Very long-chain acyl-coenzyme A dehydrogenase deficiency is a

fatty-acid metabolism disorder A broad classification for genetic disorders that result from an inability of the body to produce or utilize one enzyme that is required to oxidize fatty acids. The enzyme can be missing or improperly constructed, resulting in it not working. This ...

which prevents the body from converting certain fats to energy, particularly during periods without food. Those affected by this disorder have inadequate levels of an enzyme that breaks down a group of fats called very long-chain fatty acids.

Signs and symptoms

Signs and symptoms can include: *

hypoglycemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose belo ...

lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...

hepatomegaly Hepatomegaly is the condition of having an enlarged liver. It is a non-specific medical sign having many causes, which can broadly be broken down into infection, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdomi ...

* muscle pain *

cardiomyopathy Cardiomyopathy is a group of diseases that affect the heart muscle. Early on there may be few or no symptoms. As the disease worsens, shortness of breath, feeling tired, and swelling of the legs may occur, due to the onset of heart failure. A ...

*Early onset-pericardial effusion *

heart arrhythmias Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose. Vomiting can be the result of ailments like Food-poisoning, foo ...

Coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

Death Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...

Rhabdomyolysis Rhabdomyolysis (also called rhabdo) is a condition in which damaged skeletal muscle breaks down rapidly. Symptoms may include muscle pains, weakness, vomiting, and confusion. There may be tea-colored urine or an irregular heartbeat. Some of th ...

*Hypoketotic Hypoglycemia

Causes

VLCAD (very long-chain-acyl-dehydrogenase) deficiency is exclusively linked to genetic mutations in DNA. A change of the gene that codes for very long-chain-acyl-CoA-dehydrogenase (VLCAD) results in a deficiency or malfunction of the produced VLCAD enzyme. This mutation occurs on chromosome 17 and can be altered via a variety of pathways. These can range from frameshift mutations, deletion mutations, insertion mutations, and missense mutations. All of which cause the enzyme to function differently in the mitochondria, or in some cases not at all. Due to this mutation, effective levels of very long-chain-acyl-CoA-dehydrogenase are low or absent in the body, giving rise to the array of symptoms listed above.

Genetics

Mutations in the ''

ACADVL Very long-chain specific acyl-CoA dehydrogenase, mitochondrial (VLCAD) is an enzyme that in humans is encoded by the ACADVL gene. Mutations in the ACADVL are associated with very long-chain acyl-coenzyme A dehydrogenase deficiency. The protein ...

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

lead to inadequate levels of an enzyme called very long-chain acyl-coenzyme A (CoA) dehydrogenase. Without this enzyme, long-chain fatty acids from food and fats stored in the body cannot be degraded and processed. As a result, these fatty acids are not converted into energy, which can lead to characteristic signs and symptoms of this disorder, such as lethargy and hypoglycemia. Levels of very long-chain fatty acids or partially degraded fatty acids may build up in tissues and can damage the heart, liver, and muscles, causing more serious complications. VLCAD deficiency is characterized as an inherited genetic disorder. The mutations that occur within the gene itself are recessive, meaning that an individual has to acquire both recessive mutated genes in order for the disease to manifest. There are various forms of the disease that can be manifested in infancy, adolescence, and adulthood. However, it is still unknown at to what causes the disease to manifest itself in the different life stages.

Diagnosis

Typically, initial signs and symptoms of this disorder occur during infancy and include low blood sugar (

), lack of energy (

), and

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

weakness. There is also a high risk of complications such as

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

abnormalities and life-threatening

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

problems. Symptoms that begin later in childhood, adolescence, or adulthood tend to be milder and usually do not involve heart problems. Episodes of very long-chain acyl-coenzyme A dehydrogenase deficiency can be triggered by periods of fasting, illness, and exercise. It is common for babies and children with the early and childhood types of VLCAD to have episodes of illness known as metabolic crises. Some of the first symptoms of a metabolic crisis are: extreme sleepiness, behavior changes, irritable mood, poor appetite. Some of these other symptoms of VLCAD in infants may also follow:

fever Fever, also referred to as pyrexia, is defined as having a body temperature, temperature above the human body temperature, normal range due to an increase in the body's temperature Human body temperature#Fever, set point. There is not a single ...

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...

. Evaluation of symptom combinations can aid in a positive diagnosis of VLCAD."American College of Medical Genetics ACT Sheet" (PDF). American College of Medical Genetics. 2010. Retrieved October 8, 2019. Since symptoms vary depending on age and onset of the patient, consultation with a metabolic specialist should be considered. Diagnosis is further confirmed through genetic analysis of the VLCAD gene.

Treatment

Treatment and management of VLCAD deficiency involve dietary restrictions as well as implementation of proper hydration to avoid further complications. Hospitalization due to VLCAD deficiency can be treated with intravenous (IV) glucose for hydration and alkalization of urine and prevention of renal malfunction or failure. Avoidance of fasting periods, high-fat diets, and dehydration is recommended for those who are affected. A diet consisting of low-fat intake and supplemental calories is common for management of VLCAD deficiency. If a metabolic crisis is not treated, a child with VLCAD can develop: breathing problems, seizures,

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

, sometimes leading to death.

Prognosis

Medical screening can confirm occurrences of VLCAD most often in neonatal and infancy stages. Approximately half of all patients show signs of VLCAD deficiency during the neonatal period, one-fourth present later in the first year of infancy, and the final quarter is split between manifestations in childhood and adulthood. Comorbidity of cardiomyopathy, arrhythmias and rhabdomyolysis are extremely common in patients under 1 year old which can lead to complications later in life. Loss of awareness or seizure can occur from hypoketotic hypoglycemia, which is often fatal if not caught in screening. However, prompt treatment shows high promise for improvement. Late-onset myopathic sufferers may only experience muscle-related, vague, sporadic symptoms, and may never be diagnosed. There is an extremely high genotype-phenotype correlation in a presentation. Mitigation of VLCAD symptoms can be achieved through dietary management.

References

External links

{{DEFAULTSORT:Very Long-Chain Acyl-Coenzyme A Dehydrogenase Deficiency Autosomal recessive disorders Fatty-acid metabolism disorders Rare diseases