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Propionic Acidemia (PA)
Monday, 18 August 2003
Sunday, 25 January 2004

What

Propionic acidemia (PA) is an inherited metabolic disorder characterized by the deficiency of an enzyme called propionyl-CoA carboxylase (PCC). PCC is involved in the breakdown of protein into amino acids, which are the building blocks of protein. With a lack of this enzyme functioning properly, the child cannot tolerate the normal amount of dietary protein. This leads to a build up of products that are toxic to the body. High protein diets, constipation, and infections usually trigger recurrent episodes of metabolic decompensation and these recurrent episodes are usually separated by periods of normal health.

Who

The incidence is about 1 in 100,000 births, equally found in males and females.

Signs and Symptoms

Children with propionic acidemia usually present with serious illness very early in life. The initial symptom is often vomiting. Some infants have such severe vomiting that they are operated on with a diagnosis of pyloric stenosis. Vomiting associated with episodes of metabolic decompensation can lead to dehydration and decreased responsiveness that can progress to coma. Episodes are related to diet. Children cannot handle the usual dietary quantities of protein. Before diagnosis there is often a recurrent pattern of illness. Metabolic decompensation leads to admission to the hospital where children are started on intravenous fluids and not allowed to eat. Since children are not eating, they are able to clear the toxic metabolites and they become well. They are discharged home where they are started on a regular diet. Once the children begin to eat, they become sick again as soon as a toxic quantity of intermediates has reaccumulated. Children can also have suppression of their bone marrow that leads to a decreased ability to fight infection. Infants with propionic acidemia also have very low muscle tone that may lead to a delay in achieving motor developmental milestones. Many of these children exhibit delays in all areas of development. Other signs and symptoms associated with propionic acidemia are low blood sugar levels, poor appetite and seizures.

Possible Causes

Propionic acidemia is an autosomal recessive disorder, meaning that a child has inherited a defective gene for the enzyme PCC from each parent. A person needs to inherit two defective genes to be born with the disease and this is why the parents are unaffected since they are each carrying one defective gene and have one normal gene. The gene responsible is found on chromosome 13. Proteins are made up of amino acids. When someone eats food containing protein, the body breaks down the protein into its amino acid components. These amino acids are then used to build proteins that are used in the body for growth, repair, and maintaining body tissues. If there is any type of problem with this pathway, harmful substances and byproducts accumulate in the body. A deficiency in the PCC enzyme results in the inability to break down proteins that contain the amino acids methionine, threonine, isoleucine, and valine. This results in an accumulation of harmful toxins and propionic acid in the body, which is damaging to the child.

Diagnosis

The diagnosis of propionic acidemia is usually suspected with the finding of the signs and symptoms described above, along with specific laboratory findings including urine organic acid and plasma amino acid analysis. The activity of the deficient enzyme is measured in white blood cells or fibroblasts (which are cells that make up the connective tissue in the body) to confirm the diagnosis.

Treatment

Children with propionic acidemia must have a diet containing low amounts of the involved amino acids to avoid high levels of toxins and propionic acid in the body. Without the appropriate treatment, the child’s health is in danger because complications are serious and can be life threatening. During an acute episode of metabolic decompensation, patients are admitted to the hospital for intravenous hydration and management of any associated complications. The patients are protein restricted in order to aid the body in clearing the toxins.

Prognosis

The prognosis of the child depends on how severe the enzyme deficiency is, how early the child is diagnosed, and how early the child is given treatment. If this disorder is not treated early, brain damage, including coma, seizures and death can occur.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Propionic Acidemia Foundation
Great website for families who want to know more about PA, and want to keep track of how much research is being done on this disorder.

Educating Parents of Extra-special Children
A website with a quick overview of PA, as well as helpful links to other websites.

Organic Acidemia Association
A good website with more information on PA, as well as other organic acidemias. They also have a very informative newsletter that families can subscribe to.

National Coalition for PKU and Allied Disorders
A great website with information abou tPA as well as on special diets and ongoing research.

Google Search for Propionic Acidemia (PA)

References and Sources

Emedicine: www.emedicine.com/PED/topic1906.htm Pediatric database: www.icondata.com/health/pedbase/files/PROPIONI.HTM NORD: www.rarediseases.org/search/rdbdetail_abstract.html?disname=Acidemia%2C%20Propionic