Methylmalonic acidemia with homocystinuria
Overview
MMA+HCU stands for “methylmalonic acidemia 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.
Causes
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 homocysteine, methylmalonic acid and other harmful substances to build up in the blood. This can lead to serious health problems.
Treatment
Your baby’s primary doctor will work with a metabolic doctor and a dietician familiar with MMA+HCU 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: 1. Low-protein diet, medical foods and medical formula Low-protein diet A food plan low in the amino acids leucine, valine, methionine, and threonine with limited amounts of protein is often recommended. 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 metabolic crises. Foods high in protein that may need to be avoided or limited include: milk and dairy products meat and poultry fish eggs dried beans and legumes nuts and peanut butter 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 In addition to a low-protein diet, your child may be given a special formula. This formula contains the correct amount of protein and nutrients needed for normal growth and development. Your metabolic doctor and dietician will tell you whether your child needs formula, what type is best, and how much to use. 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. Some states offer help with payment or require private insurance to pay for the formula and other special medical foods. 2. Medication Vitamin B12 Babies and children with MMA+HCU may be given vitamin B12 injections in the form of hydroxocobalamin (OH-cbl). This treatment seems to lessen the symptoms in some children but not others. Your doctor may need to treat your child with OH-cbl for a short period of time to determine whether this treatment is useful. L-Carnitine Some children with MMA+HCU may benefit by taking L-carnitine. This is a safe and natural substance that helps the body make energy. It also helps get rid of harmful wastes. 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. Betaine Betaine is a vitamin-like substance found in grains and other foods. It can also be bought in pill form as a supplement. Betaine helps lower the amount of homocysteine in the blood. It may lessen the risk of blood clots. Your metabolic specialist will decide whether your child needs betaine. He or she will need to write a prescription. Hospital care Children with extreme sleepiness or lack of energy and those who are ill may need to be treated in the hospital. If your child has metabolic acidosis, he or she may be given medications such as bicarbonate by IV to help reduce the acid levels in the blood. Glucose is given by IV to prevent the breakdown of body stores of protein and fat. Do not use any medication without checking with your doctor or metabolic specialist. 3. Avoid going a long time without food Infants and young children with MMA+HCU need to eat frequently to prevent a metabolic crisis. Your metabolic doctor 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 dietician 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. 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. 5. Call your doctor at the start of any illness In children with MMA+HCU, even minor illness could lead to serious health problems. In order to prevent problems, call your doctor right away when your child has any of the following: loss of appetite vomiting diarrhea infection or illness fever 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.