New York, Aug 18 (IANS): Parents, please take note. The frequency of brain tumours has been underestimated in children with the common genetic syndrome -- neurofibromatosis type 1 (NF1), a new study has found.

According to the researchers, this disorder is characterised by birthmarks on the skin and benign nerve tumours that develop in or on the skin. Brain tumours are also known to occur in children and adults with NF1.

They estimated that only 15-20 per cent of kids with NF1 develop brain tumours. But the study, published in the journal Neurology: Clinical Practice, found that the frequency of brain tumours in this population was more than three times higher.

"I'm not delivering the message anymore that brain tumours are rare in NF1. This study has changed how I decide which children need more surveillance and when to let the neuro-oncologists know that we may have a problem," said senior author David H. Gutmann from the Washington University School of Medicine.

Brain Magnetic Resonance Imaging (MRI) scans of children with NF1 characteristically show bright spots that are absent in the scans of unaffected children. Unlike tumours, they are generally thought to disappear in teenage years, the researchers said.

Since brain tumours can be confused with harmless bright spots, it has never been clear whether finding these abnormalities via MRI should be a cause for concern, they added.

For the study, the team developed a set of criteria to distinguish tumours from other bright spots. The researchers then analysed scans from 68 NF1 patients and 46 children without NF1 for comparison.

All but four (94 per cent) of the children with NF1 had bright spots, and none of the children without NF1 did. Further, in 57 per cent of the children with bright spots, at least one of the spots was deemed likely to be a tumour, the research team found.

Applying the new criteria to MRI scans will help physicians identify probable tumours, but that does not mean that all children with NF1 should be scanned regularly, the researchers cautioned.