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Exercise intolerance is a condition of inability or decreased ability to perform physical exercise at the normally expected level or duration for people of that age, size, sex, and muscle mass. It also includes experiences of unusually severe post-exercise pain, fatigue, nausea, vomiting or other negative effects. Exercise intolerance is not a disease or syndrome in and of itself, but can result from various disorders.
Ferroportin-1, also known as solute carrier family 40 member 1 (SLC40A1) or iron-regulated transporter 1 (IREG1), is a protein that in humans is encoded by the SLC40A1 gene, and is part of the Ferroportin (Fpn)Family. Ferroportin is a transmembrane protein that transports iron from the inside of a cell to the outside of the cell. Ferroportin is the only known iron exporter.
Folate deficiency, also known as vitamin B9 deficiency, is a low level of folate and derivatives in the body. Signs of folate deficiency are often subtle. A low number of red blood cells (anemia) is a late finding in folate deficiency and folate deficiency anemia is the term given for this medical condition. It is characterized by the appearance of large-sized, abnormal red blood cells (megaloblasts), which form when there are inadequate stores of folic acid within the body.
SLC22A5 is a membrane transport protein associated with primary carnitine deficiency. This protein is involved in the active cellular uptake of carnitine. It acts a symporter, moving sodium ions and other organic cations across the membrane along with carnitine. Such polyspecific organic cation transporters in the liver, kidney, intestine, and other organs are critical for the elimination of many endogenous small organic cations as well as a wide array of drugs and environmental toxins. Mutations in the SLC22A5 gene cause systemic primary carnitine deficiency, which can lead to heart failure.
Thiamine transporter 1, also known as thiamine carrier 1 (TC1) or solute carrier family 19 member 2 (SLC19A2) is a protein that in humans is encoded by the SLC19A2 gene. SLC19A2 is a thiamine transporter. Mutations in this gene cause thiamine-responsive megaloblastic anemia syndrome (TRMA), which is an autosomal recessive disorder characterized by diabetes mellitus, megaloblastic anemia and sensorineural deafness.
Thiamine transporter 2 (ThTr-2), also known as solute carrier family 19 member 3, is a protein that in humans is encoded by the SLC19A3 gene. SLC19A3 is a thiamine transporter.
The sulfate transporter is a solute carrier family protein that in humans is encoded by the SLC26A2 gene. SLC26A2 is also called the diastrophic dysplasia sulfate transporter (DTDST), and was first described by Hästbacka et al. in 1994. A defect in sulfate activation described by Superti-Furga in achondrogenesis type 1B was subsequently also found to be caused by genetic variants in the sulfate transporter gene. This sulfate (SO42−) transporter also accepts chloride, hydroxyl ions (OH−), and oxalate as substrates. SLC26A2 is expressed at high levels in developing and mature cartilage, as well as being expressed in lung, placenta, colon, kidney, pancreas and testis.
Electron-transferring-flavoprotein dehydrogenase is an enzyme that transfers electrons from electron-transferring flavoprotein in the mitochondrial matrix, to the ubiquinone pool in the inner mitochondrial membrane. It is part of the electron transport chain. The enzyme is found in both prokaryotes and eukaryotes and contains a flavin and FE-S cluster. In humans, it is encoded by the ETFDH gene. Deficiency in ETF dehydrogenase causes the human genetic disease multiple acyl-CoA dehydrogenase deficiency.
Mitochondrially encoded tRNA leucine 1 (UUA/G) also known as MT-TL1 is a transfer RNA which in humans is encoded by the mitochondrial MT-TL1 gene.
Methionine synthase reductase also known as MSR is an enzyme that in humans is encoded by the MTRR gene.
Mitochondrial import inner membrane translocase subunit Tim8 A, also known as Deafness-dystonia peptide or protein is an enzyme that in humans is encoded by the TIMM8A gene. This translocase has similarity to yeast mitochondrial proteins that are involved in the import of metabolite transporters from the cytoplasm into the mitochondrial inner membrane. The gene is mutated in Deafness-dystonia syndrome and it is postulated that MTS/DFN-1 is a mitochondrial disease caused by a defective mitochondrial protein import system.
Cytochrome b is a protein that in humans is encoded by the MT-CYB gene. Its gene product is a subunit of the respiratory chain protein ubiquinol–cytochrome c reductase, which consists of the products of one mitochondrially encoded gene, MT-CYB, and ten nuclear genes—UQCRC1, UQCRC2, CYC1, UQCRFS1, UQCRB, "11kDa protein", UQCRH, Rieske protein presequence, "cyt c1 associated protein", and Rieske-associated protein.
Monocarboxylate transporter 8 (MCT8) is an active transporter protein that in humans is encoded by the SLC16A2 gene.
Y+L amino acid transporter 1 is a protein that in humans is encoded by the SLC7A7 gene.
Mitochondrially encoded tRNA proline also known as MT-TP is a transfer RNA that in humans is encoded by the mitochondrial MT-TP gene.
Mitochondrially encoded tRNA arginine also known as MT-TR is a transfer RNA which in humans is encoded by the mitochondrial MT-TR gene.
Hereditary folate malabsorption (HFM) is a rare autosomal recessive disorder caused by loss-of-function mutations in the proton-coupled folate transporter (PCFT) gene, resulting in systemic folate deficiency and impaired delivery of folate to the brain.
Cerebral folate deficiency is a condition in which concentrations of 5-methyltetrahydrofolate are low in the brain as measured in the cerebral spinal fluid despite being normal in the blood. Symptoms typically appear at about 5 to 24 months of age. Without treatment there may be poor muscle tone, trouble with coordination, trouble talking, and seizures.
Solute carrier family 39 member 12 is a protein that in humans is encoded by the SLC39A12 gene.
Riboflavin-responsive exercise intolerance is a rare disorder caused by mutations of the SLC25A32 gene that encodes the mitochondrial folate transporter. Patients suffer from exercise intolerance and may have disrupted motor function. Treatment with riboflavin may lead to a drastical improvement.
References
- ↑ Titus SA, Moran RG (November 2000). "Retrovirally mediated complementation of the glyB phenotype. Cloning of a human gene encoding the carrier for entry of folates into mitochondria". The Journal of Biological Chemistry. 275 (47): 36811–7. doi:10.1074/jbc.M005163200. PMID 10978331.
- ↑ Schiff M, Veauville-Merllié A, Su CH, Tzagoloff A, Rak M, Ogier de Baulny H, Boutron A, Smedts-Walters H, Romero NB, Rigal O, Rustin P, Vianey-Saban C, Acquaviva-Bourdain C (February 2016). "SLC25A32 Mutations and Riboflavin-Responsive Exercise Intolerance". The New England Journal of Medicine. 374 (8): 795–7. doi:10.1056/NEJMc1513610. PMC 4867164 . PMID 26933868.
- ↑ Hellebrekers DM, Sallevelt SC, Theunissen TE, Hendrickx AT, Gottschalk RW, Hoeijmakers JG, Habets DD, Bierau J, Schoonderwoerd KG, Smeets HJ (June 2017). "Novel SLC25A32 mutation in a patient with a severe neuromuscular phenotype". European Journal of Human Genetics : EJHG. 25 (7): 886–888. doi:10.1038/ejhg.2017.62. PMC 5520074 . PMID 28443623.
- ↑ Al Shamsi B, Al Murshedi F, Al Habsi A, Al-Thihli K (November 2021). "Hypoketotic hypoglycemia without neuromuscular complications in patients with SLC25A32 deficiency". European Journal of Human Genetics : EJHG. doi:10.1038/s41431-021-00995-7. PMID 34764427.
- ↑ Steele JW, Kim SE, Finnell RH (June 2020). "One-carbon metabolism and folate transporter genes: Do they factor prominently in the genetic etiology of neural tube defects?". Biochimie. 173: 27–32. doi:10.1016/j.biochi.2020.02.005. PMC 7253344 . PMID 32061804.