Propionic acidaemia is a rare inherited metabolic disorder where the body cannot properly break down certain proteins and fats, leading to the buildup of toxic substances that can affect multiple organs and cause serious health complications if not managed carefully.

Understanding Treatment Goals for Propionic Acidaemia

Living with propionic acidaemia requires ongoing medical attention and a carefully managed approach to prevent serious health problems. The main goal of treatment is to stop toxic substances from building up in the body, which happens when certain proteins and fats cannot be processed normally. When these toxic compounds accumulate, they can damage the brain, heart, kidneys, and other vital organs^[1].

Treatment focuses on several important objectives. First, it aims to prevent metabolic crises—sudden, dangerous episodes where the body becomes overwhelmed with toxic acids. Second, it works to support normal growth and development, particularly in children. Third, it seeks to minimize long-term complications such as intellectual disability, heart problems, and kidney disease. Finally, treatment helps maintain the best possible quality of life for people affected by this condition^[2].

The approach to treating propionic acidaemia depends heavily on when symptoms first appear and how severe they are. Some babies show signs within the first few days of life, while others may not develop symptoms until later in childhood or even adulthood. Early diagnosis through newborn screening—a simple blood test done shortly after birth—has dramatically improved outcomes, as it allows treatment to begin before serious damage occurs^[3].

Medical societies and expert groups have developed guidelines to help doctors manage this complex condition. These recommendations are based on years of experience and research, though much of the evidence comes from individual patient experiences rather than large-scale studies. Alongside these established treatments, researchers are actively investigating new therapies in clinical trials, offering hope for better options in the future^[10].

Standard Treatment Approaches

The cornerstone of managing propionic acidaemia is dietary modification. People with this condition must follow a carefully controlled low-protein diet that restricts the intake of four specific amino acids: valine, isoleucine, threonine, and methionine. These are called propiogenic amino acids because they are converted into propionyl-CoA, a substance that cannot be properly processed by people with propionic acidaemia. When too much of these amino acids enters the body, toxic propionic acid builds up, leading to serious health problems^[8].

The diet must be individualized for each person and adjusted regularly based on age, growth, and laboratory results. Infants might receive precise amounts of breast milk or regular infant formula to provide just enough of these amino acids for growth without causing toxicity. As children grow and begin eating solid foods, they must limit high-protein items such as meat, poultry, fish, eggs, dairy products, beans, nuts, and even regular breads and pastas. A metabolic dietitian—a specialist trained in managing inherited metabolic disorders—works closely with families to design meal plans that meet nutritional needs while keeping the diet safe^[14].

Because natural protein is so restricted, most people with propionic acidaemia need medical formula supplementation. These special formulas contain individual amino acids, but the four problematic ones are either removed entirely or included in very small amounts. This allows patients to get enough protein for normal growth and development without the parts that would be harmful. These formulas also provide essential calories, vitamins, and minerals. They can be consumed as drinks or delivered through a feeding tube for those who cannot take enough nutrition by mouth^[21].

L-carnitine (also called levocarnitine or Carnitor) is a medication commonly prescribed for propionic acidaemia. This supplement helps the body eliminate toxic compounds by binding to propionic acid and allowing it to be removed through urine. Many people with this condition develop carnitine deficiency naturally because so much is used up trying to clear the toxic acids. L-carnitine comes as a liquid or tablet and is usually taken daily. One notable side effect is that it can cause a fishy body odor in some people taking it^[14].

Some patients also take antibiotics, such as metronidazole (Flagyl), on a regular schedule or during illness. The reason for this is that bacteria living in the intestines can produce propionic acid, adding to the body’s toxic load. By reducing these bacteria with antibiotics, the total amount of propionic acid can be lowered. This approach may be used daily, at regular intervals, or specifically during periods of illness when the risk of metabolic crisis is higher^[14].

When someone with propionic acidaemia becomes seriously ill, immediate hospitalization is essential. During a metabolic crisis, treatment focuses on stopping the body’s catabolic state—a condition where the body breaks down its own proteins for energy, releasing more of the problematic amino acids. Doctors provide high-calorie intravenous fluids, often containing glucose, to reverse this process. They also treat any underlying cause such as infection, control vomiting and dehydration, and manage complications like hyperammonemia (dangerously high ammonia levels in the blood) and metabolic acidosis (excessive acid in body fluids). Stopping all protein intake temporarily is crucial during the acute crisis^[9].

In 2018, a medication called Carbaglu (carglumic acid) received approval from the U.S. Food and Drug Administration specifically to treat acute hyperammonemia associated with propionic acidaemia and a related condition called methylmalonic acidaemia. This medication works by activating an enzyme involved in removing ammonia from the blood. It represents an important addition to the treatment options available during metabolic crises^[14].

Treatment is lifelong and requires regular monitoring. Patients need frequent blood and urine tests to check levels of amino acids, organic acids, ammonia, blood sugar, and kidney function. Growth and development must be tracked carefully, especially in children. Heart function should be monitored because cardiomyopathy (heart muscle disease) is a known complication. Kidney function also requires ongoing attention since chronic kidney disease develops in many patients over time. Some may eventually need dialysis or kidney transplantation^[2].

Treatment Options in Clinical Trials

While standard dietary and medical management helps many people with propionic acidaemia, researchers recognize that current treatments have limitations. Some patients continue to experience metabolic crises despite careful management, and long-term complications remain common. This has driven the search for innovative therapies that might address the underlying problem more effectively^[10].

One promising area of research involves messenger RNA (mRNA) therapeutics. This cutting-edge approach uses the same technology that powered some COVID-19 vaccines. The idea is to deliver working copies of the genetic instructions—mRNA—that cells need to produce the missing or defective enzyme. If successful, this could help cells temporarily make functional propionyl-CoA carboxylase enzyme, potentially reducing toxic buildup. The pharmaceutical company Moderna is actively developing an mRNA treatment for propionic acidaemia^[7].

Moderna’s clinical trial, called the Paramount Study, is currently recruiting participants aged one year and older who have propionic acidaemia. This study is evaluating whether the investigational mRNA treatment can reduce symptoms and improve the condition. Clinical trials like this one typically proceed through several phases. Phase I trials focus primarily on safety, determining whether the treatment causes harmful side effects and identifying safe doses. Phase II trials examine whether the treatment actually works to improve the disease, while continuing to monitor safety. Phase III trials compare the new treatment to existing standard treatments in larger groups of patients to confirm effectiveness^[7].

The mechanism behind mRNA therapy is based on providing temporary genetic instructions to cells. Unlike gene therapy, which permanently alters DNA, mRNA therapy delivers a temporary message that cells use to make the needed protein. The mRNA breaks down naturally after a short time, so treatments would likely need to be given repeatedly. This approach offers potential advantages in safety, as it does not permanently change a person’s genetic material^[7].

To participate in clinical trials for propionic acidaemia, patients must meet specific eligibility criteria. These typically include having a confirmed diagnosis through genetic testing or enzyme analysis, being within a certain age range, and meeting health requirements. Families interested in participating can contact trial coordinators to learn more about whether they qualify. Participation in any clinical trial is entirely voluntary, and patients can withdraw at any time. Many trials provide compensation for time and travel expenses^[7].

Another area of investigation involves liver transplantation. Because the liver is where most of the problematic enzyme activity normally occurs, replacing it with a healthy liver could theoretically reduce the metabolic problems. Some medical centers have performed liver transplants, and in select cases, combined liver-kidney or liver-heart transplants for patients with severe organ damage. However, transplantation is a major surgical procedure with significant risks, and debate continues in the medical community about which patients might benefit most. Transplantation does not cure all aspects of the disease, and patients still require careful monitoring afterward. The decision to pursue transplantation must be made on a case-by-case basis after thorough discussion between families and their medical team^[14].

Research into enzyme replacement therapy and gene therapy approaches is also ongoing, though these remain in earlier stages of development. Enzyme replacement would involve giving infusions of the missing propionyl-CoA carboxylase enzyme, similar to treatments available for other metabolic disorders. Gene therapy would aim to insert working copies of the PCCA or PCCB genes into patients’ cells, potentially providing a long-term or permanent correction. These approaches face technical challenges specific to propionic acidaemia but represent important areas of future research^[10].

Clinical trials for rare diseases like propionic acidaemia often take place at specialized medical centers with expertise in metabolic disorders. In the United States, major centers include Children’s National Medical Center in Washington, D.C., Baylor College of Medicine in Houston, and others. European centers in countries such as the United Kingdom, Switzerland, Germany, and Spain also conduct research on this condition. International collaboration is essential because the rarity of propionic acidaemia means that no single center sees enough patients to conduct large studies alone^[10].

Most common treatment methods

• Dietary management
  • Low-protein diet restricting valine, isoleucine, threonine, and methionine intake to prevent toxic acid buildup^[8]
  • Individualized meal plans developed with metabolic dietitians based on age, growth, and laboratory results^[14]
  • Limitation of high-protein foods including meat, dairy, eggs, beans, and nuts^[21]
• Medical formula supplementation
  • Special formulas containing amino acids with propiogenic amino acids removed or minimized^[21]
  • Provision of adequate protein, calories, vitamins, and minerals for growth and development^[14]
  • Administration by mouth or through feeding tubes as needed^[4]
• L-carnitine (levocarnitine) supplementation
  • Medication that binds to toxic propionic acid and helps remove it through urine^[14]
  • Replaces carnitine depleted by the disease process^[14]
  • Available as liquid or tablets for daily use^[14]
• Antibiotic therapy
  • Metronidazole (Flagyl) used to reduce intestinal bacteria that produce propionic acid^[14]
  • May be given daily, at intervals, or during illness to reduce toxic acid production^[14]
• Emergency management of metabolic crises
  • Immediate hospitalization with high-calorie intravenous fluids to stop protein breakdown^[9]
  • Treatment of infections, dehydration, and vomiting^[8]
  • Management of hyperammonemia and metabolic acidosis^[9]
  • Use of Carbaglu (carglumic acid) for acute hyperammonemia^[14]
• mRNA therapeutics (investigational)
  • Experimental treatment delivering genetic instructions to produce functional enzyme^[7]
  • Currently being tested in the Paramount Study for patients aged one year and older^[7]
  • Aims to reduce symptoms by helping cells temporarily make the missing enzyme^[7]
• Organ transplantation
  • Liver transplantation considered in select severe cases^[14]
  • Combined liver-kidney or liver-heart transplants for patients with multiple organ damage^[14]
  • Decision made case-by-case after thorough evaluation of risks and benefits^[14]