Short answer
A de novo RET variant means the variant appears to be new in the person tested rather than clearly inherited from a parent. In MEN2 and related RET conditions, that does not make the result low-stakes. The person with the germline pathogenic variant may still need variant-specific endocrine follow-up, and their children can be at risk. Parent testing, exact variant review, possible mosaicism, and genetic counseling help clarify who else in the family should be tested.
How to frame the result
| Situation | Common next question | Why it matters |
|---|---|---|
| Report says de novo | Were both biological parents tested with a clinical assay? | Family risk depends on confirmation. |
| Parent tests negative | Was mosaicism discussed? | Rare mosaicism can affect recurrence counseling. |
| Person has children or may have children | Was autosomal dominant inheritance explained? | Children can still need targeted testing. |
Most de novo RET questions are really about how much confidence the genetics team has in the inheritance story. If the wording is loose, the report may need more clarification before family decisions are made.
Why parent testing matters
Parent testing helps distinguish a truly new germline variant from a family variant that was missed, a low-level mosaic parent result, or a report that simply has not been fully worked up. That distinction changes how relatives are counseled and whether children need targeted testing.
In practice, genetics teams look at the exact RET variant, the phenotype, whether the report came from germline testing or a tumor-oriented assay, and whether parental follow-up has already happened. A de novo label is a starting point, not the last word.
What it cannot prove
A de novo-looking RET result cannot by itself prove that relatives are unaffected forever. It also cannot rule out mosaicism without a proper review of the report and, when needed, testing of the right parent or tissue. The safest interpretation is that the result lowers the chance of simple inherited transmission, but it does not erase follow-up questions.
Questions to ask
- Is the RET variant classified as pathogenic, likely pathogenic, or uncertain?
- Was the result from germline testing, tumor testing, or a consumer test needing clinical confirmation?
- Have biological parents, siblings, and children been discussed separately?
- Who is coordinating MEN2 surveillance, calcitonin questions, thyroid planning, and family communication?
When follow-up matters more
Follow-up matters more when a hereditary tumor result could change who in the family should be tested, when tumor-only and germline questions are still mixed together, or when a specialist plan should decide surveillance timing rather than a single lab result. Genetics counseling helps keep the finding tied to the actual family question.
FAQ
What does de novo mean for a RET variant?
It means the variant appears to have arisen new in the person tested rather than being clearly inherited from a parent.
Does de novo mean the family has no risk?
No. It can change which relatives are most likely affected, but children and sometimes parents still need a careful discussion.
Why does parent testing matter?
Parent testing helps confirm whether the variant is truly de novo or whether mosaicism or inheritance could still be part of the story.
Can mosaicism make a de novo-looking result more complicated?
Yes. Mosaicism can mean the variant is present in only some cells, so sample type and confirmatory review matter.
Should children be tested automatically?
Not automatically. The exact variant, the inheritance pattern, and specialist guidance should decide whether children need testing.
What should I ask the genetics team?
Ask whether the result is truly de novo, whether mosaicism was considered, and how MEN2 surveillance and family testing should be coordinated.