Short answer
SDHx genetic testing looks for inherited variants in SDHA, SDHB, SDHC, SDHD, or SDHAF2 when paraganglioma or pheochromocytoma suggests a hereditary syndrome. The exact gene can change surveillance, parent-of-origin counseling, and how strongly the team worries about metastatic risk, multifocal disease, or family testing. Tumor-only SDHx findings still need germline confirmation before relatives are managed as at risk.
How testing is usually framed
| Finding | Testing question | Why it matters |
|---|---|---|
| Paraganglioma or pheochromocytoma at any age | Should hereditary PGL/PCC panel testing be considered? | Most PPGL cases deserve a genetics review. |
| Extra-adrenal or multifocal disease | Which SDHx gene best fits the pattern? | Tumor location and multiplicity can help prioritize the gene list. |
| SDHB result | Does metastatic-risk counseling need extra attention? | SDHB often gets more follow-up scrutiny. |
| SDHD or SDHAF2 family variant | Does parent-of-origin inheritance affect risk counseling? | Some SDHx syndromes show parent-of-origin effects. |
Gene-specific clues
| Gene clue | Why the team notices it | What it can change |
|---|---|---|
| SDHB | Can be associated with higher concern for metastatic behavior or extra-adrenal disease | Follow-up often includes closer imaging and counseling |
| SDHD / SDHAF2 | Parent-of-origin effects can matter in family history | Inheritance counseling may be more nuanced for relatives |
| SDHA | May show lower penetrance or incidental findings in some families | Family testing and surveillance still matter, but context is key |
| Tumor-only SDHx finding | The change could be somatic rather than inherited | Germline confirmation is usually needed before cascade testing |
What the result can change
A pathogenic SDHx result can change tumor surveillance, biochemical testing, imaging strategy, family testing, and interpretation of related tumor risks such as gastrointestinal stromal tumor or renal cancer in selected genes. The result can also change whether the team thinks in terms of one tumor event or a broader inherited syndrome.
Questions to ask
- Was the test germline, tumor-only, or paired tumor-normal testing?
- Which genes were included beyond SDHA, SDHB, SDHC, SDHD, and SDHAF2?
- Does the result affect relatives, surveillance intervals, or imaging from head and neck through abdomen and pelvis?
- How should a VUS be followed without treating it as a confirmed inherited syndrome?
What the result still cannot prove
An SDHx result can point toward hereditary risk, but it does not by itself tell you which tumors will occur, how aggressive they will be, or whether another gene or mosaic pattern is part of the story.
When follow-up matters more
Follow-up matters more when a paraganglioma or pheochromocytoma 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 do SDHx genes do?
SDHx genes help code for parts of the succinate dehydrogenase complex. When they carry pathogenic variants, they can be linked to hereditary paraganglioma-pheochromocytoma patterns.
Which SDHx gene raises the most metastatic concern?
SDHB often gets extra attention because of its stronger association with metastatic behavior in PPGL, but the exact tumor pattern still matters.
Why does parent-of-origin matter for SDHD or SDHAF2?
Some SDHx syndromes show parent-of-origin effects, so the family history can matter even when the same variant is shared.
Does a tumor-only SDHx finding count as inherited risk?
No. A tumor-only finding may be somatic, so germline testing is usually needed before relatives are treated as at risk.
What if blood testing is negative?
A negative blood test lowers the chance of an inherited SDHx variant, but it does not always end the question if tumor testing or the clinical picture still suggests a hereditary syndrome.
Who should review the result?
A genetics professional or endocrine tumor specialist is often helpful because the gene, tissue type, and family history all matter.
Related guides: VHL genetic testing, MEN1 genetic testing, hereditary cancer genetic testing, and genetic counselor guide.