The most common clinical history in patients with glycogen-storage disease type 0 (GSD-0) is that of an infant or child with symptomatic hypoglycemia or seizures that occur before breakfast or after an inadvertent fast. In affected infants, this event typically begins after they outgrow their nighttime feeds. In children, this event may occur during acute GI illness or periods of poor enteral intake.

Mild hypoglycemic episodes may be clinically unrecognized, or they may cause symptoms such as drowsiness, sweating, lack of attention, or pallor. Uncoordinated eye movements, disorientation, seizures, and coma may accompany severe episodes.

Glycogen-storage disease type 0 affects only the liver. Growth delay may be evident with height and weight percentiles below average. Abdominal examination findings may be normal or reveal only mild hepatomegaly.Signs of acute hypoglycemia may be present, including the following:

Hypoglycemia is the central clinical problem, the one that is most damaging, and the one that most often prompts the initial diagnosis.

Maternal glucose transferred across the placenta prevents hypoglycemia in a fetus with GSD I, but the liver is enlarged with glycogen at birth. The inability to generate and release glucose soon results in hypoglycemia, and occasionally in lactic acidosis fulminant enough to appear as a primary respiratory problem in the newborn period. Neurological manifestations are less severe than if the hypoglycemia were more acute. The brain's habituation to mild hypoglycemia is at least partly explained by use of alternative fuels, primarily lactate.

More commonly, infants with GSD I tolerate without obvious symptoms a chronic, mild hypoglycemia, and compensated lactic acidosis between feedings. Blood glucose levels are typically 25 to 50 mg/dl (1.4–2.8 mM). These infants continue to need oral carbohydrates every few hours. Many never sleep through the night even in the second year of life. They may be pale, clammy, and irritable a few hours after a meal. Developmental delay is not an intrinsic or inevitable effect of glucose-6-phosphatase deficiency but is common if the diagnosis is not made in early infancy.

Although mild hypoglycemia for much of the day may go unsuspected, the metabolic adaptations described above make severe hypoglycemic episodes, with unconsciousness or seizure, uncommon before treatment. Episodes which occur are likely to happen in the morning before breakfast. GSD I is therefore a potential cause of ketotic hypoglycemia in young children.

Once the diagnosis has been made, the principal goal of treatment is to maintain an adequate glucose level and prevent hypoglycemia.

Intestinal involvement can cause mild malabsorption with steatorrhea, greasy stools, but usually requires no treatment.

Glycogen storage disease type 0 is a disease characterized by a deficiency in the glycogen synthase enzyme (GYS). Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver, it is often classified as a glycogen storage disease because it is another defect of glycogen storage and can cause similar problems. There are two isoforms (types) of glycogen synthase enzyme; GYS1 in muscle and GSY2 in liver, each with a corresponding form of the disease. Mutations in the liver isoform (GYS2), causes fasting hypoglycemia, high blood ketones, increased free fatty acids and low levels of alanine and lactate. Conversely, feeding in these patients results in hyperglycemia and hyperlactatemia.

In fructose bisphosphatase deficiency, there is not enough fructose bisphosphatase for gluconeogenesis to occur correctly. Glycolysis (the breakdown of glucose) will still work, as it does not use this enzyme.

Without effective gluconeogenesis (GNG), hypoglycaemia will set in after about 12 hours of fasting. This is the time when liver glycogen stores have been exhausted, and the body has to rely on GNG. When given a dose of glucagon (which would normally increase blood glucose) nothing will happen, as stores are depleted and GNG doesn't work. (In fact, the patient would already have high glucagon levels.)

There is no problem with the metabolism of glucose or galactose, but fructose and glycerol cannot be used by the liver to maintain blood glucose levels. If fructose or glycerol are given, there will be a buildup of phosphorylated three-carbon sugars. This leads to phosphate depletion within the cells, and also in the blood. Without phosphate, ATP cannot be made, and many cell processes cannot occur.

High levels of glucagon will tend to release fatty acids from adipose tissue, and this will combine with glycerol that cannot be used in the liver, to make triacylglycerides causing a fatty liver.

As three carbon molecules cannot be used to make glucose, they will instead be made into pyruvate and lactate. These acids cause a drop in the pH of the blood (a metabolic acidosis). Acetyl CoA (acetyl co-enzyme A) will also build up, leading to the creation of ketone bodies.

Glycogen storage disease type III presents during infancy with hypoglycemia and failure to thrive. Clinical examination usually reveals hepatomegaly. Muscular disease, including hypotonia and cardiomyopathy, usually occurs later. The liver pathology typically regresses as the individual enter adolescence, as does splenomegaly, should the individual so develop it.

In undiagnosed and untreated children, the accumulation of precursor metabolites due to the deficient activity of galactose 1-phosphate uridylyltransferase (GALT) can lead to feeding problems, failure to thrive, liver damage, bleeding, and infections. The first presenting symptom in an infant is often prolonged jaundice. Without intervention in the form of galactose restriction, infants can develop hyperammonemia and sepsis, possibly leading to shock. The accumulation of galactitol and subsequent osmotic swelling can lead to cataracts which are similar to those seen in galactokinase deficiency. Long-term consequences of continued galactose intake can include developmental delay, developmental verbal dyspraxia, and motor abnormalities. Galactosemic females frequently suffer from ovarian failure, regardless of treatment in the form of galactose restriction.

Lactic acidosis is commonly found in people who are unwell, such as those with severe heart and/or lung disease, a severe infection with sepsis, the systemic inflammatory response syndrome due to another cause, severe physical trauma, or severe depletion of body fluids. Symptoms in humans include all those of typical metabolic acidosis (nausea, vomiting, generalized muscle weakness, and rapid breathing).

Symptoms vary according to individuals' hydration level and sensitivity to the rate and/or magnitude of decline of their blood glucose concentration.

A crash is usually felt within four hours or less of heavy carbohydrate consumption. Symptoms of reactive hypoglycemia include:

- double vision or blurry vision

- unclear thinking

- insomnia

- heart palpitation or fibrillation

- fatigue

- dizziness

- light-headedness

- sweating

- headaches

- depression

- nervousness

- muscle twitches

- irritability

- tremors

- flushing

- craving sweets

- increased appetite

- rhinitis

- nausea, vomiting

- panic attack

- numbness/coldness in the extremities

- confusion

- irrationality

- bad temper

- paleness

- cold hands

- disorientation

- the need to sleep or 'crash'

- coma can be a result in severe untreated episodes

The majority of these symptoms, often correlated with feelings of hunger, mimic the effect of inadequate sugar intake as the biology of a crash is similar in itself to the body’s response to low blood sugar levels following periods of glucose deficiency.

The key identifying feature of HFI is the appearance of symptoms with the introduction of fructose to the diet. Affected individuals are asymptomatic and healthy, provided they do not ingest foods containing fructose or any of its common precursors, sucrose and sorbitol. In the past, infants often became symptomatic when they were introduced to formulas that were sweetened with fructose or sucrose. These sweeteners are not common in formulas used today. Symptoms such as vomiting, nausea, restlessness, pallor, sweating, trembling and lethargy can also first present in infants when they are introduced to fruits and vegetables. These can progress to apathy, coma and convulsions if the source is not recognized early.

When patients are diagnosed with HFI, a dietary history will often reveal an aversion to fruit and other foods that contain large amounts of fructose. Most adult patients do not have any dental caries.

Lactic acidosis is a medical condition characterized by the buildup of lactate (especially L-lactate) in the body, which results in an excessively low pH in the bloodstream. It is a form of metabolic acidosis, in which excessive acid accumulates due to a problem with the body's metabolism of lactic acid.

Lactic acidosis is typically the result of an underlying acute or chronic medical condition, medication, or poisoning. The symptoms are generally attributable to these underlying causes, but may include nausea, vomiting, rapid deep breathing, and generalised weakness.

The diagnosis is made on biochemical analysis of blood (often initially on arterial blood gas samples), and once confirmed, generally prompts an investigation to establish the underlying cause to treat the acidosis. In some situations, hemofiltration (purification of the blood) is temporarily required. In rare chronic forms of lactic acidosis caused by mitochondrial disease, a specific diet or dichloroacetate may be used. The prognosis of lactic acidosis depends largely on the underlying cause; in some situations (such as severe infections), it indicates an increased risk of death.

Essential fructosuria, caused by a deficiency of the enzyme hepatic fructokinase, is a clinically benign condition characterized by the incomplete metabolism of fructose in the liver, leading to its excretion in urine. Fructokinase (sometimes called ketohexokinase) is the first enzyme involved in the degradation of fructose to fructose-1-phosphate in the liver. This defective degradation does not cause any clinical symptoms, fructose is either excreted unchanged in the urine or metabolized to fructose-6-phosphate by alternate pathways in the body, most commonly by hexokinase in adipose tissue and muscle.

Horses with Type 1 PSSM usually appear normal at rest, but show signs of exertional rhabdomyolysis ("tying up") such as shortened stride, stiffness, firm musculature, sweating, pain or reluctance to exercise, when asked to perform light work. While episodes of exertional rhabdomyolysis is one of the most frequent signs associated with affected horses (reported in ~37% of affected animals), other common signs include gait abnormalities, shifting lameness, muscle weakness that may result in an inability to rise, colic-like pain, and muscle fasciculation, atrophy, and/or stiffness (most commonly seen in the semimembranosis, semitendinosis, and longissimus muscles).

These clinical signs usually first become apparent when the horse is placed into training as a young animal; however, affected horses will show histological changes consistent with muscle damage at one month of age, and may also show elevations in creatine kinase (CK), an enzyme that elevates with muscle damage. Concurrent illness, such as respiratory or gastrointestinal infection, can lead to elevations in CK and potentially life-threatening rhabdomyolysis, even without exercise. Horses with PSSM often have a persistently elevated CK at rest, which differentiates the disease from recurrent exertional rhabdomyolysis, in which horses have normal CK concentrations between episodes.

Glycogen storage disease type III is an autosomal recessive metabolic disorder and inborn error of metabolism (specifically of carbohydrates) characterized by a deficiency in glycogen debranching enzymes. It is also known as Cori's disease in honor of the 1947 Nobel laureates Carl Cori and Gerty Cori. Other names include Forbes disease in honor of clinician Gilbert Burnett Forbes (1915–2003), an American Physician who further described the features of the disorder, or limit dextrinosis, due to the limit dextrin-like structures in cytosol. Limit dextrin is the remaining polymer produced after hydrolysis of glycogen. Without glycogen debranching enzymes to further convert these branched glycogen polymers to glucose, limit dextrinosis abnormally accumulates in the cytoplasm.

Glycogen is a molecule the body uses to store carbohydrate energy. Symptoms of GSD-III are caused by a deficiency of the enzyme amylo-1,6 glucosidase, or debrancher enzyme. This causes excess amounts of an abnormal glycogen to be deposited in the liver, muscles and, in some cases, the heart.

A diagnosis of essential fructosuria is typically made after a positive test for reducing substances in the urine. The excretion of fructose in the urine is not constant, it depends largely on dietary intake.

Ketoacidosis is a metabolic state associated with high concentrations of ketone bodies, formed by the breakdown of fatty acids and the deamination of amino acids. The two common ketones produced in humans are acetoacetic acid and β-hydroxybutyrate.

Ketoacidosis is a pathological metabolic state marked by extreme and uncontrolled ketosis. In ketoacidosis, the body fails to adequately regulate ketone production causing such a severe accumulation of keto acids that the pH of the blood is substantially decreased. In extreme cases ketoacidosis can be fatal.

Ketoacidosis is most common in untreated type 1 diabetes mellitus, when the liver breaks down fat and proteins in response to a perceived need for respiratory substrate. Prolonged alcoholism may lead to alcoholic ketoacidosis.

Ketoacidosis can be smelled on a person's breath. This is due to acetone, a direct by-product of the spontaneous decomposition of acetoacetic acid. It is often described as smelling like fruit or nail polish remover. Ketosis may also give off an odor, but the odor is usually more subtle due to lower concentrations of acetone.

Treatment consists most simply of correcting blood sugar and insulin levels, which will halt ketone production. If the severity of the case warrants more aggressive measures, intravenous sodium bicarbonate infusion can be given to raise blood pH back to an acceptable range. However, serious caution must be exercised with IV sodium bicarbonate to avoid the risk of equally life-threatening hypernatremia.

Inborn errors of carbohydrate metabolism are inborn error of metabolism that affect the catabolism and anabolism of carbohydrates.

An example is lactose intolerance.

Carbohydrates account for a major portion of the human diet. These carbohydrates are composed of three principal monosaccharides: glucose, fructose and galactose; in addition glycogen is the storage form of carbohydrates in humans. The failure to effectively use these molecules accounts for the majority of the inborn errors of human carbohydrates metabolism.

Equine polysaccharide storage myopathy (EPSM, PSSM, EPSSM) is an inheritable glycogen storage disease of horses that causes exertional rhabdomyolysis. It is most commonly associated with heavy horse breeds and the American Quarter Horse. While incurable, PSSM can be managed with appropriate diet and exercise. There are currently 2 subtypes, known as Type 1 PSSM and Type 2 PSSM.

"Common symptoms of NDM includes:"

- Thirst and Frequent Urination

An excessive thirst (also known as polydipsia) and increased urination (also known as polyuria) are common signs of diabetes. An individual with diabetes, have accumulated blood glucose. Their kidneys are working overtime to filter and uptake excess sugar. However, their kidneys cannot keep up, excess sugar is excreted into their urine, and this drag along fluids from the diabetic's tissues. This may lead to more frequent urination and lead to dehydration. As a diabetic individual drinks more fluids to satisfy their thirst, he or she urinates even more.

- Dehydration

Effected areas of the body are the eyes, mouth, kidneys, heart, and pancreas. Other symptoms of dehydration includes headache, thirst and dry mouth, dizziness, tiredness, and dark colored urine. In severe cases of dehydration in diabetics, low blood pressure, sunken eyes, a weak pulse or rapid heart beat, feeling confused or fatigue. Dehydration and high blood glucose for extended period of time, the diabetic's kidney would try to filter the blood of access glucose and excrete this as urine. As the kidneys are filtering the blood, water is being removed from the blood and would need to be replaced. This leads to an increased thirst when the blood glucose is elevated in a diabetic individual. Water is needed to re-hydrate the body. Therefore, the body would take available from other parts of the body, such as saliva, tears, and from cells of the body. If access water is not available, the body would not be able to pass excess glucose out of the blood by urine and can lead to further dehydration.

"Severe symptoms of NDM (Deficiency of insulin):"

- Ketoacidosis

Is a diabetic complication that occurs when the body produces high levels of acid in the blood (ketones). This effects the pancreas, fat cells, and kidneys. This condition occurs when the body cannot produce enough insulin. In the absence or lack of insulin, the body of an diabetic individual will break down fat as fuel. This process produces a buildup of acids in the bloodstream known as ketones, in which leads to ketoacidosis if left untreated. The symptoms of ketoacidosis develop rapidly or within 24 hours. Symptoms of ketoacidosis are excessive thirst, frequent urination, nausea or vomiting, stomach pain, tiredness, shortness or fruity smell on breath and confusion.

- Intrauterine Growth Restriction

A condition in which the unborn baby is smaller than he or she should be, due to the fact he or she not growing at a normal rate in the womb. Delayed growth puts the baby at risk of certain problems during pregnancy, delivery, and after birth. The problems are as follows: baby's birth weight is 90% less than normal weight, difficulty handling vaginal delivery, decreased oxygen levels, hypoglycemia (low blood glucose), low resistance to infection, low Apgar scores (a test given after birth to test the baby's physical condition and evaluate if special medical care is needed), Meconium aspiration (inhaling of stools passed while in the uterus) which causes breathing issues, irregular body temperature and high red blood cell count.

- Hyperglycemia

A condition characterized as high blood glucose, which occurs when the body has too little insulin or when the body cannot use insulin properly. Hyperglycemia affects the pancreas, kidneys, and body's tissues. Characterization of hyperglycemia is high blood glucose, high levels of sugar in the urine, frequent urination and increase thirst.

- Hypoglycemia

A condition characterized an extremely low blood glucose, usually less than 70 mg/dL. Areas of the body that are affected, pancreas, kidneys, and mental state.

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.

Galactose-1-phosphate uridylyltransferase deficiency, also called galactosemia type 1, classic galactosemia or GALT deficiency, is the most common type of galactosemia, an inborn error of galactose metabolism, caused by a deficiency of the enzyme galactose-1-phosphate uridylyltransferase. It is an autosomal recessive metabolic disorder that can cause liver disease and death if untreated. Treatment of galactosemia is most successful if initiated early and includes dietary restriction of lactose intake. Because early intervention is key, galactosemia is included in newborn screening programs in many areas. On initial screening, which often involves measuring the concentration of galactose in blood, classic galactosemia may be indistinguishable from other inborn errors of galactose metabolism, including galactokinase deficiency and galactose epimerase deficiency. Further analysis of metabolites and enzyme activities are needed to identify the specific metabolic error.

The onset of this disease is usually noticed in childhood, but often not diagnosed until the third or fourth decade of life. Symptoms include exercise intolerance with muscle pain, early fatigue, painful cramps, and myoglobin in the urine (often provoked by a bout of exercise). Myoglobinuria may result from the breakdown of skeletal muscle known as rhabdomyolysis, a condition in which muscle cells breakdown, sending their contents into the bloodstream.

Patients may exhibit a “second wind” phenomenon. This is characterized by the patient’s better tolerance for aerobic exercise such as walking and cycling after approximately 10 minutes. This is attributed to the combination of increased blood flow and the ability of the body to find alternative sources of energy, like fatty acids and proteins. In the long term, patients may exhibit renal failure due to the myoglobinuria, and with age, patients may exhibit progressively increasing weakness and substantial muscle loss.

Patients may present at emergency rooms with severe fixed contractures of the muscles and often severe pain. These require urgent assessment for rhabdomyolysis as in about 30% of cases this leads to acute renal failure. Left untreated this can be life-threatening. In a small number of cases compartment syndrome has developed, requiring prompt surgical referral.

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.

Galactosemia (British galactosaemia) is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. Galactosemia follows an autosomal recessive mode of inheritance that confers a deficiency in an enzyme responsible for adequate galactose degradation.

Friedrich Goppert (1870–1927), a German physician, first described the disease in 1917, with its cause as a defect in galactose metabolism being identified by a group led by Herman Kalckar in 1956.

Its incidence is about 1 per 60,000 births for people of European ancestry. In other populations the incidence rate differs. Galactosaemia is about one hundred times more common (1:480 births) within the Irish Traveller population.