Cells throughout the human body are constantly being damaged as a part of natural life, normal cellular processes, UV and chemical exposure and environmental factors — resulting in what are called DNA double-strand breaks. Thankfully, to prevent the accumulation of DNA damage that could eventually lead to cell dysfunction, cancer or death, the healthy human body has developed ways of locating and repairing the damage.
Unfortunately, these DNA repair mechanisms themselves are not impervious to genetic errors. Genetic mutations that disrupt DNA repair can contribute to devastating disease.
Across the early-stage progenitor cells that give rise to the human brain’s 80 billion neuronal cells, genomic alterations impacting DNA repair processes have been linked to neuropsychiatric disorders and the childhood brain cancer medulloblastoma. But until now, it was not known exactly which disruptions in DNA repair were involved.
Can sequencing of newborns’ genomes provide useful medical information beyond what current newborn screening already provides? What results are appropriate to report back to parents? What are the potential risks and harms? How should DNA sequencing information be integrated into patient care?
DNA sequences were once thought to be the same in every cell, but the story is now known to be more complicated than that. The brain is a case in point: Mutations can arise at different times in brain development and affect only a percentage of neurons, forming a mosaic pattern.
Now, thanks to new technology described last week in Neuron, these subtle “somatic” brain mutations can be mapped spatially across the brain and even have their ancestry traced.
Like my family, who lived in Eastern Europe, migrated to lower Manhattan and branched off to Boston, California and elsewhere, brain mutations can be followed from the original mutant cells as they divide and migrate to their various brain destinations, carrying their altered DNA with them.
“Some mutations may occur on one side of the brain and not the other,” says Christopher Walsh, MD, PhD, chief of Genetics and Genomics at Boston Children’s Hospital and co-senior author on the paper. “Some may be ‘clumped,’ affecting just one gyrus [fold] of the brain, disrupting just a little part of the cortex at a time.” …
It’s become clear that our DNA is far from identical from cell to cell and that disease-causing mutations can happen in some of our cells and not others, arising at some point after we’re conceived. These so-called somatic mutations—affecting just a percentage of cells—are subtle and easy to overlook, even with next-generation genomic sequencing. And they could be more important in neurologic and psychiatric disorders than we thought.
“There are two kinds of somatic mutations that get missed,” says Christopher Walsh, MD, PhD, chief of Genetics and Genomics at Boston Children’s Hospital. “One is mutations that are limited to specific tissues: If we do a blood test, but the mutation is only in the brain, we won’t find it. Other mutations may be in all tissues but in only a fraction of the cells—a mosaic pattern. These could be detectable through a blood test in the clinic but aren’t common enough to be easily detectable.”
That’s where deep sequencing comes in. Reporting last month in The New England Journal of Medicine, Walsh and postdoctoral fellow Saumya Jamuar, MD, used the technique in 158 patients with brain malformations of unknown genetic cause, some from Walsh’s clinic, who had symptoms such as seizures, intellectual disability and speech and language impairments. …
Genomic sequencing and molecular diagnostics are becoming a global business. At the recent American Society of Human Genetics meeting, dazzling technologies for reading genetic code were on display—promising faster, cheaper, sleeker.
Nevertheless, it’s become clear that the ability to determine someone’s DNA or RNA sequence doesn’t automatically translate into useful diagnostics or even actionable information. In fact, the findings are often confusing and hard to interpret, even by physicians.
That’s where academic-industry partnerships can flourish—tapping the deep expertise of medical research centers to bring clinical meaning to sequencing findings. Yesterday, Boston Children’s Hospital and Life Technologies Corp. announced a new venture with a great list of ingredients: fast, accurate, scalable sequencing technology—Life’s Ion Proton® Sequencer—but also research and clinical experience in rare and genetic diseases, bioinformatics expertise to handle the big data, and the medical and counseling expertise to create meaning from the results. …
It’s been more than a decade since the Human Genome Project cracked our genetic code. DNA sequencing is getting cheaper and cheaper. So why isn’t it being used every day in medicine?
The truth is that while we have the technology to blow apart a patient’s DNA and piece it back together, letter by letter, and compare it with normal “reference” DNA, doctors don’t really know what to do with this information. How much of it is really relevant or useful? Should they be giving it back to patients and their families, and how?
Handled badly, the information could do more harm than good. “We don’t want to scare patients for no reason, or for the wrong reason,” says Isaac Kohane, MD, PhD, who chairs the Children’s Hospital Informatics Program.
Seeking a set of best practices for safe, clinically useful genomic sequencing, Boston Children’s Hospital took a crowd-sourcing approach. …
One extended family has a range of unexplained heart defects—sometimes a hole in the heart, sometimes an arrhythmia. One child, Liam Burns, died days after birth from an underdeveloped heart, a narrowed artery to the lungs and an electrical block. Yet other family members have little more than a heart murmur. All of the defects are on the right side of the heart.
Another family’s son, 11-year-old AJ Foye, has unexplained muscle weakness and fatigue. He can walk only short distances and needs a ventilator at night to support his breathing.
These families—and a third that chose to remain anonymous—decided to submit their DNA to a challenge sponsored by Boston Children’s Hospital called CLARITY. Not only have their complete genomes been sequenced, but 30 teams all over the world—from biotech startups to the National Institutes of Health—were given access to the sequences and set loose to come up with “best practices” for interpreting the results. Two dozen turned in submissions, now being evaluated by a panel of judges.…
Sequencing a patient’s genome to figure out the exact source of his or her disease isn’t standard operating procedure — yet. But falling sequencing costs and a growing number of successes are starting to bring this approach into the mainstream, helping patients and families while advancing a broader understanding of their diseases.
The Stone family is a case in point. When John and Warren Stone were born, their parents were envisioning life raising identical twins, when suddenly everything changed. On their second day of life, the twins started to have seizures with stiffening of their arms and legs; more alarmingly, they would stop breathing from time to time, requiring a ventilator to help them breathe. Further work-up revealed that both John and Warren were having persistent seizures consistent with Ohtahara syndrome, a rare, debilitating seizure disorder.
Warren died a few weeks later, and the family transferred John’s care to Boston Children’s Hospital. An extensive clinical and genetic work-up here and at several other hospitals involved in his care — including sequencing all the genes known to cause Ohtahara syndrome – identified no cause for John’s unique seizures. …
Recently, in the hospital cafeteria, I overheard a group of researchers discussing the upcoming availability of whole-genome sequencing to physicians. “We should devise a way to study how physicians will use this,” said one of them—underscoring the disruptive nature of the transformation that is currently happening in medicine.
The ability to immediately obtain whole-genome sequences from patients holds enormous potential for understanding and treating human disease. The list of studies reporting successful diagnosis of otherwise elusive orphan conditions is already too long to recount—more than 600 articles in PubMed as of the date of this posting—including poignant examples of advancing clinical care. …