Propionic acidemia
The rate of positive results in confirmatory testing for suspected propionic acidemia in newborn screening is approximately 50%.
Propionic acidemia is a rare inherited metabolic disorder caused by a deficiency of the enzyme propionyl-CoA carboxylase, which is essential for the metabolism of certain amino acids and fatty acids.
This deficiency leads to the accumulation of propionic acid in the blood, resulting in metabolic acidosis and other serious health issues.
Da Bo, 40~49 year old female. Ask Date: 2005/10/11
Dr. Jian Yingxiu reply Rare Disease
For information on propionic acidemia, please refer to http://ntuh.mc.ntu.edu.tw/gene/genehelp/database/disease/Propionic_acidemia_940429.htm.
A positive result in newborn screening does not necessarily indicate that the infant is affected by the disease.
Please ensure to follow up for confirmation and monitor for any abnormal symptoms such as lethargy or vomiting.
The positive rate and values of retesting are related to the standards of each screening center, making it difficult to estimate the likelihood of the disease based on these results.
Thank you.
Reply Date: 2005/10/11
More Info
Propionic Acidemia (PA) is a rare inherited metabolic disorder that affects the body's ability to break down certain proteins and fats. It is caused by a deficiency of the enzyme propionyl-CoA carboxylase, which is essential for the metabolism of branched-chain amino acids (valine, isoleucine, and methionine) and odd-chain fatty acids. When this enzyme is deficient, toxic levels of propionic acid can accumulate in the blood, leading to various health issues, including metabolic acidosis, neurological impairment, and developmental delays.
Newborn screening for PA is typically performed using tandem mass spectrometry (MS/MS), which measures the levels of various metabolites in the blood. A positive screening result for PA indicates that the levels of certain metabolites, such as propionylcarnitine (C3), are elevated. However, it is important to note that a positive screening result does not confirm the diagnosis; it merely indicates that further testing is necessary.
Follow-up testing usually involves confirmatory tests, such as genetic testing or additional biochemical assays, to determine whether the infant has PA. The positive predictive value (PPV) of newborn screening tests can vary based on the population being screened and the specific screening protocols used. Generally, the PPV for PA is relatively low compared to other metabolic disorders, often ranging from 1% to 10%. This means that while a positive screening result may indicate the possibility of PA, the majority of infants who screen positive will not have the disorder upon further testing.
In terms of follow-up testing, if a newborn screens positive for PA, healthcare providers typically recommend:
1. Confirmatory Testing: This may include measuring the levels of propionylcarnitine and other metabolites in the blood, as well as genetic testing to identify mutations in the PCCA or PCCB genes, which are responsible for PA.
2. Clinical Evaluation: A thorough clinical assessment by a metabolic specialist is crucial. This may involve evaluating the infant for symptoms of metabolic disorders, such as lethargy, poor feeding, vomiting, or developmental delays.
3. Dietary Management: If PA is confirmed, dietary management is essential. This typically involves a low-protein diet to reduce the intake of amino acids that contribute to propionic acid production. In some cases, supplementation with specific nutrients may be necessary.
4. Regular Monitoring: Infants diagnosed with PA require ongoing monitoring for metabolic control, growth, and development. Regular follow-ups with a metabolic specialist are essential to adjust dietary plans and manage any complications.
In summary, Propionic Acidemia is a serious metabolic disorder that requires prompt diagnosis and management. The follow-up testing after a positive newborn screening result is critical to confirm the diagnosis and initiate appropriate treatment. While the positive rates for follow-up testing can vary, it is essential for healthcare providers to communicate clearly with families about the implications of screening results and the importance of further evaluation. If you have concerns about a specific case or screening results, it is advisable to consult with a healthcare professional who specializes in metabolic disorders for personalized guidance and support.
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