TAILIEUCHUNG - Chapter 100. Megaloblastic Anemias (Part 5)

An underlying maternal folate metabolic abnormality has also been postulated. One abnormality has been identified: reduced activity of the enzyme 5,10-methylene-THF reductase (MTHFR) (Fig. 100-1) caused by a common 677CÆT polymorphism in the MTHFR gene. In one study, the prevalence of this polymorphism was found to be higher in the parents of NTD fetuses and in the fetuses themselves: homozygosity for the TT mutation was found in 13% compared with 5% in control subjects. The polymorphism codes for a thermolabile form of MTHFR. The homozygous state results in a lower mean serum and red cell folate level compared with. | Chapter 100. Megaloblastic Anemias Part 5 An underlying maternal folate metabolic abnormality has also been postulated. One abnormality has been identified reduced activity of the enzyme 5 10-methylene-THF reductase MTHFR Fig. 100-1 caused by a common 6 77C ET polymorphism in the MTHFR gene. In one study the prevalence of this polymorphism was found to be higher in the parents of NTD fetuses and in the fetuses themselves homozygosity for the TT mutation was found in 13 compared with 5 in control subjects. The polymorphism codes for a thermolabile form of MTHFR. The homozygous state results in a lower mean serum and red cell folate level compared with control subjects as well as significantly higher serum homocysteine levels. Tests for mutations in other enzymes possibly associated with NTDs . methionine synthase or serine-glycine hydroxymethylase have been negative. Autoantibodies to folate receptors have however been detected in 9 of 12 women who were or had been pregnant with a fetus with a NTD but in only 2 of 20 control women. Antiserum to folate receptors results in resorption or multiple developmental abnormalities in mouse embryos. It is possible therefore that the association of antibodies to maternal folate receptors and NTDs reflects a causal relation. Cardiovascular Disease Children with severe homocystinuria blood levels 100 pmol L due to deficiency of one of three enzymes methionine synthase MHTFR or cystathionine synthase Fig. 100-1 suffer from vascular disease . ischemic heart disease cerebrovascular disease or pulmonary embolus as teenagers or in young adulthood. Lesser degrees of raised serum homocysteine and low levels of serum folate have been found to be associated with cerebrovascular peripheral vascular and coronary heart disease and with deep vein thrombosis. Prospective randomized trials of lowering homocysteine levels with supplements of folic acid vitamin B12 and vitamin B6 against placebo over a 5-year period in patients with .

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