Long-term N-carbamylglutamate treatment of hyperammonemia in patients with classic organic acidemias

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.

Real-World Experience of Carglumic Acid for Methylmalonic and Propionic Acidurias: An Interim Analysis of the Multicentre Observational PROTECT Study

BACKGROUND AND OBJECTIVE

Methylmalonic aciduria (MMA) and propionic aciduria (PA) are organic acidurias characterised by the accumulation of toxic metabolites and hyperammonaemia related to secondary N-acetylglutamate deficiency. Carglumic acid, a synthetic analogue of N-acetylglutamate, decreases ammonia levels by restoring the functioning of the urea cycle. However, there are limited data available on the long-term safety and effectiveness of carglumic acid. Here, we present an interim analysis of the ongoing, long-term, prospective, observational PROTECT study (NCT04176523), which is investigating the long-term use of carglumic acid in children and adults with MMA and PA.

METHODS

Individuals with MMA or PA from France, Germany, Italy, Norway, Spain, Sweden and the UK who have received at least 1 year of carglumic acid treatment as part of their usual care are eligible for inclusion. The primary objective is the number and duration of acute metabolic decompensation events with hyperammonaemia (ammonia level >159 µmol/L during a patient's first month of life or >60 µmol/L thereafter, with an increased lactate level [> 1.8 mmol/L] and/or acidosis [pH < 7.35]) before and after treatment with carglumic acid. Peak plasma ammonia levels during the last decompensation event before and the first decompensation event after carglumic acid initiation, and the annualised rate of decompensation events before and after treatment initiation are also being assessed. Secondary objectives include the duration of hospital stay associated with decompensation events. Data are being collected at approximately 12 months' and 18 months' follow-up.

RESULTS

Of the patients currently enrolled in the PROTECT study, data from ten available patients with MMA (n = 4) and PA (n = 6) were analysed. The patients had received carglumic acid for 14-77 (mean 36) months. Carglumic acid reduced the median peak ammonia level of the total patient population from 250 µmol/L (range 97-2569) before treatment to 103 µmol/L (range 97-171) after treatment. The annualised rate of acute metabolic decompensations with hyperammonaemia was reduced by a median of - 41% (range - 100% to + 60%) after treatment with carglumic acid. Of the five patients who experienced a decompensation event before treatment and for whom a post-treatment rate could be calculated, the annualised decompensation event rate was lower after carglumic acid treatment in four patients. The mean duration of hospital inpatient stay during decompensation events was shorter after than before carglumic acid treatment initiation in four of five patients for whom length of stay could be calculated.

CONCLUSIONS

In this group of patients with MMA and PA, treatment with carglumic acid for at least 1 year reduced peak plasma ammonia levels in the total patient population and reduced the frequency of metabolic decompensation events, as well as the duration of inpatient stay due to metabolic decompensations in a subset of patients.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT04176523. Registered 25 November, 2019, retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04176523 .

Prevalence of propionic acidemia in China

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

A glance at transient hyperammonemia of the newborn: Pathophysiology, diagnosis, and treatment: A review

Hyperammonemia is the excessive accumulation of ammonia in the blood, and is usually defined as a plasma level above 100 µmol/L in neonates or above 50 µmol/L in term infants, children, and adolescents. Patients with hyperammonemia usually experience life-threatening neuropsychiatric symptoms, especially newborns. It is routinely caused by inherited metabolic diseases and also by acquired disorders, such as liver failure, portosystemic shunting, gastrointestinal hemorrhage, ureterosigmoidostomy, renal tubular acidosis, hypoxic ischemic encephalopathy, infections with urea-metabolizing organisms, and some drugs. Transient hyperammonemia of the newborn (THAN) is a special type of hyperammonemia acknowledged in the field of metabolic disease as an inwell-defined or well-understood entity, which can be diagnosed only after the exclusion of genetic and acquired causes of hyperammonemia. Although the prognosis for THAN is good, timely identification and treatment are essential. Currently, THAN is underdiagnosed and much less is mentioned for early diagnosis and vigorous treatment. Herein, we present common themes that emerge from the pathogenesis, diagnosis, and management of THAN, based on current evidence. When a newborn presents with sepsis, intracranial hemorrhage, or asphyxia that cannot explain coma and seizures, doctors should always keep this disease in mind.

Management of methylmalonic acidemia (MMA) with N-carbamylglutamate: A case report from Italy

BACKGROUND

Methylmalonic acidemia (MMA) is an inborn error of metabolism whose optimal management, especially in the long-term remains to be established.

METHODS

We describe the case of a child with MMA mut⁰ who was in a cycle of episodes of decompensation and hospitalization when we started to use carglumic acid (CA), a well-known adjunctive therapy to standard care for the treatment of acute hyperammonemia due to MMA.

RESULTS

Using the lowest effective therapeutic dose of CA and adjusting the patient's diet with caloric and protein intake adequate for her age and pathology, we managed to keep ammonium levels within the normal range, and to ensure a normal growth pattern.

CONCLUSION

The present case adds further confirmation of the long-term management of MMA using CA, focusing on the long duration of follow up and on the use of a lower dose of CA in real life settings.