A 2006 study of 279 patients found that of those with symptoms (185, 66%), 95% had suffered an encephalopathic crises usually with following brain damage. Of the persons in the study, 49 children died and the median age of death was 6.6 years. A Kaplan-Meier analysis of the data estimated that about 50% of symptomatic cases would die by the age of 25.

Due to the rarity of the disease, it is hard to estimate mortality rates or life expectancy. One 2003 study which followed 88 cases receiving two different kinds of treatment found that very few persons lived beyond age 20 and none beyond age 30.

A 1994 study of the entire population of New South Wales (Australia) found 20 patients. Of these, 5 (25%) had died at or before 30 months of age. Of the survivors, 1 (5%) was severely disabled and the remainder had either suffered mild disability or were making normal progress in school. A 2006 Dutch study followed 155 cases and found that 27 individuals (17%) had died at an early age. Of the survivors, 24 (19%) suffered from some degree of disability, of which most were mild. All the 18 patients diagnosed neonatally were alive at the time of the follow-up.

Stress caused by infection, fever or other demands on the body may lead to worsening of the signs and symptoms, with only partial recovery.

Less than 20 patients with MGA type I have been reported in the literature (Mol Genet Metab. 2011 Nov;104(3):410-3. Epub 2011 Jul 26.)

In the world less than 1 in 1.00.000 have HIDS [5]. 200 individuals throughout the world do suffer from MVK.

There is a deficiency of malate in patients because fumarase enzyme can't convert fumarate into it therefore treatment is with oral malic acid which will allow the krebs cycle to continue, and eventually make ATP.

Fumarase deficiency is caused by a mutation in the fumarate hydratase (FH) gene in humans, which encodes the enzyme that converts fumarate to malate in the mitochondria. Other mutant alleles of the FH gene, located on human Chromosome 1 at position 1q42.1, cause multiple cutaneous and uterine leiomyomata, hereditary leiomyomatosis and renal cell cancer. Fumarase deficiency is one of the few known deficiencies of the Krebs cycle or tricarboxylic acid cycle, the main enzymatic pathway of cellular aerobic respiration.

The condition is an autosomal recessive disorder, and it is therefore usually necessary for an affected individual to receive the mutant allele from both parents. A number of children diagnosed with the disorder have been born to parents who were first cousins. It can also be associated with uniparental isodisomy.

PDE is inherited in an autosomal recessive manner and is estimated to affect around 1 in 400,000 to 700,000 births, though one study conducted in Germany estimated a prevalence of 1 in 20,000 births. The ALDH7A1 gene encodes for the enzyme antiquitin or α -aminoadipic semialdehyde dehydrogenase, which is involved with the catabolism of lysine.

This condition is sometimes mistaken for 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.

Saccharopinuria (an excess of saccharopine in the urine), also called saccharopinemia, saccharopine dehydrogenase deficiency or alpha-aminoadipic semialdehyde synthase deficiency, is a variant form of hyperlysinemia. It is caused by a partial deficiency of the enzyme saccharopine dehydrogenase, which plays a secondary role in the lysine metabolic pathway. Inheritance is thought to be autosomal recessive, but this cannot be established as individuals affected by saccharopinuria typically have only a 40% reduction in functional enzyme.

The treatment of 2-Hydroxyglutaric aciduria is based on seizure control, the prognosis depends on how severe the condition is.

Mevalonate kinase deficiency, also called mevalonic aciduria and hyper immunoglobin D syndrome is an autosomal recessive metabolic disorder that disrupts the biosynthesis of cholesterol and isoprenoids.

It is characterized by an elevated level of immunoglobin D in the blood.

The enzyme is involved in biosynthesis of cholesterols and isoprenoids. The enzyme is necessary for the conversion of mevalonate to mevalonate-5-phosphate in the presence of Mg2+ [Harper’s biochemistry manual]. Mevalonate kinase deficiency causes the accumulation of mevalonate in urine and hence the activity of the enzyme is again reduced Mevalonate kinase deficiency. It was first described as HIDS in 1984.

Glutaric acidemia type 2 often appears in infancy as a sudden metabolic crisis, in which acidosis and low blood sugar (hypoglycemia) cause weakness, behavior changes, and vomiting. There may also be enlargement of the liver, heart failure, and a characteristic odor resembling that of sweaty feet. Some infants with glutaric acidemia type 2 have birth defects, including multiple fluid-filled growths in the kidneys (polycystic kidneys). Glutaric acidemia type 2 is a very rare disorder. Its precise incidence is unknown. It has been reported in several different ethnic groups.

Plasma and cerebrospinal fluid levels of pipecolic acid are frequently elevated in patients with PDE, though it is a non-specific biomarker. α-aminodipic semialdehyde is elevated in urine and plasma and is a more specific biomarker for PDE. Improvements in these biomarkers have been reported with the implementation of a lysine-restricted diet. Initial studies evaluating the safety and efficacy of lysine restriction evaluated developmental and cognitive outcomes by age-appropriate tests and parental observations.

It has been documented, to date, in more than 120 males (see Human Tafazzin ("TAZ") Gene Mutation & Variation Database). It is believed to be severely under-diagnosed and may be estimated to occur in 1 out of approximately 300,000 births. Family members of the Barth Syndrome Foundation and its affiliates live in the US, Canada, the UK, Europe, Japan, South Africa, Kuwait, and Australia.

Barth syndrome has been predominately diagnosed in males, although by 2012 a female case had been reported.

Argininosuccinic aciduria occurs in approximately 1 in 70,000 live births. Many patients can now be detected on the newborn screen if their blood citrulline is elevated.

The diagnosis of sepiapterin reductase deficiency in a patient at the age of 14 years was delayed by an earlier diagnosis of an initially unclassified form of methylmalonic aciduria at the age of 2. At that time the hypotonia and delayed development were not considered to be suggestive of a neurotransmitter defect. The clinically relevant diagnosis was only made following the onset of dystonia with diurnal variation, when the patient was a teenager. Variability in occurrence and severity of other symptoms of the condition, such as hypotonia, ataxia, tremors, spasticity, bulbar involvement, oculogyric crises, and cognitive impairment, is comparable with autosomal dominant GTPCH and tyrosine hydroxylase deficiency, which are both classified as forms of DOPA-responsive dystonia.

The disorder is caused by a mutation in the "ACADSB" gene, located on the long arm of human chromosome 10 (10q25-q26). It is inherited in an autosomal recessive manner, which means an affected individual must inherit one copy of the mutation from each parent.

Several scientists have developed murine models of SSADH (Aldh5a1-/-) by typical gene methodology to create a uniform absence of the SSADH enzyme activity as well as accumulations of GHB and GABA in tissues and physiological fluids. The mice are born at the expected Mendelian frequencies for an autosomal recessive disorder. Most of the models include distinctive neurological phenotypes and exhibit hypotonia, truncal ataxia, generalized tonic-clonic seizures associated with 100% mortality. The mice uniformly die at 3-4 postnatal weeks. While this model is considered to be more severe than the phenotypes seen in humans, currently, it is the most highly regarded, valid, metabolic model to study potential therapeutic interventions for the disorder.

Studies have shown that alterations of both the GABA receptor and the GABA receptor early in the life of the Aldh5a1-/- mice can increase levels of GHB and enhance GABA release. Besides these effects, it has also been shown that "...a developmental down-regulation of GABA receptor mediated neurotransmission in Aldh5a1-/- mice likely contributes to the progression of generalized convulsive seizures seen in mutant animals." Other studies have confirmed the relationship between elevated levels of GHB and MAP kinase in mutant animals contribute to profound myelin abnormalities.

Hyperlysinemia is an autosomal recessive metabolic disorder characterized by an abnormal increase of lysine in the blood, but appears to be benign. It is caused by mutations in "AASS", which encodes α-aminoadipic semialdehyde synthase.

Hyperlysinemia is associated with ectopia lentis (a displacement or malposition of the eye's crystalline lens) in humans.

Most individuals with SBCADD are identified through newborn screening, where they present with an elevation of a five carbon acylcarnitine species. Confirmatory testing includes plasma and urine analysis to identify the carnitine and glycine conjugates of 2-methylbutyryl-CoA.

Glutaric acidemia type 2 is an autosomal recessive metabolic disorder that is characterised by defects in the ability of the body to use proteins and fats for energy. Incompletely processed proteins and fats can build up, leading to a dangerous chemical imbalance called acidosis.

The D2 form is rare, with symptoms including macrocephaly, cardiomyopathy, mental retardation, hypotonia, and cortical blindness. It is caused by recessive mutations in "D2HGDH" (type I) or by dominant gain-of-function mutations in "IDH2" (type II).

MCADD is most prevalent in individuals of Northern European Caucasian descent. The incidence in Northern Germany is 1:4000, currently the highest in the world. Northern Europe is also the origin of the common mutation in MCADD. For populations without origins in Northern Europe, the incidence is significantly lower, 1:51,000 in Japan and 1:700,000 in Taiwan. The common mutation has not been identified in MCADD cases identified in Asian populations.