Arginase deficiency

Newborn screening for arginase deficiency is done using a small amount of blood collected from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.

During screening, a special machine measures how much arginine is in your baby’s blood. Babies with high levels of arginine might have arginase deficiency.

If your baby’s blood spot screening result for arginase deficiency is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.

An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.

Your baby may need the following tests after an out-of-range screening result:

• Blood and/or urine tests
• Genetic testing using a blood sample

You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems soon after birth if they are not diagnosed and treated quickly.

False-positive newborn screening results for this condition are rare. Babies who receive supplemental nutrition (also called total parenteral nutrition [TPN] or hyperalimentation) may have out-of-range results.

Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.

Signs of arginase deficiency can vary widely and may appear anytime from infancy to childhood. These signs may be triggered by eating foods high in protein, going a long time without eating (prolonged fasting), illnesses, and infections.

Signs of the condition may include the following:

• High levels of ammonia (hyperammonemia)
• Poor feeding
• Sleepiness or lack of energy (lethargy)
• Vomiting
• Tight, rigid muscles (spasticity)
• Breathing trouble
• Seizures
• Developmental delays
• Speech problems
   

The condition is caused by a change in the ARG1 gene. This gene gives the body instructions for making arginase. Arginase is an enzyme that helps break down the amino acid arginine.

Without a working ARG1 gene, your baby’s body cannot make enough working arginase enzyme. As a result, their body has trouble breaking down arginine and getting rid of ammonia.

If arginine is not broken down, harmful levels of arginine and ammonia build up in your baby’s body. Nerve cells in your brain are very sensitive to arginine and ammonia levels, so high levels of arginine can cause brain damage.

Arginase deficiency is a genetic condition. Babies inherit it from their biological (birth) parents. To learn more about genetic conditions, visit MedlinePlus Genetics.

• Arginase deficiency is an autosomal recessive condition. Babies inherit it when each parent passes down a nonworking ARG1 gene to their baby. Only babies with two nonworking ARG1 genes—one from the mom and one from the dad—have this condition.
  • People with one working copy and one nonworking copy of the ARG1 gene are called carriers.
  • Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
  • If two parents are carriers of a nonworking copy of the ARG1 gene, they have a 1 in 4 chance of having a child with arginase deficiency.
  • Carriers for arginase deficiency often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with arginase deficiency.
  • Parents who already have a child with arginase deficiency still have a 1 in 4 chance of having another child with arginase deficiency. This 1 in 4 chance stays the same for future children. 
• Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.