Browsing Pathways

Congenital Bile Acid Synthesis Defect Type III (CBASIII) is caused by a defect in 25-hydroxycholesterol 7-alpha-hydroxylase, which plays a role in synthesis of bile acids. The synthesis of primary bile acids from cholesterol occurs via two pathways: the classic neutral pathway involving cholesterol 7-alpha-hydroxylase (CYP7A1), and the acidic pathway involving a distinct microsomal oxysterol 7-alpha-hydroxylase (CYP7B1). CBASIII is characterized by accumulation of bile acids in the urine. Symptoms include severe cholestasis, cirrhosis, and liver failure.

The condition pyridoxine dependent-epilepsy is a condition that sees seizures beginning in infancy. In some cases, the seizures begin before birth. The seizures involve status epilepticus, which are seizures that last several minutes. The symptoms specific to pyridoxine dependent seizures can include hypothermia, dystonia and irritability right before an episode. They also include loss of consciousness, convulsions, and muscle rigidity. Rarely does this condition manifest between 1 to 3 years of age, although it has occured. Traditional anticonvulsant medication has proven ineffective in patients with this condition; patients are instead treated with pyridoxine daily in large doses. This compound is a b-vitamin found in food. Encephalopathy can occur if this condition is not treated, which can result in permanent brain damage. Although this condition is treated with pyridoxine, it can still cause neurological issues, such as learning disorders or developmental delay, regardless of treatment.

Saccharopinuria (also known as: saccharopinemia, saccharopine dehydrogenase deficiency, and alpha-aminoadipic semialdehyde synthase deficiency, hyperlysinemia type II) is an autosomal recessive disease characterized by high concentrations of saccharopine in the plasma and urine.It is caused by the deficiency of the enzyme alpha-aminoadipic semialdehyde synthase (AASS). AASS contains a lysine ketoglutarate reductase (LKR) domain which catalyzes the conversion of lysine to saccharopine, and a saccharapine dehydrogenase (SDH) domain which catalyzes the conversion of saccharopine to alpha-aminoadipic semialdehyde. Hyperlysinemia type II is categorized by the loss in SDH activity but the preservation of significant amounts of LKR activity. This leads to the accumulation of saccharopine. The loss of both enyzmatic functions is categorized as hyperlysinemia type I.

Saccharopinuria (also known as: saccharopinemia, saccharopine dehydrogenase deficiency, and alpha-aminoadipic semialdehyde synthase deficiency) is caused by a partial deficiency of aminoadipic semialdehyde synthase (AASS) enzyme and causes an increase in saccharopine in the urine. Saccharopinuria is another form of hyperlysinemia. AASS has lysine ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH) activity. AASS acts in the first 2 steps in lysine degradation. A defect in this enzyme results in accumulation of citrulline, lysine and saccharopin in the plasma; lysine in the spinal fluid; and citrulline, lysine and saccharopine in the urine. Symptoms include growth and mental retardation.

Lysinuric protein intolerance (LPI), also called hyperdibasic aminoaciduria, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of the kidney function pathway. It is caused by a mutation in the SLC7A7 gene which encodes the Y+L amino acid transporter 1 protein, which is involved in the uptake of amino acids, both with sodium for neutral amino acids, and without for dibasic amino acids. In this disorder, the amino acids lysin, arginine and ornithine, found in protein, cannot be broken down, which can cause problems in the systems that use these amino acids, such as the urea cycle. LPI is characterized by a shortage of lysine, arginine and ornithine within the body, causing elevated ammonia levels in the blood. Symptoms of the disorder include failure to thrive after weaning, nausea and vomiting following a meal containing large amounts of protein, as well as osteoporosis, and lung and kidney problems. Treatment with a protein restricted diet is effective, as well as prescription of medication to lower the levels of ammonia in the blood. It is estimated that the LPI affects 1 in 60,000 individuals in certain populations such as in Finland and Japan, and less frequently outside these populations.

Blue diaper syndrome is a recessive metabolic disorder that has not yet been determined to be X-linked or autosomal. This syndrome is caused by a mutation in the large neutral amino acids transporter small subunit 1 protein, which allows tryptophan, among other amino acids, to be reabsorbed in the kidneys. The excess tryptophan found in the intestine is digested by bacteria which excrete indole, which can undergo oxidation to produce indigo blue. This is seen in the diapers of infants affected by blue diaper syndrome, due to the increased levels of indole in their urine or feces. Other symptoms can include bacterial infections, damage to various parts of the eye, hypercalcemia, and impaired kidney function due to this. Treatment can include a calcium restricted diet in order to prevent hypercalcemia, and a tryptophan restricted diet to prevent all systems. If bacterial infections are common, antibiotics may be prescribed.

Lysinuric protein intolerance (Hyperdibasic aminoaciduria II; Dibasic aminoaciduria II; Hyperdibasic aminoaciduria II; LPI), also called hyperdibasic aminoaciduria type 2 or familial protein intolerance, is an autosomal recessive metabolic disorder affecting amino acid transport. LPI is caused by a defect in SLC7A7, Solute carrier family 7, a cationic amino acid transporter. A defect in this enzyme results in accumulation of ammmonia and reticulocytes in blood; glutamine in plasma, carnitine and ferritin in serum, and arginine, lysine and ornithine in urine. Symptoms include bone marrow abnormality, growth retardation, hyperammoniemia, mental retardation, pancreatitis, and seizures.

Hartunup Disorder (HND, Hartnup Disease) is an autosomal recessive disease caused by a mutation in the SLC6A19 which codes for sodium-dependent neutral amino acid transporter B(0). A deficiency in this enzyme results in accumulation of L-alanine, L-asparagine, L-histidine, indoleacetic acid, L-isoleucine, L-leucine, L-phenylalanine, L-serine, L-threonine, L-tryptophan, L-valine, and L-tyrosine in urine. Symptoms include pellagra, psychosis, ataxia, and mental retardation. Treatment includes nicotinamide.

Gamma-glutamyltranspeptidase deficiency, characterized by glutathionemia and glutathionuria, is an autosomal recessive disorder of glutathione metabolism caused by a defective gamma-glutamyl transpeptidase (GGT). GGT transfers glutamyl moieties to acceptor molecules such as amino acids and peptides. This disorder is characterized by a large accumulation of glutathione in the urine. Symptoms of the disorder include easy bruising, asthma, and mild mental retardation.

Glutathione Synthetase Deficiency (5-Oxoprolinuria; Pyroglutamic Aciduria; GSD) is a rare inborn error of metabolism (IEM) which arises from a disfunctional gene called GSS. This gene is responsible for glutathione synthetase. Glutathione synthetase is the second enzyme in the glutathione biosynthesis pathway. It catalyses the condensation of gamma-glutamylcysteine and glycine, to form glutathione. A defect in this enzyme results in accumulation of pyroglutamic acid and gamma-glutamylcysteine in urine and blood; decrease level of glutathione in erythrocytes; increase urinary excretion of 5-oxoproline. GSD is typically distinguished by three levels of severity. Those levels naturally being mild, moderate and severe. Being with the former, mild GSD can lead to a harmful condition known as hemolytic anemia. This occurs when red blood cells are destroyed. Although not as common, it is also possible for patients affected with GSD to excrete in their urine elevated quantities of 5-oxoproline (hence the other name for this condition shown in the first sentence of this description). The accumulation of high levels of 5-oxoproline (and hence the elevated level of secretion of this compound) is a direct consequence of glutathione being improperly processed by the body. Turning now to the second level of severity, moderate, it is typical to see affected patients experience experience the two symptoms described above, in addition to metabolic acidosis. The latter condition being the consequence of high acidity levels in the blood as well as other tissues. Finally, individuals with severe GSD may suffer from a wide variety of neurological symptoms. This could include anything from ataxia and slowed reactions, to psychomotor retardation, mental retardation and seizures.