Children and Youth with Special Health Needs (CYSHN)
3-Hydroxy 3-Methylglutaric Aciduria (HMG)
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- What is HMG?
- What causes HMG?
- What causes the HMG CoA lyase enzyme to be absent or not working correctly?
- How is HMG inherited?
- Is there genetic testing available?
- What other testing is available?
- Can you test during pregnancy?
- Can other members of the family have HMG or be carriers?
- Can other family members be tested?
- How many people have HMG?
- Does HMG happen more frequently in a certain ethnic group?
- Does HMG go by any other names?
- What is the treatment for HMG?
- What happens when HMG is treated?
- If HMG is not treated, what problems occur?
This fact sheet has general information about 3-hydroxy 3-methylglutaric aciduria (HMG). 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 HMG should be followed by a metabolic doctor in addition to their primary doctor.
What is HMG?
HMG is one type of organic acid disorder. People with this condition have problems breaking down an amino acid called leucine 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 HMG?
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 order for the body to use fat for energy, enzymes break down fatty acids into ketone bodies. Normally, during long periods without eating, ketones are made by the body and used for fuel.
HMG occurs when an enzyme, called “HMG CoA lyase”, is either missing or not working properly. This enzyme has two jobs. The first is to help break down leucine. Leucine is found in all foods that contain protein. The second job is to help the body make ketone bodies from stored fat.
When children with this condition eat food containing leucine, harmful substances build up in the blood. In addition, children with HMG can‟t make ketone bodies from stored fat like most people. So, when they don‟t eat for a long period of time, they can develop low blood sugar (hypoglycemia) and serious health problems.
What causes the HMG CoA lyase enzyme to be absent or not working correctly?
Genes tell the body to make various enzymes. People with HMG have a pair of genes that do not work correctly. Because of the changes in this pair of genes, the HMG CoA lyase enzyme either does not work properly or is not made at all.
How is HMG inherited?
HMG is inherited in an autosomal recessive manner. It affects both boys and girls equally.
Everyone has a pair of genes that make the HMG CoA lyase enzyme. In children with HMG, neither of these genes works correctly. These children inherit one non-working gene for the condition from each parent.
Parents of children with HMG rarely have the disorder. Instead, each parent has a single non-working gene for HMG. 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 HMG. 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 HMG. 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 genetic testing available?
Genetic testing for this condition may be possible. Genetic testing, also called DNA testing, looks for changes in the pair of genes that causes HMG. 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 HMG. 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 HMG, 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.
It may also be possible to test for HMG using an enzyme test on cells from the fetus. The sample needed for this test is obtained by either CVS or amniocentesis.
Testing has also been done in late pregnancy (after 23 weeks) using a urine sample from the mother
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 HMG or be carriers?
The brothers and sisters of a baby with HMG have a chance of being affected even if they haven't had symptoms. Finding out whether 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 HMG 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 HMG.
When both parents are carriers for HMG, 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 HMG can be tested using blood, urine, or skin samples.
If both gene changes have been found in your child with HMG, other family members can have DNA testing to see if they are carriers.
If DNA testing is not possible or is not 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 HMG?
This condition is very rare. The actual incidence is unknown.
Does HMG happen more frequently in a certain ethnic group?
HMG happens in all ethnic groups throughout the world. It happens more frequently in people from Saudi Arabia.
Does HMG go by any other names?
HMG is sometimes also called:
- 3-hydroxy-3-methylglutaryl-CoA lyase deficiency
- HMG-CoA lyase deficiency
- Hydroxymethylglutaric aciduria
- HL deficiency
- 3-OH 3-CH3 glutaric aciduria
- 3-OH 3-methyl glutaric aciduria
What is the treatment for HMG?
Your baby's primary doctor may work with a metabolic doctor and a dietician to care for your child.
Prompt treatment is needed to prevent metabolic crises and the health effects that follow. You need to start treatment as soon as you know your child has HMG. Certain treatments may be advised for some children but not others. Treatment is usually needed throughout life.
The following are treatments often recommended for babies and children with this condition:
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.
Low-leucine diet, including medical foods and formula
Most food in the diet will be carbohydrates (bread, cereal, pasta, fruit, vegetables, etc.). Carbohydrates give the body many types of sugar that can be used as energy. Eating a diet high in carbohydrates and low in protein and fat can help prevent low blood sugar and metabolic crises.
Foods high in protein and fat that your child may need to avoid or limit:
Many vegetables and fruits have only small amounts of protein and fat and can be eaten in carefully measured amounts. Do not remove all protein and fat from the diet. Your child needs a certain amount of each to grow properly.
Your dietician will create a food plan that contains the right amount of protein, fat, nutrients, and energy to keep your child healthy. Your child may need to be on a special food plan throughout life.
Medical foods and formula
Some children are also given a special leucine-free medical formula. Your metabolic doctor and dietician will decide whether your child needs this formula.
Children with symptoms of a metabolic crisis need medical treatment right away. They often need to be treated in the hospital. During a metabolic crisis, children may be given glucose, bicarbonate, and other medications by IV to treat hypoglycemia and other symptoms of a metabolic crisis. Ask your metabolic doctor if you should carry a special travel letter with medical instructions for your child‟s care.
Call your doctor at the start of any illness
Children with HMG need to eat more carbohydrates and drink more fluids when they are ill – even if they‟re not hungry – or they could have a metabolic crisis. Also, they need to avoid eating protein and fat during any illness.
Children who are ill often don‟t want to eat. If they can‟t eat, or if they show signs of a metabolic crisis, they may need to be treated in the hospital.
With prompt and careful treatment, children who have shown symptoms of HMG have a good chance to live healthy lives with typical growth and development.
Even with treatment, some children still have repeated bouts of metabolic crisis. This can cause brain damage and may lead to life-long learning problems or mental retardation.
If HMG is not treated, what problems occur?
Each child with HMG will have somewhat different effects. Babies with this condition are usually healthy at birth. Most babies start to have symptoms between 3 months and two years of age. A few babies, though, have had their first symptoms just a few days after birth.
HMG causes episodes of illness called metabolic crises. Some of the first symptoms of a metabolic crisis are:
- poor appetite
- extreme sleepiness or lack of energy
- behavior changes
- irritable mood
- muscle weakness
Some or all of these symptoms may also occur:
- increased levels of acidic substances in the blood, called metabolic acidosis
- high levels of ammonia in the blood
- enlarged liver
If a metabolic crisis is not treated, a child with HMG can develop:
- breathing problems
- coma, sometimes leading to death
If not treated, many babies with HMG die during their first metabolic crisis. In surviving babies, repeated episodes of metabolic crisis can cause brain damage. This can result in life-long learning problems or mental retardation.
Episodes of metabolic crisis can be triggered by:
- illness or infection
- going without food for long periods of time
- eating large amounts of protein
When a child is ill or goes without food for too long, the body breaks down its own protein and fat to use for energy. In people with HMG, this can trigger a metabolic crisis, as described above.
Between episodes of metabolic crisis, children with this condition are usually healthy.
Long-term effects can happen in some children. These may include:
- enlarged heart
- inflammation of the pancreas, called pancreatitis
- hearing loss
- vision loss
- learning disabilities or mental retardation
Some people with HMG never have symptoms and are only found to be affected after a brother or sister is diagnosed.
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
National Library of Medicine Genetics Home Reference: HMG-CoA Lyase Deficiency http://ghr.nlm.nih.gov/condition/3-hydroxy-3-methylglutaryl-coa-lyase-deficiency
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 13:55:01 CDT|