Histidinemia is a rare autosomal recessive disorder. However, histidinemia is considered the most prevalent inborn error of metabolism with a reported incidence of 1:8600 (Quebec); 1:180,000 (New York) and 1:9600 (Japan); and an average of 1:12,000 observed in the neonatal screening of over 20 million newborns.

PNP-deficiency is extremely rare. Only 33 patients with the disorder in the United States have been documented. In the United Kingdom only one child has been diagnosed with this disorder.

A 2005 study on rats suggested that hyperprolininemia causes cognitive dysfunction.

The addition of SPCD to newborn screening panels has offered insight into the incidence of the disorder around the world. In Taiwan, the incidence of SPCD in newborns was estimated to be approximately 1:67,000, while maternal cases were identified at a higher frequency of approximately 1:33,000. The increased incidence of SPCD in mothers compared to newborns is not completely understood. Estimates of SPCD in Japan have shown a similar incidence of 1:40,000. Worldwide, SPCD has the highest incidence in the relatively genetically isolated Faroe Islands, where an extensive screening program was instituted after the sudden death of two teenagers. The incidence in the Faroe Islands is approximately 1:200.

It has been suggested that a possible method of treatment for histidinemia is through the adoption of a diet that is low in histidine intake. However, the requirement for such dietary restrictions is typically unnecessary for 99% of all cases of histidinemia.

Purine nucleoside phosphorylase deficiency, often called PNP-deficiency, is a rare autosomal recessive metabolic disorder which results in immunodeficiency.

Sarcosinemia (SAR), also called hypersarcosinemia and SARDH deficiency, is a rare autosomal recessive metabolic disorder characterized by an increased concentration of sarcosine in blood plasma and urine ("sarcosinuria"). It can result from an inborn error of sarcosine metabolism, or from severe folate deficiency related to the folate requirement for the conversion of sarcosine to glycine. It is thought to be a relatively benign condition.

Delayed growth and development was noted in some patients, although not fully explained, this may be generally associated with the physiological difficulties implicit in errors of energy metabolism. In particular neurological impairment was conjecturally linked with the predominant role of aldolase A in the brain during development. However, this was not substantiated with direct enzymatic kinetic study.

Elevated liver glycogen in one patent was rationalised through an accumulation of fructose-1,6-bisphosphate leading to impaired glucose metabolism and increased diversion of hexose sugars from peripheral tissues. Within the liver the aldolase C isoform is unaffected and therefore hepatic metabolism is assumed to be normally functioning and compensatory processes may be operating.

Compromised immunity has also been indicated, relating to the predominance or exclusivity of aldolase A in leukocytes. This was correlated with recurrent infection in the Sicilian case.

Focal disruption of vital energy metabolism has thus far prevented complete investigation of non-catalytic perturbation. However relation to membrane structural stability has been implicated in the concurrence of aldolase A deficiency and dominant (mild) hereditary elliptocytosis, speculatively also relating to ATP depletion.

According to Clinicaltrials.gov, there are no current studies on hyperglycerolemia.

Clinicaltrials.gov is a service of the U.S. National Institutes of Health. Recent research shows patients with high concentrations of blood triglycerides have an increased risk of coronary heart disease. Normally, a blood glycerol test is not ordered. The research was about a child having elevated levels of triglycerides when in fact the child had glycerol kinase deficiency. This condition is known as pseudo-hypertriglyceridemia, a falsely elevated condition of triglycerides. Another group treated patients with elevated concentrations of blood triglycerides with little or no effect on reducing the triglycerides. A few laboratories can test for high concentrations of glycerol, and some laboratories can compare a glycerol-blanked triglycerides assay with the routine non-blanked method. Both cases show how the human body may exhibit features suggestive of a medical disorder when in fact it is another medical condition causing the issue.

Different genetic causes and types of Leigh syndrome have different prognoses, though all are poor. The most severe forms of the disease, caused by a full deficiency in one of the affected proteins, cause death at a few years of age. If the deficiency is not complete, the prognosis is somewhat better and an affected child is expected to survive 6–7 years, and in rare cases, to their teenage years.

Hyperprolinemia type II results in proline levels in the blood between 10 and 15 times higher than normal, and high levels of a related compound called pyrroline-5-carboxylate. This rare form of the disorder may appear benign at times, but often involves seizures, convulsions, and intellectual disability.

Hyperprolinemia can also occur with other conditions, such as malnutrition or liver disease. In particular, individuals with conditions that cause elevated levels of lactic acid in the blood, such as lactic acidemia, are likely to have elevated proline levels, because lactic acid inhibits the breakdown of proline.

Galactose epimerase deficiency, also known as GALE deficiency, Galactosemia III and UDP-galactose-4-epimerase deficiency, is a rare, autosomal recessive form of galactosemia associated with a deficiency of the enzyme "galactose epimerase".

Sarcosinemia is thought to be caused by a mutation in the sarcosine dehydrogenase (SARDH) gene, which is located at human chromosome 9q34.

The disease is inherited in an autosomal recessive manner, which means the defective gene responsible for the disorder is located on an autosome (chromosome 9 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

Aldolase A deficiency, also called ALDOA deficiency, red cell aldolase deficiency or glycogen storage disease type 12 (GSD XII) is an autosomal recessive metabolic disorder resulting in a deficiency of the enzyme aldolase A; the enzyme is found predominantly in red blood cells and muscle tissue. The deficiency may lead to hemolytic anaemia as well as myopathy associated with exercise intolerance and rhabdomyolysis in some cases.

Glycogen storage disease type VI (GSD VI) is a type of glycogen storage disease caused by a deficiency in liver glycogen phosphorylase or other components of the associated phosphorylase cascade system. It is also known as "Hers' disease", after Henri G. Hers, who characterized it in 1959. The scope of GSD VI now also includes glycogen storage disease type VIII, IX (caused by phosphorylase b kinase deficiency) and X (deficiency protein kinase A).

The incidence of GSD VI is approximately 1 case per 65,000–85,000 births, representing approximately 30% all cases of glycogen storage disease. Approximately 75% of these GSD VI cases result from the X-linked recessive forms of phosphorylase kinase deficiency, all other forms are autosomal recessive.

Urocanic aciduria, also called urocanate hydratase deficiency or urocanase deficiency, is an autosomal recessive metabolic disorder caused by a deficiency of the enzyme urocanase. It is a secondary disorder of histidine metabolism.

Urocanic aciduria is thought to be relatively benign. Although aggressive behavior and mental retardation have been reported with the disorder, no definitive neurometabolic connection has yet been established.

Carnitine deficiency has been extensively studied, although most commonly as a secondary finding to other metabolic conditions. The first case of SPCD was reported in the 1980s, in a child with fasting hypoketotic hypoglycemia that resolved after treatment with carnitine supplementation. Later cases were reported with cardiomyopathy and muscle weakness. Newborn screening expanded the potential phenotypes associated with SPCD, to include otherwise asymptomatic adults.

Patients generally have a benign course, and typically present with hepatomegaly and growth retardation early in childhood. Mild hypoglycemia, hyperlipidemia, and hyperketosis may occur. Lactic acid and uric acid levels may be normal. However, lactic acidosis may occur during fasting.

Individuals presenting with Type III galactosemia must consume a lactose- and galactose-restricted diet devoid of dairy products and mucilaginous plants. Dietary restriction is the only current treatment available for GALE deficiency. As glycoprotein and glycolipid metabolism generate endogenous galactose, however, Type III galactosemia may not be resolved solely through dietary restriction.

Prognosis for recovery following administration of succinylcholine is excellent when medical support includes close monitoring and respiratory support measures.

In nonmedical settings in which subjects with pseudocholinesterase deficiency are exposed to cocaine, sudden cardiac death can occur.

In adults, fibrates and statins have been prescribed to treat hyperglycerolemia by lowering blood glycerol levels. Fibrates are a class of drugs that are known as amphipathic carboxylic acids that are often used in combination with Statins. Fibrates work by lowering blood triglyceride concentrations. When combined with statins, the combination will lower LDL cholesterol, lower blood triglycerides and increase HDL cholesterol levels.

If hyperglycerolemia is found in a young child without any family history of this condition, then it may be difficult to know whether the young child has the symptomatic or benign form of the disorder. Common treatments include: a low-fat diet, IV glucose if necessary, monitor for insulin resistance and diabetes, evaluate for Duchenne muscular dystrophy, adrenal insufficiency & developmental delay.

The Genetic and Rare Diseases Information Center (GARD) does not list any treatments at this time.

The main complication resulting from pseudocholinesterase deficiency is the possibility of respiratory failure secondary to succinylcholine or mivacurium-induced neuromuscular paralysis.

Individuals with pseudocholinesterase deficiency also may be at increased risk of toxic reactions, including sudden cardiac death, associated with recreational use of cocaine.

Leigh syndrome (also called Leigh disease and subacute necrotizing encephalomyelopathy) is an under-recognized inherited neurometabolic disorder that affects the central nervous system. It is named after Archibald Denis Leigh, a British neuropsychiatrist who first described the condition in 1951.

The most common X-linked recessive disorders are:

- Red-green color blindness, a very common trait in humans and frequently used to explain X-linked disorders. Between seven and ten percent of men and 0.49% to 1% of women are affected. Its commonness may be explained by its relatively benign nature. It is also known as daltonism.

- Hemophilia A, a blood clotting disorder caused by a mutation of the Factor VIII gene and leading to a deficiency of Factor VIII. It was once thought to be the "royal disease" found in the descendants of Queen Victoria. This is now known to have been Hemophilia B (see below).

- Hemophilia B, also known as Christmas Disease, a blood clotting disorder caused by a mutation of the Factor IX gene and leading to a deficiency of Factor IX. It is rarer than hemophilia A. As noted above, it was common among the descendants of Queen Victoria.

- Duchenne muscular dystrophy, which is associated with mutations in the dystrophin gene. It is characterized by rapid progression of muscle degeneration, eventually leading to loss of skeletal muscle control, respiratory failure, and death.

- Becker's muscular dystrophy, a milder form of Duchenne, which causes slowly progressive muscle weakness of the legs and pelvis.

- X-linked ichthyosis, a form of ichthyosis caused by a hereditary deficiency of the steroid sulfatase (STS) enzyme. It is fairly rare, affecting one in 2,000 to one in 6,000 males.

- X-linked agammaglobulinemia (XLA), which affects the body's ability to fight infection. XLA patients do not generate mature B cells. B cells are part of the immune system and normally manufacture antibodies (also called immunoglobulins) which defends the body from infections (the humoral response). Patients with untreated XLA are prone to develop serious and even fatal infections.

- Glucose-6-phosphate dehydrogenase deficiency, which causes nonimmune hemolytic anemia in response to a number of causes, most commonly infection or exposure to certain medications, chemicals, or foods. Commonly known as "favism", as it can be triggered by chemicals existing naturally in broad (or fava) beans.