Mental disability often caused by spontaneous mutation

RNW archive

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Recent research carried out at Radboud University Nijmegen Medical Centre shows that in 30 percent of all cases mental disability in newborn infants is the result of a spontaneous mutation in the sperm cell or egg cell.

“We have been searching for an explanation for three-and-a-half years,” these are the words of the parents of Sven van Berkel. They have been struggling to  understand what is wrong with their son.

“We’ve said often enough  that we’ll stop all these tests and examinations: blood samples, putting him under  anaesthetic. We don’t like all that  either, but you want to find out what is wrong.”

In about half of all children born with a mental disability the cause is not apparent: no outer abnormalities in the child, seemingly ‘normal’ parents, no problems during pregnancy, no apparent genetic problems, and yet there is a problem with the child’s mental development. How is this possible?

One mutant gene
Clinical geneticist Han Brunner and his colleague Joris Veltman conducted research into the causes of mental disability in this group of children. According to Dr Brunner:

“We now have equipment which allows us to scan all a person’s  genes at once. And we use this technique to compare a child with its parents. We studied ten mentally-disabled children and their parents. In six of them we found an abnormality in one gene, an abnormality not present in either parent. This abnormality is probably the cause”.

The technique used by Brunner and Veltman is called Next Generation Sequencing. It enabled them to study all 20,000 genes of the human genome and to compare a child’s genome to those of its parents. The two scientists say that the abnormality in a single gene is the result of spontaneous mutation.

Relief
Dr Veltman explains that this holds true for all of us, we all show  minor changes in DNA compared to that of our parents:

“We can now tell the parents that the mutation occurred during the production of the sperm cell or egg cell. The chance of a recurrence in a second pregnancy will be minimal compared to the general risk of having a disabled child. About two in every 100 children are born with a mental disability”.

The Nijmegen research could provide clarity for the parents of a sizeable group of mentally-disabled children. Parents are often relieved to know what caused their child’s disability. And information about whether or not a disability is hereditary  is also important to parents who would like to have a second child.
“It won’t change a thing  about the way Sven is,” is the comment from Sven’s father, now that his son has undergone gene check. His wife adds: “But it is a reassuring  to know what caused it. Now we can put a label on it”.

At present Next Generation Sequencing is still too costly to be put into general use, but the researchers expect the hardware will become cheaper soon. Unfortunately, this does not mean the test will become  available worldwide in the next few years. Simply having the equipment is not enough, it takes specialist  knowledge to process and interpret the data.

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