‘Next-generation’ whole exome sequencing project diagnosing rare diseases

If you’re lucky enough to see Holly Burns smile, you know it’s for real.

The mousy-blonde-haired, blue-eyed four-year-old who will never walk, run or speak more than a few words physically can’t fake it.

Mum Amanda Burns says Holly is strong-willed and determined to try to play the games her siblings play. Mum Amanda Burns says Holly is strong-willed and determined to try to play the games her siblings play. Photo: Supplied

Ask her to pose for a photo and she tries and tries but a rare genetic disease affecting one in 40 million has eaten away at the white matter in her brain.

“Because the messages don’t get from her brain out to different parts of her body … if you say ‘Holly, smile’, she can’t do it,” mum Amanda said as she bit back tears.

Holly will likely never speak properly or walk. Holly will likely never speak properly or walk. Photo: Supplied

“If she gives you a smile, she has to feel it to be able to actually smile.”

For the first year-and-a-half of Holly’s life, Amanda and her husband, Daniel, knew something was amiss with their otherwise perfect second daughter.

At six months old, she was a bit behind where she should have been but doctors couldn’t put their finger on it.

When at 19 months she was struck down by a virus that saw her rushed in for an MRI, Holly was yet to stand or talk and even sitting up by herself could be a struggle.

The tests showed the Sydney toddler’s brain “glowing white”. Doctors immediately knew something was wrong but couldn’t say what.

That task fell to an international team including researchers from the University of Queensland and the US-based Children’s National Health System’s Myelin Disorders Program.

They used whole exome sequencing – a method to examine all the genes in a person’s entire genetic code at once – to pinpoint the problem: The terminal and incurable vanishing white matter leukodystrophy.

Now four, Holly will likely never speak properly or walk. Doctors put average survival rates at between five and 10 years after diagnosis. She’s unlikey to live to be a teenager. Her parents, along with two young sisters and a brother, are making the most of the time they have left.

“She’s just gorgeous. She’s so determined,” Mrs Burns said.

“She can’t walk and never has been able to but she’s so determined to be able to play all the games that her sister and her brother play and try to do everything they can do.

“So she’s very determined, very strong-willed but so gentle and loving.”

Various types of white matter disorders affect about one in 7000 children each year, damaging the nerves that connect different regions of the brain and the spinal cord.

The exome sequencing project successfully diagnosed 30 out of 70 children using what biotech company Illumina’s scientific research director, Dr Ryan Taft, termed “next-generation sequencing-based whole exome sequencing”  to “dramatically” improve diagnosis rates.

The diagnosis was a huge relief to the Burns because it allowed doctors to perform a simple blood test to check their other children.

It also significantly changed the way Mrs Burns cared for Holly as she learnt that catching a fever or getting hot in other ways would trigger increased symptoms. A bump on the head could be devastating.

The team’s research was published in Annals of Neurology this week.

The scientists are now investigating the possibilities for whole genome sequencing, which costs more and takes longer but yields more data.

Money is being raised for vastly under-funded research into white matter degenerative diseases at Saving Chloe Saxby, named for another girl with the rare illness.