Most of the DNA that clinical genetics relies on came from people of European descent. That fact rarely reaches patients, but it quietly shapes which diseases get caught and which slip through. A study published this week in Nature Medicine puts a number on the gap. When researchers ran the Hong Kong Genome Project against gene lists designed for European ancestries, 38 clinically important genes would have gone unexamined in the Chinese population.
The project sequenced more than 20,000 participants and split them into two groups. One was a rare disease cohort of 2,227 patients whose doctors suspected a genetic cause but could not name it. The other was a population cohort of 18,261 people who signed up for genomic screening to see whether they carried anything medically actionable, meaning a variant a doctor could actually do something about.
A quarter of the hardest cases got an answer
For the rare disease group, the headline figure is a diagnostic rate of 25 percent. One in four patients who had been living without an explanation walked away with one. That may sound modest, but these are the cases that ordinary testing already failed. For a family that has spent years cycling through specialists, a name for the condition changes what happens next: which specialists to see, which treatments to try, what to tell relatives who might carry the same variant.
The population cohort tells a different kind of story. Among people who considered themselves healthy, 3.7 percent carried a pathogenic or likely pathogenic variant tied to a dominant disorder. Dominant means a single bad copy of the gene is enough to raise risk. Finding that early, before symptoms, is the whole premise of predictive genomic screening.
The panels were built for the wrong population
The most pointed result is about what standard tools miss. Benchmarked against panels tuned for European ancestries, 48 percent of the Hong Kong participants carried a recessive disorder gene on that European list. Recessive carriers usually stay healthy themselves but can pass a condition to children if their partner carries the same gene, which matters for family planning.
Then came the genes the European panels did not think to look for. The team identified 38 additional clinically important genes that would have been overlooked in this population. Ancestry is not a small footnote in genomics. A reference built on one group can be blind to variants that are common and consequential in another.
Drug response showed the same pattern at scale. Nearly every participant carried at least one actionable pharmacogenomic phenotype, meaning a genetic trait that affects how they process a medication. The authors estimate this could inform close to one million annual prescriptions in Hong Kong. That is the difference between a standard dose and a dangerous one, worked out from a blood sample rather than a bad reaction.
What the numbers do not settle
A diagnostic rate is not a cure. Identifying the gene behind a rare disease often leaves families without a treatment, only a clearer picture. The 25 percent figure also means three-quarters of the rare disease cohort still have no genetic answer, and some of those causes may sit outside what current sequencing can read.
The screening findings carry their own uncertainty. Carrying a pathogenic variant raises risk. It does not guarantee illness, and telling healthy people they have a dangerous gene can cause worry that outlasts any benefit. The study reports what the genomes contain, not how the participants fared over the following years. And a resource curated for the Hong Kong Chinese population is exactly that. It sharpens care for one group without fixing the broader imbalance in whose DNA gets studied.
Still, the point lands. The authors frame the effort as a blueprint for precision medicine in underrepresented populations, and the 38-gene gap is the argument in miniature. Genomic medicine works better when the reference looks like the patient. For most of the world, it still does not.
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