Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is an inherited metabolic disorder that affects how the body breaks down fats into energy. It's crucial to understand the dietary guidelines for managing this condition effectively. This article provides a detailed overview of MCAD deficiency and its dietary management, incorporating information from various studies and expert recommendations.
Understanding MCAD Deficiency
What is MCAD Deficiency?
Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency prevents the body from turning fats into energy. This condition is most prevalent when you fast or don’t eat food for long periods. MCAD deficiency is one type of fatty acid oxidation disorder that is inherited if both parents carry the gene for MCADD. Individuals with this type of disorder have problems breaking down fat into energy for the body.
In the body, enzymes process food. A specific enzyme, medium-chain acyl-CoA dehydrogenase, targets medium-chain fatty acids to convert them into a substance the body can use (metabolize) as energy. People with MCAD deficiency don't have enough of this enzyme and are unable to metabolize medium-chain fatty acids.
MCAD deficiency is caused by harmful genetic changes in the ACADM gene. These changes result in a buildup of harmful fatty acids that can accumulate in body tissues and cause damage to the brain, liver, and other organs.
How Common is MCAD Deficiency?
MCAD deficiency occurs in about 1 out of every 15,000 to 1 in 25,000 individuals and is most common among people with northern European ancestry.
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How MCAD Deficiency Affects the Body
MCAD deficiency affects the body's ability to turn fat into a source of energy. In MCADD, the enzyme that breaks down certain fats in the food is either missing or not working properly. Because of this, the body cannot use fat for energy and must rely only on glucose, a type of sugar. Once the glucose is used up, the body tries to use fat without success.
Symptoms of MCAD Deficiency
For most individuals with MCAD deficiency, symptoms first appear in infancy or early childhood and can be triggered by long periods without eating (fasting) or by illness. Symptoms include vomiting, lack of energy, low blood sugar, and an enlarged liver. Without treatment, symptoms can quickly develop into life-threatening problems including seizures, breathing problems, brain damage, coma, and death. A small percentage of sudden infant death syndrome (SIDS) is likely due to undiagnosed MCAD deficiency. In some cases, symptoms may not appear until late childhood or adulthood and can be milder.
Common symptoms often occur after a child has nothing to eat for more than a few hours. During long periods without eating food, the glucose in the body is used up. Some of the first symptoms include:
- Sleepiness
- Behavior changes
- Irritable mood
- Poor appetite
- Low Energy
- Fatigue
- Vomiting
Metabolic Crisis and Hypoglycemia
MCADD can cause a metabolic crisis, which may start with symptoms of fever, diarrhea, and vomiting, followed by low blood sugar. If a metabolic crisis is not treated, it can lead to breathing problems, coma, or death. Prompt treatment can prevent these consequences.
If children with MCADD go too long without food, low blood sugar (hypoglycemia) can occur, with or without other symptoms of a metabolic crisis. Low blood sugar can cause weakness, shakiness, dizziness, or cold, clammy skin.
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General Dietary Guidelines for MCAD Deficiency
The Role of Diet in Managing MCAD Deficiency
The key treatment for individuals with MCAD deficiency is to avoid fasting. Early diagnosis and dietary management are crucial for the best outcome. If dietary management starts early (especially before the onset of symptoms) and is consistent, individuals with MCAD deficiency have a good prognosis with normal or near-normal lifespan. In undiagnosed and untreated cases of MCAD deficiency, symptoms can quickly cause irreversible damage or even lead to death.
General Dietary Recommendations
- Avoid Fasting: Infants must be frequently fed a formula low in fat but high in carbohydrates. For children and adults, consuming cornstarch can also provide a sustained release of energy and allow for longer gaps between meals.
- Regular Meals and Snacks: All MCADD individuals should avoid skipping meals and weight loss diets which recommend fasting.
- Hydration and Carbohydrate Intake during Exercise: Prolonged and/or intense exercise should be "covered" with adequate carbohydrate intake and hydration.
- Heart-Healthy Diet: After infancy, heart-healthy diets with appropriate Kcal for age and size are recommended. Nutritional intervention may be needed to counsel individuals about meal planning so that they get approximately 30% of Kcal from fat, include fruits and vegetables on a daily basis, utilize complex carbohydrates, and avoid overfeeding or exceeding their kcal needs.
Importance of Glucose
Glucose is the preferred energy source in cells, and glucose derived from stored glycogen is used during short term fasting. The long term benefits of appropriate weight gain, the health consequences of obesity, and the danger of fasting for an MCADD individual should be emphasized.
Specific Dietary Recommendations for Infants
Regular infant formula or breast milk can be continued in MCADD infants. Typical infant formulas and breast milk can contain up to 55% of the Kcal as fat, much of which is used for anabolic processes during the first year of life. If an infant is breast feeding, it is important to monitor adequate breast milk production by assessing the infant's weight gain and satiety. Formulas (and breast milk enhancers) containing MCT oil are not appropriate for the MCADD infant.
- Frequency of Feedings: The frequency of feeding for an MCADD infant (9), who is well, should be no different than that for a non-MCADD infant. A rule of thumb: maximum time of nighttime 'fasting" between birth and 4 months of age should not exceed 4 hours; between 5 and 12 months, an additional hour can be added for each month.
- Monitoring Blood Glucose: Some clinics recommend checking an infant's blood glucose levels before feeding in the morning to determine tolerance to nighttime fasting and to individualize fasting recommendations, if necessary.
Dietary Recommendations for Children and Adults
In childhood, age-appropriate meal and snack schedules should be followed. For children and adults, consuming cornstarch can also provide a sustained release of energy and allow for longer gaps between meals.
- Diet Composition: Heart healthy diets with appropriate Kcal for age and size are recommended after infancy. Nutritional intervention may be needed to counsel individuals about meal planning so that they get approximately 30% of Kcal from fat, include fruits and vegetables on a daily basis, utilize complex carbohydrates, and avoid overfeeding or exceeding their kcal needs.
Managing Illness in Individuals with MCAD Deficiency
Increased Caloric Demands During Illness
For the individual with MCADD, intervention during illness is crucial. Illness increases caloric demands, while at the same time poor appetite and/or vomiting and diarrhea may limit intake.
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At-Home Care
At home care for an ill MCADD individual is possible only if fasting can be avoided by providing adequate oral carbohydrate and fluid. Although rehydration fluids such as Pedialyte are extremely useful for ill infants and children without MCADD, the solution, when used exclusively, does not contain adequate glucose to maintain blood glucose levels in an ill MCADD infant or child. Sweetened fluids containing approximately 1/2 tsp sugar per ounce should be able to maintain blood glucose if given in quantities to meet the fluid requirement. Fluids and/or meals should be small and frequent. Ill infants and children should be awakened during the night for feeding and assessing their condition. NOTE: Low blood glucose levels may not develop until later in an illness.
Emergency Care
Emphasized that emergency care must be initiated if symptoms are present. If an individual is unable to eat or drink food on their own, it may be necessary to give them glucose by intravenous fluids.
- Oral Glucose: The use of a concentrated oral glucose source ( see above) may be lifesaving while awaiting emergency care.
- IV Carnitine: When oral intake of carnitine is decreased and/or carnitine requirements increased due to catabolism, IV carnitine at a dose of 100mg/kg body weight may be needed for the short term. Because not all hospitals have IV carnitine available, it may be possible to continue to give liquid carnitine orally since only small volumes are typically needed.
AAP Guidelines for Acute Illness
The American Academy of Pediatric (AAP) has issued guidance on the management of patients with MCADD with acute illness. Concerning symptoms in these patients include vomiting, lethargy, and decreased oral intake. Regular rehydration drinks and solutions do not contain adequate glucose for patients with MCADD. Instead, sports drinks or juice are recommended for patients no longer consuming human milk. The patient should be brought to an emergency department (ED) to receive glucose before symptoms worsen, especially when consistent oral intake cannot be maintained.
Additional Considerations
Carnitine Supplementation
L-carnitine, which is synthesized endogenously, may become relatively depleted in MCADD as it remains conjugated to the accumulated medium chain fatty acids and is excreted as the acylcarnitine. Recommended dosages for infants are 50-100 mg/kg. The need for, and the amount of, supplemetation in children and adults is determined by monitoring plasma free carnitine concentration according to the individual clinic's protocols.
Glucose Source
A few clinics use cornstarch, Polycose or other high carbohydrate supplements/snacks as a glucose source for MCADD infants and children before the nighttime fast.
Anthropometrics
MCADD infants and children should follow a normal growth curve pattern for age and sex.
Glucose Testing
There is no need to do frequent blood glucose measurements in MCADD individuals. Some clinics instruct parents to measure blood glucose levels at the end of the longest recommended sleeping interval to determine if the infant needs to be awakened earlier for a feeding. These measurements can also provide a baseline glucose measurement for an individuaI that can be helpful when evaluating glucose measurements during illness. Some clinics also recommend checking a glucose level when the infant or young child seems unusually sleepy, is difficult to awaken or is uninterested in eating, but without any other signs of illness.
Laboratory Testing
After the initial confirmatory testing has been done, the only routine laboratory measurement needed is blood carntine which gives total carnitine, free carnitine and acyl carnitine. Individuals who are on supplemental carnitine should have periodic assessment of their free carnitine.
Dietary Assessment
Diet records should be assessed at each clinic visit.
Surgery and Trauma
- Surgery: Fasting before surgical procedures and during recovery puts an MCADD individual at risk. Most agree that clear liquids can be given up to 4 hours before surgery, but IV glucose should be started before the procedure and continued until the patient can consume adequate oral intake and can maintain normoglycemia.
- Trauma: Trauma and injury increase caloric needs, but pain and possible alteration in mental status may decrease intake. Careful monitoring is very important.
Pregnancy and Neonatal Care
- Pregnancy and Child Birth in an MCADD Female: During pregnancy, plasma free carnitine levels will decline(10). Dosages of 100mg/kg are recommended, but free carnitine may still not reach pre-pregnancy levels.
- Neonatal Care for an MCADD Sibling: Families, who already have a child/children with MCADD, have a 25% risk of reccurence of MCADD with each pregnancy. If they do not have prenatal diagnosis, it may take several days to have either screening or diagnostic testing results available. It is important to monitor this at-risk infant closely.
Additional Considerations for Carriers
Carriers of MCAD deficiency do not typically show symptoms of the disease. However, there is increased risk of serious pregnancy complications, particularly in the third trimester, in individuals carrying a fetus affected with MCAD deficiency. These complications may include acute fatty liver disease and a life-threatening condition called HELLP syndrome which presents with headache, nausea, swelling, and chest pain. An individual whose pregnancy may be affected by MCAD deficiency should speak with their physician for recommendations and may benefit from consultation with a high-risk physician.
Emergency Preparedness
Emergency Letter and Medical Alert Tag
Families should be provided with an emergency protocol/letter that can be carried with them at all times. They should be strongly advised to seek medical attention if the individual with MCADD has an acute illness accompanied by poor intake, vomiting and/or lethargy. A medical alert tag may be helpful when children are no longer under constant surveillence by their caregivers (i.e, in school or traveling).
Glucose Source
A concentrated glucose source should be available at all times to be used to treat hypoglycemia until emergency care can be accessed.
Recognizing Symptoms and Seeking Help
Talk with your health care provider about what to do if symptoms of low blood sugar develop so that you have an emergency plan. Seeking emergency medical care if you can't eat or if you have diarrhea or vomiting.
School Considerations
Parents asked that teachers inform them if:
- There is sickness going around school that might place their child at risk.
- A special snack will be served that is higher in fat than the child should eat (e.g. cupcakes for a birthday party).
- Their child is unable to focus in school, seems overly fatigued, or is acting different than usual.
- The class will be outside in hot weather for a long period of time (Because energy is required to keep cool, a child with MCADD may need to sit in the shade or have extra nutrients to maintain energy levels).
Note: These recommendations may not apply to all children with MCADD.
Coping and Support
Caring for a child or family member with a lifelong disorder such as MCAD deficiency can be challenging.
- Learn about the disorder: Learn as much as you can about MCAD deficiency. Then you can make the best choices and be an advocate for yourself or your child.
- Find a team of trusted professionals: You'll need to make important decisions every day about care.
- Seek out other families: Talking to people who are dealing with similar challenges can give you information and emotional support. Ask your health care provider about support groups in your community. If a group isn't for you, maybe your provider can put you in touch with a family who has dealt with the disorder.
- Ask for help from family and friends: Ask for or accept help from family and friends in caring for your loved one when needed.
- Take time for your own interests and activities.
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