Mayo Clinic. US: Precision medicine is getting a jump-start from a new national
initiative announced in President Obama's State of the Union message.
One Georgia family has already experienced its benefits: genomic testing
called whole exome sequencing helped Mayo Clinic neurologist Zbigniew Wszolek, M.D.,
solve a medical mystery that had left a boy with painful, jerking
spasms that at times prevented him from walking or talking. Dr. Wszolek
describes the case in a newly published article in the medical journal Mayo Clinic Proceedings.
As a toddler, Dustin Bennett could not keep his balance, and as he
grew older, the rigid, jerking spasms mysteriously appeared and
disappeared. Over time, he also developed learning disabilities.
Dustin’s adoptive mother, Linda Bennett, took him to several doctors
to find the cause of his movement problems, but years of tests,
medications and hospital stays came up empty for the Pearson, Georgia,
family.
“I wasn’t willing to give up, because I felt there had to be an answer somewhere,” Linda says.
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Then a physician suggested that Dustin, now 23, visit Mayo Clinic’s campus in Jacksonville, Florida.
Dr. Wszolek used whole exome sequencing to finally give Dustin a
diagnosis — episodic ataxia type 1. Fewer than 100 cases in the world
have been described for this rare condition of the nervous system, which
can severely, suddenly affect movement. In addition to loss of
coordination and balance, symptoms may include vertigo, blurred vision,
epilepsy, slurred or incomprehensible speech, difficulty breathing,
cognitive disability and carpal spasm.
In the Mayo Clinic Proceedings article, Dr.
Wszolek, the lead author, describes how he and his colleagues at Mayo
Clinic were able to find a specific mutation for this condition hiding
in one of Dustin’s genes. To conduct the genomic test, blood samples
were taken from Dustin and his biological parents and sister.
“Whole exome sequencing allowed us to make the diagnosis precisely and quickly,” says Dr. Wszolek.
Gianrico Farrugia, M.D., chief executive officer of Mayo Clinic in Jacksonville, Florida and former director of the Mayo Clinic Center for Individualized Medicine
attended a White House event on Friday where details of the precision
medicine initiative were released. More than half ($130 million) of the
total $215 million budget request is for a national biobanking program
that draws on existing collections across the country. Mayo Clinic has
among the country's largest collections through the Mayo Clinic Biobank and the Biorepositories Program.
In 2013, Mayo Clinic’s campus in Florida became one of the few
institutions in the nation to offer whole exome sequencing to diagnose
patients like Dustin, who have been on a medical diagnostic odyssey for
years. Teams of physicians, researchers and geneticists combine their
expertise to offer this testing and interpretation to Mayo physicians
and their patients.
“Since the sequencing of the first human genome in 2000, we’ve been
waiting for the technology to advance to a point where we can use it in
the clinic to help patients,” says Alexander Parker, Ph.D., associate director of the Mayo Clinic Center for Individualized Medicine and an author of the Proceedings
paper. “That day has arrived. Dustin is a wonderful example of exactly
how genomic sequencing can be used in the clinic to find meaningful
answers for patients.”
Whole exome sequencing scans a patient’s DNA for mutations in all
22,000 human genes at once. Previous methods required focusing on one
gene at a time, which was costly and inefficient.
“Before genomic sequencing our approach to these situations was to
guess where in our DNA the problem might be and look at single genes one
at a time in the hopes we were looking in the right area,” says Dr.
Parker. “Now that genomic sequencing technology is faster and more
affordable, instead of guessing where in our DNA the answer lies, we can
look at all of our DNA at the same time and find the answer.”
There is no cure for Dustin’s condition, but there are medications
available to help with symptoms. Dr. Wszolek is seeing improvement in
Dustin’s motor and cognitive functioning since placing him on
medication.
“When I saw Dustin for the first time, he was not able to function
from the motor standpoint,” says Dr. Wszolek. “He was clumsy, falling
and had episodes of wracking movements. Now he is able to do activities
such as playing basketball and going to school. He is a completely
different man.”
Dr. Wszolek has spent 27 years collecting genetic samples and medical histories from families with Parkinson’s disease
and related disorders to discover new genetic markers. When Mayo Clinic
began offering whole exome sequencing as part of its clinical practice
to help patients who are seeking answers, he realized that the potential
of this technology could help Dustin.
“This makes my own interest in the genetics of neurological
conditions even more exciting,” Dr. Wszolek says. “It’s nice to see the
fruits of our work and our discoveries in genetics entering the clinical
practice to help patients.”
For Linda, having a firm diagnosis for Dustin brings a newfound peace
of mind. “We’re just praying it will make it a little less strenuous on
him, and maybe down the road it will help someone else.”
Additional authors of the Proceedings paper include Pawel Tacik, M.D.; Kimberly Guthrie, M.S.; Audrey Strongosky, B.S.; Daniel Broderick, M.D.; Douglas Riegert-Johnson, M.D.; Sha Tang, Ph.D.; Dima El-Kechen, M.S.; and Owen Ross, Ph.D.
This work was supported by the Max Kade Foundation, grants P50 NS072187 and ROI NS078086 from the National Institutes of Health/National Institutes of Neurological Disorders and Stroke; a gift from Carl Edward Bolch Jr., and Susan Bass Bolch; and funding from the Mayo Clinic Center for Individualized Medicine.