DNA (cytosine-5)-methyltransferase 3B (DNMT 3B) polymorphism and risk of Down syndrome offspring.

Down syndrome (DS) is the most common form of human genetic mental retardation. Several polymorphisms in genes coding folic acid cycle enzymes have been associated to the risk of bearing a DS child; however, the results are controversial. S-adenosyl-l-methionine (SAM) is an important intermediate of folic acid pathway and acts as methyl donor and substrate for DNA (cytosine-5)-methyltransferase 3B (DNMT3B - EC 2.1.1.37) de novo methylation processes during embryogenesis. Recent studies suggest that a functional polymorphism of DNMT 3B in maternal genotype may be associated with a decreased risk of having a DS child. We herein investigate the association of this polymorphism with the occurrence of DS in a Brazilian population. We have genotyped 111 mothers of DS infants (MDS) and 212 control mothers (CM) through PCR-RFLP. The observed genotypic frequencies were CC = 0.22; CT = 0.49 and TT = 0.29 in CM, and CC = 0.30; CT = 0.52 and TT = 0.18 in MDS. Allelic frequencies were C = 0.47 and T = 0.53 in CM and C = 0.56 and T = 0.44 in MDS. No deviation of HWE was observed, and both DNMT 3B rs2424913 genotype (χ2 = 4.53; DF = 1; P = 0.03) and allelic (χ2 = 4.90; DF = 1; P = 0.03) frequencies show significant differences between MDS and CM. The presence of the mutant DNMT 3B T allele decreases 30% the risk of bearing a DS child (OR = 0.69; 95% CI: 0.50-0.96; P = 0.03), and the risk is diminished up to 45% in association with the homozygous genotype (OR = 0.54; 95% CI: 0.31-0.96; P = 0.04). Our results suggest that women harboring the single nucleotide polymorphism DNMT 3B rs2424913 have a decreased risk of a DS pregnancy, and further studies are necessary to confirm this protective effect.

Development of a simple and low-cost enzymatic methodology for quantitative analysis of carbamates in meat samples of forensic interest.

Foods contaminated with a granulated material similar to Temik (a commercial pesticide formulation containing the carbamate insecticide aldicarb) are often involved in accidental ingestion, suicides, and homicides in Brazil. We developed a simple technique to detect aldicarb. This technique is based on the inhibition of a stable preparation of the enzyme acetylcholinesterase, and it is specially adapted for forensic purposes. It comprises an initial extraction step with the solvent methylene chloride followed by a colorimetric acetylcholinesterase assay. We propose that results of testing contaminated forensic samples be expressed in aldicarb equivalents because, even though all other carbamates are also potent enzyme inhibitors, aldicarb is the contaminant most frequently found in forensic samples. This method is rapid (several samples can be run in a period of 2 h) and low cost. This method also proved to be precise and accurate, detecting concentrations as low as 40 microg/kg of aldicarb in meat samples.