Ornithine transcarbamylase deficiency

Newborn screening for OTC deficiency requires collecting a small amount of blood from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.

Screening measures how much citrulline is in your baby’s blood. Citrulline is one of the products of the urea cycle and does not form when the OTC enzyme is not working. Babies with very low levels of citrulline might have OTC deficiency.

If your baby’s blood spot screening result for OTC 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 can happen. Screening samples collected too early (before the baby is 24 hours of age) may cause false positive results. Babies with other conditions that have low citrulline levels may also be detected through this screening. An example of another condition that may be detected is carbamoyl phosphate synthetase I deficiency.

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 OTC deficiency in boys may appear within the first few days of life. Some boys and most girls with OTC deficiency may also have signs and symptoms of the disease that are less severe and happen at a later age.

Signs of the condition may include the following:

• High levels of ammonia (hyperammonemia)
• Floppy arms and legs (hypotonia)
• Poor feeding
• Sleepiness or lack of energy (lethargy)
• Vomiting, especially after eating
• Breathing trouble
• Seizures

A change in the OTC gene causes this condition. This gene gives the body instructions for making the OTC enzyme, which helps remove ammonia from the body.

Without a working OTC gene, ammonia builds up in your baby’s body. High levels of ammonia can cause brain damage.

OTC deficiency is a genetic condition that babies typically inherit from their biological mother. To learn more about genetic conditions, visit MedlinePlus Genetics.

• OTC deficiency is inherited in an X-linked recessive pattern, which means babies inherit this condition on their X‑chromosome.
  • Baby boys only have one X-chromosome. All boys with one nonworking OTC gene (on their only X chromosome) have OTC deficiency, which means this condition is more common in boys.
  • Baby girls have two X chromosomes. This means that the chance of a baby girl having serious OTC deficiency is lower, but still possible.
• Girls with one working copy of OTC and one nonworking copy of OTC are called heterozygotes.
  • Heterozygotes may or may not have symptoms. If they have symptoms, they are usually less severe than in boys.
  • Heterozygotes with and without symptoms can pass a nonworking copy of the gene to their children.
• Parents who have a child with OTC deficiency are at risk to have another child with OTC deficiency. However, additional testing is needed in order to know the exact risk.
• 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.