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Washington, Feb 25 - Test tube babies are at a higher risk for genetic defects leading to chronic disorders, American health experts have claimed.
Researchers at the Temple University School of Medicine in Philadelphia, who studied two groups of children -- one who were conceived naturally and the other born with the help of a reproductive technology, found that the later group faces greater health risks.
Lead researcher Carmen Sapienza said, Children born through assisted reproduction may have altered expression of genes implicated in chronic metabolic disorders like obesity and type 2 diabetes.
Since the birth of the first test tube baby in 1978, more than three million children have been born with the help of the reproductive technology and most of them are healthy, but as a group they're at a higher risk for low birth weight which is associated with chronic disorders later in life.
In the study, to identify epigenetic (changes in gene expression caused by molecular mechanisms other than mutations in the DNA sequence itself) differences among the naturally born kids and test tube babies, the scientists found that 5 to 10 per cent of chromosome modifications called DNA methylation were different in both the groups, Scientific American said.
We found that 5 to 10 per cent of these chromosome modifications were different in children born through assisted reproduction, and this altered the expression of nearby genes, Sapienza says.
Several of the genes whose expression differed between the two groups have been implicated in chronic metabolic disorders, such as obesity and type 2 diabetes.
Because we have identical DNA in each of our cells, our bodies have mechanisms such as DNA methylation, to control which genes are expressed in certain cell types a process called genomic imprinting.
When a methyl group (a carbon atom with three hydrogen atoms attached) binds to a cytosine molecule (one of the four nucleotides that make up DNA), it tells the cell's transcription machinery not to transcribe that gene.
It's important, because all the same genes can't be expressed in every cell, Sapienza explains.
DNA methylation in the kidney is different from DNA methylation in the liver, he says. That's what makes each organ unique.
Defects in methylation also cause the rare chromosomal disorders Angel man syndrome and BeckwithWiedemann syndrome both of these complex congenital afflictions are characterized by abnormal birth weight, he added.
Their risk increases as much as fivefold with assisted reproduction jumping from one in 15,00020,000 to one in 4,000, Sapienza says.
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