Sometimes one tiny clue holds the key to a baffling medical mystery. That was the case for a San Francisco Bay Area child whose family and doctors struggled for the first three years of her life to pinpoint the cause of her developmental delays and neurologic, muscle, eye and liver problems. The essential clue? Grace Wilsey doesn’t make tears when she cries.
Grace’s combination of symptoms didn’t fit any known condition. Her team of caregivers at Lucile Packard Children’s Hospital Stanford, led by pediatric geneticist Gregory Enns, MB, ChB, strongly suspected that she had an as-yet-undiscovered genetic disease. Several genetics experts at Stanford helped sequence her genome, then came up with a list of eight mutated genes that might be responsible for her symptoms. They ranked the genes in order of likelihood that each was involved and began working down the list to try to pinpoint the culprit.
At the bottom of the list was a gene called NGLY1, which normally codes for N-glycanase 1, a housekeeping enzyme that helps cells break down and recycle mis-folded proteins. Part way through the investigation of the list of eight suspect genes, Grace’s parents, Matt and Kristen Wilsey, contacted a team at Baylor College of Medicine that had also previously performed whole genome sequencing on Grace and consulted on Grace’s case. A postdoctoral associate there, Matthew Bainbridge, PhD, reran Grace’s raw sequence data against the latest algorithms. NGLY1 jumped to the top of the candidate list of what was causing Grace’s underlying condition. As a next step, Dr. Bainbridge searched the scientific literature and found something so new that the Stanford researchers hadn’t yet run across it: a report of one child with suspected NGLY1 deficiency. From our press release about the discovery:
Bainbridge read in the medical literature of another child, studied at Duke University, whose caregivers there suspected his unusual symptoms were tied to an NGLY1 gene defect. But without a second patient for comparison, they weren’t sure.
As part of his detective work, Bainbridge emailed Kristen Wilsey to ask if Grace produced tears when she cried. Wilsey replied that although Grace’s eyes were moist, she never really made tears. Bainbridge wrote back, “I think I have it.”
“My heart jumped out of my chest,” Wilsey said. The first patient identified with NGLY1 deficiency, it turned out, also did not make tears, and the same characteristic has since been observed in seven of the eight children with NGLY1 gene defects whom the researchers have identified.
The scientific implications of the diagnosis are profound: Researchers can start looking for treatments or a cure. So far, the way that malfunctioning N-glycanase 1 causes the children’s symptoms is not understood, so unraveling the connection is a large area of focus for scientists.
They can also look for variants of the disease, Enns told me. “We are likely detecting the most severe form of NGLY1 deficiency – ascertainment bias – and it is quite possible that more mild forms of the disease exist,” he said. The first eight children found with NGLY1 deficiency are described in a new scientific paper publishing today in Genetics in Medicine; Enns and Bainbridge are both primary authors. Of the children, six have the same mutation in their NGLY1 gene and (probably not coincidentally) also share a very severe manifestation of the disease. Two children, including Grace, have different NGLY1 mutations and also have less severe disease, a finding that hints that other children with as-yet-unexplained developmental delays may also have less-severe variants of NGLY1 deficiency.
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