FATTY ACID DISORDER

Disorder Name: Carnitine transporter deficiency
Acronym: CTD
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• What is CTD?
• What causes CTD?
• If CTD is not treated, what problems occur?
• What is the treatment for CTD?
• What happens when CTD is treated?
• What causes the CT enzyme to be absent or not working correctly?
• How is CTD inherited?
• Is genetic testing available?
• What other testing is available?
• Can you test during a future pregnancy?
• Can other members of the family have CTD or be carriers?
• Can other family members be tested?
• How many people have CTD?
• Does CTD happen more often in a certain ethnic group?
• Does CTD go by any other names?
• Where can I find more information?

This fact sheet contains general information about CTD. Every child is different and some of this information may not apply to your child specifically. Not all is known about CTD. At present, there is no standard treatment plan. Certain treatments may be recommended for some children but not others. Children with CTD should be followed by a metabolic doctor in addition to their primary doctor.

WHAT IS CTD?

CTD stands for “carnitine transporter deficiency.” It is one type of fatty acid oxidationThis is the process used by the body to change fatty acids, the building blocks of fat, into energy. It happens in the mitochondria – the small energy-producing parts found in each cell of the body. disorder. People with CTD have problems using fat as energy for the body.

Fatty Acid Oxidation Disorders: Fatty acid oxidation disorders (FAODs)This is a group of rare inherited conditions. FAODs are caused by missing or non-working enzymes. Normally, many enzymes are used by the body to break down fat into energy. In people with FAODs, one of these enzymes is not working and fat cannot be used for energy. If these conditions are not treated, they can lead to serious health problems. are a group of rare inheritedAcquiring a trait from one’s parents. Most traits, such as eye color or hair color, are inherited from a parent through genes. conditions. They are caused by enzymes that do not work properly. A number of enzymesA molecule that helps chemical reactions take place. For example, enzymes in the stomach speed up the process of breaking down food. Each enzyme can participate in many chemical reactions without changing or being used up. are needed to break down fats in the body (a process called fatty acid oxidation). Problems with any of these enzymes can cause a fatty acid oxidation disorder. People with FAODs cannot properly break down fatFat is one of the three main nutrients in food (carbohydrates, fat, protein). Some foods that contain fat are butter, margarine, oils, nuts, meats, poultry, fish and some dairy products. Extra calories from food are stored as body fat. Stored body fat provides the body with a reserve supply of energy. from either the food they eat or from fat stored in their bodies. The symptoms and treatment vary between different FAODs. They can also vary from person to person with the same FAOD. See the fact sheets for each specific FAOD. FAODs are inherited in an autosomal recessive manner and affect both males and females.

WHAT CAUSES CTD?

CTD is caused by problems with the enzyme “carnitine transporter” (CT). In people with CTD, the CT enzyme is either missing or not working properly. This enzyme’s job is to carry a substance called carnitine into our cellsThe smallest living unit. Cells make up all organs and tissues in multi-cellular organisms, like humans. They can also live independently, as in bacteria and other microorganisms. At a minimum, a cell is surrounded by a membrane, contains DNA at some stage in its life, and is able to replicate itself into two equal parts.. Carnitine helps the body make energy from the fat in food. It also helps us use fat already stored in the body.

Energy from fat keeps us going whenever our bodies run low of their main source of energy, a type of sugar called glucoseThis is a type of sugar made from the carbohydrates in food. Glucose is found in the blood. It is the main source of energy for the body and brain..  Our bodies rely on fat when we don’t eat for a stretch of time – like when we miss a meal or when we sleep.

When the normal CT enzyme is missing or not working well, the body cannot use fat for energy. Instead, it must rely solely on glucose. Although glucose is a good source of energy, there is a limited amount available. Once the glucose has been used up, the body tries to use fat without success. This leads to low blood sugar, called hypoglycemiaThis happens when there is too little sugar (glucose) in the blood. It may cause a person to feel nervous, shaky, weak, or sweaty. It may also cause headache, blurred vision, and hunger. If left untreated, it can cause unconsciousness (coma) and sometimes even death., and to the build up of harmful substances in the blood.

IF CTD IS NOT TREATED, WHAT PROBLEMS OCCUR?

There are two main types of CTD: one begins in infancy, the other in childhood.

CTD in infants

Babies with CTD first show symptoms between birth and age three. CTD can cause bouts of illness called metabolic crisisThis is a serious health condition caused by low blood sugar and the build-up of toxic substances in the blood. Symptoms of a metabolic crisis are poor appetite, nausea, vomiting, diarrhea, extreme sleepiness, irritable mood and behavior changes. If not treated, breathing problems, seizures, coma, and sometimes even death can occur.Metabolic crises happen more often in people with certain metabolic disorders (some fatty acid oxidation disorders, amino acid disorders, and organic acid disorders). They are often triggered by things like illness or infection, going without food for a long time, and, in some cases, heavy exercise.. Some of the first symptoms of a metabolic crisis are:

• extreme sleepiness
• behavior changes
• irritable mood
• poor appetite

Other symptoms then follow:

• fever
• nausea
• diarrhea
• vomiting
• hypoglycemia

If a metabolic crisis is not treated, a child with CTD can develop:

• breathing problems
• swelling of the brain
• seizuresThese are also called "convulsions" or "fits." During a seizure, a person loses consciousness and control of his or her muscles. It may also cause involuntary movements. Seizures can happen for many reasons. Some causes are metabolic disorders, a metabolic crisis, brain injury, and infection.
• comaThis is a sleep-like condition from which a person cannot be awakened. People in a coma are unconscious. A coma can be caused by many things. Two causes are untreated low blood sugar (hypoglycemia) and a metabolic crisis., sometimes leading to death

Babies who are not treated may have other effects:

• enlarged heart
• enlarged liver
• muscle weakness
• anemiaThis is a condition in which the blood has too few red blood cells or too little hemoglobin, the oxygen carrying molecule in the blood. People with anemia are often pale, tired, weak, dizzy and short of breath.

Repeated episodes of metabolic crisis can cause brain damage. This can result in learning problems or intellectual disabilities.

Symptoms of a metabolic crisis often happen after having nothing to eat for more than a few hours. Symptoms are also more likely when a child with CTD gets sick or has an infection.

CTD in children
Children with CTD appear perfectly normal until symptoms begin, usually between the ages of one and seven. Some of the effects of childhood CTD are:

• enlarged heart
• muscle weakness
• if left untreated, risk of heart failure and death

Children with this type of CTD do not have episodes of hypoglycemia or metabolic crises. Their intelligence is not affected.

Some children with CTD never have symptoms and are only found to be affected after a brother or sister is diagnosed. Many infants diagnosed with CTD, based on newborn screeningA screening test that looks for different disorders using a small sample of blood taken from a newborn’s heel. A positive or abnormal newborn screening result means that there are slight differences that were found in the baby’s blood, and further testing is needed to figure out if the baby has a metabolic disorder. results, never develop symptoms of CTD.

WHAT IS THE TREATMENT FOR CTD?

Your baby’s primary doctor will work with a metabolic doctor to care for your child. Your doctor may also suggest that you meet with a dietician familiar with CTD.

Certain treatments may be advised for some children but not others. When necessary, treatment is usually needed throughout life. The following are treatments often recommended for children with CTD:

1.  L-carnitineThis is a natural substance found in muscle cells. It helps the body make energy from the fat in food and the fat stored in the body. It also helps the cells get rid of harmful wastes made during the breakdown of fat. Carnitine supplements may be used as a treatment for some metabolic disorders.
The main treatment for CTD is lifelong use of L-carnitine. This is a safe and natural substance that helps body cells make energy. It also helps the body get rid of harmful wastes. L-carnitine can reverse the heart problems and muscle weakness that happen in children with CTD.

Your doctor will decide whether or not your child needs L-carnitine. Unless you are advised otherwise, use only L-carnitine prescribed by your doctor.  Do not use L-carnitine without checking with your doctor.

2.  Avoid going a long time without food
Infants and young children with CTD need to eat frequently to prevent a metabolic crisis. Your metabolic doctorThis is a doctor or medical geneticist who has special training in diagnosing and treating metabolic disorders. They often work in university hospitals or large medical centers. will tell you how often your child needs to be fed.  In general, it is often suggested that infants be fed every four to six hours. Some babies need to eat even more frequently than this. It is important that infants be fed during the night. They may need to be woken up to eat if they do not wake up on their own. Your metabolic doctor and dieticianThis is a person with special training in food and nutrition. A registered dietician (RD) has met the necessary educational requirements and has passed a national examination. If your child has a metabolic disorder, it is important for you to work with a registered dietician. They help create healthy food plans for people with metabolic disorders or other special needs. will give you an appropriate feeding plan for your infant. Your doctor will also give you a ‘sick day’ plan tailored to your child’s needs for you to follow during illnesses or other times when your child will not eat.

Your metabolic doctor will continue to advise you on how often your child should eat as he or she gets older.  When they are well, many teens and adults with CTD can go without food for up to 12 hours without problems. The other treatments usually need to be continued throughout life.

3.  Diet
Sometimes, in addition to L-carnitine treatment, a diet low in fat and high in carbohydratesThis is one of the three types of nutrients in food (carbohydrates, fats, proteins). Sugars and starches are the most important types of carbohydrates. They are broken down by the body into glucose, the main source of energy for the body. Carbohydrates are found in foods such as: bread, cereal, pasta, grains, fruits and vegetables. Milk and dairy products, fruit drinks, sugar, candy, and sweet desserts also contain carbohydrates. is recommended. Any diet changes should be made under the guidance of a dietician familiar with CTD. Ask your doctor whether your child needs to have any changes in his or her diet.

4. TrackingThe process of testing a disease for a person who does not appear to have the disease (non-symptomatic or asymptomatic). The goal of tracking is to find the disease in its earliest stages. carnitine levels
Your child will have regular blood tests to measure their carnitine levels. The diet and medication may need to be adjusted based on blood test levels.

5.  If your baby has CTD, call your doctor at the start of any illness
Always call your health care provider when your baby has any of the following:

• poor appetite
• low energy or excessive sleepiness
• vomiting
• diarrhea
• an infection
• a fever
• persistent muscle pain or weakness

Babies with CTD need to eat extra starchy food and drink more fluids during any illness – even if they may not feel hungry – or they could have a metabolic crisis. Children who are sick often don’t want to eat. If they won’t or can’t eat, they may need to be treated in the hospital to prevent serious health problems.

Ask your metabolic doctor if you should carry a special travel letter with medical instructions for your child’s care.

WHAT HAPPENS WHEN CTD IS TREATED?

With prompt and careful treatment, children with CTD usually live healthy lives with typical growth and development. Treatment with L-carnitine can often reverse heart enlargement and muscle weakness.

Babies with CTD who have repeated episodes of metabolic crisis may have permanent brain damage. This can cause learning problems or intellectual disabilities.

WHAT CAUSES THE CT ENZYME TO BE ABSENT OR NOT WORKING CORRECTLY?

Genes tell the body how to make enzymes. The SLC22A5 gene instructs the body to make the CT enzyme. Everyone has two copies of the SLC22A5 gene. People with CTD have changes, also called variantsA variant is a change or alteration in a person’s DNA sequence. Variants can happen in genes and affect how the gene functions. There are different types of variants – they can be non-problem causing (benign), disease-causing (pathogenic) or of unknown significance. The term variants is now used in place of the term mutation. in both copies of their SLC22A5 genesA segment of DNA that contains the instructions to make a specific protein (or part of a protein). Genes are contained on chromosomes. Chromosomes, and the genes on those chromosomes, are passed on from parent to child. Errors in the DNA that make up a gene are called variants and can lead to diseases. that cause them to not work correctly. Because of the variants in the SLC22A5 genes, the CT enzyme either does not work properly or is not made at all.

HOW IS CTD INHERITED?

CTD is inherited in an autosomal recessive manner. It affects both boys and girls equally.

Everyone has two copies of the SLC22A5 gene that make the CT enzyme. In children with CTD, neither of these genes works correctly. These children inherit one non-working SLC22A5 gene from each parent.

Parents of children with CTD are rarely affected with the disorder. Instead, each parent has a single non-working SLC22A5 gene for CTD. They are called carriersA person who has one copy of a gene mutation for a particular autosomal recessive disorder (remember genes come in pairs). Carriers are not affected by the disorder. However, they can pass on the gene variant to their children. Children who inherit two such gene variants will be affected by the disorder. The term variants is now used in place of the term mutation.. Carriers do not have CTD because their other SLC22A5 gene is working correctly.

When both parents are carriers, there is a 25% chance in each pregnancy for the child to have CTD. There is a 50% chance for the child to be a carrier, just like the parents. And, there is a 25% chance for the child to have two working genes.

GeneticRelating to (or due to) genes and heredity or the field of studying genes and heredity. counseling is available to families who have children with CTD. Genetic counselors can answer your questions about how CTD is inherited, choices during future pregnancies, and how to test other family members. Ask your doctor about a referral to a genetic counselorThese are health care providers who have special training in genetic conditions. They help families understand genetic disorders and how they are passed down. Genetic counselors offer information and support to people who have genetic conditions in their families or are concerned that they may have a child with an inherited disorder..

IS GENETIC TESTING AVAILABLE?

Genetic testing for CTD can be done on a blood sample. Genetic testing, also called DNA testing, looks for changes (variants) in the SLC22A5 genes that cause CTD. In some affected children, both gene changes can be found. However, in other children, neither or only one of the two gene changes can be found, even though we know they are present.

DNADeoxyribonucleic acid (DNA) is a molecule found in the chromosomes that carries genetic information. DNA is composed of four units (called bases) that are designated A, T, G, and C. The sequence of the bases spell out instructions for making all of the proteins needed by an organism. A gene is a section of DNA that holds the instructions for a specific protein. A change in one or more of the DNA bases making up a gene is called a mutation. Some mutations change the protein instructions and can lead to particular health problems or disorders. Each parent passes half of their chromosomes, and thus half of their DNA instructions, onto their children. It is these instructions that cause certain traits, such as eye or hair color, to be inherited. testing is not necessary to diagnose your child. When available, it can be helpful for carrier testing or prenatal diagnosis, discussed below. Talk with your metabolic doctor or genetic counselor if you have questions about genetic testing for CTD.

WHAT OTHER TESTING IS AVAILABLE?

CTD can be confirmed by a carnitine uptake test on a skin sample. Talk to your doctor or genetic counselor if you have questions about genetic testing for CTD.

CAN YOU TEST DURING A FUTURE PREGNANCY?

If both gene changes have been found in the child with CTD, DNA testing can be done during future pregnancies. The sample needed for this test is obtained by either CVS or amniocentesisThis is a test done during pregnancy. A needle is used to remove a small sample of fluid from the sac around the fetus. The sample can be used to test for certain genetic disorders in the fetus. Amniocentesis to test for genetic conditions is usually done between 13 and 20 weeks of pregnancy..

If DNA testing would not be helpful, testing during pregnancy can be attempted by performing special tests on fetal cells. Again, the sample needed for these tests is obtained by either CVSThis is a special test done early in pregnancy. During CVS, a small sample of the placenta is removed for testing. This sample can be used to test for certain genetic disorders in the fetus. CVS is usually done between 10 and 12 weeks of pregnancy. or amniocentesis.

Parents may either choose to have testing during pregnancy or wait until birth to have the baby tested. Parents may also choose to use assisted reproductive techniques to decrease the chance that their future children would have CTD. A genetic counselor can talk to you about your choices and answer other questions you may have about prenatal testing or testing your baby after birth.

CAN OTHER MEMBERS OF THE FAMILY HAVE CTD OR BE CARRIERS?

Having CTD
The brothers and sisters of a baby with CTD have a small chance of being affected, even if they haven’t had symptoms. Finding out whether any other children in the family have CTD is important because early treatment may prevent serious health problems. Talk to your doctor or genetic counselor about testing your other children for CTD.

Occasionally, a mother is diagnosed with CTD when her infant has a positive newborn screeningThe process of testing for disease in a person who does not show signs of having the disease (nonsymptomatic or asymptomatic person). The goal of screening is to catch the disease in its early stages. test for CTD. The baby’s low carnitine level at birth is because of the mother’s low carnitine levels. This is a condition called secondary carnitine deficiency. Infants with secondary carnitine deficiency are treated with L-carnitine until their carnitine levels are normal. They do not need lifelong treatment.

Mothers diagnosed with CTD because their infant had a positive newborn screen for CTD often have no symptoms of CTD. However, it is important that they talk to their doctor about treatment to prevent serious health problems.

CTD carriers
Brothers and sisters who do not have CTD still have a chance to be carriers like their parents. Except in special cases, carrier testing should only be done in people over 18 years of age.

If you are a parent of a child with CTD, your brothers and sisters have a 50% chance to be a CTD carrier. It is important for other family members to be told that they could be carriers. There is a very small chance they are also at risk to have children with CTD.

All states offer newborn screening for CTD. However, when both parents are carriers, newborn screening results are not sufficient to rule out CTD in a newborn baby. In this case, special diagnostic testing should be done in addition to newborn screening. It is very important that this testing be done immediately – ideally at 24 hours of age.

During pregnancy, women carrying fetuses with CTD may be at increased risk to develop serious medical problems. Some women carrying fetuses with Fatty Acid Oxidation Disorders have developed:

• excessive vomiting
• abdominal pain
• high blood pressure
• jaundiceThis is a yellow color to the skin and whites of the eyes. It is often a sign of liver damage.
• abnormal fat storage in the liver
• severe bleeding

All women with a family history of CTD should share this information with their obstetricians and other health care providers before and during any future pregnancies. Knowing about these risks allows better medical care and early treatment if needed.

CAN OTHER FAMILY MEMBERS BE TESTED?

Diagnostic testing for CTD
Brothers and sisters of a baby with CTD can be tested using a special test done on a skin sample or by DNA testing using a blood sample to determine if they also have CTD.

Mothers suspected of having CTD will have blood and urine tests to measure their carnitine levels. Some may also have a special test done on a skin sample or by DNA testing using a blood sample.

CTD carrier testing
If both gene changes have been found in the child with CTD, other family members can have DNA testing to see if they are carriers.

If DNA testing would not be helpful, other methods of carrier testing may be available. Your metabolic doctor or genetic counselor can answer your questions about carrier testing.

HOW MANY PEOPLE HAVE CTD?

About one in every 50,000 babies in the United States is born with CTD.

DOES CTD HAPPEN MORE OFTEN IN A CERTAIN ETHNIC GROUP?

CTD occurs in all ethnic groups. It is more common in people from the Faroe Islands in the United Kingdom. About 1 in 300 babies born in the Faroe Island has CTD.

DOES CTD GO BY ANY OTHER NAMES?

CTD is also called:

• Systemic primary carnitine deficiency (SPCD)
• Systemic carnitine deficiency (SCD)
• Primary carnitine deficiency
• Carnitine uptake defect (CUD)

WHERE CAN I FIND MORE INFORMATION?

Fatty Oxidation Disorders (FOD) Family Support Group
http://www.fodsupport.org

Organic Acidemia Association
http://www.oaanews.org

United Mitochondrial Disease Foundation
http://www.umdf.org

Metabolic Support UK
http://www.metabolicsupportuk.org

Baby’s First Test
http://www.babysfirsttest.org

Medline Plus
https://medlineplus.gov/genetics/condition/primary-carnitine-deficiency/

 

DOCUMENT INFO:

Created by:	www.newbornscreening.info
Reviewed by:	HI, CA, OR, and WA metabolic specialists
Review date:	September 31, 2007 April 18, 2011 June 30, 2013 April 29, 2020 March 1, 2023
Update on:	March 1, 2023

 

DISCLAIMER:

THIS INFORMATION DOES NOT PROVIDE MEDICAL ADVICE. All content (“Content”), including text, graphics, images and information are for general informational purposes only. You are encouraged to confer with your doctor or other health care professional with regard to information contained on this information sheet. After reading this information sheet, you are encouraged to review the information carefully with your doctor or other healthcare provider. The Content is not intended to be a substitute for professional medical advice, diagnosis or treatment. NEVER DISREGARD PROFESSIONAL MEDICAL ADVICE, OR DELAY IN SEEKING IT, BECAUSE OF SOMETHING YOU HAVE READ ON THIS INFORMATION SHEET. This project is supported by a grant from the MaternalHaving to do with the mother. and Child Health Bureau, Health Resources and Service Administration, Genetic Services Branch, MCH Project #:UH7MC30774-01-00 http://mchb.hrsa.gov