What is PCCB-related Propionic Acidemia?
Propionic acidemia is an inherited condition caused by a deficiency in the enzyme propionyl-CoA carboxylase. This results in the body being unable to properly process certain parts of proteins and fats, causing harmful substances to build up in the the body. This build up in the blood, urine, and tissues can be toxic and cause serious health problems.
Symptoms of propionic acidemia most often begin within the first few days after birth. Initial symptoms include poor feeding, lack of energy, weak muscle tone, and vomiting. If untreated, these symptoms can progress to more serious medical complications, including organ damage, seizures, coma, and possibly death. Propionic acidemia may be associated with developmental regression, intellectual disability, frequent infection, nutritional problems, and heart problems. The severity of symptoms can be variable amongst individuals with the condition. Typically, if an individual has symptoms beginning in infancy and does not receive treatment, they do not live past the first year of life.
Less commonly, the signs and symptoms of propionic acidemia appear during childhood or later in life. In individuals with this later-onset form, symptoms may be triggered by periods of fasting, fever, or infection. In some cases, the only symptom present is thickening of the heart muscle (cardiomyopathy).
At a cellular level, propionic acidemia is caused by mutations in either the PCCA or PCCB gene. Although the genetic mutations are different, the resulting symptoms are the same because PCCA and PCCB combine together to make the enzyme propionyl-CoA carboxylase. Of the known cases of propionic acidemia, approximately 35-50% have been attributed to mutations in PCCA, while 50-65% have been attributed to PCCB mutations.
How common is PCCB-related Propionic Acidemia?
The worldwide incidence of propionic acidemia has not been estimated, but is generally accepted to be 1 in 100,000 overall. However, the incidence of this condition varies significantly across the world. Where estimates are available, the incidence is between 1 in 1500 and 1 in 520,000. It is more common among in Japan (1 in 17,400 including an asymptomatic form identified in newborn screening), the Middle East (1 in ~27,000 in Saudi Arabia and and 1 in 2000-5000 in specific tribes, 1 in 10,000 in Bahrain, and as high as 1 in 20,000 in the United Arab Emirates), and in Greenland (1 in 1600 in the Inuit population). Again, depending on region, the percent of cases attributed to the PCCB gene is between 10% and 80% with most countries showing that 60% of cases are due to PCCB mutations.
How is PCCB-related Propionic Acidemia treated?
At this time, there is no cure for propionic acidemia. Treatment primarily focuses on individualized dietary management to ensure proper nutrition. Dietary supplements and medication to manage medical complications may be used. Regular assessment for growth, nutritional needs, feeding, kidney function, cardiac problems, and development is recommended. Prompt identification and treatment of stressors such as fasting, fever, illness, and injury may decrease the chance of organ damage. Any time a child with propionic acidemia experiences an event causing fasting or illness, he or she needs prompt treatment, which may include a hospital visit. Liver transplant may be beneficial in some cases.
What is the prognosis for a person with PCCB-related Propionic Acidemia?
If an individual presenting with symptoms of propionic acidemia is not treated early in infancy, they do not usually live past the first year of life. If the condition is recognized promptly and treated diligently, survival and long term outcome is potentially improved. Even with treatment, affected individuals may still have significant intellectual and neurological impairment. Normal development is possible in some patients with later onset forms of the condition, with strict dietary management and close monitoring.