Argininemia

There is newborn screening for argininemia. During routine newborn screening, a tiny sample of blood is taken from the heel of a newborn. This test, called a heel prick, involves getting a few drops of blood from a pinprick in the newborn's heel. The blood is run through a machine that can detect elevated levels of arginase. Sometimes, newborn screening missing a child with a disorder normally detectable through screening. Other times, there may be a 'false positive.' Further testing of a blood sample, called an enzyme assay, can detect reduced activity of the arginase enzyme and confirm a diagnosis.

Information about newborn screening programs can be found at Save Babies Through Screening Foundation or Baby's First Test.

Infants with argininemia may be detected through newborn screening (NBS). NBS can detect elevated levels of arginine in the dried blood spots. Further testing of a blood sample, called an enzyme assay, can detect reduced activity of the arginase enzyme and confirm a diagnosis. Doctors may also test the urine for orotic acid (a compound that naturally occurs in the body), but is increased in urine samples from people with argininemia.

Doctors may also conduct molecular genetic testing on infants with argininemia. These tests involve studying the ARG1 gene for changes (mutations) that cause the disorder. This can include sequence analysis, where a part or sequence of DNA within a gene is examined, or deletion/duplication analysis, where missing or extra regions of DNA are looked for within a specific gene. Molecular genetic testing must be done at specialized laboratories.

In a family with argininemia, tests can be done to see whether other family members are carriers for the disorder. (Carriers do not have symptoms and have one working and one non-working copy of the ARG1 gene.) However, the specific gene changes in that family needs to be known. If known, all siblings and other at-risk relatives can be tested. Molecular genetic testing, which are tests that look for changes to genes, can be performed. A newborn child in a family with a history of argininemia should be tested through molecular genetic testing. A genetic counselor or a physician with experience in argininemia can provide advice about how a confirmed diagnosis can affect other family members. Medical geneticists can be found through the American College of Medical Genetics and a genetic counselor can be found through the National Society of Genetic Counselors.

Some parents may choose to have their child tested for argininemia before they are born. This is known as prenatal diagnosis. If the gene change(s) that causes argininemia are known in a family, then molecular genetic testing (which can detect these changes) can be used for prenatal diagnosis. A sample of tissue can be taken from the placenta to test for changes in the ARG1 gene. This test is called chorionic villus sampling. Another test is called amniocentesis, which involves taking a sample of the amniotic fluid that surrounds and protects a developing fetus. Cells known as amniocytes are taken from the fluid and studied for changes in the ARG1 gene. There are risks to the unborn baby of doing these tests before birth.

If molecular genetic testing is not possible, doctors can make a prenatal diagnosis through biochemical testing. This is testing to measure the activity of the enzyme arginase, which is significantly reduced in argininemia. Doctors test fetal red blood cells taken from a sample of umbilical cord blood after 18 weeks gestation. Severe reduction of arginase activity indicates a diagnosis of argininemia. In other disorders, samples of tissue or cells from the amniotic fluid or placenta are used. They cannot be used to diagnose argininemia because these tissues do not have any arginase activity.

Prenatal diagnosis of conditions that are treatable like argininemia are not common, although different medical professionals may have different opinions about whether it is appropriate. Talk to your doctor or a genetic counselor in your area to discuss the risks and benefits of prenatal diagnosis.