A federally-supported database, ClinVar, allows laboratories to publicly share data on genetic mutations and what they are thought to mean. But some companies, like Myriad, which host huge databases on genetic mutations, do not contribute to ClinVar.

Even the terminology for DNA variants may not be widely shared. Different labs have different naming schemes.

For example, ClinVar renders one DNA variant this way:

NM_004004.5(GJB2):c.101T>C (p.Met34Thr).

But another lab does it like this:

c.101T>C, p.Met34Thr, GJB2.

Patients searching for information on their own “would not be sure what to type into ClinVar,” said Dr. Heidi Rehm, a clinical geneticist at Massachusetts General Hospital and the Broad Institute.

In addition to the terminology problem, Dr. Ross said, there is a problem of discordance among labs.

When one big lab “reports a reclassification and the other labs do not, and you have family members who get tested at different labs, we have different interpretations of the same patient data,” Dr. Ross said. “How do we deal with that? What do we tell our patients?”

Labs like Myriad often notify a doctor who ordered a genetic test when the results were reclassified. But even when they do, doctors may not be able to reach and inform their patients.

“I’ve changed my practice location over the years, and my patients have moved,” Dr. Plon said. “I have received updated reports for patients who no longer live in Houston, and we have no idea where they live.”