Argininemia (ARG) is a condition that causes harmful amounts of arginine and ammonia to build up in the body. It is considered an amino acid condition because people affected with ARG are unable to break down an amino acid, a small molecule that makes up proteins, known as arginine. You may also hear ARG called a urea cycle condition. This name is used to describe conditions that cause ammonia to accumulate in the body. If untreated, argininemia can cause muscle problems and developmental delay. However, if the condition is detected early and proper treatment is initiated, individuals with argininemia can often lead healthy lives.
Amino Acid Disorders
Argininemia affects as many as one in every 300,000 babies born in the United States.
Also known as
- Arginase deficiency
- ARG1 deficiency
- Arginase deficiency disease
Your baby’s doctor may ask you if your baby is showing any of the signs of ARG (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.
If your baby’s newborn screening result for argininemia (ARG) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your child to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, as a few babies do have the condition, it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated ARG can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.
Follow-up testing will involve checking your baby’s urine and blood samples for signs of ARG. Harmful amounts of certain substances build up in the body when a child has an amino acid condition, so measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. High amounts of arginine in the blood and orotic acid in the urine might indicate that your baby has ARG.
Signs of argininemia (ARG) can begin any time from infancy to childhood. Usually, signs begin to show at around one to three years of age. Signs of ARG include:
- Delayed growth
- Developmental delays
- Balancing trouble
- Tight, rigid muscles (called spasticity)
- Poor appetite
- Sleeping longer or more often
- Weak muscle tone (called hypotonia)
- Breathing trouble
- Trouble regulating body temperature (your baby might get cold easily)
- Small head size
Many of these signs may occur when your baby eats foods that their body cannot break down. They can be triggered by long periods of time without eating, illnesses, and infections.
If your baby shows any of these signs, be sure to contact your baby’s health care provider immediately.
Your baby may need to be on a restricted diet in order to avoid the proteins that their body cannot break down. A dietician or a nutritionist can help you plan a healthy diet for your child.
Your baby’s doctor may recommend special foods or formulas for children with argininemia (ARG). These formulas will likely need to continue through adulthood.
Often, eating may help prevent many of the signs of ARG mentioned in the Early Signs section.
Supplements and Medications
Your baby’s health care provider may prescribe medications to help your baby’s body get rid of excess arginine and ammonia.
Children who are treated early for argininemia (ARG) can have healthy growth and development. This is why newborn screening for ARG is so important.
Even with treatment, some children may experience learning disabilities, intellectual disabilities, or tight muscles (spasticity), which are commonly associated with ARG.
Children who do not receive treatment for ARG are at risk for seizures, brain damage, or coma.
When we eat food, enzymes help break it down. Some enzymes help break down proteins into their building blocks, called amino acids. Other enzymes break down these amino acids further to their base molecules. In argininemia (ARG), the enzyme arginase is not working correctly.
Arginase’s job is to help break down the amino acid arginine and remove ammonia from the body through the urine. If your baby has ARG, then their body either does not make enough or makes non-working arginase enzymes.
When arginase is not working correctly, the body cannot break down arginine correctly or get rid of ammonia in the blood. This causes high levels of ammonia and arginine in the blood, which can be dangerous. Everyone has some ammonia and arginine in their blood, but too much can be toxic.
ARG is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for ARG, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with ARG is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.
Support for Argininemia
Support groups can help connect families who have a child or other family member affected with argininemia with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates:
Work with your baby’s health care provider to determine the next steps for your baby’s care. Your baby’s doctor may help you coordinate care with a physician that specializes in metabolism, a dietician who can help plan your child’s specialized diet, and other medical resources in your community. Some children with ARG have developmental delays. If you think that your baby is not meeting their developmental milestones, ask your baby’s doctor about the next steps in accessing a developmental evaluation and care.
Because ARG is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for ARG, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the American College of Medical Genetics and Genomics and the Find a Genetic Counselortool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.