Propionic acidaemia – Diagnostics – Overview of Information and Clinical Research

Propionic acidemia is a rare inherited condition where the body cannot properly break down certain proteins and fats, causing harmful acids to build up in the blood and tissues. Early and accurate diagnosis is crucial to prevent serious complications and begin life-saving treatment. Understanding when to seek diagnostic testing and what tests are involved can help families navigate this challenging condition with greater confidence.

Who Should Undergo Diagnostics and When

Newborn babies are the primary group who should undergo diagnostic testing for propionic acidemia, particularly if they show signs of illness in the first days or weeks of life. Many states and countries now include propionic acidemia in their newborn screening programs, which means a simple blood test taken shortly after birth can identify affected infants before symptoms even appear.^[1] This early detection through routine screening represents one of the most important advances in managing this condition, as it allows treatment to begin immediately.

When newborn screening is not available or when a baby was born before screening became routine, parents should watch for warning signs that indicate diagnostic testing is needed. Infants who show poor feeding, excessive sleepiness that goes beyond normal newborn drowsiness, vomiting, or a lack of energy in the first few days or weeks of life should be evaluated urgently.^[2] These symptoms can progress rapidly to more serious complications including seizures, altered consciousness, or even coma, making prompt diagnosis absolutely essential.

Siblings of children already diagnosed with propionic acidemia should also be tested, even if they appear healthy. Because this condition is inherited in a pattern where both parents carry one copy of a changed gene, each child they have together has a one-in-four chance of being affected.^[4] Testing siblings allows doctors to start protective treatment before any symptoms develop, which significantly improves outcomes.

⚠️ Important

If a child with propionic acidemia becomes ill with fever, infection, or shows signs of dehydration or vomiting, immediate medical attention is required. These situations trigger what doctors call a metabolic crisis, where the body breaks down its own proteins and the condition can become life-threatening within hours. Families should be educated to recognize these early warning signs and seek emergency care without delay.^[3]

Older children or adults who have never been diagnosed but experience unexplained symptoms may also need testing. Although most cases are identified in infancy, some people have a milder form of the condition that appears later in life. These individuals might have episodes of vomiting, periods of extreme tiredness, difficulty gaining weight and growing properly, developmental delays, or unusual movement problems.^[2] In rare cases, heart problems can develop without other obvious metabolic symptoms, which can make diagnosis particularly challenging.

Classic Diagnostic Methods

The journey to diagnosing propionic acidemia typically begins with newborn screening, which has become the first line of defense against this condition. During expanded newborn screening, a few drops of blood are taken from a baby’s heel and placed on a special filter paper. This sample is sent to a laboratory where sophisticated equipment measures levels of various substances in the blood. For propionic acidemia, doctors look for elevated levels of a compound called C3, also known as propionylcarnitine.^[2] When this marker is abnormally high, it signals that something may be wrong with the body’s ability to process certain proteins and fats.

If newborn screening suggests propionic acidemia, or if a child develops symptoms that concern doctors, the next step is usually a urine test called organic acid analysis. This test uses a technology called gas chromatography-mass spectrometry, which sounds complex but essentially separates and identifies different chemicals in the urine.^[2] In someone with propionic acidemia, this test reveals a characteristic pattern of abnormal acids. Specifically, doctors look for elevated levels of 3-hydroxypropionate and the presence of methylcitrate, tiglylglycine, propionylglycine, and lactic acid. These substances are the toxic byproducts that accumulate when the enzyme propionyl-CoA carboxylase isn’t working properly.

Blood tests also play a crucial role in diagnosis. A plasma amino acid test typically shows elevated levels of glycine, an amino acid that builds up when propionic acid metabolism is blocked.^[2] This finding of elevated glycine is so common in propionic acidemia that the condition was once called “ketotic hyperglycinemia.” Additional blood work during a metabolic crisis often reveals a dangerous combination of problems including low blood sugar, high levels of ammonia, excessive acid in the blood with an increased anion gap, the presence of ketones in urine, and sometimes reduced counts of blood cells.^[8]

To confirm the diagnosis with certainty, doctors turn to genetic testing. This involves analyzing a person’s DNA to look for changes, called pathogenic variants or mutations, in either the PCCA or PCCB genes. These genes provide instructions for making the two parts of the propionyl-CoA carboxylase enzyme.^[1] Finding two disease-causing variants—one inherited from each parent—confirms the diagnosis. Genetic testing not only establishes the diagnosis definitively but can also help predict how severe the condition might be and identify other family members who might be carriers.

In some situations, particularly when genetic test results are unclear or conflicting, doctors may order an enzymatic activity test. This specialized test directly measures how well the propionyl-CoA carboxylase enzyme is functioning. It can be performed on white blood cells or on cells taken from a skin biopsy that are then grown in the laboratory.^[2] If the enzyme shows very low or absent activity, this provides strong biochemical confirmation of the diagnosis.

During a metabolic crisis, which can happen when someone with propionic acidemia becomes sick, additional emergency laboratory tests become essential. Doctors check blood gas levels to assess how acidic the blood has become, measure ammonia levels which can rise dangerously high, monitor blood sugar which often drops too low, and examine blood cell counts which may show abnormally low numbers of white blood cells or other blood cells.^[12] These tests don’t diagnose propionic acidemia on their own, but they help doctors understand how severely the condition is affecting the body and guide emergency treatment decisions.

⚠️ Important

Diagnosing propionic acidemia requires experience and specialized knowledge. The pattern of abnormal test results can sometimes be confused with other metabolic conditions, particularly methylmalonic acidemia, which is closely related. Doctors must carefully distinguish propionic acidemia from conditions like neonatal sepsis, other organic acid disorders, or common causes of acidosis.^[6] This is why testing should be done at specialized laboratories and results interpreted by physicians experienced in metabolic disorders.

Imaging tests, while not used to make the initial diagnosis, can reveal important complications of propionic acidemia. Brain imaging with CT scans or MRI may show characteristic damage to a region called the basal ganglia, which are clusters of nerve cells deep in the brain that control movement.^[3] This damage appears as areas of injury or infarction involving specific structures called the caudate, putamen, and globus pallidus. These findings help doctors understand the extent of brain injury and predict what neurological problems a person might face.

For families expecting a baby when propionic acidemia has already been diagnosed in another child, prenatal diagnosis is possible. Two main approaches exist: measuring specific markers in amniotic fluid obtained through amniocentesis, or performing DNA testing or enzyme analysis on cells obtained through chorionic villus sampling.^[6] These tests allow parents and doctors to know before birth whether the baby is affected, enabling immediate treatment starting right after delivery.

Diagnostics for Clinical Trial Qualification

Clinical trials testing new treatments for propionic acidemia require participants to meet specific diagnostic criteria to ensure the study includes only people with confirmed disease. These enrollment requirements are more stringent than general medical practice because research studies need precise, standardized diagnosis to produce reliable results.

For most clinical trials involving propionic acidemia, participants must have documented genetic confirmation showing biallelic pathogenic variants—meaning two disease-causing changes—in either the PCCA or PCCB genes.^[2] This genetic proof serves as the gold standard for trial enrollment because it provides unambiguous evidence of the condition. Some trials may also accept enzyme testing showing deficient propionyl-CoA carboxylase activity if genetic testing results are inconclusive, but genetic confirmation is generally preferred.

Beyond confirming the diagnosis, clinical trials typically require comprehensive baseline testing to document each participant’s current health status. This usually includes a complete set of laboratory tests measuring blood levels of propionic acid metabolites, amino acid profiles showing glycine and other amino acids, and markers of organ function including kidney and liver tests. These baseline measurements establish a starting point against which the experimental treatment’s effects can be measured.

Trials may also require documentation of disease severity and complications through medical records showing past metabolic crises, hospital admissions, or chronic complications like cardiomyopathy or kidney disease. Some studies focus specifically on patients with more severe disease, while others may include a broader range of disease severity. Age restrictions are common, with some trials limited to children of specific ages and others open to adults who have lived with the condition since childhood.^[7]

Imaging studies showing complications of propionic acidemia may be required for certain trials, particularly those testing treatments aimed at preventing brain damage or improving neurological outcomes. Brain MRI or CT scans demonstrating basal ganglia lesions or other characteristic changes might be part of the enrollment criteria. Similarly, trials testing treatments for heart complications would require echocardiograms or other cardiac testing to document cardiomyopathy at baseline.

Participants in clinical trials must also undergo testing to ensure they don’t have other conditions that might interfere with the study or make the experimental treatment unsafe. This typically includes tests to verify adequate liver and kidney function, normal blood counts, and absence of active infections. These safety tests protect both the individual participant and the integrity of the research.

Throughout the trial, participants typically undergo regular monitoring with the same diagnostic tests used at enrollment. Repeated blood tests track metabolite levels to see if the treatment is reducing harmful acid accumulation. Periodic imaging studies may assess whether the treatment prevents or reduces organ damage. These ongoing measurements allow researchers to determine whether the experimental treatment is working and to detect any unexpected side effects early.

Prognosis and Survival Rate

Prognosis

The prognosis for people with propionic acidemia varies considerably depending on when diagnosis occurs and how severe the disease is. Individuals diagnosed before birth or through newborn screening who receive immediate treatment generally have better outcomes than those diagnosed after developing symptoms.^[3] Early-onset disease presenting in the first week of life historically carried a more serious prognosis, with some studies showing median survival of about three years in this group before modern treatments were available. In contrast, late-onset disease appearing after six weeks of age tends to have better survival but often results in permanent neurological problems including severe movement disorders and abnormal muscle tone.^[3]

Long-term outcomes depend heavily on preventing metabolic crises and managing complications. Many affected individuals experience growth problems, intellectual disability ranging from mild learning difficulties to severe developmental delays, seizures, and movement disorders. Serious organ complications develop over time in many patients, including chronic kidney disease that occurs almost exclusively in propionic acidemia compared to similar disorders, and cardiomyopathy which affects heart function and is a major concern.^[2] Some people develop other complications like pancreatitis, optic nerve damage causing vision problems, hearing loss, and in females, premature ovarian insufficiency affecting fertility.

Despite these challenges, development may be normal in some individuals, particularly those diagnosed early through screening and managed aggressively. The risk of brain damage increases with each metabolic crisis, which is why preventing these episodes through careful dietary management and prompt treatment of illnesses is crucial.^[3] The fact that metabolic decompensation plays such a major role in causing neurological damage underscores the importance of early recognition of warning signs and immediate medical intervention.

Survival Rate

Specific survival statistics for propionic acidemia have improved over time with better diagnosis and management, though the condition remains serious. Historical data from before widespread newborn screening showed that individuals with severe neonatal-onset disease had a median survival of approximately three years, with early death often occurring due to metabolic crises complicated by overwhelming infection, severe hyperammonemia causing brain damage, heart complications, or other organ failures.^[3] However, these statistics likely don’t reflect current outcomes since they predate modern screening programs and improved treatment protocols.

With contemporary care including early diagnosis through newborn screening, immediate dietary intervention, careful monitoring, and aggressive treatment of metabolic crises, survival has improved significantly, though precise current survival rates are difficult to establish because the condition is so rare and outcomes vary widely. The introduction of newborn screening in particular has shifted the landscape, allowing treatment to begin before irreversible damage occurs. Still, the condition remains life-threatening, and even with treatment, serious complications can develop that affect both quality of life and longevity.^[2]

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