Genetic Test Pinpoints Cause of Patient Illness

About a decade ago, scientists decoded the human genome, creating a gene-by-gene map of our DNA. In the decade since, genetic research has accelerated, but mostly it's stayed in the laboratory. Now, genetic science is taking its first steps into medical practice.

The Beery twins were born in 1996, and were diagnosed with cerebral palsy two years later. But as the children got older, their symptoms suggested a different diagnosis, a lack of the neurotransmitter dopamine. Around age six, the twins started taking a drug called L-dopa, which dramatically lessened their muscle spasms and other symptoms.

Fast forward a decade or so, and new symptoms appeared. To see what other factor might be at work, a team at the Baylor College of Medicine in Texas analyzed DNA samples from each of the twins, looking for a mutation that might be responsible.

Genetic tests then available didn't find anything unusual, however researcher Matthew Bainbridge says sequencing the entire genome of each of the twins later identified mutated copies of a gene called SPR (sepiapterin reductase).

"But mutations in SPR mean that, not only do you not make dopamine in the brain, you also don't make serotonin. And so these kids were getting this L-dopa treatment, which helped them with their lack of dopamine, but they weren't getting anything for their serotonin," he says.

A serotonin supplement was added to their medications, and within a month their mother says there were noticeable improvements in Alexis Beery's breathing and in her twin brother Noah's school work.

It seems almost every week there's a story about scientists who have identified a gene linked to some disease or another. Those discoveries are important, but Bainbridge says the Beery case represents something else.

"The difference is that we can actually do something, because we found these mutations and we knew that they were causing the disease. We could actually change the therapy the children got," Bainbridge says.

Whole-genome sequencing is still an expensive, specialized activity. But the cost is coming down, and Bainbridge says this individualized approach to diagnosis and treatment may move out of the research lab and into the doctor's office, at least for some conditions, in as little as two to three years.

"I think eventually it will be routine. I can imagine a future - and not too distantly, in five to ten years - where children will be born and their whole genome will be sequenced immediately."

Bainbridge and his colleagues describe their work in the journal Science Translational Medicine.