Neuroscientist Dr Tracy Dixon-Salazar gives hope to future generations of epilepsy

Catherine Shanahan meets neuroscientist Dr Tracy Dixon-Salazar, a former stay-at-home mother, who spent 12 years studying to find effective treatments for her daughter’s epilepsy.
Neuroscientist Dr Tracy Dixon-Salazar gives hope to future generations of epilepsy

MOST kids don protective headgear for high contact sport, cycling or horseriding, but Savannah Salazar wore a helmet all day everyday for 15 years.

“Parents look back at their kids’ school photographs and they see how they developed over the years.

"I look at Savannah and I see scars and injuries,” her mother, Dr Tracy Dixon-Salazar, says.

The reason for the helmet and the cause of the scars is epilepsy, the same reason Dixon-Salazar has the title “Doctor”.

Before her daughter developed the condition, Dixon-Salazar was a young stay-at-home mother-of-two who knew nothing about seizures.

Now she’s a neuroscientist and genetic researcher responsible for the discovery of a number of genes underlying her daughter’s condition.

Her incredible journey took Dixon-Salazar from the kitchen to the lab, eventually evaluating her own daughter’s DNA.

Savannah, from Los Angeles, was a “normal” toddler for her first two-and-a-half years. Then, one fateful night in 1995 her parents woke to horrible gagging sounds.

“I thought she was choking. I didn’t know anything about seizures,” Dixon-Salazar says.

They called the paramedics who suggested Savannah may have suffered a seizure.

She recovered quickly that night, but had another seizure a few weeks later and then four inside two months.

Amid growing alarm, Savannah’s parents put her through a battery of tests.

Nothing showed up, not even in an electroencephalography (EEG) test, used to detect abnormalities related to the brain’s electrical activity.

Then for a while, the seizures subsided.

“There was nothing for six months,” Dixon-Salazar says.

Nonetheless, they maintained their vigilance, moving Savannah into their bedroom.

And then the seizures returned with a vengeance, hundreds occurring every week.

The next two years were fraught.

Eight EEGs were normal and doctors struggled to deliver a definitive diagnosis.

By now, Savannah was five-years-old and clearly lagging behind her kindergarten peers.

The developmental delays, along with changes in her EEG, eventually led to a diagnosis of Lennox-Gastaut syndrome (LGS), characterised by multiple seizure types and mental and developmental delays.

However, the causes of LGS did not apply in Savannah’s case — structural issues with the brain, birth trauma, head injury, exposure to toxins — leaving Dixon-Salazar deeply frustrated as to the cause of her daughter’s seizures.

Determined not to be beaten, at he age of 24, she cast off her apron strings, rolled up her sleeves and set about identifying the cause herself.

“ I hadn’t done very well at high school, so I had to spend a couple of years learning all the stuff I should have learned then,” she says.

She had difficulty understanding scientific jargon while trying to educate herself about epilepsy and took a couple of English classes thinking she had poor vocabulary.

Then she started taking science classes, and “fell in love” with the subject.

She says she didn’t set out on a path to cure her daughter or to save the world, but to “find a way of giving hope to future generations”.

Her studies took 12 years but in the end, she graduated with a PhD in neuroscience.

By then, Dixon-Salazar had counted 40,000 seizures in her daughter.

So how did she manage the journey from housewife to neuroscientist?

“Basically, my husband and myself didn’t see each other for a couple of years.

"He was a police officer at the time. I’d go to school during the day and he would work a night shift.

"The only way we could do it was to take turns looking after Savannah,” she says.

Telling herself she’d quit her studies in the morning if her kids needed her, but she got there eventually, taking it one day at a time.

Post PhD, she approached Joseph Gleeson, a neuroscientist investigating genetic causes and treatments for childhood brain diseases, and asked him for a job.

While working with him, she says there was a “revolution in technology” that transformed gene sequencing.

“My job was to bring that technology into the lab and use it to sequence the genes of families we were working with,” she says.

One day, Gleeson asked her how Savannah was doing.

“I told him she was doing horribly, up to 300 seizures a month, sleeping 17-18 hours a day. We were losing her.”

Gleeson suggested sequencing Savannah’s exome, which essentially meant evaluating her entire DNA.

“So she went from daughter to lab sample,” Dixon-Salazar says.

It took more than a year but Dixon-Salazar spotted mutations in a group of genes regulating how calcium enters Savannah’s brain cells.

Over the years, medics had recommended Savannah take calcium supplements, because antiepileptic drugs leached calcium away from her bones, but every time they gave her the supplements, the seizures worsened.

Dixon-Salazar identified a drug called verapamil, commonly used to treat heart problems, that specifically targets the channel where many of Savannah’s mutations were located.

After checking Savannah’s heart function, her doctors agreed to try the medication.

“She’s been on it for five years now and for the first time in 20 years, myself and my husband have been able to go on a trip and leave her at home.

"That’s why I’m in Ireland today,” says Dixon-Salazar, who was here recently to speak at an event hosted by Epilepsy Ireland and the Royal College of Surgeons in Ireland.

She says she feels like she “finally met Savannah for the first time five years ago”.

Dixon-Salazar now heads up the Epilepsy Genetics Initiative (EGI), a major American research project run by the CURE organisation, which aims to revolutionise how epilepsy is treated by driving the development of genetic-based personalised medicine.

She laughs at how her life has turned out.

“I didn’t set out to build an international reputation, but I thought all the suffering we went through must be worth something.

"And if Savannah’s story offers some hope, then that’s good enough for me.”

Seizure types

Seizures are divided into two major groups: primary generalised seizures and partial seizures.

Each group contains several seizure types.

Primary generalised seizures:

Absence seizures: These are brief episodes of staring during which awareness and responsiveness are impaired.

Atypical absence seizures: Periods of staring during which the individual is somewhat responsive.

Myoclonic seizures: These are brief, shock-like jerks of a muscle or a group of muscles.

Atonic seizures: Muscles suddenly lose strength.

Tonic seizures: Muscle tone is greatly increased and the body, arms, or legs make sudden stiffening movements.

Clonic seizures: Involve rhythmic jerking movements of the arms and legs.

Tonic clonic seizures: Also known as grand mal seizures, involve the entire body.

Partial seizures:

These include seizures localised to one area of the brain but may spread, consciousness remains intact.

Complex partial seizures can begin an any lobe but cause altered awareness due to spreading of seizure.

Secondarily generalised seizures begin in one part of the brain, and then spread to involve both sides of the brain with associated loss of consciousness

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