Browsing Pathways

Adult Refsum Disease (Classic Refsum Disease; Phytanic Acid Oxidase Deficiency; Heredopathia Atactica Polyneurtiformis; Hereditary Motor and Sensory Neuropathy IV; HSMN4; Adult Refsum Disease I; Adult Refsum Disease II), can be caused by mutations in the PHYH (or PAHX) gene, which encodes Phytanoyl-CoA hydroxylase (, the first enzyme in the Phytanic Acid Peroxisomal Oxidation pathway) on chromosome 10 (adult Refsum disease I), and by mutation of the PEX7 gene. A defect in phytanoyl-CoA hydroxylase results in accumulation of phytanic acid in the plasma, as well as low levels of pristanic acid due to the inability for phytanic acid to undergo alpha and beta oxidation. Symptoms include anosmia, ataxia, nystagmus, neurological deterioration and peripheral neuropathy. Adult Refsum disease is distinctly different from Infantile Refsum disease both genetically and phenotypically. Infantile Refsum disease involves mutations of the PEX1, PEX2 and PEX26 genes.

Myoneurogastrointestinal encephalopathy, or mitochondrial neurogastrointestinal encephalopathy syndrome (MNGIE), is a multisystem disorder caused by mutations in the gene encoding thymidine phosphorylase, which normally uses thymidine and phosphate as substrates to catalyze the reaction between these two substrates to create thymine and 2-deoxy-alpha-D-ribose 1-phosphate. MNGIE causes accumulation of thymidine and deoxyuridine in the urine. Symptoms of MNGIE include ptosis, progressive external ophthalmoplegia, gastrointestinal dysmotility (often pseudoobstruction), diffuse leukoencephalopathy, peripheral neuropathy, and myopathy.

Pyruvate dehydrogenase complex deficiency results from a mutation in the E1-alpha polypeptide gene (PDHA1). PDHA1 encodes the pyruvate dehydrogenase complex (PDC) a critical complex that converts pyruvate from glycolysis to acetyl CoA for the citric acid cycle. This conversion step links glycolysis and the citric acid cycle. A defect in this complex causes accumulation of lactate and pyruvate in the blood; lactate and pyruvic acid in the spinal fluid; and lactate in the urine. Symptoms include lactic and metabolic acidosis, motor retardation, dystonia, growth and mental retardation, and respiratory distress.

Molybdenium cofactor deficiency (Sulfite oxidase deficiency) is caused by mutations in the genes MOCS1 and MOCS2 in the formation of molybdenum cofactor. A molybdenum-containing cofactor is essential to the function of 3 enzymes: sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. Xanthine dehydrogenase is a molybdenum-containing hydroxylase involved in the oxidative metabolism of purines. Defects in this enzyme cause accumulation of hypoxanthine,, s-s-sulfocysteine, taurine, and xanthine in the urine. Symptoms include hemorrhage, cerebral atrophy, encephalopathy, lactic acidosis, nystagmus, spastic diplegia/quadriplegia, and vomiting.

Pyruvate Decarboxylase E1 Component Deficiency is caused by a defect in the PDHA1 gene which codes for mitochondrial pyruvate dehydrogenase E1 component subunit alpha, somatic form. This is a homotetrameric enzyme that catalyses the decarboxylation of pyruvic acid to acetaldehyde and carbon dioxide. A defect in this enzyme results in accumulation of lacate and pyruvate. Symptoms and signs include severe lactic acidosis in the newborns that usually leading to death, hypotonic, lethargic, seizures, mental retardation and spasticity.

Non Ketotic Hyperglycinemeia (Glycine encephalopathy; Glycine cleavage system deficiency; NKH) is caused by mutations in several genes in the mitochondrial glycine cleavage system. These include the genes encoding P protein (GLDC), T protein (GCST), and, in one case, the H protein (GCSH). Most patients with GCE (Glycine Encephalopathy, or NKH) have a defect in the GLDC gene.The enzyme system for cleavage of glycine (glycine cleavage system), which is confined to the mitochondria, is composed of 4 protein components: P protein (a pyridoxal phosphate-dependent glycine decarboxylase), H protein (a lipoic acid-containing protein), T protein (a tetrahydrofolate-requiring enzyme), and L protein (a lipoamide dehydrogenase). NKH is characterized by accumulation of glycine in plasma, spinal fluid and urine. Symptoms include seizures, respiratory distress, mental retardation, chorea, visual impairment and hydrocephalus.

Pyruvate carboxylase deficiency is caused by mutation in the pyruvate carboxylase gene. Serine—pyruvate aminotransferase catalyzes the reaction of serine and pyruvate to produce 3-hydroxypyruvate and L-alanine, as well as the reaction from L-alanine and glyodxylate to pyruvate and glycine. A defect in this results in accumulation of ammonia, glucose and pyruvate in blood; proline, lysine, citrulline, and alanine in plasma; and 2-oxoglutaric acid, fumaric acid, ketone bodies and succinate in urine. Symptoms include ataxia, lactic acidosis, mental retardation, metabolic acidosis, siezures, and dyspnea.

Purine nucleoside phosphorylase deficiency (Nucleoside phosphorylase; Immunodeficiency) is a rare disease causing severe immunodeficiency. The disease is caused by a mutation in the enzyme purine nucleoside phosphorylase. The enzyme is necessary for purine breakdown. The mutation causes deoxy-GTP (dGTP) to accumulate which causes T-cell toxicity. The disease results in accumulation of guanosine, inosine, and uric acid in serum; and orotic acid in some cases in the urine. Symptoms include anemia, ataxia, hypotonia, lymphopenia, mental retardation, and tremor or twitching.

Propionic acidemia (Ketotic hyperglycinemia) is caused by mutation in the genes encoding propionyl-CoA carboxylase, PCCA or PCCB. The break down of Propionyl-CoA is catalyzed by Propionyl-CoA carboxylase (PCC). Propionyl-CoA plays an important role in amino acid metabolism. A mutation in this enzyme causes accumulation of ammonia and propionylcarnitine (C3) in the blood; carnitine , glutamine, glycine, and propionic acid in the plasma; 3-hydroxypropionic acid, 3-hydroxyvaleric acid, 5-oxoproline, acylcarnitin, glycine, methylcitric acid, propionylglycine and tiglylcine in the urine. Symptoms include cardio myopathy, growth retardation, hypothermia, ketosis, neutropenia, strokelike episodes, pyloric stenosis and spastic diplegia/quadriplegia.

Ornithine aminotransferase deficiency (OAT deficiency, ornithine keto acid aminotransferase deficiency, OKT deficiency, ornithine-delta-aminotransferase deficiency, gyrate atrophy of the choroid and retina) is an autosomal recessive disorder of ornithine metabolism caused by a defective ornithine aminotransferase (OAT). OAT catalyzes the conversion of ornithine into proline which is a conditionally essential amino acid. This disease is characterized by a very large accumulation of ornithine in the blood. Symptoms of the disease include tunnel vision, night blindness, myopia, and progressive vision loss.