Quick Dips

Large Growth Linked to Cancer

A genetic malfunction linked to massive over-growth and cancerous kidney tumours in young children has been discovered by scientists from the Cancer Genetics Laboratory in Otago University's Department of Biochemistry.

Supported by the Cancer Society of New Zealand and the Health Research Council, Otago PhD student and HRC Training Fellow, Ian Morison, Research Fellow Tak Taniguchi, Pathologist David Becroft and Professorial Research Fellow Tony Reeve, have spent the last three years investigating the effects of a malfunction which leads to the "insulin-like growth factor II (IGF2) over-growth disorder".

An "overexpression" of IGF2 causes children to grow at unusually large rates, being large at birth and remaining very large throughout childhood.

"It has been known for a long time that many children with some types of childhood cancer have high birth weights," Morison says. "Now we know it is possibly linked with this growth disruption. The overall rate of cell growth is increased such that there is a predisposition toward developing some kind of cancer."

Reeve equates the likelihood of these children getting cancerous kidney tumours to the chances of a person who consistently drives a car at high speed having an accident -- they may not, but the chances are increased that they will.

The events leading to this condition are complex and rare. By a process called gene imprinting, normally only the gene inherited from the father is used to make IGF2. In the case of these over-grown children, the mother's copy of the growth factor gene also produces IGF2, so the foetus receives a double dose of the gene by mistake, causing the child to grow with unusual rapidity.

One of four children identified as having this disorder was the size of an average four-year-old when only two years of age, and one the size of a twelve-year-old at eight years. Two of the children had already had kidney tumours removed, one child at six months and one at two and a half years.

"This is only one of the causes of over-growth in children," says Morison. He is anxious to allay the fears of parents with large children, assuring them that this condition appears to be very rare.

Reeve, also Director of the Cancer Genetics Laboratory, says, "All four children have very large kidneys, as the kidney is affected by the growth factor. We don't have enough information about the other organs, but the kidneys were obviously large and the most susceptible to tumours."

Three of the children were from New Zealand and one from Australia. They all came to the attention of Morison or Reeve via clinical geneticists or paediatricians who had encountered large children with growth disorders that were undiagnosable.