Children and Youth with Special Health Needs (CYSHN)

Multiple Carboxylase Deficiency (MCD)

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Condition Information

Treatment Options: Taking Action

Family Support Resources

CONDITION INFORMATION

This fact sheet has general information about MCD. Every child is different and some of these facts may not apply to your child specifically. Certain treatments may be recommended for some children but not others. Children with MCD should be followed by a metabolic doctor in addition to their primary doctor.

What is MCD?

MCD stands for “multiple carboxylase deficiency”. It is one type of organic acid disorder. People with MCD have problems changing protein and carbohydrates from food into energy for the body.

Organic Acid Disorders:

Organic acid disorders (OAs) are a group of rare inherited conditions. They are caused by enzymes that do not work properly. A number of enzymes are needed to process protein from the food we eat for use by the body. Problems with one or more of these enzymes can cause an organic acid disorder.

People with organic acid disorders cannot break down protein properly. This causes harmful substances to build up in their blood and urine. These substances can affect health, growth and learning.

The symptoms and treatment vary between different organic acid disorders. They can also vary from person to person with the same organic acid disorder. See the fact sheets for each specific organic acid disorder.

Organic acid disorders are inherited in an autosomal recessive manner and affect both males and females.

 

What causes MCD?

MCD occurs when an enzyme called “holocarboxylase synthetase” (HCS), is either missing or not working properly. This enzyme‟s job is to add a vitamin called „biotin‟ to other enzymes called „carboxylases‟ so that they can change the food we eat into energy for the body. When the HCS enzyme is not working, certain harmful substances build up in the blood and urine. This can cause serious health problems.


MCD Diagram

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What causes the HCS enzyme to be absent or not working correctly?

Genes tell the body to make various enzymes. People with MCD have a pair of genes that do not work correctly. Because of the changes in this pair of genes, the HCS enzyme either does not work properly or is not made at all.

How is MCD inherited?

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

Everyone has a pair of genes that make the HCS enzyme. In children with MCD, neither of these genes works correctly. These children inherit one non-working gene for the condition from each parent.

Parents of children with MCD rarely have the disorder. Instead, each parent has a single non-working gene for MCD. They are called carriers. Carriers do not have the condition because the other gene of this pair is working correctly.

When both parents are carriers, there is a 25% chance in each pregnancy for the child to have MCD. 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.

Autosomal Recessive Inheritance Chart

Genetic counseling is available to families who have children with MCD. Genetic counselors can answer your questions about how the condition is inherited, choices during future pregnancies, and how to test other family members. Ask your doctor about a referral to a genetic counselor.

Is there genetic testing available?

Genetic testing for MCD may be possible. Genetic testing, also called DNA testing, looks for changes in the pair of genes that causes MCD. Talk with your genetic counselor or metabolic doctor if you have questions about DNA testing.

DNA testing is not necessary to diagnose your child. However, it can be helpful for carrier testing or prenatal diagnosis, discussed below.

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What other testing is available?

Special tests on blood or skin samples can be done to confirm MCD. Talk to your metabolic doctor if you have questions about testing for this condition.

Can you test during pregnancy?

If both gene changes have been found in the child with MCD, DNA testing can be done during future pregnancies. The sample needed for this test is obtained by either CVS or amniocentesis. CVS stands for Chorionic Villus Sampling, which is a special test done early in pregnancy. During CVS, a small sample of the placenta is removed for genetic testing.

An enzyme test can be done using cells from the fetus. The sample needed for this test is obtained by amniocentesis.

Parents may either choose to have testing during pregnancy or wait until birth to have the baby tested. A genetic counselor can talk to you about your choices and answer questions about prenatal testing or testing your baby after birth.

Can other members of the family have MCD or be carriers?

Having MCD
The brothers and sisters of a baby with MCD have a small chance of being affected even if they haven't had symptoms. Finding out whether other children in the family have this condition is important because early treatment may prevent serious health problems. Ask your metabolic doctor whether your other children should be tested.

MCD carriers
Brothers and sisters who do not have MCD 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.

Each of the parents' brothers and sisters has a 50% chance to be a carrier. It is important for other family members to be told that they could be carriers. There is a small chance they are also at risk to have children with MCD.

When both parents are carriers for MCD, newborn screening results are not sufficient to rule out the condition in a newborn baby. In this case, special diagnostic testing should be done in addition to newborn screening.

Can other family members be tested?

Diagnostic testing
Diagnostic testing on blood or skin samples can be done for brothers or sisters of a child with MCD. Talk to your doctor or genetic counselor if you have questions about testing for MCD.

Carrier testing
Carrier testing for MCD may be available. If you have questions about carrier testing, ask your genetic counselor or metabolic doctor.

How many people have MCD?

Less than one in 100,000 babies in the United States is born with MCD.

Does MCD happen more frequently in a certain ethnic group?

No, MCD does not happen more often in any specific race, ethnic group, geographical area or country.

Does MCD go by any other names?

MCD is sometimes also called:

  • Holocarboxylase synthetase deficiency
  • Holocarboxylase deficiency
  • HLCS deficiency
  • Multiple carboxylase deficiency, early-onset
  • Infant multiple carboxylase deficiency
  • MCD, neonatal form

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TREATMENT OPTIONS: TAKING ACTION

What is the treatment for MCD?

Your baby‟s primary doctor will work with a metabolic doctor to provide care for your child.

The main treatment for MCD is a type of B vitamin called biotin. In babies found to have MCD through newborn screening, biotin treatment can prevent symptoms from occurring. It can also reverse some of the health problems in children who have already shown symptoms. You will need a prescription from your doctor in order to purchase the amount of biotin your child will need.

Prompt treatment with biotin is needed to prevent mental retardation and serious medical problems. You should start the treatment as soon as you know your child has MCD. Your child will need to take biotin by mouth on a daily basis throughout life.

Biotin is usually the only medication needed to treat MCD. Your child will not need to restrict any activities or change his or her diet.

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What happens when MCD is treated?

Babies who receive prompt and ongoing treatment with biotin before they have a metabolic crisis are expected to have normal growth and development.

Even with treatment, a few children have developed life-long learning problems or mental retardation. In children who have already shown delays in learning, or loss of hearing or eyesight, treatment can prevent additional effects. But, it may not be able to correct the effects that are already present.

If MCD is not treated, what problems occur?

Each child with MCD is likely to experience slightly different effects. Many babies with this condition start to have symptoms within hours of birth or during the first few days or weeks of life. Other babies have their first symptoms sometime in infancy, usually before two years of age.

A small number of people with MCD never show symptoms and are only found to be affected after a brother or sister is diagnosed.

MCD causes episodes of illness called metabolic crises. Some of the first symptoms of a metabolic crisis are:

  • poor appetite
  • vomiting
  • extreme sleepiness or lack of energy
  • irritability
  • low muscle tone (floppy muscles and joints)
  • severe peeling skin rash

Common lab findings are:

  • low blood sugar, called hypoglycemia
  • high levels of acidic substances in the blood, called metabolic acidosis
  • slightly high levels of ammonia in the blood
  • low platelets
  • ketones in the urine
  • high levels of substances called organic acids in the urine

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

  • breathing problems
  • seizures
  • swelling of the brain
  • coma, sometimes leading to death

Untreated children with MCD often have other symptoms, whether or not they have metabolic crises. These can include:

  • skin rashes or skin infections
  • hair loss
  • learning disabilities or mental retardation
  • delays in walking and motor skills
  • problems coordinating movements, called ataxia
  • rigid muscle tone, called spasticity
  • poor growth
  • seizures
  • hearing loss
  • vision loss

Without treatment, most babies with MCD will die.

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FAMILY SUPPORT RESOURCES

Where can I find more information?

Midwest Organic Families Networking Group – a parent-led networking group. Contact: health.cyshn@state.mn.us

Minnesota Pediatric Metabolic Providers List

Medically Prescribed Formula: a table that provides a list of commonly prescribed medical foods and formulas and /or medication for this disorder

National Library of Medicine Genetics Home Reference:
Holocarboxylase Synthetase Deficiency http://ghr.nlm.nih.gov/condition/holocarboxylase-synthetase-deficiency

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

Save Babies Through Screening Foundation
http://www.savebabies.org

CLIMB (Children Living with Inherited Metabolic Disorders)
http://www.climb.org.uk

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For additional genetics information and resources:

More help available from Children and Youth with Special Health Needs (CYSHN):

We would like to acknowledge the Star G Project. The information on the fact sheet was obtained from the Star G Project. For the most up-to-date information on the disorder please visit their web site at http://www.newbornscreening.info. Each fact sheet was extensively reviewed by family support groups, metabolic specialists across the country and the Star G steering committee.

THIS INFORMATION DOES NOT PROVIDE MEDICAL ADVICE. All 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.
Updated Wednesday, 01-Aug-2012 13:55:00 CDT