Browsing Pathways

Methylhistidine is a modified amino acid that is produced in myocytes during the methylation of actin and myosin. It is also formed from the methylation of L-histidine, which takes the methyl group from S-adenosylmethionine and forms S-adenosylhomocysteine as a byproduct. After its formation in the myocytes, methylhistidine enters the blood stream and travels to the kidneys, where it is excreted in the urine. Methylhistidine is present in the blood and urine in higher concentrations after skeletal muscle protein breakdown, which can occur due to disease or injury. Because of this, it can be used to judge how much muscle breakdown is occurring. Methylhistidine levels are also affected by diet, and may differ between vegetarian diets and those containing meats.

11-beta-Hydroxylase Deficiency, also called congenital adrenal hyperplasia (CAH), is an autosomal recessive disorder and caused by a defective 11-beta-hydroxylase. 11-beta-hydroxylase catalyzes the conversion of cortexolone into cortisol which is useful for maintaining blood sugar levels and suppressing inflammation. This disorder is characterized by a large accumulation of cortexolone in the endoplasmic reticulum (ER). Symptoms of the disorder include abnormality of hair growth rate and menstrual cycle. It is estimated that 11-beta-hydroxylase deficiency affects 1 in 100,000 to 200,000 newborns.

17-alpha-hydroxylase deficiency, also known as congenital adrenal hyperplasia (CAH) due to 17-alpha-hydroxylase deficiency or congenital adrenal hyperplasia type 5, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of the steroidogenesis pathway. It is caused by a mutation in the CYP17A1 gene which encodes the enzyme steroid 17-alpha-hydroxylase. This enzyme hydroxylates both progesterone and pregnenolone into 17-hydroxyprogesterone and 17a-hydroxypregnenolone respectively in the mitochondria, as well as hydroxylating 21-deoxycortisol to 11b-hydroxyprogesterone within the endoplasmic reticulum. When mutated, it leads to an accumulation of pregnenolone, progesterone, deoxycorticosterone and 11-dehydrocorticosterone throughout the cell. 17-alpha hydroxylase deficiency is characterized by a deficiency of sex steroids, as well as glucocorticoids. Symptoms include male undervirilization, as well as lack of development during puberty including amenorrhea for females. Low levels of potassium in the blood due to the increased levels of mineralocorticoids can occur, as well as hypertension. Treatment with dexamethasone has been able to normalize blood pressure and blood potassium levels. It is estimated that 17-alpha-hydroxylase deficiency affects 1 in 1,000,000 individuals.

17-beta hydroxysteroid dehydrogenase III deficiency, also known as 17-KSR deficiency or male pseudohermaphroditism with gynecomastia (MPH), is as rare inborn error of metabolism (IEM) and autosomal recessive disorder of the androgen and estrogen metabolism pathway. It is caused by a mutation in the HSD17B3 gene, which encodes the enzyme testosterone 17-beta-dehydrogenase 3, which is responsible for catalyzing the reversible formation of androstenedione from testosterone. This leads to an accumulation of androstenedione and dehydroepiandrosterone in the body, as well as a lack of testosterone produced. 17-KSR deficiency is characterized by an absence of testosterone in the testis until puberty, where testosterone is produced outside of the gonads. Symptoms include infertility and external female genitalia until puberty, when secondary male sex characteristics occur, as well as gynecomastia. Due to this, many individuals with this disorder are raised as female despite being genetically male, until puberty. Treatment can include removal of testes before puberty, preventing any masculinization at puberty, as well as surgical treatment of genitalia. However, there is no known treatment for restoring the fertility of affected individuals. It is estimated that 17-KSR deficiency affects 1 in 150,000 individuals in The Netherlands, without much information for the rest of the world.

This pathway is part of a major route of the degradation of L-tryptophan. It begins with 2-amino-3-carboxymuconate-6-semialdehyde which is generated from L-tryptophan degradation. The 2-amino-3-carboxymuconate-6-semialdehyde first is acted upon by a decarboxylase, forming 2-aminomuconic acid semialdehyde, which is then dehydrogenated by 2-aminomuconic semialdehyde dehydrogenase to form 2-aminomuconic acid. An unknown protein forms a 2-aminomuconate deaminase which forms (3E)-2-oxohex-3-enedioate, and a second unknown protein forms a 2-aminomuconate reductase, which forms oxoadipic acid from (3E)-2-oxohex-3-enedioate. Finally, within the mitochondria, oxoadipic acid is dehydrogenated and a coenzyme A is attached by the organelle’s oxoglutarate dehydrogenase complex, forming glutaryl-CoA. Glutaryl-CoA can then be further degraded.

2-Aminoadipic 2-oxoadipic aciduria is a disorder of lysine metabolism caused by a defective DHTKD1 gene. DHTKD1 is predicted to code for a component of a supercomplex similar to the 2-oxoglutarate dehydrogenase complex (OGDHc) which catalyzes the conversion of 2-oxoadipate into glutaryl-CoA. This disease is characterized by a large accumulation of 2-oxoadipate and 2-hydroxyadipate in the urine. Symptoms of the disease include mild to severe intellectual disability, developmental delay, ataxia, muscular hypotonia, and epilepsy. However, most cases are asymptomatic.

L-2-Hydroxyglutaric Aciduria (D-2-Hydroxyglutaric Aciduria ) is an autosomal recessive disease caused by a mutation in the L2HGDH gene which codes for L-2-Hydroxygluarate dehydrogenase. A deficiency in this enzyme results in accumulation of L-2-Hydroxyglutaric acid in plasma, spinal fluid, and urine; and L-lysine in plasma and spinal fluid. Symptoms, which present at birth, include ataxia, hypotonia, mental retardation, and seizures. Premature death often results. D-2-Hydroxyglutaric Aciduria is an autosomal recessive disease caused by a mutation in the D2HGDH gene which does for D-2-Hydroxygluarate dehydrogenase. A deficiency in this enzyme results in accumulation of D-2-Hydroxyglutaric acid in plasma, spinal fluid, and urine; oxoglutaric acid in urine; and gabba-aminobutyric acid in spinal fluid. Symptoms, which present at birth, include ataxia, hypotonia, mental retardation, and seizures. Premature death often results.

2-Ketoglutarate dehydrogenase complex deficiency, also known as alpha-ketoglutarate dehydrogenase deficiency or oxoglutaric aciduria, is an autosomal recessive disorder of the Krebs cycle caused by a defective oxoglutarate dehydrogenase complex (OGDC). OGDC catalyzes the conversion of 2-ketoglutarate into succinyl-CoA. This disorder is characterized by a large accumulation of 2-ketoglutarate in the urine. Symptoms of the disorder include opisthotonus, ataxia, developmental delay, and seizures.

2-Methyl-3-hydroxybutyryl CoA dehydrogenase deficiency (Hydroxyl-CoA dehydrogenase deficiency; MHBD) is a rare inborn disease of metabolism caused by a mutation in the HSD17B10 gene which codes for 3-hydroxyacyl-CoA dehydrogenase type-2. A deficiency in this enzyme results in accumulation of L-lactic acid in blood, spinal fluid, and urine; 2-ethylhydracrylic acid, 2-methyl-3-hydroxybutyric acid, and tiglylglycine in urine. Symptoms include cerebal atrophy, motor and mental retardation, overactivity and behavior issues, seizures and progressive neurological defects leading to early death. Treatment includes a high carbohydrate and low protein diet.

Congenital adrenal hyperplasia (CAH) refers to any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the steps of biosynthesis of cortisol from cholesterol in the adrenal glands, also known as steroidogenesis. 21-hydroxylase deficiency, also known as CYP21 deficiency or CAH1, is an autosomal recessive disorder that accounts for the vast majority of cases of CAH. This deficiency affects cells in the adrenal cortex of the adrenal glands, and due to the deficiency in an enzyme used in many pathways. This prevents the completion of several hormone biosynthesis pathways, including those producing aldosterone and cortisol, and leads to a buildup of their precursors, including 17a-hydroxypregnenolone, which are then processed by the pathways that produce androgen hormones including testosterone. This disorder can vary in severity, depending on the amount of functional enzyme present. The most severe form is known as the salt-wasting form of 21-hydroxylase, and is caused by a complete lack of functional enzyme. This form is called the salt-wasting form, as the lack of aldosterone produced leads to high levels of sodium excreted in the urine, causing infant blood volume to decrease. High potassium levels in blood are also often observed, but if properly diagnosed, saline solution and hydrocortisone can restore normal blood levels and sodium content. In addition, males are typically visually unaffected, but females often possess ambiguous genitalia due to the excess exposure to testosterone during development. The second most severe form is known as the simple virilising form, which does not involve the salt loss of the salt-wasting form, due to a partially functional 21-hydroxylase enzyme. However, the androgen hormones build up similarly, leading to females with some amount of virilisation, or some amount of male characteristics, including ambiguous genitalia. The third and least severe form, known as the non-classical or late onset form, has the highest function in 21-hydroxylase enzymes, and leads to the smallest buildup of androgen hormones. This means that females exhibit little to no virilisation at birth, but as they age can experience male-associated hair growth and baldness, as well as decreased fertility and menstruation irregularities. It can also lead to an early puberty in both males and females, though treatment can help prevent this if it is caught in time.