Signs and symptoms of this disorder include low levels of ketones (products of fat breakdown that are used for energy) and low blood sugar (hypoglycemia). Together these signs are called hypoketotic hypoglycemia. People with this disorder typically also have an enlarged liver (hepatomegaly), muscle weakness, and elevated levels of carnitine in the blood.

Typically, initial signs and symptoms of this disorder occur during infancy or early childhood and can include feeding difficulties, lethargy, hypoglycemia, hypotonia, liver problems, and abnormalities in the retina. Muscle pain, a breakdown of muscle tissue, and abnormalities in the nervous system that affect arms and legs (peripheral neuropathy) may occur later in childhood. There is also a risk for complications such as life-threatening heart and breathing problems, coma, and sudden unexpected death. Episodes of LCHAD deficiency can be triggered by periods of fasting or by illnesses such as viral infections.

Typically, initial signs and symptoms of this disorder occur during infancy or early childhood and can include poor appetite, vomiting, diarrhea, lethargy, hypoglycemia, hypotonia, liver problems, and abnormally high levels of hyperinsulinism. Insulin controls the amount of sugar that moves from the blood into cells for conversion to energy. Individuals with 3-hydroxyacyl-coenzyme A dehydrogenase deficiency are also at risk for complications such as seizures, life-threatening heart and breathing problems, coma, and sudden unexpected death.

Problems related to 3-hydroxyacyl-coenzyme A dehydrogenase deficiency can be triggered by periods of fasting or by illnesses such as viral infections. This disorder is sometimes mistaken for Reye syndrome, a severe disorder that may develop in children while they appear to be recovering from viral infections such as chicken pox or flu. Most cases of Reye syndrome are associated with the use of aspirin during these viral infections.

The signs of carnitine-acylcarnitine translocase deficiency usually begin within the first few hours of life. Seizures, an irregular heartbeat, and breathing problems are often the first signs of this disorder. This disorder may also cause extremely low levels of ketones (products of fat breakdown that are used for energy) and low blood sugar (hypoglycemia). Together, these two signs are called hypoketotic hypoglycemia. Other signs that are often present include ammonia in the blood (hyperammonemia), an enlarged liver (hepatomegaly), heart abnormalities (cardiomyopathy), and muscle weakness. This disorder can cause sudden infant death.

Short-chain acyl-coenzyme A dehydrogenase deficiency affected infants will have vomiting, low blood sugar, a lack of energy (lethargy), poor feeding, and failure to gain weight and grow. Additional features of this disorder may include poor muscle tone (hypotonia), seizures, developmental delays, and microcephaly. The symptoms of short-chain acyl-CoA dehydrogenase deficiency may be triggered during illnesses such as viral infections. In some cases, signs and symptoms may not appear until adulthood, when some individuals may develop muscle weakness, while other individuals mild symptoms may never be diagnosed.

Typically, initial signs and symptoms of this disorder occur during infancy and include low blood sugar (hypoglycemia), lack of energy (lethargy), and muscle weakness. There is also a high risk of complications such as liver abnormalities and life-threatening heart 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 VLCADD to have episodes of illness called 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 VLCADD in infants may also follow: fever, nausea, diarrhea, vomiting, hypoglycemia.

Signs and symptoms can include:

- hypoglycemia

- lethergy

- hepatomegaly

- muscle pain

- cardiomyopathy

3-hydroxyacyl-coenzyme A dehydrogenase deficiency (HADH deficiency) is a rare condition that prevents the body from converting certain fats to energy, particularly during fasting. Normally, through a process called fatty acid oxidation, several enzymes work in a step-wise fashion to metabolize fats and convert them to energy. People with 3-hydroxyacyl-coenzyme A dehydrogenase deficiency have inadequate levels of an enzyme required for a step that metabolizes groups of fats called medium chain fatty acids and short chain fatty acids; for this reason this disorder is sometimes called medium- and short-chain 3-hydroxyacyl-coenzyme A dehydrogenase (M/SCHAD) deficiency.

Succinyl-CoA:3-oxoacid CoA transferase deficiency (SCOT deficiency) is an inborn error of ketone body utilization. Succinyl-CoA:3-oxoacid CoA transferase catalyzes the transfer of coenzyme A from succinyl-coenzyme A to acetoacetate. It can be caused by mutation in the "OXCT1" gene.

First described in 1972, more than 30 people have been reported in the medical literature with this inborn error of metabolism. They experience attacks of ketoacidosis during illness, and even when unwell may have elevated levels of ketone bodies in blood and urine (ketonemia and ketonuria, respectively). Not all people with SCOT deficiency have persistent ketonemia and ketonuria, particularly those with milder defects of enzyme activity.

The presentation of mitochondrial trifunctional protein deficiency may begin during infancy, features that occur are: low blood sugar, weak muscle tone, and liver problems. Infants with this disorder are at risk for heart problems, breathing difficulties, and pigmentary retinopathy. Signs and symptoms of mitochondrial trifunctional protein deficiency that may begin "after" infancy include hypotonia, muscle pain, a breakdown of muscle tissue, and a loss of sensation in the extremities called peripheral neuropathy. Some who have MTP deficiency show a progressive course associated with myopathy, and recurrent rhabdomyolysis.

Medium-chain acyl-CoA dehydrogenase deficiency, often known as MCAD deficiency or MCADD, is a disorder of fatty acid oxidation that impairs the body's ability to break down medium-chain fatty acids into acetyl-CoA. The disorder is characterized by hypoglycemia and sudden death without timely intervention, most often brought on by periods of fasting or vomiting.

Prior to expanded newborn screening, MCADD was an underdiagnosed cause of sudden death in infants. Individuals who have been identified prior to the onset of symptoms have an excellent prognosis.

MCADD is most prevalent in individuals of Northern European Caucasian descent, with an incidence of 1:4000 to 1:17,000 depending on the population. Treatment of MCADD is mainly preventative, by avoiding fasting and other situations where the body relies on fatty acid oxidation to supply energy.

The presentation of patient with SPCD can be incredibly varied, from asymptomatic to lethal cardiac manifestations. Early cases were reported with liver dysfunction, muscular findings (weakness and underdevelopment), hypoketotic hypoglycemia, cardiomegaly, cardiomyopathy and marked carnitine deficiency in plasma and tissues, combined with increased excretion in urine. Patients who present clinically with SPCD fall into two categories, a metabolic presentation with hypoglycemia and a cardiac presentation characterized by cardiomyopathy. Muscle weakness can be found with either presentation.

In countries with expanded newborn screening, SPCD can be identified shortly after birth. Affected infants show low levels of free carnitine and all other acylcarnitine species by tandem mass spectrometry. Not all infants with low free carnitine are affected with SPCD. Some may have carnitine deficiency secondary to another metabolic condition or due to maternal carnitine deficiency. Proper follow-up of newborn screening results for low free carnitine includes studies of the mother to determine whether her carnitine deficiency is due to SPCD or secondary to a metabolic disease or diet. Maternal cases of SPCD have been identified at a higher than expected rate, often in women who are asymptomatic. Some mothers have also been identified through newborn screening with cardiomyopathy that had not been previously diagnosed. The identification and treatment of these asymptomatic individuals is still developing, as it is not clear whether they require the same levels of intervention as patients identified with SPCD early in life based on clinical presentation.

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency, often shortened to LCHAD deficiency, is a rare autosomal recessive fatty acid oxidation disorder that prevents the body from converting certain fats into energy. This can become life-threatening, particularly during periods of fasting.

The term fatty acid oxidation disorder (FAOD) is sometimes used, especially when there is an emphasis on the oxidation of the fatty acid.

In addition to the fetal complications, they can also cause complications for the mother during pregnancy.

Examples include:

- trifunctional protein deficiency

- MCADD, LCHADD, and VLCADD

Carnitine palmitoyltransferase I deficiency is a rare metabolic disorder that prevents the body from converting certain fats called long-chain fatty acids into energy, particularly during periods without food.

Carnitine, a natural substance acquired mostly through the diet, is used by cells to process fats and produce energy. People with this disorder have a faulty enzyme, carnitine palmitoyltransferase I, that prevents these long-chain fatty acids from being transported into the mitochondria to be broken down.

Babies with this disorder are usually healthy at birth. The signs and symptoms may not appear until later in infancy or childhood and can include poor feeding and growth (failure to thrive), a weakened and enlarged heart (dilated cardiomyopathy), seizures, and low numbers of red blood cells (anemia). Another feature of this disorder may be very low blood levels of carnitine (a natural substance that helps convert certain foods into energy).

Isobutyryl-CoA dehydrogenase deficiency may be worsened by long periods without food (fasting) or infections that increase the body's demand for energy. Some individuals with gene mutations that can cause isobutyryl-CoA dehydrogenase deficiency may never experience any signs and symptoms of the disorder.

MCADD presents in early childhood with hypoketotic hypoglycemia and liver dysfunction, often preceded by extended periods of fasting or an infection with vomiting. Infants who are exclusively breast-fed may present in this manner shortly after birth, due to poor feeding. In some individuals the first manifestation of MCADD may be sudden death following a minor illness. A number of individuals with MCADD may remain completely asymptomatic, provided they never encounter a situation that sufficiently stresses their metabolism. With the advent of expanded newborn screening, some mothers have been identified with MCADD after their infants had positive newborn screens for low carnitine levels.

The enzyme "MCAD" is responsible for the dehydrogenation step of fatty acids with chain lengths between 6 and 12 carbons as they undergo beta-oxidation in the mitochondria. Fatty acid beta-oxidation provides energy after the body has used up its stores of glucose and glycogen. This oxidation typically occurs during periods of extended fasting or illness when caloric intake is reduced, and energy needs are increased.

Carnitine-acylcarnitine translocase deficiency is a rare, autosomal recessive metabolic disorder that prevents the body from converting long-chain fatty acids into energy, particularly during periods without food. Carnitine, a natural substance acquired mostly through the diet, is used by cells to process fats and produce energy. People with this disorder have a faulty enzyme that prevents long-chain fatty acids from being transported into the innermost part of the mitochondria for processing.

Short-chain acyl-coenzyme A dehydrogenase deficiency (SCADD), also called ACADS deficiency and SCAD deficiency, is an autosomal recessive fatty acid oxidation disorder which affects enzymes required to break down a certain group of fats called short chain fatty acids.

Infants with this disorder appear normal at birth but usually develop signs and symptoms during the first year of life or in early childhood. The characteristic features of this condition, which can range from mild to life-threatening, include feeding difficulties, recurrent episodes of vomiting and diarrhea, excessive tiredness (lethargy), and weak muscle tone (hypotonia). If untreated, this disorder can lead to delayed development, seizures, and coma. Early detection and lifelong management (following a low-protein diet and using appropriate supplements) may prevent many of these complications. In some cases, people with gene mutations that cause 3-methylcrotonyl-CoA carboxylase deficiency never experience any signs or symptoms of the disorder.

The characteristic features of this condition are similar to those of Reye syndrome, a severe disorder that develops in children while they appear to be recovering from viral infections such as chicken pox or flu. Most cases of Reye syndrome are associated with the use of aspirin during these viral infections.

Systemic primary carnitine deficiency (SPCD), also known as carnitine uptake defect, carnitine transporter deficiency (CTD) or systemic carnitine deficiency is an inborn error of fatty acid transport caused by a defect in the transporter responsible for moving carnitine across the plasma membrane. Carnitine is an important amino acid for fatty acid metabolism. When carnitine cannot be transported into tissues, fatty acid oxidation is impaired, leading to a variety of symptoms such as chronic muscle weakness, cardiomyopathy, hypoglycemia and liver dysfunction. The specific transporter involved with SPCD is OCTN2, coded for by the "SLC22A5" gene located on chromosome 5. SPCD is inherited in an autosomal recessive manner, with mutated alleles coming from both parents.

Acute episodes due to SPCD are often preceded by metabolic stress such as extended fasting, infections or vomiting. Cardiomyopathy can develop in the absence of an acute episode, and can result in death. SPCD leads to increased carnitine excretion in the urine and low levels in plasma. In most locations with expanded newborn screening, SPCD can be identified and treated shortly after birth. Treatment with high doses of carnitine supplementation is effective, but needs to be rigorously maintained for life.

SPCD is more common in the Faroe Islands than in other countries, at least one out of every 1000 inhabitants of the Faroes has the illness, while the numbers for other countries are one in every 100,000. Around 100 persons in the islands have been diagnosed, around one third of the whole population of 48,000 people have been screened for SPCD. Several young Faroese people and children have died a sudden death with cardiac arrest because of SPCD. Scientists believe that around 10% of the Faroese population are carriers of the gene for SPCD. These people are not ill, but may have a lower amount of carnitine in their blood than non-carriers.

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 leaves the body unable to produce energy within the liver and muscles from fatty acid sources.

The body's primary source of energy is glucose; however, when all the glucose in the body has been expended, a normal body digests fats. Individuals with a fatty-acid metabolism disorder are unable to metabolize this fat source for energy, halting bodily processes. Most individuals with a fatty-acid metabolism disorder are able to live a normal active life with simple adjustments to diet and medications.

If left undiagnosed many complications can arise. When in need of glucose the body of a person with a fatty-acid metabolism disorder will still send fats to the liver. The fats are broken down to fatty acids. The fatty acids are then transported to the target cells but are unable to be broken down, resulting in a build-up of fatty acids in the liver and other internal organs.

Fatty-acid metabolism disorders are sometimes classified with the lipid metabolism disorders, but in other contexts they are considered a distinct category.

People with methylmalonyl CoA mutase deficiency exhibit many symptoms similar to other diseases involving inborn errors of metabolism. Sometimes the symptoms appear shortly after birth, but other times the onset of symptoms is later.

Newborn babies experience with vomiting, acidosis, hyperammonemia, hepatomegaly (enlarged livers), hyperglycinemia (high glycine levels), and hypoglycemia (low blood sugar). Later, cases of thrombocytopenia and neutropenia can occur.

In some cases intellectual and developmental disabilities, such as autism, were noted with increased frequency in populations with methylmalonyl-CoA mutase deficiency.

This disorder usually appears within the first year of life. The signs and symptoms of HMG-CoA lyase deficiency include vomiting, dehydration, lethargy, convulsions, and coma. When episodes occur in an infant or child, blood sugar becomes extremely low (hypoglycemia), and harmful compounds can build up and cause the blood to become too acidic (metabolic acidosis). These episodes are often triggered by an infection, fasting, strenuous exercise, or sometimes other types of stress.

Depending on the affected gene(s), this disorder may present symptoms that range from mild to life-threatening.

- Stroke

- Progressive encephalopathy

- Seizure

- Kidney failure

- Vomiting

- Dehydration

- Failure to thrive and developmental delays

- Lethargy

- Repeated Yeast infections

- Acidosis

- Hepatomegaly

- Hypotonia

- Pancreatitis

- Respiratory distress