3beta-hydroxysteroid dehydrogenase

Stop codon suppression or translational readthrough occurs when in translation a stop codon is interpreted as a sense codon, that is, when a (standard) amino acid is 'encoded' by the stop codon. Mutated tRNAs can be the cause of readthrough, but also certain nucleotide motifs close to the stop codon. Translational readthrough is very common in viruses and bacteria, and has also been found as a gene regulatory principle in humans, yeasts, bacteria and drosophila. [17] [18] This kind of endogenous translational readthough constitutes a variation of the genetic code , because a stop codon codes for an amino acid. In the case of human malate dehydrogenase , the stop codon is read through with a frequency of about 4%. [19] Amino acids inserted at the stop codon depends of the identity of the stop codon itself: Gln, Tyr and Lys; have been found for UAA and UAG codon, while Cys, Trp, Arg for UGA codon have been identified by mass spectrometry. [20]

Rossi et al. (2007) provided follow-up on the patient reported by Brunetti-Pierri et al. (2002) and described her affected sib. The sib was a fetus aborted at 21 weeks' gestation following a routine ultrasound that revealed multiple malformations. Postmortem findings included type II Arnold-Chiari malformation, microcephaly, postaxial polydactyly (hands and feet), bilateral clubfeet, and lumbosacral meningocele. A diagnosis of lathosterolosis was suspected on the basis of the pattern of limb and craniofacial anomalies. Molecular analysis in DNA samples obtained from stored pathologic specimens of the SC5DL gene revealed the same mutations identified in her living sister (-), confirming the diagnosis. The sister had developed bilateral lens opacities at age 6, which subsequently evolved to a total cataract of the right eye, requiring surgery. She had severe cholestasis with liver fibrosis and persistently elevated serum levels of transaminases, gamma-glutamyltransferase, alkaline phosphatase, total and direct bilirubin, and ammonia. Portal hypertension was noted on abdominal Doppler ultrasound at 7 years of age. The girl had experienced 2 pathologic fractures, and DEXA scan at years revealed severe generalized osteoporosis. Blood smears revealed anisopoikilocytosis, acanthocytes, schistocytes, large platelets, and vacuolated monocytes. Electron microscopy of cultured fibroblasts showed concentric lamellar inclusion bodies, similar to lysosomal vacuoles visible in fibroblasts from patients with Niemann-Pick type C disease (257220).

The fetal adrenal cortex lacks expression of the enzyme early on, thus mineralocorticoids (. aldosterone ) and glucocorticoids (. cortisol ) cannot be synthesized. This is significant because cortisol induces type II pneumocytes of the lungs to synthesize and secrete pulmonary surfactant ; without pulmonary surfactant to reduce the alveolar surface tension , premature neonates may die of neonatal respiratory distress syndrome . If delivery is unavoidable (. because of placental abruption , or pre-eclampsia / HELLP syndrome ), then glucocorticoids (. cortisol) can be administered.

3beta-hydroxysteroid dehydrogenase

3beta-hydroxysteroid dehydrogenase

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