Improvement in the prognosis and development of patients with methylmalonic acidemia after living donor liver transplant

Role of carglumic acid in the long-term management of propionic and methylmalonic acidurias

Propionic aciduria (PA) and methylmalonic aciduria (MMA) are rare inherited disorders caused by defects in the propionate metabolic pathway. PA due to propionyl coenzyme A carboxylase deficiency results in accumulation of propionic acid, while in MMA, deficiency in methylmalonyl coenzyme A mutase leads to accumulation of methylmalonic acid. Hyperammonemia is related to a secondary deficiency of N-acetylglutamate (NAG), the activator of carbamoyl phosphate synthetase 1, which is an irreversible rate-limiting enzyme in the urea cycle. Carglumic acid (CGA) is a synthetic structural analog of human NAG and is approved for the treatment of patients with hyperammonemia due to PA or MMA. CGA is well tolerated and its use in normalizing ammonia levels during acute hyperammonemic episodes in patients with PA and MMA is well established. This expert opinion analyzed clinical evidence for CGA and discussed its place, along with other management strategies, in the long-term management of PA or MMA. A literature search of PubMed was undertaken to identify publications related to the chronic use of CGA, transplantation, dietary management, ammonia scavengers, and gene therapy for treatment of patients with PA or MMA. The authors selected the most relevant studies for inclusion. Four clinical studies, one single center case series, and three case reports show that CGA is safe and effective in the chronic treatment of PA and MMA. In particular, the addition of CGA is associated with a reduction in hyperammonemic decompensation episodes and admission to hospital, compared with conventional dietary treatment alone. Current treatment guidelines and recommendations include the use of CGA mainly in acute decompensation, however, lag in considering the benefits of long-term CGA treatment on clinical and biochemical outcomes in patients with PA or MMA. CGA is safe and effective in the chronic treatment of PA and MMA and may help to resolve some of the issues associated with other strategies used to treat these disorders. Thus, CGA appears to have potential for the chronic management of patients with PA and MMA and should be recommended for inclusion in the chronic treatment of these disorders.

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.

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.

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.

Growth advantage of corrected hepatocytes in a juvenile model of methylmalonic acidemia following liver directed adeno-associated viral mediated nuclease-free genome editing

Methylmalonic acidemia (MMA) is a rare and severe inherited metabolic disease typically caused by mutations of the methylmalonyl-CoA mutase (MMUT) gene. Despite medical management, patients with MMA experience frequent episodes of metabolic instability, severe morbidity, and early mortality. In several preclinical studies, systemic gene therapy has demonstrated impressive improvement in biochemical and clinical phenotypes of MMA murine models. One approach uses a promoterless adeno-associated viral (AAV) vector that relies upon homologous recombination to achieve site-specific in vivo gene addition of MMUT into the last coding exon of albumin (Alb), generating a fused Alb-MMUT transcript after successful editing. We have previously demonstrated that nuclease-free AAV mediated Alb editing could effectively treat MMA mice in the neonatal period and noted that hepatocytes had a growth advantage after correction. Here, we use a transgenic knock-out mouse model of MMA that recapitulates severe clinical and biochemical symptoms to assess the benefits of Alb editing in juvenile animals. As was first noted in the neonatal gene therapy studies, we observe that gene edited hepatocytes in the MMA mice treated as juveniles exhibit a growth advantage, which allows them to repopulate the liver slowly but dramatically by 8-10 months post treatment, and subsequently manifest a biochemical and enzymatic response. In conclusion, our results suggest that the benefit of AAV mediated nuclease-free gene editing of the Alb locus to treat MMA could potentially be therapeutic for older patients.

Treatment of metabolic disorders using genomic technologies: Lessons from methylmalonic acidemia

Hereditary methylmalonic acidemia (MMA) caused by deficiency of the enzyme methylmalonyl-CoA mutase (MMUT) is a relatively common and severe organic acidemia. The recalcitrant nature of the condition to conventional dietary and medical management has led to the use of elective liver and combined liver-kidney transplantation in some patients. However, liver transplantation is intrinsically limited by organ availability, the risks of surgery, procedural and life-long management costs, transplant comorbidities, and a remaining underlying risk of complications related to MMA despite transplantation. Here, we review pre-clinical studies that present alternative approaches to solid organ transplantation as a treatment for MMUT MMA, including adeno-associated viral gene addition therapy, mRNA therapy, and genome editing, with and without nuclease enhancement.

Review of neuropsychological outcomes in isolated methylmalonic acidemia: recommendations for assessing impact of treatments

Methylmalonic acidemia (MMA) due to methylmalonyl-CoA mutase deficiency (OMIM #251,000) is an autosomal recessive disorder of organic acid metabolism associated with life-threatening acute metabolic decompensations and significant neuropsychological deficits. "Isolated" MMA refers to the presence of excess methylmalonic acid without homocysteine elevation. Belonging to this class of disorders are those that involve complete deficiency (mut⁰) and partial deficiency (mut^-) of the methylmalonyl-CoA mutase enzyme and other disorders causing excess methylmalonic acid excretion. These other disorders include enzymatic subtypes related to cobalamin A defect (cblA) (OMIM #25,110), cobalamin B defect (cblB) (OMIM #251,110) and related conditions. Neuropsychological attributes associated with isolated MMA have become more relevant as survival rates increased following improved diagnostic and treatment strategies. Children with this disorder still are at risk for developmental delay, cognitive difficulties and progressive declines in functioning. Mean IQ for all types apart from cblA defect enzymatic subtype is rarely above 85 and much lower for mut⁰ enzymatic subtype. Identifying psychological domains responsive to improvements in biochemical status is important. This review suggests that processing speed, working memory, language, attention, and quality of life may be sensitive to fluctuations in metabolite levels while IQ and motor skills may be less amenable to change. Due to slower developmental trajectories, Growth Scale Values, Projected Retained Ability Scores and other indices of change need to be incorporated into clinical trial study protocols. Neuropsychologists are uniquely qualified to provide a differentiated picture of cognitive, behavioral and emotional consequences of MMA and analyze benefits or shortcomings of novel treatments.

Aberrant methylmalonylation underlies methylmalonic acidemia and is attenuated by an engineered sirtuin

Organic acidemias such as methylmalonic acidemia (MMA) are a group of inborn errors of metabolism that typically arise from defects in the catabolism of amino and fatty acids. Accretion of acyl-CoA species is postulated to underlie disease pathophysiology, but the mechanism(s) remain unknown. Here, we surveyed hepatic explants from patients with MMA and unaffected donors, in parallel with samples from various mouse models of methylmalonyl-CoA mutase deficiency. We found a widespread posttranslational modification, methylmalonylation, that inhibited enzymes in the urea cycle and glycine cleavage pathway in MMA. Biochemical studies and mouse genetics established that sirtuin 5 (SIRT5) controlled the metabolism of MMA-related posttranslational modifications. SIRT5 was engineered to resist acylation-driven inhibition via lysine to arginine mutagenesis. The modified SIRT5 was used to create an adeno-associated viral 8 (AAV8) vector and systemically delivered to mutant and control mice. Gene therapy ameliorated hyperammonemia and reduced global methylmalonylation in the MMA mice.

Promoterless, Nuclease-Free Genome Editing Confers a Growth Advantage for Corrected Hepatocytes in Mice With Methylmalonic Acidemia

BACKGROUND AND AIMS

Adeno-associated viral (AAV) gene therapy has shown great promise as an alternative treatment for metabolic disorders managed using liver transplantation, but remains limited by transgene loss and genotoxicity. Our study aims to test an AAV vector with a promoterless integrating cassette, designed to provide sustained hepatic transgene expression and reduced toxicity in comparison to canonical AAV therapy.

APPROACH AND RESULTS

Our AAV vector was designed to insert a methylmalonyl-CoA mutase (MMUT) transgene into the 3' end of the albumin locus and tested in mouse models of methylmalonic acidemia (MMA). After neonatal delivery, we longitudinally evaluated hepatic transgene expression, plasma levels of methylmalonate, and the MMA biomarker, fibroblast growth factor 21 (Fgf21), as well as integration of MMUT in the albumin locus. At necropsy, we surveyed for AAV-related hepatocellular carcinoma (HCC) in all treated MMA mice and control littermates. AAV-mediated genome editing of MMUT into the albumin locus resulted in permanent hepatic correction in MMA mouse models, which was accompanied by decreased levels of methylmalonate and Fgf21, and improved survival without HCC. With time, levels of transgene expression increased and methylmalonate progressively decreased, whereas the number of albumin-MMUT integrations and corrected hepatocytes in MMA mice increased, but not in similarly treated wild-type animals. Additionally, expression of MMUT in the setting of MMA conferred a selective growth advantage upon edited cells, which potentiates the therapeutic response.

CONCLUSIONS

In conclusion, our findings demonstrate that AAV-mediated, promoterless, nuclease-free genome editing at the albumin locus provides safe and durable therapeutic benefit in neonatally treated MMA mice.

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.

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.

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.

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.

Methylmalonic and propionic acidemia among hospitalized pediatric patients: a nationwide report

BACKGROUND

Methylmalonic acidemia (MMA) and propionic acidemia (PA) are two kinds of diseases caused by inborn errors of metabolism. So far, the epidemiological data on them are limited in China. The aim of our study is to investigate the proportion and characteristics of hospitalized pediatric patients with MMA and PA in China.

METHODS

The data in this study were obtained from the Hospital Quality Monitoring System, a national inpatient database in China, with information on the patients hospitalized during the period from 2013 to 2017. We identified the data related to the patients who were under 18 years old and were diagnosed with MMA/PA, and extracted the information on demographic characteristics, hospital location, total cost and other related clinical presentations from the data.

RESULTS

Among all hospitalized pediatric patients with liver diseases, there were increasing trends in the proportion of individuals diagnosed with MMA or PA during the period from 2013 (0.76% for MMA; 0.13% for PA) to 2017 (1.61% for MMA; 0.32% for PA). For both MMA and PA, children under 2-year-old accounted for the highest proportion. The median of total cost per hospitalization was relatively high (RMB 7388.53 for MMA; RMB 4999.66 for PA). Moreover, most patients hospitalized in tertiary class A hospitals (MMA: 80.96%, PA: 76.21%); and a majority of pediatric patients admitted in the hospitals in Shanghai and Beijing are from outside districts. Manifestations of nervous system-related symptoms, and metabolic acidosis or anemia in laboratory findings were more common during hospitalization.

CONCLUSIONS

The study is the first nationwide one in providing epidemiological and clinical information on hospitalized pediatric patients with MMA/PA. An increasing hospitalization with various presentations and a heavy financial burden were observed. In addition, geographically, the medical resources in China have been unevenly distributed.

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.

A New Era for Rare Genetic Diseases: Messenger RNA Therapy

Exogenous delivery of messenger RNA (mRNA) is emerging as a new class of medicine with broad applicability including the potential to treat rare monogenic disorders. Recent advances in mRNA technology, including modifications to the mRNA itself along with improvements to the delivery vehicle, have transformed the utility of mRNA as a potential therapy to restore or replace different types of therapeutic proteins. Preclinical proof-of-concept has been demonstrated for mRNA therapy for three different rare metabolic disorders: methylmalonic acidemia, acute intermittent porphyria, and Fabry disease. Herein, we review those preclinical efficacy and safety studies in multiple animal models. For all three disorders, mRNA therapy restored functional protein to therapeutically relevant levels in target organs, led to sustained and reproducible pharmacology following each dose administration of mRNA, and was well tolerated as supported by liver function tests evaluated in animal models including nonhuman primates. These data provide compelling support for the clinical development of mRNA therapy as a treatment for various rare metabolic disorders.

Messenger RNA therapy for rare genetic metabolic diseases

Decades of intense research in molecular biology and biochemistry are fructifying in the emergence of therapeutic messenger RNAs (mRNA) as a new class of drugs. Synthetic mRNAs can be sequence optimised to improve translatability into proteins, as well as chemically modified to reduce immunogenicity and increase chemical stability using naturally occurring uridine modifications. These structural improvements, together with the development of safe and efficient vehicles that preserve mRNA integrity in circulation and allow targeted intracellular delivery, have paved the way for mRNA-based therapeutics. Indeed, mRNAs formulated into biodegradable lipid nanoparticles are currently being tested in preclinical and clinical studies for multiple diseases including cancer immunotherapy and vaccination for infectious diseases. An emerging application of mRNAs is the supplementation of proteins that are not expressed or are not functional in a regulated and tissue-specific manner. This so-called 'protein replacement therapy' could represent a solution for genetic metabolic diseases currently lacking effective treatments. Here we summarise this new class of drugs and discuss the preclinical evidence supporting the potential of liver-mediated mRNA therapy for three rare genetic conditions: methylmalonic acidaemia, acute intermittent porphyria and ornithine transcarbamylase deficiency.

Kidney disease and organ transplantation in methylmalonic acidaemia

OBJECTIVES

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

The Value of Liver Transplantation for Methylmalonic Acidemia

Introduction: MMA is a rare autosomal recessive disorder with the manifestation of recurrent and severe episodes of acute metabolic decompensation or a variety of long-term complications that require timely treatment. While conventional long-term medical and dietary management cannot prevent rapid progression of conditions in patients with severe complications, LT, or CKLT has become an option. Methods: We reviewed the literature for MMA patients undergoing LT/CKLT published since 2006, and data on metabolic decompensation status, protein dietary, neurological damage, renal insufficiency, and developmental delay before and after transplantations were compared to evaluate the clinical value of the procedure in the treatment of MMA. Results: To date, some successful LTs/CKLT procedures have prolonged survival and resulted in better quality of life in patients (lowered urine/plasma MMA levels but still much higher than normal, reduced onset of metabolic stroke, occasional improved developmental delay, and relaxed protein diet), although these procedures cannot reverse neurological damage or thoroughly stop the progress of complications, such as renal dysfunction. Conclusion: LT is the only effective treatment for MMA patients with recurrent metabolic decompensation. However, it is still possible that neurological and renal damage remains irreversible. Metabolism-correcting medications should be administered even after surgery.

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

Propionic acidemia (PA) and methylmalonic acidemia (MMA) comprise the most common organic acidemias and account for profound morbidity in affected individuals. Although liver transplantation (LT) has emerged as a bulk enzyme-replacement strategy to stabilize metabolically fragile patients, it is not a metabolic cure because patients remain at risk for disease-related complications. We retrospectively studied LT and/or liver-kidney transplant in 9 patients with PA or MMA with additional focus on the optimization of metabolic control and management in the perioperative period. Metabolic crises were common before transplant. By implementing a strategy of carbohydrate minimization with gradual but early lipid and protein introduction, lactate levels significantly improved over the perioperative period (P < 0.001). Posttransplant metabolic improvement is demonstrated by improvements in serum glycine levels (for PA; P < 0.001 × 10^-14 ), methylmalonic acid levels (for MMA; P < 0.001), and ammonia levels (for PA and MMA; P < 0.001). Dietary restriction remained after transplant. However, no further metabolic crises have occurred. Other disease-specific comorbidities such as renal dysfunction and cardiomyopathy stabilized and improved. In conclusion, transplant can provide a strategy for altering the natural history of PA and MMA providing stability to a rare but metabolically brittle population. Nutritional management is critical to optimize patient outcomes.

Systemic Messenger RNA Therapy as a Treatment for Methylmalonic Acidemia

Isolated methylmalonic acidemia/aciduria (MMA) is a devastating metabolic disorder with poor outcomes despite current medical treatments. Like other mitochondrial enzymopathies, enzyme replacement therapy (ERT) is not available, and although promising, AAV gene therapy can be limited by pre-existing immunity and has been associated with genotoxicity in mice. To develop a new class of therapy for MMA, we generated a 5-methoxyU-modified codon-optimized mRNA encoding human methylmalonyl-CoA mutase (hMUT), the enzyme most frequently mutated in MMA, and encapsulated it into biodegradable lipid nanoparticles (LNPs). Intravenous (i.v.) administration of hMUT mRNA in two different mouse models of MMA resulted in a 75%–85% reduction in plasma methylmalonic acid and was associated with increased hMUT protein expression and activity in liver. Repeat dosing of hMUT mRNA reduced circulating metabolites and dramatically improved survival and weight gain. Additionally, repeat i.v. dosing did not increase markers of liver toxicity or inflammation in heterozygote MMA mice.

An et al. find that systemically delivered LNP-encapsulated mRNA results in hepatic protein expression. hMUT mRNA expresses functional mitochondrial MUT enzyme, and MMA mouse models show a metabolic and clinical response after mRNA therapy.