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.

Background: Maple syrup urine disease (MSUD) is an autosomal recessive inborn error of metabolism caused by a deficiency of branched-chain ketoacid dehydrogenase, the enzyme involved in the second step of branched-chain amino acid catabolism. Of the three branched-chain amino acids (leucine, valine, and isoleucine), accumulation of leucine is the predominant factor causing acute metabolic decompensation in patients with MSUD. Main body: In February 2025, eight expert physicians met to discuss the management of acute metabolic decompensation and propose recommendations after literature review (four guidelines and 20 other articles of interest). A practical clinical algorithm was established. Newborn screening was acknowledged to be a successful method of diagnosing MSUD at birth, facilitating early intervention to prospectively manage MSUD and reduce the frequency and severity of acute metabolic decompensation, although it was noted that infants with severe MSUD often present with acute metabolic decompensation before being diagnosed. The experts also identified several barriers to and gaps in the management of acute metabolic decompensation, and MSUD more generally, proposing potential actions to improve clinical outcomes. Acute metabolic decompensation requires prompt, effective treatment by a multidisciplinary team to ensure that circulating plasma leucine levels are rapidly reduced without causing complications (particularly cerebral edema). Where available, intravenous branched chain amino acid-free solutions (e.g., Maapliv, now approved in Europe) may represent an important treatment option. Adequate resources (treatments, laboratory services, dialysis units) are essential for effective management of acute metabolic decompensation. Liver transplantation is an accepted viable option for the long-term prevention of acute metabolic decompensation in eligible patients. Research is ongoing into new treatment options for MSUD, such as gene therapy. Conclusion: Optimal management of acute metabolic decompensation in patients with MSUD requires prompt, effective treatment to reduce leucine levels without causing complications. A ready-to-use branched chain amino acid-free intravenous solution has been recently approved in Europe and research into new treatment options is ongoing.

Cystinosis is a rare lysosomal storage disease characterised by cystine crystal formation within cells. In the eyes, crystals accumulate in the cornea causing photophobia, loss of visual acuity, and corneal complications. Strict adherence to topical cysteamine treatment is the only therapy that reduces corneal crystal accumulation. Cystinosis, a crystallopathy, is also a disease of inflammation. As the disease progresses the inflammatory processes have a greater impact on the ocular manifestations. The age at which inflammation becomes increasingly significant is dependent on the adequacy of early patient management and adherence with therapy. As patients are living longer with cystinosis, optimising ocular management is increasingly important. No clinical guidelines addressing the long-term ocular management of cystinosis exist. Similarly, there is little recognition in the literature of how to address the inflammatory component of the disease. This paper presents management guidelines, linked to the 3C Classification of severity, used at our centre that provides a framework for optimising care. Adoption of these can help preserve the sight of cystinosis patients. The paper also hypothesises the molecular pathway leading to corneal inflammation.