Children and Youth with Special Health Needs (CYSHN)
Methylmalonic Acidemia with Homocystinuria (MMA+HCU)
On this page...
- What is MMA+HCU?
- What causes MMA+HCU?
- What causes the enzyme to be absent or not working correctly?
- How is MMA+HCU inherited?
- Is there genetic testing available?
- What other testing is available?
- Can you test during pregnancy?
- Can other members of the family have MMA+HCU or be carriers?
- Can other family members be tested?
- How many people have MMA+HCU?
- Does MMA+HCU happen more frequently in a certain ethnic group?
- Does MMA+HCU go by any other names?
- What is the treatment for MMA+HCU?
- What happens when MMA+HCU is treated?
- If MMA+HCU is not treated, what problems occur?
This fact sheet has general information about methylmalonic academia with homocystinuria (MMA+HCU). 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 MMA+HCU should be followed by a metabolic doctor in addition to their primary doctor.
What is MMA+HCU?
MMA+HCU stands for “methylmalonic academia with homocystinuria”. It is one type of organic acid disorder. People with MMA+HCU have problems breaking down and using certain amino acids and fatty acids from the food they eat.
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 MMA+HCU?
In order for the body to use protein from the food we eat, it is broken down into smaller parts called amino acids. Special enzymes then make changes to the amino acids so the body can use them. In the same way, fat from the food we eat is broken down into fatty acids that the body can use for energy.
MMA+HCU occurs when one of these special enzymes is either missing or not working properly. The job of these enzymes is to change vitamin B12 (also called cobalamin) into a form that the body can use. When the body is not able to use vitamin B12 correctly, it causes homocystine, methylmalonic acid and other harmful substances to build up in the blood. This can lead to serious health problems.
There are a number of forms of MMA+HCU. The most common form is called Cobalamin C deficiency (CblC). Rarer forms include Cobalamin D deficiency (CblD) and Cobalamin F deficiency (CblF).
There are other forms of MMA that occur without homocystinuria. These are described in a separate fact sheet - see MMA.
Isoleucine, valine, methionine, and threonine are the four amino acids that cannot be used correctly by people with MMA+HCU. They are found in all foods that contain protein. Large amounts are found in meat, eggs, milk, and other dairy products. Smaller amounts are found in flour, cereal, and some vegetables and fruits.
What causes the enzyme to be absent or not working correctly?
Genes tell the body to make various enzymes. People with MMA+HCU have a pair of genes that do not work correctly. Because of the changes in this pair of genes, the needed enzyme either does not work properly or is not made at all.
How is MMA+HCU inherited?
MMA+HCU is inherited in an autosomal recessive manner. It affects both boys and girls equally.
Everyone has a pair of genes that make the needed enzyme. In children with MMA+HCU, neither of these genes works correctly. These children inherit one non-working gene for the condition from each parent.
Parents of children with MMA+HCU rarely have the disorder. Instead, each parent has a single non-working gene for MMA+HCU. 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 MMA+HCU. 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.
Genetic counseling is available to families who have children with MMA+HCU. 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 MMA+HCU is available. Genetic testing, also called DNA testing, looks for changes in the pair of genes that cause MMA+HCU. 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.
Special tests on blood, urine or skin samples can be done to confirm MMA+HCU. 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 MMA+HCU, 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.
If DNA testing would not be helpful, an enzyme test can be done using cells from the fetus. The sample needed for this test is obtained by either CVS or amniocentesis.
Parents may 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 MMA+HCU or be carriers?
If they are healthy and growing normally, older brothers and sisters of a baby with MMA+HCU are unlikely to have the condition. However, finding out if other children in the family have this condition may be important because early treatment may prevent serious health problems. Ask your metabolic doctor whether your other children should be tested.
Brothers and sisters who do not have MMA+HCU 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 MMA+HCU.
When both parents are carriers for MMA+HCU, 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?
Brothers and sisters of a child with MMA+HCU can be tested using blood, urine, or skin samples. Talk to your doctor or genetic counselor if you have questions about whether your other children should be tested for MMA+HCU.
If the gene changes have been found in your child with MMA+HCU, other family members can have DNA testing to see if they are carriers. Your metabolic doctor or genetic counselor can answer your questions about carrier testing.
How many people have MMA+HCU?
MMA+HCU is thought to be rare. The actual incidence is unknown.
Does MMA+HCU happen more frequently in a certain ethnic group?
MMA+HCU does not happen more often in any specific race, ethnic group, geographical area or country.
Does MMA+HCU go by any other names?
MMA+HCU is sometimes also called:
- Combined deficiency of methylmalonyl CoA mutase and homocystinuria
- Methyltetrahydrofolate methyltransferase deficiency
- Vitamin B12 metabolic defect, Type 2
- Methylmalonic acidemia and homocystinuria
- Cbl C deficiency
- Cbl D deficiency
- Cbl F deficiency
What is the treatment for MMA+HCU?
Your baby's primary doctor may work with a metabolic doctor and a dietician to care for your child.
It is not known how effective treatment is in preventing effects of MMA+HCU. However, prompt and ongoing treatment may lessen the chance for mental retardation, psychiatric disorders, and serious health problems.
Most children need to be on a low-protein diet and drink a special medical formula. Many children are given injections of vitamin B12. It is important to start treatment as soon as you know your child has MMA+HCU.
The following are treatments often recommended for children with MMA+HCU:
Low-protein diet, medical foods and medical formula
Foods high in protein that may need to be avoided or limited include:
Many vegetables and fruits have only small amounts of protein and can be eaten in carefully measured amounts. Do not remove all protein from the diet. Children with MMA+HCU need a certain amount to grow properly.
Your dietician can create a food plan that contains the right amount of protein, nutrients, and energy to keep your child healthy. Your child will need to be on a special food plan throughout life.
Medical formula and foods
There are also medical foods such as special low-protein flours, pastas, and rice that are made especially for people with organic acid disorders. Your dietician will tell you how to use these foods as part of your child‟s diet.
Do not use any medication without checking with your doctor or metabolic specialist.
Avoid going a long time without food
Your metabolic doctor will continue to advise you on how often your child should eat as he or she gets older.
|4.||Regular blood and urine tests
Your child will likely need regular blood and urine tests to measure the level of amino acids and other substances. Your child‟s diet and medication may need to be adjusted based on the results of these tests.
Call your doctor at the start of any illness
When ill, your child needs extra fluids and carbohydrates to prevent more serious health problems. During an illness, you should restrict protein and give your child starchy foods and fluids.
Children with MMA+HCU may need to be treated in the hospital during illness. Ask your metabolic doctor if you should carry a special travel letter with medical instructions for your child‟s care.
Treatment may help some children but not others. Even with treatment, some babies and children may die. Others may have life-long learning problems or mental retardation. Some children develop psychiatric disorders that are difficult to treat.
If MMA+HCU is not treated, what problems occur?
Each child with MMA+HCU is likely to have somewhat different effects:
Most babies with CblC deficiency have shown symptoms within the first year, often by one month of age. A small number of children with CblC deficiency have not had symptoms until after 4 years of age. One child was reported to show symptoms for the first time at age 14 and a few adults have had their first symptoms in their twenties.
Babies with CblF deficiency usually have their first symptoms shortly after birth.
Children with CblD deficiency usually show initial symptoms later in childhood.
It is possible that a small number of people with this condition never develop symptoms.
In babies who have symptoms, common findings are:
- poor appetite
- poor growth
- extreme sleepiness or lack of energy
- low muscle tone (floppy muscles and joints)
- small head and brain size, called microcephaly
- water on the brain, called hydrocephalus
- other brain abnormalities
- delays in learning or mental retardation
- vision problems
- heart problems
- kidney problems
- skin rashes
Lab findings can include:
- high levels of homocysteine and methylmalonic acid in the blood and urine
- high levels of acidic substances in the blood, called metabolic acidosis
- protein or blood in the urine
- low platelets
- low white blood cells
- excess clotting of the blood
If not treated, metabolic acidosis can cause:
- breathing problems
- swelling of the brain
- coma, sometimes leading to death
Metabolic acidosis and other symptoms can be triggered by:
- eating large amounts of protein
- illness or infection
- going too long without food
- stressful events such as surgery
Children who do not have symptoms until later in childhood often have some or all of the following symptoms:
- sudden loss of mental skills
- forgetfulness and confusion
- episodes of psychosis or delirium
- behavior problems
- numbness or weakness in the limbs
- unsteady gait
- slurred speech
- blood clots
- anemia, low platelets, and/or low white blood cells
- vision problems
- kidney problems
Where can I find more information?
Midwest Organic Families Networking Group – a parent-led networking group. Contact: email@example.com
Medically Prescribed Formula: a table that provides a list of commonly prescribed medical foods and formulas and /or medication for this disorder
Organic Acidemia Association
Save Babies Through Screening Foundation
CLIMB (Children Living with Inherited Metabolic Disorders)
For additional genetics information and resources:
- Genetic Alliance
- Region 4 Genetics Collaborative
- Partnering with your Doctor The Medical Home Approach: A guide for families with children who have genetic conditions - The Guide is intended to be a user-friendly, hands-on tool to support families of children who have genetic conditions to move forward in obtaining and providing a medical home for their children. The guide provides definitions, examples and tools for families to use when working with the doctor to develop a medical home.
More help available from Children and Youth with Special Health Needs (CYSHN):
- Resources: Financial and Other
- Early Childhood Intervention
- Resources for Children and Families
- Youth and Young Adults - Planning for the Future
- Emergency Planning
- Medical Home
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 13:54:59 CDT|