Washington: 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
Defects in methylation also cause the rare chromosomal
disorders Angelman syndrome and Beckwith Wiedemann
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.