Current research suggests that nearly 8% of the population has at least partial DPD deficiency. A diagnostics determination test for DPD deficiency is available and it is expected that with a potential 500,000 people in North America using 5-FU this form of testing will increase. The whole genetic events affecting the DPYD gene and possibly impacting on its function are far from being elucidated, and epigenetic regulations could probably play a major role in DPD deficiency. It seems that the actual incidence of DPD deficiency remains to be understood because it could depend on the very technique used to detect it. Screening for genetic polymorphisms affecting the "DPYD" gene usually identify less than 5% of patients bearing critical mutations, whereas functional studies suggest that up to 20% of patients could actually show various levels of DPD deficiency.

Women could be more at risk than men. It is more common among African-Americans than it is among Caucasians.

Infant mortality is high for patients diagnosed with early onset; mortality can occur within less than 2 months, while children diagnosed with late-onset syndrome seem to have higher rates of survival. Patients suffering from a complete lesion of mut0 have not only the poorest outcome of those suffering from methylaonyl-CoA mutase deficiency, but also of all individuals suffering from any form of methylmalonic acidemia.

This disorder, epidemiologically speaking, is thought to affect approximately 1 in 50,000 newborns according to Jethva, et al. While in the U.S. state of California there seems to be a ratio of 1 in 35,000.

Babies with this disorder are usually healthy at birth. The signs and symptoms may not appear until later in infancy or childhood and can include poor feeding and growth (failure to thrive), a weakened and enlarged heart (dilated cardiomyopathy), seizures, and low numbers of red blood cells (anemia). Another feature of this disorder may be very low blood levels of carnitine (a natural substance that helps convert certain foods into energy).

Isobutyryl-CoA dehydrogenase deficiency may be worsened by long periods without food (fasting) or infections that increase the body's demand for energy. Some individuals with gene mutations that can cause isobutyryl-CoA dehydrogenase deficiency may never experience any signs and symptoms of the disorder.

A 2001 study followed up on 50 patients. Of these 38% died in childhood while the rest suffered from problems with morbidity.

Since biotin is in many foods at low concentrations, deficiency is rare except in locations where malnourishment is very common. Pregnancy, however, alters biotin catabolism and despite a regular biotin intake, half of the pregnant women in the U.S. are marginally biotin deficient.

Isobutyryl-coenzyme A dehydrogenase deficiency, commonly known as IBD deficiency, is a rare metabolic disorder in which the body is unable to process certain amino acids properly.

People with this disorder have inadequate levels of an enzyme that helps break down the amino acid valine, resulting in a buildup of valine in the urine, a symptom called valinuria.

Short-chain acyl-coenzyme A dehydrogenase deficiency (SCADD), also called ACADS deficiency and SCAD deficiency, is an autosomal recessive fatty acid oxidation disorder which affects enzymes required to break down a certain group of fats called short chain fatty acids.

A small number of genetic variants have been repeatedly associated with DPD deficiency, such as IVS14+1G>A mutation in intron 14 coupled with exon 14 deletion (a.k.a. DPYD*2A), 496A>G in exon 6; 2846A>T in exon 22 and T1679G (a.k.a. DPYD*13) in exon 13. However, testing patients for these allelic variants usually show high specificity (i.e., bearing the mutation means that severe toxicity will occur indeed)but very low sentivity (i.e., not bearing the mutation does not mean that there is no risk for severe toxicities). Alternatively, phenotyping DPD using ex-vivo enzymatic assay or surrogate testing (i.e., monitoring physiological dihydrouracil to uracil ratio in plasma) has been presented as a possible upfront strategy to detect DPD deficiency. 5-FU test dose (i.e., preliminary administration of a small dose of 5-FU with pharmacokinetics evaluation) has been proposed as another possible alternative strategy to secure the use of fluoropyrimidine drugs.

2,4 Dienoyl-CoA reductase deficiency is an inborn error of metabolism resulting in defective fatty acid oxidation caused by a deficiency of the enzyme 2,4 Dienoyl-CoA reductase. Lysine degradation is also affected in this disorder leading to hyperlysinemia. The disorder is inherited in an autosomal recessive manner, meaning an individual must inherit mutations in "NADK2," located at 5p13.2 from both of their parents. NADK2 encodes the mitochondrial NAD kinase. A defect in this enzyme leads to deficient mitochondrial nicotinamide adenine dinucleotide phosphate levels. 2,4 Dienoyl-CoA reductase, but also lysine degradation are performed by NADP-dependent oxidoreductases explaining how NADK2 deficiency can lead to multiple enzyme defects.

2,4-Dienoyl-CoA reductase deficiency was initially described in 1990 based on a single case of a black female who presented with persistent hypotonia. Laboratory investigations revealed elevated lysine, low levels of carnitine and an abnormal acylcarnitine profile in urine and blood. The abnormal acylcarnitine species was eventually identified as 2-trans,4-cis-decadienoylcarnitine, an intermediate of linoleic acid metabolism. The index case died of respiratory failure at four months of age. Postmortem enzyme analysis on liver and muscle samples revealed decreased 2,4-dienoyl-CoA reductase activity when compared to normal controls. A second case with failure to thrive, developmental delay, lactic acidosis and severe encephalopathy was reported in 2014.

2,4-Dienoyl-CoA reductase deficiency was included as a secondary condition in the American College of Medical Genetics Recommended Uniform Panel for newborn screening. Its status as a secondary condition means there was not enough evidence of benefit to include it as a primary target, but it may be detected during the screening process or as part of a differential diagnosis when detecting conditions included as primary target. Despite its inclusion in newborn screening programs in several states for a number of years, no cases have been identified via neonatal screening.

The human GALK1 gene contains 8 exons and spans approximately 7.3 kb of genomic DNA. The GALK1 promoter was found to have many features in common with other housekeeping genes, including high GC content, several copies of the binding site for the Sp1 transcription factor and the absence of TATA-box and CCAAT-box motifs typically present in eukaryotic polymerase II promoters. Analysis by 5-prime-RACE PCR indicated that the GALK1 mRNA is heterogeneous at the 5-prime end, with transcription sites occurring at many locations between 21 and 61 bp upstream of the ATG start site of the coding region. In vitro translation experiments of the GALK1 cDNA indicated that the protein is cytosolic and not associated with endoplasmic reticulum membrane.

That MMA can have disastrous effects on the nervous system has been long reported; however, the mechanism by which this occurs has never been determined. Published on June 15th 2015, research performed on the effects of methylmalonic acid on neurons isolated from fetal rats in an in vitro setting using a control group of neurons treated with an alternate acid of similar pH. These tests have suggested that methylmalonic acid causes decreases in cellular size and increase in the rate of cellular apoptosis in a concentration dependent manner with more extreme effects being seen at higher concentrations. Furthermore, micro-array analysis of these treated neurons have also suggested that on a epigenetic-level methylmalonic acid alters the transcription rate of 564 genes, notably including those involved in the apoptosis, p53, and MAPK signaling pathways.

Mutations in the "HADHA" gene lead to inadequate levels of an enzyme called long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase, which is part of a protein complex known as mitochondrial trifunctional protein. Long-chain fatty acids from food and body fat cannot be metabolized and processed without sufficient levels of this enzyme. As a result, these fatty acids are not converted to energy, which can lead to characteristic features of this disorder, such as lethargy and hypoglycemia. Long-chain fatty acids or partially metabolized fatty acids may build up in tissues and damage the liver, heart, retina, and muscles, causing more serious complications.

Mutations in the "HADH" gene lead to inadequate levels of an enzyme called 3-hydroxyacyl-coenzyme A dehydrogenase. Medium-chain and short-chain fatty acids cannot be metabolized and processed properly without sufficient levels of this enzyme. As a result, these fatty acids are not converted to energy, which can lead to characteristic features of this disorder, such as lethargy and hypoglycemia. Medium-chain and short-chain fatty acids or partially metabolized fatty acids may build up in tissues and damage the liver, heart, and muscles, causing more serious complications.

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.

In the United States, biotin supplements are readily available without a prescription in amounts ranging from 1,000 to 10,000 micrograms (30 micrograms is identified as Adequate Intake).

Coenzyme Q10 deficiency is a deficiency of Coenzyme Q10.

It can be associated with "COQ2", "APTX", "PDSS2", "PDSS1", "CABC1", and "COQ9".

Some forms may be more treatable than other mitochondrial diseases.

Galactokinase deficiency is an autosomal recessive disorder, which means the defective gene responsible for the disorder is located on an autosome (chromosome 17 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.

Unlike galactose-1-phosphate uridyltransferase deficiency, the symptoms of galactokinase deficiency are relatively mild. The only known symptom in affected children is the formation of cataracts, due to production of galactitol in the lens of the eye. Cataracts can present as a failure to develop a social smile and failure to visually track moving objects.

The term fatty acid oxidation disorder (FAOD) is sometimes used, especially when there is an emphasis on the oxidation of the fatty acid.

In addition to the fetal complications, they can also cause complications for the mother during pregnancy.

Examples include:

- trifunctional protein deficiency

- MCADD, LCHADD, and VLCADD

Succinyl-CoA:3-oxoacid CoA transferase deficiency (SCOT deficiency) is an inborn error of ketone body utilization. Succinyl-CoA:3-oxoacid CoA transferase catalyzes the transfer of coenzyme A from succinyl-coenzyme A to acetoacetate. It can be caused by mutation in the "OXCT1" gene.

First described in 1972, more than 30 people have been reported in the medical literature with this inborn error of metabolism. They experience attacks of ketoacidosis during illness, and even when unwell may have elevated levels of ketone bodies in blood and urine (ketonemia and ketonuria, respectively). Not all people with SCOT deficiency have persistent ketonemia and ketonuria, particularly those with milder defects of enzyme activity.

Methylmalonyl-CoA mutase is a mitochondrial homodimer apoenzyme (EC. 5. 4.99.2) that focuses on the catalysis of methylmalonyl CoA to succinyl CoA. The enzyme is bound to adenosylcobalamin, a hormonal derivative of vitamin B12 in order to function. Methylmalonyl-CoA mutase deficiency is caused by genetic defect in the MUT gene responsible for encoding the enzyme. Deficiency in this enzyme accounts for 60% of the cases of methylmalonic acidemia.

This condition is sometimes mistaken for fatty acid and ketogenesis disorders such as Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCAD), other long-chain fatty acid oxidation disorders such as Carnitine palmitoyltransferase II deficiency (CPT-II) and Reye syndrome.

If a metabolic crisis is not treated, a child with VLCADD can develop: breathing problems, seizures, coma, sometimes leading to death.

Mutations in the "CPT1A" gene cause carnitine palmitoyltransferase I deficiency by producing a defective version of an enzyme called carnitine palmitoyltransferase I. Without this enzyme, long-chain fatty acids from food and fats stored in the body cannot be transported into mitochondria to be broken down and processed. As a result, excessive levels of long-chain fatty acids may more rapidly build up in tissues, damaging the liver, heart and/or brain.

This condition has an autosomal recessive inheritance pattern, which means the defective gene is located on an autosome, and two copies of the gene - one from each parent - must be inherited to be affected by the disorder. The parents of a child with an autosomal recessive disorder are carriers of one copy of the defective gene, but are usually not affected by the disorder.

The prevalence of mutations associated with this condition reach 68% to 81% in certain arctic coastal populations, suggesting that the condition had some adaptive value in those habitats at some time.

Typically, initial signs and symptoms of this disorder occur during infancy or early childhood and can include poor appetite, vomiting, diarrhea, lethargy, hypoglycemia, hypotonia, liver problems, and abnormally high levels of hyperinsulinism. Insulin controls the amount of sugar that moves from the blood into cells for conversion to energy. Individuals with 3-hydroxyacyl-coenzyme A dehydrogenase deficiency are also at risk for complications such as seizures, life-threatening heart and breathing problems, coma, and sudden unexpected death.

Problems related to 3-hydroxyacyl-coenzyme A dehydrogenase deficiency can be triggered by periods of fasting or by illnesses such as viral infections. This disorder is sometimes mistaken for Reye syndrome, a severe disorder that may develop 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.

The inherited forms of methylmalonic acidemia cause defects in the metabolic pathway where methylmalonyl-coenzyme A (CoA) is converted into succinyl-CoA by the enzyme methylmalonyl-CoA mutase.

Vitamin B is also needed for the conversion of methylmalonyl-CoA to Succinyl-CoA. Mutations leading to defects in vitamin B metabolism or in its transport frequently result in the development of methylmalonic acidemia.

This disorder has an autosomal recessive inheritance pattern, which means the defective gene is located on an autosome, and two copies of the gene—one from each parent—must be inherited to be affected by the disorder. The parents of a child with an autosomal recessive disorder are carriers of one copy of the defective gene, but are usually not affected by the disorder.