasing levels of the relevant biomarker(s) when compared to control-treated animals. These preclinical data were then used to develop translational PK/PD models, which were scaled allometrically to humans to predict starting doses for first-in-human clinical studies for each disease. The predicted first-in-human doses for mRNA-3927, mRNA-3705, and mRNA-3210 were determined to be 0.3, 0.1, and 0.4 mg/kg, respectively.

Living-donor liver transplantation for methylmalonic acidemia patient with hepatocellular carcinoma: A case report and literature review

BACKGROUND

Methylmalonic acidemia (MMA) is an autosomal recessive disorder caused by defects in propionyl-CoA (P-CoA) catabolism; of note, liver neoplasms rarely occur as a long-term complication of the disorder. Herein, we report the case of a patient with MMA and hepatocellular carcinoma (HCC) who was successfully treated with a living-donor liver transplant (LDLT) following prior kidney transplantation.

CASE REPORT

A 25-year-old male patient with MMA underwent LDLT with a left lobe graft because of metabolic instability and liver neoplasms. He had presented with chronic symptoms of MMA, which had been diagnosed by genetic testing. Additionally, he had undergone living-donor kidney transplantation with his father as the donor due to end-stage kidney disease 6 years before the LDLT. He had an episode of metabolic decompensation triggered by coronavirus disease in 2019. Imaging studies revealed an intrahepatic neoplasm in the right hepatic lobe. Due to concerns about metabolic decompensation after hepatectomy, LDLT was performed using a left lobe graft obtained from the patient's mother. Pathological findings were consistent with the characteristics of well-to-moderately differentiated HCC. The postoperative course was uneventful, and the patient was discharged 48 days after the LDLT without any complications. At the 9-month follow-up, the patient's condition was satisfactory, with sufficient liver graft function and without metabolic decompensation.

CONCLUSION

This case indicates that although HCC is a rare complication in patients with MMA, clinicians should be aware of hepatic malignancies during long-term follow-up.

Current status and future directions of liver transplantation for metabolic liver disease in children

Orthotopic liver transplantation (OLT) in the care of children with inborn errors of metabolism (IEM) is well established and represent the second most common indication for pediatric liver transplantation in most centers worldwide, behind biliary atresia. OLT offers cure of disease when a metabolic defect is confined to the liver, but may still be transformative on a patient's quality of life reducing the chance of metabolic crises causing neurological damage in children be with extrahepatic involvement and no "functional cure." Outcomes post-OLT for inborn errors of metabolism are generally excellent. However, this benefit must be balanced with consideration of a composite risk of morbidity, and commitment to a lifetime of post-transplant chronic disease management. An increasing number of transplant referrals for children with IEM has contributed to strain on graft access in many parts of the world. Pragmatic evaluation of IEM referrals is essential, particularly pertinent in cases where progression of extra-hepatic disease is anticipated, with long-term outcome expected to be poor. Decision to proceed with liver transplantation is highly individualized based on the child's dynamic risk-benefit profile, their family unit, and their treating multidisciplinary team. Also to be considered is the chance of future treatments, such as gene therapies, emerging in the medium term.

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.

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.

Transplantation in paediatric patients with MMA requires multidisciplinary approach for achievement of good clinical outcomes

BACKGROUND

As modern medicine is advancing, younger, small, and more complex children are becoming multi-organ transplant candidates. This brings up new challenges in all aspects of their care.

METHODS

We describe the first report of a small child receiving a simultaneous liver and kidney transplant and abdominal rectus sheath fascia transplant on the background of Williams syndrome and methylmalonic acidaemia. At the time of transplantation, the child was 3 years old, weighed 14.0 kg, had chronic kidney disease stage V, and had not yet started any other form of kidney replacement therapy.

RESULTS

There were many anaesthetic, medical, metabolic, and surgical challenges to consider in this case. A long general anaesthetic time increased the risk of cardiac complications and metabolic decompensation. Additionally, the small size of the patient and the organ size mis-match meant that primary abdominal closure was not possible. The patient's recovery was further complicated by sepsis, transient CNI toxicity, and de novo DSAs.

CONCLUSIONS

Through a multidisciplinary approach between 9 specialties in 4 hospitals across England and Wales, and detailed pre-operative planning, a good outcome was achieved for this child. An hour by hour management protocol was drafted to facilitate transplant and included five domains: 1. management at the time of organ offer; 2. before the admission; 3. at admission and before theatre time; 4. intra-operative management; and 5. post-operative management in the first 24 h. Importantly, gaining a clear and in depth understanding of the metabolic state of the patient pre- and peri-operatively was crucial in avoiding metabolic decompensation. Furthermore, an abdominal rectus sheath fascia transplant was required to achieve abdominal closure, which to our knowledge, had never been done before for this indication. Using our experience of this complex case, as well as our experience in transplanting other children with MMA, and through a literature review, we propose a new perioperative management pathway for this complex cohort of transplant recipients.

Biomarkers to predict disease progression and therapeutic response in isolated methylmalonic acidemia

Methylmalonic Acidemia (MMA) is a heterogenous group of inborn errors of metabolism caused by a defect in the methylmalonyl-CoA mutase (MMUT) enzyme or the synthesis and transport of its cofactor, 5'-deoxy-adenosylcobalamin. It is characterized by life-threatening episodes of ketoacidosis, chronic kidney disease, and other multiorgan complications. Liver transplantation can improve patient stability and survival and thus provides clinical and biochemical benchmarks for the development of hepatocyte-targeted genomic therapies. Data are presented from a US natural history protocol that evaluated subjects with different types of MMA including mut-type (N = 91), cblB-type (15), and cblA-type MMA (17), as well as from an Italian cohort of mut-type (N = 19) and cblB-type MMA (N = 2) subjects, including data before and after organ transplantation in both cohorts. Canonical metabolic markers, such as serum methylmalonic acid and propionylcarnitine, are variable and affected by dietary intake and renal function. We have therefore explored the use of the 1-13 C-propionate oxidation breath test (POBT) to measure metabolic capacity and the changes in circulating proteins to assess mitochondrial dysfunction (fibroblast growth factor 21 [FGF21] and growth differentiation factor 15 [GDF15]) and kidney injury (lipocalin-2 [LCN2]). Biomarker concentrations are higher in patients with the severe mut0 -type and cblB-type MMA, correlate with a decreased POBT, and show a significant response postliver transplant. Additional circulating and imaging markers to assess disease burden are necessary to monitor disease progression. A combination of biomarkers reflecting disease severity and multisystem involvement will be needed to help stratify patients for clinical trials and assess the efficacy of new therapies for MMA.

Evaluation of living donors for hereditary liver disease (siblings, heterozygotes)

Living donor liver transplantation (LDLT) is recognised as an alternative treatment modality to reduce waiting list mortality and expand the donor pool. Over recent decades, there have been an increasing number of reports on the use of LT and specifically LDLT for familial hereditary liver diseases. There are marginal indications and contraindications that should be considered for a living donor in paediatric parental LDLT. No mortality or morbidity related to recurrence of metabolic diseases has been observed with heterozygous donors, except for certain relevant cases, such as ornithine transcarbamylase deficiency, protein C deficiency, hypercholesterolemia, protoporphyria, and Alagille syndrome, while donor human leukocyte antigen homozygosity also poses a risk. It is not always essential to perform preoperative genetic assays for possible heterozygous carriers; however, genetic and enzymatic assays must hereafter be included in the parental donor selection criteria in the aforementioned circumstances.

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.

The re-occurrence of dilated cardiomyopathy in propionic acidemia after liver transplantation requiring heart transplant, first case from Middle East

Propionic acidemia is a rare autosomal recessive inborn error of metabolism. It is relatively common in Middle East. Dilated cardiomyopathy is one of the leading causes of morbidity and mortality for patients with propionic acidemia. Liver transplantation has been used for patient with frequent metabolic decompensations and was shown to be beneficial in propionic acidemia-related dilated cardiomyopathy. Up to our knowledge, there has been one reported case of recurrent dilated cardiomyopathy 3 years after liver transplantation. We report the first case, from Middle East, of recurrent dilated cardiomyopathy, 6 years after liver transplantation.

Sex-Gender-Based Differences in Metabolic Diseases

Sexual dimorphism creates different biological and cellular activities and selective regulation mechanisms in males and females, thus generating differential responses in health and disease. In this scenario, the sex itself is a source of physiologic metabolic disparities that depend on constitutive genetic and epigenetic features that characterize in a specific manner one sex or the other. This has as a direct consequence a huge impact on the metabolic routes that drive the phenotype of an individual. The impact of sex is being clearly recognized also in disease, whereas male and females are more prone to the development of some disorders, or have selective responses to drugs and therapeutic treatments. Actually, very less is known regarding the probable differences guided by sex in the context of inherited metabolic disorders, owing to the scarce consideration of sex in such restricted field, accompanied by an intrinsic bias connected with the rarity of such diseases. Metabolomics technologies have been ultimately developed and adopted for being excellent tools for the investigation of metabolic mechanisms, for marker discovery or monitoring, and for supporting diagnostic procedures of metabolic disorders. Hence, metabolomic approaches can excellently embrace the discovery of sex differences, especially when associated to the outcome or the management of certain inborn errors of the metabolism.

Renal outcome and plasma methylmalonic acid levels after isolated or combined liver or kidney transplantation in patients with methylmalonic acidemia: A multicenter analysis

BACKGROUND

Methylmalonic acidemia (MMAemia) is characterized by accumulation of methylmalonic acid (MMA) in all body tissues. To minimize disease-related complications, isolated kidney (KTx), liver (LTx) or combined liver-kidney transplantation (LKTx) have been suggested. However, the impact of these different transplant strategies on outcome are unclear.

METHODS

In this multicenter retrospective observational study, we compared plasma MMA levels and estimated glomerular filtration rate (eGFR) data of 83 patients. Sixty-eight patients (82%) had a mut⁰-type MMAemia, one patient had a mut^--type MMAemia, and seven (7.3%) had an inherited defect in cobalamin metabolism (cblA- or cblB-type MMAemia). Median observation period was 3.7 years (0-15.1 years).

RESULTS

Twenty-six (31%) patients underwent KTx, 24 (29%) LTx and 33 (40%) LKTx. Posttransplant, mean plasma MMA concentration significantly decreased in all three cohorts; but at month 12, plasma MMA in KTx (1372 ± 1101 μmol/L) was 7.8-fold higher than in LTx (176 ± 103 μmol/L; P < 0.001) and 6.4-fold higher than in LKTx (215 ± 110 μmol/L; P < 0.001). Comparable data were observed at month 24. At time of transplantation, mean eGFR in KTx was 18.1 ± 24.3 mL/min/1.73 m², in LTx 99.8 ± 29.9 mL/min/1.73 m², and in LKTx 31.5 ± 21.2 mL/min/1.73 m². At month 12 posttransplant, mean eGFR in KTx (62.3 ± 30.3 mL/min/1.73 m²) was 33.4% lower than in LTx (93.5 ± 18.3 mL/min/1.73 m²; P = 0.0053) and 25.4% lower than in LKTx (83.5 ± 26.9 mL/min/1.73 m²; P = 0.0403).

CONCLUSIONS

In patients with isolated MMAemia, LTx and LKTx lead to markedly lower plasma MMA levels during the first 2 years posttransplant than KTx and are associated with a better preservation of kidney function. LTx should therefore be part of the transplant strategy in MMAemia.

Cardiac-specific deficiency of 3-hydroxy-3-methylglutaryl coenzyme A lyase in mice causes cardiomyopathy and a distinct pattern of acyl-coenzyme A-related biomarkers

Deficiency of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase (HL) is an autosomal recessive inborn error of acyl-CoA metabolism affecting the last step of leucine degradation. Patients with HL deficiency (HLD) can develop a potentially fatal cardiomyopathy. We created mice with cardiomyocyte-specific HLD (HLHKO mice), inducing Cre recombinase-mediated deletion of exon 2 at two months of age. HLHKO mice survive, but develop left ventricular hypertrophy by 9 months. Also, within minutes after intraperitoneal injection of the leucine metabolite 2-ketoisocaproate (KIC), they show transient left ventricular hypocontractility and dilation. Leucine-related acyl-CoAs were elevated in HLHKO heart (e.g., HMG-CoA, 34.0 ± 4.4 nmol/g versus 0.211 ± 0.041 in controls, p &lt; 0.001; 3-methylcrotonyl-CoA, 5.84 ± 0.69 nmol/g versus 0.282 ± 0.043, p &lt; 0.001; isovaleryl-CoA, 1.86 ± 0.30 nmol/g versus 0.024 ± 0.014, p &lt; 0.01), a similar pattern to that in liver of mice with hepatic HL deficiency. After KIC loading, HMG-CoA levels in HLHKO heart were higher than under basal conditions, as were the ratios of HMG-CoA/acetyl-CoA and of HMG-CoA/succinyl-CoA. In contrast to the high levels of multiple leucine-related acyl-CoAs, biomarkers in urine and plasma of HLHKO mice show isolated hyper-3-methylglutaconic aciduria (700.8 ± 48.4 mmol/mol creatinine versus 37.6 ± 2.4 in controls, p &lt; 0.001), and elevated C5-hydroxyacylcarnitine in plasma (0.248 ± 0.014 μmol/L versus 0.048 ± 0.005 in controls, p &lt; 0.001). Mice with liver-specific HLD were compared, and showed normal echocardiographic findings and normal acyl-CoA profiles in heart. This study of nonhepatic tissue-specific HLD outside of liver reveals organ-specific origins of diagnostic biomarkers for HLD in blood and urine and shows that mouse cardiac HL is essential for myocardial function in a cell-autonomous, organ-autonomous fashion.

Clinical, phenotypic and genetic landscape of case reports with genetically proven inherited disorders of vitamin B12 metabolism: A meta-analysis

Inherited disorders of B₁₂ metabolism produce a broad spectrum of manifestations, with limited knowledge of the influence of age and the function of related genes. We report a meta-analysis on 824 patients with a genetically proven diagnosis of an inherited disorder of vitamin B₁₂ metabolism. Gene clusters and age categories are associated with patients' manifestations. The "cytoplasmic transport" cluster is associated with neurological and ophthalmological manifestations, the "mitochondrion" cluster with hypotonia, acute metabolic decompensation, and death, and the "B₁₂ availability" and "remethylation" clusters with anemia and cytopenia. Hypotonia, EEG abnormalities, nystagmus, and strabismus are predominant in the younger patients, while neurological manifestations, such as walking difficulties, peripheral neuropathy, pyramidal syndrome, cerebral atrophy, psychiatric disorders, and thromboembolic manifestations, are predominant in the older patients. These results should prompt systematic checking of markers of vitamin B₁₂ status, including homocysteine and methylmalonic acid, when usual causes of these manifestations are discarded in adult patients.

Safety and long-term outcomes of early liver transplantation for pediatric methylmalonic acidemia patients

BACKGROUND

LT is a treatment option for MMA patients, but renal function impairment is one of the long-term concerns. The aim of this study was to evaluate the outcomes of early LT in these patients.

METHODS

A total of 11 MMA mut-type patients (including 10 mut0 cases and 1 mut-case) who received LT in our institute were reviewed. Their metabolic profiles were compared between the pre/post-transplant periods. Their immunosuppressant and renal function changes after transplantation were assessed.

RESULTS

After a mean follow-up of 97.5 ± 38.4 months, there were two deaths, and the actual survival rate was 81.8%. Their metabolic profiles had improved (mean blood ammonia level 366.8 ± 105.5 vs. 53.1 ± 17.4 μg/dl, p < .001; C3/C2 ratio 2.68 ± 0.87 vs. 0.73 ± 0.22, p = .003; mean urine MMA level 920.5 ± 376.6 vs. 196.2 ± 85.4, p = .067), and hospital stays were decreased (78.8 ± 74.5 vs. 7.4 ± 7.0 days/year, p = .009) after transplantation. The mean age at transplant was 1.81 ± 2.02 years old, and nine of these patients received LT before the age of 1.5 years old (early LT). Under prospective immunosuppressant dose reduction, three of these early LT patients discontinued the drug and were sustained for more than 5 years. Most of the patients had a preserved renal function, and no patient is currently on dialysis.

CONCLUSIONS

In addition to the improvement in the metabolic parameters, early LT in MMA patients may allow for a dose reduction of the immunosuppressant, and the patient's renal function could be preserved in the long term.

Messenger RNA as a personalized therapy: The moment of truth for rare metabolic diseases

Inborn errors of metabolism (IEM) encompass a group of monogenic diseases affecting both pediatric and adult populations and currently lack effective treatments. Some IEM such as familial hypercholesterolemia or X-linked protoporphyria are caused by gain of function mutations, while others are characterized by an impaired protein function, causing a metabolic pathway blockage. Pathophysiology classification includes intoxication, storage and energy-related metabolic disorders. Factors specific to each disease trigger acute metabolic decompensations. IEM require prompt and effective care, since therapeutic delay has been associated with the development of fatal events including severe metabolic acidosis, hyperammonemia, cerebral edema, and death. Rapid expression of therapeutic proteins can be achieved hours after the administration of messenger RNAs (mRNA), representing an etiological solution for acute decompensations. mRNA-based therapy relies on modified RNAs with enhanced stability and translatability into therapeutic proteins. The proteins produced in the ribosomes can be targeted to specific intracellular compartments, the cell membrane, or be secreted. Non-immunogenic lipid nanoparticle formulations have been optimized to prevent RNA degradation and to allow safe repetitive administrations depending on the disease physiopathology and clinical status of the patients, thus, mRNA could be also an effective chronic treatment for IEM. Given that the liver plays a key role in most of metabolic pathways or can be used as bioreactor for excretable proteins, this review focuses on the preclinical and clinical evidence that supports the implementation of mRNA technology as a promising personalized strategy for liver metabolic disorders such as acute intermittent porphyria, ornithine transcarbamylase deficiency or glycogen storage disease.

Medium branched chain fatty acids improve the profile of tricarboxylic acid cycle intermediates in mitochondrial fatty acid β-oxidation deficient cells: A comparative study

Inherited errors of mitochondrial fatty acid β-oxidation (FAO) are life threatening, even with optimum care. FAO is the major source of energy for heart and is critical for skeletal muscles especially during physiologic stress. Clinical trials revealed that triheptanoin (commercially known as Dojolvi; C7G), improved heart function and decreased hypoglycemia in long chain FAO disorders, but other symptoms including rhabdomyolysis persisted, suggesting suboptimal tissue distribution/utilization of heptanoic acid (C7) conjugates and/or rapid liver breakdown. In this study, medium branched chain fatty acids were tested as potential anaplerotic treatments in fibroblasts from patients deficient in very long chain acyl-CoA dehydrogenase (VLCAD), long chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD), trifunctional protein (TFP), and carnitine palmitoyltransferase II (CPT II). Cells were cultured to near confluency and treated with C7, 2,6-dimethylheptanoic acid (dMC7), 6-amino-2,4-dimethylheptanoic acid (AdMC7), or 4,8-dimethylnonanoic acid (dMC9) for 72 h and targeted metabolomics performed. The profile of TCA cycle intermediates was improved in cells treated with these branched chain fatty acids compared with C7. Intracellular propionate was higher in AdMC7 treated cells compared with C7 in VLCAD, LCHAD, and TFP deficient cell lines. With AdMC7 treatment, succinate was higher in CPT II and VLCAD deficient cells, compared with C7. Malate and glutamate were consistently higher in AdMC7 treated VLCAD, LCHAD, TFP, and CPT II deficient cells compared with the C7 treatment. The results provide the impetus to further evaluate and consider branched chain fatty acids as viable anaplerotic therapy for fatty acid oxidation disorders and other diseases.

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.

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.

ImmTOR nanoparticles enhance AAV transgene expression after initial and repeat dosing in a mouse model of methylmalonic acidemia

A major barrier to adeno-associated virus (AAV) gene therapy is the inability to re-dose patients due to formation of vector-induced neutralizing antibodies (Nabs). Tolerogenic nanoparticles encapsulating rapamycin (ImmTOR) provide long-term and specific suppression of adaptive immune responses, allowing for vector re-dosing. Moreover, co-administration of hepatotropic AAV vectors and ImmTOR leads to an increase of transgene expression even after the first dose. ImmTOR and AAV Anc80 encoding the methylmalonyl-coenzyme A (CoA) mutase (MMUT) combination was tested in a mouse model of methylmalonic acidemia, a disease caused by mutations in the MMUT gene. Repeated co-administration of Anc80 and ImmTOR was well tolerated and led to nearly complete inhibition of immunoglobulin (Ig)G antibodies to the Anc80 capsid. A more profound decrease of plasma levels of the key toxic metabolite, plasma methylmalonic acid (pMMA), and disease biomarker, fibroblast growth factor 21 (FGF21), was observed after treatment with the ImmTOR and Anc80-MMUT combination. In addition, there were higher numbers of viral genomes per cell (vg/cell) and increased transgene expression when ImmTOR was co-administered with Anc80-MMUT. These effects were dose-dependent, with the higher doses of ImmTOR providing higher vg/cell and mRNA levels, and an improved biomarker response. Combining of ImmTOR and AAV can not only block the IgG response against capsid, but it also appears to potentiate transduction and enhance therapeutic transgene expression in the mouse model.

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.

Orthopaedic Problems in 35 Patients With Organic Acid Disorders

INTRODUCTION

Organic acid disorders (OADs) are a subset of inborn errors of metabolism that result in a toxic accumulation of organic acids in the body, which can lead to metabolic derangements and encephalopathy. Patients with these disorders are managed by a team of biochemical geneticists and metabolic nutritionists. However, subspecialists such as neurologists and orthopaedic surgeons are often needed to help manage the sequelae of the metabolic derangements. The breadth of orthopaedic sequelae of these disease states is poorly understood. Herein, we describe orthopaedic problems associated with 5 types of OAD most commonly seen at our institution: maple syrup urine disease, methylmalonic aciduria, propionic aciduria, pyruvate dehydrogenase deficiency, and glutaric aciduria type 1.

METHODS

We retrospectively reviewed medical records of 35 patients with an OAD who were seen at our academic tertiary care center from May 1999 to May 2020. Patients were grouped into cohorts according to OAD type and analyzed for orthopaedic presentations of hip, knee, or foot disorders, presence and severity of scoliosis, history of fracture, movement disorders, and osteopenia/osteoporosis.

RESULTS

Of the 35 patients, 13 had maple syrup urine disease, 12 had methylmalonic aciduria, 4 had propionic aciduria, 4 had pyruvate dehydrogenase deficiency, and 2 had glutaric aciduria type 1. Associated orthopaedic problems included spasticity causing neuromuscular scoliosis and/or hip subluxation or dislocation (10 patients), fractures (7 patients), and osteopenia/osteoporosis (7 patients). Overall, 22 of 35 patients had some orthopaedic condition.

CONCLUSIONS

Most in this cohort of patients with OAD also had an orthopaedic abnormality. It is important for physicians treating these patients to understand their propensity for musculoskeletal problems. When treating patients with OAD, it is important to initiate and maintain communication with specialists in several disciplines and to develop collaborative treatments for this unique population.

LEVEL OF EVIDENCE

Level IV-prognostic study.

Milestones in treatments for inborn errors of metabolism: Reflections on Where chemistry and medicine meet

From Sir Archibald Garrod's initial description of the tetrad of albinism, alkaptonuria, cystinuria, and pentosuria to today, the field of medicine dedicated to inborn errors of metabolism has evolved from disease identification and mechanistic discovery to the development of therapies designed to subvert biochemical defects. In this review, we highlight major milestones in the treatment and diagnosis of inborn errors of metabolism, starting with dietary therapy for phenylketonuria in the 1950s and 1960s, and ending with current approaches in genetic manipulation.

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.

Liver and/or kidney transplantation in amino and organic acid-related inborn errors of metabolism: An overview on European data

BACKGROUND

This study provides a general overview on liver and/or kidney transplantation in patients with an amino and organic acid-related disorder (AOA) with the aim to investigate patient characteristics and global outcome in Europe. This study was an initiative of the E-IMD and the AOA subnetwork of MetabERN.

METHODS

A questionnaire was sent to all clinically active European Society for the Study of Inborn Errors of Metabolism (SSIEM) members. The questionnaire focused on transplanted individuals with methylmalonic acidemia (MMA), propionic acidemia (PA), maple syrup urine disease (MSUD), and urea-cycle disorders (UCDs).

RESULTS

We identified 280 transplanted AOA patients (liver transplantation in 20 MMA, 37 PA, 47 MSUD, and 111 UCD patients, kidney or combined liver and kidney transplantation in 57 MMA patients and undefined transplantation type in 8 MMA patients), followed by 51 metabolic centers. At a median follow-up of 3.5 years, posttransplant survival ranged between 78% and 100%, being the lowest in PA patients. Overall, the risk of mortality was highest within 14 days posttransplantation. Neurological complications were mainly reported in Mut⁰ type MMA (n = 8). Nonneurological complications occurred in MMA (n = 28), PA (n = 7), and UCD (n = 14) patients, while it was virtually absent in MSUD patients. Only 116/280 patients were psychologically tested. In all, except MSUD patients, the intelligence quotient (IQ) remained unchanged in the majority (76/94, 81%). Forty-one percentage (9/22) of MSUD patient showed improved IQ.

CONCLUSION

The survival in AOA individuals receiving liver and/or kidney transplantation seems satisfactory. Evidence-based guidelines, systematic data collection, and improved cooperation between transplantation centers and European Reference Networks are indispensable to improve patient care and outcomes.

1-13C-propionate breath testing as a surrogate endpoint to assess efficacy of liver-directed therapies in methylmalonic acidemia (MMA)

PURPOSE

To develop a safe and noninvasive in vivo assay of hepatic propionate oxidative capacity.

METHODS

A modified 1-¹³C-propionate breath test was administered to 57 methylmalonic acidemia (MMA) subjects, including 19 transplant recipients, and 16 healthy volunteers. Isotopomer enrichment (¹³CO₂/¹²CO₂) was measured in exhaled breath after an enteral bolus of sodium-1-¹³C-propionate, and normalized for CO₂ production. 1-¹³C-propionate oxidation was then correlated with clinical, laboratory, and imaging parameters collected via a dedicated natural history protocol.

RESULTS

Lower propionate oxidation was observed in patients with the severe mut⁰ and cblB subtypes of MMA, but was near normal in those with the cblA and mut^- forms of the disorder. Liver transplant recipients demonstrated complete restoration of 1-¹³C-propionate oxidation to control levels. 1-¹³C-propionate oxidation correlated with cognitive test result, growth indices, bone mineral density, renal function, and serum biomarkers. Test repeatability was robust in controls and in MMA subjects (mean coefficient of variation 6.9% and 12.8%, respectively), despite widely variable serum methylmalonic acid concentrations in the patients.

CONCLUSION

Propionate oxidative capacity, as measured with 1-¹³C-propionate breath testing, predicts disease severity and clinical outcomes, and could be used to assess the therapeutic effects of liver-targeted genomic therapies for MMA and related disorders of propionate metabolism.

TRIAL REGISTRATION

This clinical study is registered in www.clinicaltrials.gov with the ID: NCT00078078. Study URL: http://clinicaltrials.gov/ct2/show/NCT00078078.

Safety and efficacy of liver transplantation for methylmalonic acidemia: A systematic review and meta-analysis

Background-objectives: Liver transplantation (LT) and combined liver and kidney transplantation (CLKT) have been proposed as enzyme replacement therapies for methylmalonic aciduria (MMA). We aimed to synthesize the available evidence on their safety and efficacy.

METHODS

Medline, Embase and Cochrane library were searched to identify studies that reported post-LT/CLKT clinical outcomes of MMA from their inception to February 1, 2020. The pooled rate was calculated using random-effects model with Freeman-Tukey double arcsine transformation method.

RESULTS

Thirty-two studies involving 109 patients were included. The pooled estimate rates were 99.9% (95% CI 95.3-100.0) for patient survival, 98.5% (95% CI 91.5-100.0) for graft survival after LT/CLKT. The combined incidence of biliary, vascular complications and rejection were 0.2% (95% CI 0.0-6.6), 7.7% (95% CI 0.1-22.1) and 18.4% (95% CI 4.6-36.3), respectively. The pooled estimate rates were 100.0% (95% CI 99.4-100.0) for metabolic eradication, 61.5% (95% CI: 33.4-87.0) for normalization of kidney function. Chronic kidney disease (CKD) remission is more promising after CLKT (70.3% VS 37.6% in LT group). The pooled estimate rates for neurodevelopmental status improvement and protein intake liberalization were 52.0% (95% CI 2.8-98.8) and 36.3% (95% CI 6.3-71.7), respectively.

CONCLUSIONS

This first quantitative systematic review confirms favorable survival outcomes and partially improved disease-related complications in transplanted MMA patients, although some results should be interpreted with caution. Future studies with detailed description of long-term outcomes and consensus on neurodevelopmental evaluation method can help provide a more accurate picture.

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.

Cardiac Complications of Propionic and Other Inherited Organic Acidemias

Clinical observations and experimental studies have determined that systemic acid-base disturbances can profoundly affect the heart. A wealth of information is available on the effects of altered pH on cardiac function but, by comparison, much less is known about the actions of the organic anions that accumulate alongside H⁺ ions in acidosis. In the blood and other body fluids, these organic chemical species can collectively reach concentrations of several millimolar in severe metabolic acidoses, as in the case of inherited organic acidemias, and exert powerful biological actions on the heart that are not intuitive to predict. Indeed, cardiac pathologies, such as cardiomyopathy and arrhythmia, are frequently reported in organic acidemia patients, but the underlying pathophysiological mechanisms are not well established. Research efforts in the area of organic anion physiology have increased dramatically in recent years, particularly for propionate, which accumulates in propionic acidemia, one of the commonest organic acidemias characterized by a high incidence of cardiac disease. This Review provides a comprehensive historical overview of all known organic acidemias that feature cardiac complications and a state-of-the-art overview of the cardiac sequelae observed in propionic acidemia. The article identifies the most promising candidates for molecular mechanisms that become aberrantly engaged by propionate anions (and its metabolites), and discusses how these may result in cardiac derangements in propionic acidemia. Key clinical and experimental findings are considered in the context of potential therapies in the near future.

Combined liver-kidney transplantation for rare diseases

Combined liver and kidney transplantation (CLKT) is indicated in patients with failure of both organs, or for the treatment of end-stage chronic kidney disease (ESKD) caused by a genetic defect in the liver. The aim of the present review is to provide the most up-to-date overview of the rare conditions as indications for CLKT. They are major indications for CLKT in children. However, in some of them (e.g., atypical hemolytic uremic syndrome or primary hyperoxaluria), CLKT may be required in adults as well. Primary hyperoxaluria is divided into three types, of which type 1 and 2 lead to ESKD. CLKT has been proven effective in renal function replacement, at the same time preventing recurrence of the disease. Nephronophthisis is associated with liver fibrosis in 5% of cases and these patients are candidates for CLKT. In alpha 1-antitrypsin deficiency, hereditary C3 deficiency, lecithin cholesterol acyltransferase deficiency and glycogen storage diseases, glomerular or tubulointerstitial disease can lead to chronic kidney disease. Liver transplantation as a part of CLKT corrects underlying genetic and consequent metabolic abnormality. In atypical hemolytic uremic syndrome caused by mutations in the genes for factor H, successful CLKT has been reported in a small number of patients. However, for this indication, CLKT has been largely replaced by eculizumab, an anti-C5 antibody. CLKT has been well established to provide immune protection of the transplanted kidney against donor-specific antibodies against class I HLA, facilitating transplantation in a highly sensitized recipient.

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.

Nutritional Management and Biochemical Outcomes during the Immediate Phase after Liver Transplant for Methylmalonic Acidemia

Methylmalonic acidemia (MMA) is caused by a deficiency of methyl-malonyl-CoA mutase. It is a multisystemic condition with poor clinical outcomes characterized by frequent metabolic decompensation with acidosis, hyperammonemia and encephalopathy. Restriction of intact protein and supplementation with amino acid-based formula play an important role in its management. Recently, liver transplant (LT) became a treatment option for MMA patients. However, there has been no current consensus on the post-operative nutrition management for MMA patients undergoing transplant, particularly during the initial phase of recovery period with catabolic stressors. We performed a retrospective analysis of clinical and nutritional management as well as biochemical profiles before and after LT in five patients with MMA. Through this study, we observed significant improvement of MMA-associated metabolites after LT. MMA patients were able to tolerate increased intact protein intake post-operatively. At least 1–1.5 g/kg/day of total protein during the acute phase after transplant may be tolerated without worsening of the metabolite levels. This information provides a guide in how to nutritionally manage MMA after LT.

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.

Long-term outcome of methylmalonic aciduria after kidney, liver, or combined liver-kidney transplantation: The French experience

Organ transplantation is discussed in methylmalonic aciduria (MMA) for renal failure, and poor quality of life and neurological outcome. We retrospectively evaluated 23 French MMA patients after kidney (KT), liver-kidney (LKT), and liver transplantation (LT). Two patients died, one after LKT, one of hepatoblastoma after KT. One graft was lost early after KT. Of 18 evaluable patients, 12 previously on dialysis, 8 underwent KT (mean 12.5 years), 8 LKT (mean 7 years), and 2 LT (7 and 2.5 years). At a median follow-up of 7.3 (KT), 2.3 (LKT), and 1.0 years (LT), no metabolic decompensation occurred except in 1 KT. Plasma and urine MMA levels dramatically decreased, more after LKT. Protein intake was increased more significantly after LKT than KT. Enteral nutrition was stopped in 7/8 LKT, 1/8 KT. Early complications were frequent after LKT. Neurological disorders occurred in four LKT, reversible in one. Five years after KT, four patients had renal failure. The metabolic outcomes were much better after LKT than KT. LKT in MMA is difficult but improves the quality of life. KT will be rarely indicated. We need more long-term data to indicate early LT, in the hope to delay renal failure and prevent neurodevelopmental complications.

Nanomedicines to Deliver mRNA: State of the Art and Future Perspectives

The use of messenger RNA (mRNA) in gene therapy is increasing in recent years, due to its unique features compared to plasmid DNA: Transient expression, no need to enter into the nucleus and no risk of insertional mutagenesis. Nevertheless, the clinical application of mRNA as a therapeutic tool is limited by its instability and ability to activate immune responses; hence, mRNA chemical modifications together with the design of suitable vehicles result essential. This manuscript includes a revision of the strategies employed to enhance in vitro transcribed (IVT) mRNA functionality and efficacy, including the optimization of its stability and translational efficiency, as well as the regulation of its immunostimulatory properties. An overview of the nanosystems designed to protect the mRNA and to overcome the intra and extracellular barriers for successful delivery is also included. Finally, the present and future applications of mRNA nanomedicines for immunization against infectious diseases and cancer, protein replacement, gene editing, and regenerative medicine are highlighted.