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‘Treasure map’ identifies first genetic clues to form of blindness

Tom Doumani was diagnosed with the degenerative eye disease MacTel 2 at 61. Photo: Stefan Postles Statistical genetecist Melanie Bahlo led the study. Photo: Walter and Eliza Hall Institute

Tom Doumani thought something was up when he started having trouble reading street signs while driving. Letters seemed to be missing and, if the street name was an unfamiliar one, he had no way of guessing what it might be.

It was enough to prompt him to go and get his eyes tested. However the results showed his long distance vision was fine.

Unconvinced all was as it should be, he mentioned it to his GP who referred him to an eye specialist. This time the tests picked it up. Dr Doumani had the rare and rather awkwardly named Macular Telangiectasia type 2.

Like many rare conditions, little is known about what causes “MacTel 2”, which in scientific circles is known as idiopathic juxtafoveal telangiectasia. Idiopathic meaning “of unknown cause”.

However that may have changed, thanks to research led by Melbourne scientists which has found “a treasure map” revealing the location of the genetic triggers behind this little-understood form of blindness.

Outlined in the journal Nature Genetics, it is the first clue as to what causes MacTel 2, an incurable and untreatable degenerative disease which affects people from age 40 upwards.

The condition is characterised by an abnormal growth of blood vessels in the macula. Patients lose their central vision and tasks such as driving and reading can become impossible.

The international study was led by Walter and Eliza Hall Institute of Medical Research scientists Melanie Bahlo??? and Thomas Scerri???.

The research team, including scientists in New York and London, analysed more than 6 million genetic markers in the genome of patients with the condition and compared them to those without.

Among the 476 people diagnosed with MacTel 2, genetic similarities were found in five key regions of the genome.

Curiously four of the five regions are associated with a person’s metabolism. Those with MacTel 2 recorded lower levels of the basic amino acids glycine and serine.

“That was a bit of a surprise to say the least,” Professor Bahlo said.

The fifth region identified, in what Professor Bahlo has described as “our treasure map”, is tied to the size of retinal blood vessels.

“This is the first time we have been able to say with certainty that this is a genetic condition,” she said. “And the map tells us where to ‘keep digging’ in order to discover the specific genes implicated in MacTel 2.”

Identifying the specific genes would lead to improved diagnostic testing for the disease – which is notoriously difficult to identify – and also developing ways to prevent or stop its progression.

Diagnosed in 2012 at the age of 61, retired corporate banker Tom Doumani was among the Melbourne participants, sourced through Centre for Eye Research . He knows that while he may not benefit directly from participating in the study, he is contributing to the global search for a cause or cure.

“To help advance the knowledge, that’s what appealed to me in taking part,” he said. “I had no hesitation in participating.”

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