Neonatal adrenoleukodystrophy is an inborn error of peroxisome biogenesis. It is part of the Zellweger spectrum. It has been linked with multiple genes (at least five) associated with peroxisome biogenesis, and has an autosomal recessive pattern of inheritance.

It is caused due to deficient Glucuronidation of bilirubin, Glucuronidation increases the molecular weight of the drug which favours its excretion in bile.

Deficient Glucuronidation is caused by congenital deficiency of hepatic bilirubin glucuronosyltransferase(BGT)

The common cause is congenital, but it can also be caused by maternal steroids passed on through breast milk to the newborn. It is different from breast feeding-associated jaundice (breast-fed infants have higher bilirubin levels than formula-fed ones).

This is a very rare disease (estimated at 0.6–1.0 per million live births), and consanguinity increases the risk of this condition (other rare diseases may be present). Inheritance is autosomal recessive.

Intense jaundice appears in the first days of life and persists thereafter. Type 1 is characterised by a serum bilirubin usually above 345 µmol/L [20 mg/dL] (range 310–755 µmol/L [18–44 mg/dL]) (whereas the reference range for total bilirubin is 2–14 μmol/L [0.1-0.8 mg/dL]).

No UDP glucuronosyltransferase 1-A1 expression can be detected in the liver tissue. Hence, there is no response to treatment with phenobarbital, which causes CYP450 enzyme induction. Most patients (type IA) have a mutation in one of the common exons (2 to 5), and have difficulties conjugating several additional substrates (several drugs and xenobiotics). A smaller percentage of patients (type IB) have mutations limited to the bilirubin-specific A1 exon; their conjugation defect is mostly restricted to bilirubin itself.

Before the availability of phototherapy, these children died of kernicterus (bilirubin encephalopathy) or survived until early adulthood with clear neurological impairment. Today, therapy includes

- exchange transfusions in the immediate neonatal period

- 12 hours/day phototherapy

- heme oxygenase inhibitors to reduce transient worsening of hyperbilirubinemia (although the effect decreases over time)

- oral calcium phosphate and carbonate to form complexes with bilirubin in the gut

- liver transplantation before the onset of brain damage and before phototherapy becomes ineffective at later age

Lucey–Driscoll syndrome is an autosomal recessive metabolic disorder affecting enzymes involved in bilirubin metabolism. It is one of several disorders classified as a transient familial neonatal unconjugated hyperbilirubinemia.

Infantile Refsum disease (IRD), also called infantile phytanic acid storage disease, is a rare autosomal recessive congenital peroxisomal biogenesis disorder within the Zellweger spectrum. These are disorders of the peroxisomes that are clinically similar to Zellweger syndrome and associated with mutations in the "PEX" family of genes. IRD is associated with deficient phytanic acid catabolism, as is Adult Refsum disease, but they are different disorders that should not be confused.

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.

Though lactic acidosis can be a complication of other congenital diseases, when it occurs in isolation it is typically caused by a mutation in the pyruvate dehydrogenase complex genes. It has either an autosomal recessive or X-linked mode of inheritance. Congenital lactic acidosis can be caused by mutations on the X chromosome or in mitochondrial DNA.

Congenital lactic acidosis (CLA) is a rare disease caused by mutations in mitochondrial DNA (mtDNA) that affect the ability of cells to use energy and cause too much lactic acid to build up in the body, a condition called lactic acidosis.

Carnitine palmitoyltransferase II deficiency (CPT-II) is an autosomal recessively inherited genetic metabolic disorder characterized by an enzymatic defect that prevents long-chain fatty acids from being transported into the mitochondria for utilization as an energy source.

The adult myopathic form of this disease was first characterized in 1973 by DiMauro and DiMauro. It is the most common inherited disorder of lipid metabolism affecting the skeletal muscle of adults. CPT II deficiency is also the most frequent cause of hereditary myoglobinuria. Symptoms of this disease are commonly provoked by prolonged exercise or periods without food.

The malabsorption resulting from lack of bile acid has resulted in elemental formula being suggested, which are low in fat with < 3% of calories derived from long chain triglycerides (LCT). However, reduced very long chain fatty acids (VLCFA) has not been shown to reduce blood VLCFA levels , likely because humans can endogenously produce most VLCFA. Plasma VLCFA levels are decreased when dietary VLCFA is reduced in conjunction with supplementation of Lorenzo’s oil (a 4:1 mixture of glyceryl trioleate and glyceryl trierucate) in X-ALD patients . Since docosahexaenoic acid (DHA) synthesis is impaired [59], DHA supplementation was recommended, but a placebo-controlled study has since showed no clinical efficacy . Due to the defective bile acid synthesis, fat soluble supplements of vitamins, A, D, E, and K are recommended.

Standard of care for treatment of CPT II deficiency commonly involves limitations on prolonged strenuous activity and the following dietary stipulations:

- The medium-chain fatty acid triheptanoin appears to be an effective therapy for adult-onset CPT II deficiency.

- Restriction of lipid intake

- Avoidance of fasting situations

- Dietary modifications including replacement of long-chain with medium-chain triglycerides supplemented with L-carnitine

Currently, there is no cure for infantile Refsum disease syndrome, nor is there a standard course of treatment. Infections should be guarded against to prevent such complications as pneumonia and respiratory distress. Other treatment is symptomatic and supportive. Patients show variable lifespans with some individuals surviving until adulthood and into old age.

The prognosis is very poor. Two studies reported typical age of deaths in infancy or early childhood, with the first reporting a median age of death of 2.6 for boys and less than 1 month for girls.

One Finnish study which followed 25 cases from 18 families found that half the infants died within 3 days of birth and the other half died before 4 months of age.

Harderoporphyria is a rare disorder of heme biosynthesis, inherited in an autosomal recessive manner caused by specific mutations in the "CPOX" gene. Mutations in "CPOX" usually cause hereditary coproporphyria, an acute hepatic porphyria, however the K404E mutation in a homozygous or compound heterozygous state with a null allele cause the more severe harderoporphyria. Harderoporphyria is the first known metabolic disorder where the disease phenotype depended on the type and location of the mutations in a gene associated with multiple disorders.

In contrast with other porphyrias, which typically present with either cutaneous lesions after exposure to sunlight or acute neurovisceral attack at any age (most commonly in adulthood), harderoporphyria is characterized by jaundice, anemia enlarged liver and spleen, often presenting in the neonatal period. Later in life, these individuals may present with photosensitivity similar to that found in cutaneous porphyrias.

Biochemically, harderoporphyria presents with a distinct pattern of increased harderoporphyrin (2-vinyl-4,6,7-tripropionic acid porphyrin) in urine and particularly in feces, a metabolite that is not seen in significant quantities in any other porphyria. Enzyme tests show markedly reduced activity of coproporphyrinogen oxidase, compared to both unaffected individuals and those affected with hereditary coproporphyria, consistent with recessive inheritance.

Harderoporphyria is a rare condition, with less than 10 cases reported worldwide. It may be underdiagnosed, as it does not have the typical presentation associated with a porphyria. It was identified as a variant type of coproporphyria in 1983, in a family with three children identified at birth with jaundice and hemolytic anemia. There is no standard treatment for harderoporphyria; care is mainly focused on the management of symptoms.

Peroxisomal disorders represent a class of medical conditions caused by defects in peroxisome functions. This may be due to defects in single enzymes important for peroxisome function or in peroxins, proteins encoded by "PEX" genes that are critical for normal peroxisome assembly and biogenesis.

Incidence of Sanfilippo syndrome varies geographically, with approximately 1 case per 280,000 live births in Northern Ireland, 1 per 66,000 in Australia, and 1 per 50,000 in the Netherlands.

The Australian study estimated the following incidences for each subtype of Sanfilippo syndrome:

Currently, no cure for Zellweger syndrome is known, nor is a course of treatment made standard. Infections should be guarded against to prevent such complications as pneumonia and respiratory distress. Other treatment is symptomatic and supportive. Patients usually do not survive beyond one year of age.

Glycine encephalopathy (also known as non-ketotic hyperglycinemia or NKH) is a rare autosomal recessive disorder of glycine metabolism. After phenylketonuria, glycine encephalopathy is the second most common disorder of amino acid metabolism. The disease is caused by defects in the glycine cleavage system, an enzyme responsible for glycine catabolism. There are several forms of the disease, with varying severity of symptoms and time of onset. The symptoms are exclusively neurological in nature, and clinically this disorder is characterized by abnormally high levels of the amino acid glycine in bodily fluids and tissues, especially the cerebral spinal fluid.

Glycine encephalopathy is sometimes referred to as "nonketotic hyperglycinemia" (NKH), as a reference to the biochemical findings seen in patients with the disorder, and to distinguish it from the disorders that cause "ketotic hyperglycinemia" (seen in propionic acidemia and several other inherited metabolic disorders). To avoid confusion, the term "glycine encephalopathy" is often used, as this term more accurately describes the clinical symptoms of the disorder.

Histidinemia, also referred to as histidinuria, is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme histidase. Histidase is needed for the metabolism of the amino acid histidine. Although originally thought to be linked to multiple developmental disorders histidinemia is now accepted as a relatively benign disorder, leading to a reduction in the prevalence of neonatal screening procedures.

GRACILE syndrome is a very rare autosomal recessive genetic disorder, one of the Finnish heritage diseases. It is caused by mutation in BCS1L gene that occurs in at least 1 out of 47,000 live births in Finnish people.

GRACILE is an acronym for growth retardation, amino aciduria (amino acids in the urine), cholestasis, iron overload, lactic acidosis, and early death. Other names for this syndrome include Finnish lethal neonatal metabolic syndrome (FLNMS); lactic acidosis, Finnish, with hepatic hemosiderosis; and Fellman syndrome.

Currently, no research has shown a higher prevalence of most leukodsytrophy types in any one place around the world. There is, however, a higher prevalence of the Canavan disease in the Jewish population for unknown reasons. 1 in 40 individuals of Ashkenazi Jewish descent are carriers of Canavan disease. This estimates to roughly 2.5%. Additionally, due to an autosomal recessive inheritance patterns, there is no significant difference found between affected males and affected females for most types of leukodystrophy including, but not limited to, metachromatic leukodystrophy, Krabbe disease, Canavan disease, and Alexander disease. The one exception to this is any type of leukodystrophy carried on a sex chromosome, such as X-linked adrenoleukodystrophy, which is carried on the X-chromosome. Because of the inheritance pattern of X-linked diseases, males are more often affected by this type of leukodystrophy, although female carriers are often symptomatic, though not as severely so as males. To date, there have been no found cases of a leukodystrophy carried on the Y chromosome.

Peroxisome biogenesis disorders (PBDs) include the Zellweger syndrome spectrum (PBD-ZSD) and rhizomelic chondrodysplasia punctata type 1 (RCDP1). PBD-ZSD represents a continuum of disorders including infantile Refsum disease, neonatal adrenoleukodystrophy, and Zellweger syndrome. Collectively, PBDs are autosomal recessive developmental brain disorders that also result in skeletal and craniofacial dysmorphism, liver dysfunction, progressive sensorineural hearing loss, and retinopathy.

PBD-ZSD is most commonly caused by mutations in the "PEX1", "PEX6", "PEX10", "PEX12", and "PEX26" genes. This results in the over-accumulation of very long chain fatty acids and branched chain fatty acids, such as phytanic acid. In addition, PBD-ZSD patients show deficient levels of plasmalogens, ether-phospholipids necessary for normal brain and lung function.

RCDP1 is caused by mutations in the "PEX7" gene, which encodes the PTS2 receptor. RCDP1 patients can develop large tissue stores of branched chain fatty acids, such as phytanic acid, and show reduced levels of plasmalogens.

Propionic acidemia, also known as propionic aciduria, propionyl-CoA carboxylase deficiency and ketotic glycinemia, is an autosomal recessive metabolic disorder, classified as a branched-chain organic acidemia.

The disorder presents in the early neonatal period with progressive encephalopathy. Death can occur quickly, due to secondary hyperammonemia, infection, cardiomyopathy, or basal ganglial stroke.

Propionic acidemia is a rare disorder that is inherited from both parents. Being autosomal recessive, neither parent shows symptoms, but both carry a defective gene responsible for this disease. It takes two faulty genes to cause PA, so there is a 1 in 4 chance for these parents to have a child with PA.