What are the next steps if genetic testing for amyloidosis is negative?

What to Do if Genetic Testing is Negative for Amyloidosis

A negative genetic test does not exclude amyloidosis—it only rules out hereditary (variant) ATTR amyloidosis, and you must proceed with comprehensive evaluation to identify wild-type ATTR or AL amyloidosis through tissue biopsy, amyloid typing, and monoclonal protein assessment. 1, 2

Understanding What Negative Genetic Testing Means

• Genetic testing only identifies TTR gene mutations—a negative result confirms wild-type (senile) ATTR amyloidosis rather than hereditary ATTR, but does not exclude amyloidosis altogether 1
• Wild-type ATTR amyloidosis is actually more common than hereditary forms, particularly in elderly patients, so negative genetic testing is frequently encountered 1
• Genetic testing provides no information about AL amyloidosis, which is the most common form of systemic amyloidosis in developed countries 3

Essential Next Steps After Negative Genetic Testing

1. Confirm Amyloid Presence and Type Through Tissue Biopsy

• Tissue biopsy with Congo red staining remains the gold standard for confirming amyloid deposits, showing characteristic apple-green birefringence under polarized light 2, 3
• Mass spectrometry (LC-MS/MS) is the gold standard for amyloid typing with 88% sensitivity and 96% specificity, and should be performed on all Congo red-positive samples 2
• If mass spectrometry is unavailable, transfer pathological samples to an experienced reference laboratory for definitive typing 2
• Consider less invasive biopsy sites first (abdominal fat aspiration, bone marrow) before proceeding to organ biopsy, though fat pad biopsy has only 15% sensitivity for wild-type ATTR 1
• Endomyocardial biopsy has approximately 100% specificity and sensitivity for detecting cardiac amyloid deposits and should be performed if non-invasive sites are negative but clinical suspicion remains high 1

2. Complete Monoclonal Protein Workup to Exclude AL Amyloidosis

• Perform serum free light chain (sFLC) assay, serum immunofixation electrophoresis (SIFE), and urine immunofixation electrophoresis (UIFE) to identify plasma cell disorders 2
• Do not rely solely on serum/urine protein electrophoresis (SPEP/UPEP) as these have lower sensitivity, especially in AL amyloidosis where monoclonal protein levels are typically low 2
• Bone marrow biopsy can demonstrate clonal proliferation of lambda or kappa-producing plasma cells if AL amyloidosis is suspected 2
• This workup is critical because over 10% of patients with monoclonal gammopathy can have ATTR deposits rather than AL, making proper typing essential to avoid inappropriate treatment 2

3. Utilize Non-Invasive Imaging When Appropriate

• Technetium-99m bone scintigraphy (DPD, PYP, or HMDP tracers) can diagnose ATTR cardiac amyloidosis non-invasively if no monoclonal protein is detected 1
• If monoclonal protein IS detected (even MGUS), endomyocardial biopsy is necessary to definitively distinguish between AL and ATTR cardiac amyloidosis, as bone scintigraphy alone is insufficient 1
• Cardiac MRI with gadolinium can assist in evaluation and has detected amyloid in previously unsuspected patients 4
• Some ATTR variants (p.Phe84Leu, p.Ser97Tyr) may show negative bone scintigraphy, requiring alternative diagnostic approaches 1

4. Perform Comprehensive Organ Assessment

• Systematically evaluate all potentially affected organs as this is critical for determining treatment strategies and prognosis 2
• Echocardiography should be performed in all patients with confirmed amyloidosis to assess cardiac involvement 2
• Assess renal function and proteinuria, as renal manifestations affect two-thirds of patients at presentation 2, 3
• Evaluate for peripheral neuropathy, autonomic dysfunction, and other systemic manifestations depending on clinical presentation 1

Critical Diagnostic Algorithm

If genetic testing is negative:

1. First, determine if monoclonal protein is present through sFLC, SIFE, and UIFE 2

   • If monoclonal protein detected: Proceed to tissue biopsy with mass spectrometry typing to distinguish AL from ATTR (cannot rely on imaging alone) 1, 2
   • If no monoclonal protein detected: Bone scintigraphy can non-invasively diagnose ATTR cardiac amyloidosis; if positive, confirms wild-type ATTR 1

2. If bone scintigraphy is negative or equivocal (Perugini score 1), proceed to endomyocardial biopsy if clinical suspicion remains high 1

3. If fat pad or bone marrow biopsy is negative, do not stop—these have high false-negative rates (85% for wild-type ATTR in fat pad), and biopsy of clinically affected organ is imperative 1

Common Pitfalls to Avoid

• Never assume negative genetic testing excludes amyloidosis—it only excludes hereditary ATTR 1, 2
• Do not assume AL amyloidosis in patients with monoclonal gammopathy without proper amyloid typing, as ATTR can coexist with MGUS 2
• Avoid relying on a single negative biopsy from non-affected sites (fat pad, bone marrow) when clinical suspicion is high—proceed to biopsy of clinically involved organ 1
• Do not use immunohistochemistry alone for typing—it is less reliable than mass spectrometry and can lead to misdiagnosis 2, 4
• Recognize that genetic testing after mass spectrometry may still be warranted as LC-MS/MS can fail to detect certain mutations (particularly homozygous V122I) in 16% of cases 5

Multidisciplinary Collaboration

• Collaborate with hematology for suspected AL amyloidosis to guide chemotherapy targeting aberrant plasma cells 2
• Cardiology consultation is essential for monitoring cardiac decompensation, as standard heart failure medications (calcium channel blockers, beta-blockers, ACE inhibitors) are ineffective or dangerous in amyloid heart disease 2, 3
• Diuretics are the mainstay of heart failure therapy in patients with cardiac amyloidosis 2