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.

Late-onset PFK deficiency, as the name suggests, is a form of the disease that presents later in life. Common symptoms associated with late-onset phosphofructokinase deficiency are myopathy, weakness and fatigue. Many of the more severe symptoms found in the classic type of this disease are absent in the late-onset form.

Classic phosphofructokinase deficiency is the most common type of this disorder. This type presents with exercise-induced muscle cramps and weakness (sometimes rhabdomyolysis), myoglobinuria, as well as with haemolytic anaemia causing dark urine a few hours later.

Hyperuricemia is common, due to the kidneys' inability to process uric acid following damage resulting from processing myoglobin. Nausea and vomiting following strenuous exercise is another common indicator of classic PFK deficiency. Many patients will also display high levels of bilirubin, which can lead to a jaundiced appearance. Symptoms for this type of PFK deficiency usually appear in early childhood.

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.

Individuals with Refsum disease present with neurologic damage, cerebellar degeneration, and peripheral neuropathy. Onset is most commonly in childhood/adolescence with a progressive course, although periods of stagnation or remission occur. Symptoms also include ataxia, scaly skin (ichthyosis), difficulty hearing, and eye problems including retinitis pigmentosa, cataracts, and night blindness. In 80% of patients diagnosed with Refsum disease, sensorineural hearing loss has been reported. This is hearing loss as the result of damage to the inner ear or the nerve connected to ear to the brain.

There are three main types of carnitine palmitoyltransferase II deficiency classified on the basis of tissue-specific symptomotology and age of onset:

- Mild to severe adult myopathic form

- Severe infantile multisystemic form

- Lethal neonatal form

It should be noted that among the few people diagnosed with CPT2, some have unknown and/or novel mutations that place them outside these three categories while remaining positive for CPT2.

The infantile form usually comes to medical attention within the first few months of life. The usual presenting features are cardiomegaly (92%), hypotonia (88%), cardiomyopathy (88%), respiratory distress (78%), muscle weakness (63%), feeding difficulties (57%) and failure to thrive (50%).

The main clinical findings include floppy baby appearance, delayed motor milestones and feeding difficulties. Moderate hepatomegaly may be present. Facial features include macroglossia, wide open mouth, wide open eyes, nasal flaring (due to respiratory distress), and poor facial muscle tone. Cardiopulmonary involvement is manifested by increased respiratory rate, use of accessory muscles for respiration, recurrent chest infections, decreased air entry in the left lower zone (due to cardiomegaly), arrhythmias and evidence of heart failure.

Median age at death in untreated cases is 8.7 months and is usually due to cardiorespiratory failure.

This exclusively myopathic form is the most prevalent and least severe phenotypic presentation of this disorder. Characteristic signs and symptoms include rhabdomyolysis (breakdown of muscle fibers and subsequent release of myoglobin), myoglobinuria, recurrent muscle pain, and weakness. It is important to note that muscle weakness and pain typically resolves within hours to days, and patients appear clinically normal in the intervening periods between attacks. Symptoms are most often exercise-induced, but fasting, a high-fat diet, exposure to cold temperature, or infection (especially febrile illness) can also provoke this metabolic myopathy. In a minority of cases, disease severity can be exacerbated by three life-threatening complications resulting from persistent rhabdomyolysis: acute kidney failure, respiratory insufficiency, and episodic abnormal heart rhythms. Severe forms may have continual pain from general life activity. The adult form has a variable age of onset. The first appearance of symptoms usually occurs between 6 and 20 years of age but has been documented in patients as young as 8 months as well as in adults over the age of 50. Roughly 80% cases reported to date have been male.

This form differs from the infantile principally in the relative lack of cardiac involvement. The onset is more insidious and has a slower progression. Cardiac involvement may occur but is milder than in the infantile form. Skeletal involvement is more prominent with a predilection for the lower limbs.

Late onset features include impaired cough, recurrent chest infections, hypotonia, progressive muscle weakness, delayed motor milestones, difficulty swallowing or chewing and reduced vital capacity.

Prognosis depends on the age of onset on symptoms with a better prognosis being associated with later onset disease.

Infants with this disease seem healthy at birth but quickly deteriorate, often with severe brain damage, which may be permanent. Death often occurs within the first five months in severe cases of the disease, when left untreated.

The symptoms of MSUD may also present later depending on the severity of the disease. Untreated in older individuals, and during times of metabolic crisis, symptoms of the condition include uncharacteristically inappropriate, extreme or erratic behaviour and moods, hallucinations, anorexia, weight loss, anemia, diarrhea, vomiting, dehydration, lethargy, oscillating hypertonia and hypotonia, ataxia, seizures, hypoglycaemia, ketoacidosis, opisthotonus, pancreatitis, rapid neurological decline, and coma. Without prompt treatment, they will likely die from cerebral edema. Additionally, maple syrup urine disease patients often experience an abnormal course of disease in simple infections that become increasingly severe and can have permanent damage. In more rare cases, concomitant osteoporosis may also appear in these patients.

Symptoms of ML I are either present at birth or develop within the first year of life. In many infants with ML I, excessive swelling throughout the body is noted at birth. These infants are often born with coarse facial features, such as a flat nasal bridge, puffy eyelids, enlargement of the gums, and excessive tongue size (macroglossia). Many infants with ML I are also born with skeletal malformations such as hip dislocation. Infants often develop sudden involuntary muscle contractions (called myoclonus) and have red spots in their eyes (cherry red spots). They are often unable to coordinate voluntary movement (called ataxia). Tremors, impaired vision, and seizures also occur in children with ML I. Tests reveal abnormal enlargement of the liver (hepatomegaly) and spleen (splenomegaly) and extreme abdominal swelling. Infants with ML I generally lack muscle tone (hypotonia) and have mental retardation that is either initially or progressively severe. Many patients suffer from failure to thrive and from recurrent respiratory infections. Most infants with ML I die before the age of 1 year.

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.

Affected individuals may have difficulty moving and may experience spasms, jerking, rigidity or decreased muscle tone and muscle weakness (which may be the result of secondary carnitine deficiency). Glutaric aciduria type 1, in many cases, can be defined as a cerebral palsy of genetic origins.

Babies with glutaric acidemia type 1 often are born with unusually large heads (macrocephaly). Macrocephaly is amongst the earliest signs of GA1. It is thus important to investigate all cases of macrocephaly of unknown origins for GCDH deficiency, given the importance of the early diagnosis of GA1.

Macrocephaly is a "pivotal clinical sign" of many neurological diseases. Physicians and parents should be aware of the benefits of investigating for an underlying neurological disorder, particularly a neurometabolic one, in children with head circumferences in the highest percentiles.

Refsum disease, also known as classic or adult Refsum disease, heredopathia atactica polyneuritiformis, phytanic acid oxidase deficiency and phytanic acid storage disease, is an autosomal recessive neurological disease that results from the over-accumulation of phytanic acid in cells and tissues. It is one of several disorders named after Norwegian neurologist Sigvald Bernhard Refsum (1907–1991). Refsum disease typically is adolescent onset and is diagnosed by above average levels of phytanic acid. Humans obtain the necessary phytanic acid primarily through diet. It is still unclear what function phytanic acid plays physiologically in humans, but has been found to regulate fatty acid metabolism in the liver of mice.

Infantile Refsum disease is one of three peroxisome biogenesis disorders which belong to the Zellweger spectrum of peroxisome biogenesis disorders (PBD-ZSD). The other two disorders are Zellweger syndrome (ZS) and neonatal adrenoleukodystrophy (NALD). Although they share a similar molecular basis for disease, Infantile Refsum disease is less severe than Zellweger syndrome.

Infantile Refsum disease is a developmental brain disorder. In addition, patients can show a reduction in central nervous system (CNS) myelin (particularly cerebral), which is referred to as (hypomyelination). Myelin is critical for normal CNS functions. Patients can also show postdevelopmental sensorineuronal degeneration that leads to a progressive loss of hearing and vision.

Infantile Refsum disease can also affect the function of many other organ systems. Patients can show craniofacial abnormalities, hepatomegaly (enlarged liver), and progressive adrenal dysfunction. Newborns may present with profound hypotonia (low muscle tone), and a poor ability to feed. In some patients, a progressive leukodystrophy has been observed that has a variable age of onset.

The signs and symptoms of beta-ketothiolase deficiency include vomiting, dehydration, trouble breathing, extreme tiredness, and occasionally convulsions. These episodes are called ketoacidotic attacks and can sometimes lead to coma. Attacks occur when compounds called organic acids (which are formed as products of amino acid and fat breakdown) build up to toxic levels in the blood. These attacks are often triggered by an infection, fasting (not eating), or in some cases, other types of stress.

The symptoms of LSD vary, depending on the particular disorder and other variables such as the age of onset, and can be mild to severe. They can include developmental delay, movement disorders, seizures, dementia, deafness, and/or blindness. Some people with LSDhave enlarged livers (hepatomegaly) and enlarged spleens (splenomegaly), pulmonary and cardiac problems, and bones that grow abnormally.

Lysosomal storage diseases (LSDs; ) are a group of about 50 rare inherited metabolic disorders that result from defects in lysosomal function. Lysosomes are sacs of enzymes within cells that digest large molecules and pass the fragments on to other parts of the cell for recycling. This process requires several critical enzymes. If one of these enzymes is defective, because of a mutation, the large molecules accumulate within the cell, eventually killing it.

Lysosomal storage disorders are caused by lysosomal dysfunction usually as a consequence of deficiency of a single enzyme required for the metabolism of lipids, glycoproteins (sugar-containing proteins), or so-called mucopolysaccharides. Individually, LSDs occur with incidences of less than 1:100,000; however, as a group, the incidence is about 1:5,000 - 1:10,000. Most of these disorders are autosomal recessively inherited such as Niemann–Pick disease, type C, but a few are X-linked recessively inherited, such as Fabry disease and Hunter syndrome (MPS II).

The lysosome is commonly referred to as the cell's recycling center because it processes unwanted material into substances that the cell can use. Lysosomes break down this unwanted matter by enzymes, highly specialized proteins essential for survival. Lysosomal disorders are usually triggered when a particular enzyme exists in too small an amount or is missing altogether. When this happens, substances accumulate in the cell. In other words, when the lysosome does not function normally, excess products destined for breakdown and recycling are stored in the cell.

Like other genetic disorders, individuals inherit lysosomal storage diseases from their parents. Although each disorder results from different gene mutations that translate into a deficiency in enzyme activity, they all share a common biochemical characteristic – all lysosomal disorders originate from an abnormal accumulation of substances inside the lysosome.

LSDs affect mostly children and they often die at a young and unpredictable age, many within a few months or years of birth. Many other children die of this disease following years of suffering from various symptoms of their particular disorder.

Symptoms range widely in their onset and severity. The onset of the most severe form, type III, begins within the first months of life and includes a quick progression of intellectual disability, liver and spleen enlargement (splenomegaly), hearing loss, respiratory infections and skeletal abnormalities. Often the appearance of an affected individual includes the following facial features: protruding forehead, leveled nasal bridge, small nose and wide mouth. Muscular weakness or spinal abnormalities can occur due to the buildup of storage materials in the muscle. A milder form of alpha-mannosidosis involves mild to moderate intellectual disability which develops during childhood or adolescence.

PDCD is generally presented in one of two forms. The metabolic form appears as lactic acidosis. The neurological form of PDCD contributes to hypotonia, poor feeding, lethargy and structural abnormalities in the brain. Patients may develop seizures and/or neuropathological spasms. These presentations of the disease usually progress to mental retardation, microcephaly, blindness and spasticity.

Females with residual pyruvate dehydrogenase activity will have no uncontrollable systemic lactic acidosis and few, if any, neurological symptoms. Conversely, females with little to no enzyme activity will have major structural brain abnormalities and atrophy. Males with mutations that abolish, or almost abolish, enzyme activity presumably die in utero because brain cells are not able to generate enough ATP to be functionally viable. It is expected that most cases will be of mild severity and have a clinical presentation involving lactic acidosis.

Prenatal onset may present with non-specific signs such as low Apgar scores and small for gestational age. Metabolic disturbances may also be considered with poor feeding and lethargy out of proportion to a mild viral illness, and especially after bacterial infection has been ruled out. PDH activity may be enhanced by exercise, phenylbutyrate and dichloroacetate.

The clinical presentation of congenital PDH deficiency is typically characterized by heterogenous neurological features that usually appear within the first year of life. In addition, patients usually show severe hyperventillation due to profound metabolic acidosis mostly related to lactic acidosis. Metabolic acidosis in these patients is usually refractory to correction with bicarbonate.

Like many other genetic disorders that affect lipid metabolism, there are several forms of MLD, which are late infantile, juvenile, and adult.

- In the "late infantile form", which is the most common form of MLD (50–60%), affected children begin having difficulty walking after the first year of life, usually at 15–24 months. Symptoms include muscle wasting and weakness, muscle rigidity, developmental delays, progressive loss of vision leading to blindness, convulsions, impaired swallowing, paralysis, and dementia. Children may become comatose. Untreated, most children with this form of MLD die by age 5, often much sooner.

- Children with the "juvenile form" of MLD (onset between 3 and 10 years of age) usually begin with impaired school performance, mental deterioration, and dementia and then develop symptoms similar to the late infantile form but with slower progression. Age of death is variable, but normally within 10 to 15 years of symptom onset although some juveniles can live for several decades or longer after onset.

- The "adult form" commonly begins after age 16 often with an onset in the 4th or 5th decade of life and presents as a psychiatric disorder or progressive dementia. Adult-onset MLD usually progresses more slowly than the late infantile and juvenile forms, with a protracted course of a decade or more.

Palliative care can help with many of the symptoms and usually improves quality of life and longevity.

Carriers have low enzyme levels compared to their family population ("normal" levels vary from family to family) but even low enzyme levels are adequate to process the body's sulfatide.

Beta-ketothiolase deficiency is a rare, autosomal recessive metabolic disorder in which the body cannot properly process the amino acid isoleucine or the products of lipid breakdown.

The typical age of onset for this disorder is between 6 months and 24 months.

Glycogen storage disease type V (GSD-V) is a metabolic disorder, more specifically a glycogen storage disease, caused by a deficiency of myophosphorylase. Its incidence is reported as 1 in 100,000, approximately the same as glycogen storage disease type I.

The disease was first reported in 1951 by Dr. Brian McArdle of Guy's Hospital, London.