Twin research reveals gene that may play a crucial part in the development of myopia

Jul 31 2004

New research carried out by doctors in the Twin Research Unit at St Thomas’ Hospital, London, indicates that a gene called PAX6 may play a crucial part in the development of myopia.

This breakthrough contributes to a growing scientific debate about whether the causes of a recent worldwide increase in myopia are genetic or due to changes in lifestyle such as children spending more time playing computer games and surfing the internet.

The research study – published in the August edition of The American Journal of Human Genetics – is based on a genomewide scan of 221 pairs of twins from the Twin Research Unit database.

Myopia, or short-sightedness, is the most common eye problem – it affects approximately 25% of people in the UK - but it has reached epidemic levels in the Far East where, for example, two-thirds of Japanese teenagers are myopic.

The incidence of myopia has increased in recent years in all countries and there is even a significant risk of permanent vision loss in individuals with high myopia (‘pathological myopia’), which is also becoming more common.

An important part of the research study was to confirm that susceptibility to myopia in a UK population is predominantly due to genetic susceptibility rather than environment. A study of 506 pairs of twins (both identical and non-identical) confirmed an earlier study by the same group that genes are by far the most important factor with a heritability of 89% - environmental factors only accounted for 11%.

Dr Chris Hammond, Honorary Consultant in the Twin Research Unit and Consultant Ophthalmologist at the West Kent Eye Centre, Princess Royal University Hospital, is lead author of the research study.

He says: “The reasons for myopia are not well understood and changes in lifestyle which mean that we spend far more focusing on close objects, such as computer screens, mobile phones and books, are clearly a factor – but our study now suggests these lifestyle factors may only have a major effect on genetically susceptible people.

“Our new research indicates that a gene called PAX6, which is already known to be fundamental to eye development and which is the sole gene causing a rare visually impairing condition called aniridia, is strongly linked to the development of myopia.

“Our genomewide scan of 221 pairs of non-identical twins shows significant linkage to four chromosome regions – the largest one is right in the region of the PAX6 gene. Further detailed examination of PAX6 is now needed to work out the exact role of the gene and exactly where the mutations occur.”

Dr Hammond urges parents: “Our research is great ammunition for mums and dads who are looking for ways to keep their children entertained during the long summer holidays – because it shows that children should balance any close reading with outdoor activities.

“Especially if both parents are myopic, I recommend as an ophthalmologist that you take a few simple steps to ward off the development of myopia – try moving the television further away from the sofa, don’t let your children play computer games or surf the net for hours on end - and ensure that they get out of the house to enjoy the summer sun and play with friends.”

The Twin Research Unit was originally set up at St Thomas’ Hospital in 1992 to look at the role that genes play in the development of rheumatic diseases in older women and has now expanded to look at most common diseases, behaviours and traits.

Professor Tim Spector, Director of the Twin Research Unit at St Thomas’ Hospital, says: “Twins are a wonderful natural experiment that provide a scientific basis for assessing the relative importance of your family history or lifestyle factors in causing diseases and behaviours.

“This study shows the enormous power and potential of twin studies to help us first identify diseases that are primarily genetic – and then find the genes causing them.”

If you are a twin (identical or non-identical) aged over 15 who would like to volunteer for the Twin Research Unit at St Thomas’ Hospital, please call 020 7188 5555 – log on at www.twin-research.ac.uk to find out more.