Conditions Carnitine Uptake Defect

Carnitine uptake defect (CUD) is an inherited condition in which the body cannot bring enough carnitine, a substance that helps the body make energy from fats, into the cells. CUD is considered a fatty acid oxidation condition because people affected by CUD are unable to break down certain fats. This can result in a build-up of unused fatty acids. If untreated, CUD can cause brain damage or death. However, with early detection and treatment, individuals with CUD can often lead healthy lives.

Condition Type

Fatty Acid Oxidation Disorders


Carnitine uptake defect (CUD) affects one out of every 100,000 babies. However, it is more common in certain populations. It is estimated to affect one out of every 40,000 babies born in Japan.

Also known as

  • CUD
  • Carnitine transport defect
  • Carnitine transporter deficiency
  • Carnitine uptake deficiency
  • Renal carnitine transport defect
  • Systemic carnitine deficiency

Follow-Up Testing

Your baby’s doctor may ask you if your baby is showing any of the signs of CUD (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 carnitine uptake defect (CUD) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your baby 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, a few babies do have the condition, so it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated CUD 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 testing your baby’s urine and blood samples in order to measure the amount of carnitine in your baby’s body. Low levels of carnitine in the blood may be sign that your baby has CUD. Sometimes follow-up testing may also include testing a very small sample of skin.

About Carnitine Uptake Defect

Early Signs

The first signs of carnitine uptake defect (CUD) usually begin between birth and 3 years of age. These signs vary from child to child. Your baby may show many of them or none at all.

Signs of CUD include:

  • Sleeping longer or more often
  • Tiredness
  • Irritability
  • Poor appetite
  • Fever
  • Vomiting
  • Diarrhea
  • Low blood sugar (called hypoglycemia)
  • Behavior changes
  • Confusion
  • Breathing troubles

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 doctor immediately.



Prescription L-carnitine supplements is the main treatment for carnitine uptake defect (CUD). L-carnitine is a substance that is naturally produced in the body, but your baby’s body might not make enough of it. These supplements help break down fats and get rid of harmful waste substances that build up in the body. Your baby’s doctor will need to write you a prescription for these supplements.

Dietary Treatment

Your baby will probably need to follow a restricted diet in order to avoid eating fats that their body cannot break down. A nutritionist or a dietician can help you plan your baby’s diet.

Your baby will also need to eat often in order to avoid many of the signs mentioned in the Early Signs section.

Expected Outcomes

Carnitine uptake defect (CUD) is easily treated. Children who receive treatment early on have healthy growth and development.

Even if your baby has not received treatment yet, L-carnitine can often reverse the heart troubles and muscle weakness that often result from CUD.

If CUD is not treated, children are at risk of heart trouble, liver damage, breathing problems, or even permanent brain damage. This is why early screening and treatment are so important.


When we eat food, enzymes help break it down. Certain enzymes help break down fats. The carnitine transporter enzyme is very important for breaking down fats. This enzyme's job is to move carnitine into the mitochondria of the cell. Mitochondria are the energy-making factories of cells.

If your baby has carnitine uptake defect (CUD), then your baby’s body either does not make enough of or makes non-working copies of the carnitine transporter. When this happens, your baby’s body cannot use fats for energy. This is harmful because your baby’s heart needs fats for energy. Your baby’s body also needs fats for energy when their body runs out of sugars to break down, such as between meals.

CUD is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for CUD, 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 CUD 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 Carnitine Uptake Defect

Support Services

Support groups can help connect people who are affected with carnitine uptake defect (CUD) with a supportive community and information. These organizations offer resources for affected individuals and their families, as well as health care providers.

Accessing Care

Work with your baby’s doctor to determine the next steps for your baby’s care. Your baby’s physician may help you coordinate care with a doctor who specializes in metabolism, a dietician who can help plan your child’s specialized diet, and other medical resources in your community. Some children with carnitine uptake defect (CUD) 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 CUD 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 CUD, 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 (ACMG) and the Find a Genetic Counselor tool 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.

Families' Experiences

At this time we have not located a family story for this particular condition. If your family is affected by carnitine uptake defect (CUD) and you would like to share your story, please contact us so other families may learn from your experience.

Each family's experience with a condition is unique, but there are some parts of the evaluation and treatment of CUD that are similar to other fatty acid oxidation conditions. You may find it useful to read the stories of families affected by other fatty acid oxidation conditions. You can read these stories on the family story page of the FOD Family Support Group website.

References & Sources

Visit MedlinePlus Genetics for more condition information

Visit the Screening, Technology And Research in Genetics (STAR-G) Project for more information on CUD

ACT Sheets

Healthcare professionals can learn more about confirmatory testing by reading the American College of Medical Genetics and Genomics' Algorithm for Diagnosis and ACT Sheet, a guide for follow-up after newborn screening. You can visit this page of the ACMG website here.

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