Genetic tooth disorders affecting multiple generations of a single family are rarely traced to their precise molecular origin — the human genome’s complexity makes such searches enormously difficult, even for trained specialists.
Dr. John Graham, a professor of medical genetics and pediatrics at Cedars-Sinai in Los Angeles, was born with something unusual: a few teeth already present at birth. Those teeth fell out almost immediately, and adult teeth never grew in their place — a condition called tooth agenesis. The rest of his mouth eventually filled in normally, but the partial absence of teeth shaped his adolescence and pushed him toward costly dental implants in adulthood.
He was not alone in his family. His mother, her siblings, his children, and his grandchildren all shared the same condition across five generations. The pattern pointed clearly toward a genetic cause.
After completing medical school, Graham began searching for the responsible mutation. The genome-sequencing tools available in 2010 were limited. An early scan identified a long stretch of chromosome 1 as the likely region — but that stretch contained over 311 mutations to examine, and some of those may have been sequencing errors rather than real variants. According to the report, the data quality was simply too unreliable to proceed. As Dr. Pedro Sanchez, director of pediatric medical genetics at Cedars-Sinai Guerin Children’s, put it: “the quality of data was just way too noisy.”
A Mentor’s Search, Taken Up by a Former Student
Graham was approaching retirement and preparing to abandon the search when Sanchez intervened. The connection between the two was personal. “He was my mentor in medical school,” Sanchez said. “He motivated me to go into medicine, into genetics.” Graham had spent his career identifying the genetic causes of other families’ conditions. His own had eluded him throughout. “Right before he retired, I said, ‘I have to do this for you,'” Sanchez said.
Sanchez and his colleagues applied a more targeted method. They sequenced and compared the genomes of two affected and two unaffected family members, looking specifically for mutations present only in those with missing teeth. One mutation met that criteria. It sat within the same region of chromosome 1 Graham had identified years earlier.
The Protein at the Center of the Diagnosis
The mutation turned out to be a single-letter change within the gene encoding a protein called keratinocyte differentiation factor 1 (KDF-1). That protein plays a role in regulating the development of both skin and teeth.
To confirm the finding, the team sequenced the gene across 21 family members. The variant appeared in 11 individuals with the condition and was absent in all 10 unaffected members. That distribution established the genetic variant as the likely cause of the family’s five-generation condition.
Using computer modeling, Sanchez and his team then simulated the shape the altered KDF-1 protein would take — work aimed at understanding precisely how the single-letter change disrupts normal protein function and, by extension, normal tooth development.
The next step described in the announcement is that computer modeling of the protein’s altered structure continues as part of the team’s effort to understand the functional impact of the identified mutation.
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