First Reported Case of Dual Hereditary Gelsolin and Transthyretin Wild-Type Cardiac Amyloidosis in a Man in his late 40s

Abstract

Amyloidosis is a group of disorders characterized by abnormal deposition of amyloid proteins in various tissues and organs, leading to progressive organ dysfunction. With over 40 precursor proteins linked to amyloid formation, identification of the amyloid type is critical to guide treatment. A man in his late 40s presenting with heart failure was diagnosed with cardiac amyloidosis based on an endomyocardial biopsy. Amyloid typing performed on the heart biopsy at Mayo Clinic Laboratories using differential laser microdissection and shotgun proteomics with mass spectrometry reported gelsolin amyloid (AGel) deposits exclusively in the vasculature and transthyretin amyloid deposits exclusively within the interstitium. Mutational analysis identified a novel p.Y474N in the gelsolin gene, establishing a diagnosis of hereditary AGel amyloidosis. Transthyretin gene mutations were absent, confirming a concurrent diagnosis of acquired transthyretin wild-type amyloidosis. The patient, who had been treated with guideline-directed medical therapy since his initial presentation, was subsequently started on tafamidis, with subsequent improvement of his ejection fraction after 6-7 months. Although rare, 2 different amyloid types may arise in the same anatomic site. Identification of all amyloid types is crucial for optimal patient management. In this case, the co-existence of 2 rare amyloid types (AGel with a novel mutation coupled with ATTRwt in a patient under 50 years of age) in mutually exclusive anatomic compartments in the same cardiac biopsy raises the possibility that an unknown systemic factor may play a role in amyloidogenesis in dual amyloid cases.

Forty-two different human amyloid precursor proteins have been described to date. The clinical manifestations of amyloidosis are largely dictated by the specific precursor protein and the organs that are impacted. Transthyretin wild-type amyloidosis (ATTRwt) is a common, slowly progressive form of systemic amyloidosis with a median age at diagnosis of 75 years and a significant male predominance. Destabilization of the transthyretin tetramer results in the formation of monomers with amyloidogenic properties that aggregate into insoluble amyloid fibrils, primarily affecting the heart. The ATTRwt often presents with cardiac symptoms, with two-thirds of patients experiencing heart failure at diagnosis. Additional features may include a history of carpal tunnel syndrome, lumbar spinal stenosis or bicep tendon rupture.¹ In contrast, hereditary systemic gelsolin (AGel) amyloidosis is rare and is usually characterized by a triad of neurological, ophthalmological, and dermatological manifestations. The AGel often manifests at 25-30 years with corneal lattice dystrophy, followed by slowly progressive cranial neuropathy and cutis laxa.² Two recurrent gelsolin mutations (p.Asp214Asn [D187N] and p.Asp214Thr [D187T]) reside in a calcium binding domain that compromises the calcium binding. The resultant unfolded conformation leads to aberrant proteolysis, ultimately resulting in the generation of amyloidogenic fragments that deposit systemically with 100% penetrance.³ Here, we report a male in his late 40s with amyloidosis found to have the co-existence of ATTRwt and hereditary AGel in mutually exclusive cardiac anatomic compartments. A signed statement of informed consent has been obtained from the patient described in this report.

Case Presentation

A male in his late 40s presented with heart failure with biventricular dysfunction. He had no family history of cardiac disease; however, he did have a personal and family history of carpal tunnel syndrome. He denied symptoms of cranial neuropathy. No arrhythmias were present. Echocardiography identified increased ventricular wall thickness and systolic dysfunction with a restrictive diastolic pattern. Cardiac magnetic resonance imaging reported an ejection fraction of 19%, with late gadolinium enhancement indicating a diffuse infiltrative process involving the left ventricle, right ventricle, and left atrium. Laboratory studies for monoclonal proteins and pyrophosphate (PyP) scan performed to evaluate for ATTR were both negative. Coronary angiography with optical coherence tomography revealed multi-vessel neointimal hyperplasia with fibrous caps, suggestive of vasculopathy. An endomyocardial biopsy, which was performed due to high clinical suspicion despite the negative PyP scan, showed involvement by amyloidosis. Formalin-fixed paraffin embedded tissue was subsequently submitted to Mayo Clinic Laboratories for amyloid typing by mass spectrometry.^4,5

Congo red staining of the endomyocardial biopsy reported interstitial and vascular amyloid deposits (Figure 1A), which were differentially dissected using laser microdissection (LMD) (Figure 1B). The microdissected interstitial and vascular amyloid samples, which were independently extracted, processed, and analyzed utilizing mass spectrometry as previously described,⁴ each contained an area of 60,000 square microns, which required microdissection of multiple vascular or interstitial deposits for each sample. Examples of microdissections of single vascular and interstitial deposits are shown in Figure 1B. Although both the interstitial and vascular amyloid deposits contained abundant amyloid signature proteins, including serum amyloid P-component, apolipoprotein A IV, and apolipoprotein E, each anatomic compartment displayed proteomic features of a single amyloid type: exclusively AGel in the vascular deposits, and exclusively ATTR in the interstitial deposits (Figure 1C). Routine bioinformatics, which detects abnormal peptide sequences corresponding to known amyloidogenic amino acid substitutions, did not identify an amino acid variant in either TTR or gelsolin (GSN).^5,6 However, a novel bioinformatics analysis configured to analyze the raw data for unexpected posttranslational modifications and single nucleotide polymorphisms using the DirecTag-TagRecon-IDPicker pipeline⁷ identified a novel missense mutation in GSN (p.Y474N) (Figure 2A). No TTR mutations were identified by this method. Sanger sequencing of DNA extracted from peripheral blood confirmed the presence of p.Y474N identified by mass spectrometry (Figure 2B) and verified the absence of variants in TTR, supporting the diagnoses of both AGel with a novel p.Y474N mutation and ATTRwt.

Figure 1.

Brightfield (A) and fluorescent (B) Congo Red images illustrate separate anatomic compartments from the endomyocardial biopsy captured during laser microdissection. Sample 1 consists of vascular plaques, whereas sample 2 consists of interstitial deposits. Single representative examples of vascular and interstitial deposits are reported in Figure 1(B) but numerous vascular and interstitial deposits were microdissected to obtain the minimum of 60,000 square microns required for analysis of each sample. The samples were processed and analyzed independently. (C) Scaffold display of the amyloid proteome from the vascular and interstitial samples. Numbers in green boxes represent number of MS/MS matches to respective protein. Universal amyloid proteins SAP, APOA-IV, and APOE are highlighted with dual stars, and type-specific markers (gelsolin and transthyretin) are highlighted with blue stars. Both samples contain abundant universal amyloid proteins. However, sample 1 (vascular) contains abundant gelsolin spectra in the absence of transthyretin spectra, whereas sample 2 (interstitial) contains abundant transthyretin spectra in the absence of gelsolin. These findings confirm the presence of pure AGel in vascular deposits and pure ATTR in interstitial deposits.

Figure 2.

(A) MS/MS spectrum corresponding to the GSN p.Y474N mutant peptide is shown. Red asterisks mark the amino acid sequence change corresponding to the genetic mutation. Evidence of the mass shift was observed in both the b and y ion series. (B) Sanger sequencing of exon 10 of GSN (NM_000039.1) in the peripheral blood revealed a heterozygous c.1420 T>A nucleotide transversion, confirming the presence of a novel p.Y474N missense variant.

Discussion

Amyloidosis is an uncommon diagnosis, and most patients are diagnosed with a single amyloid type. Although dual amyloid cases have been previously reported, most patients show involvement by ATTR and AL, which are the 2 most common amyloid types.⁸ Herein we report the first case of cardiac amyloidosis due to both wild-type transthyretin and a novel variant in the gelsolin gene (p.Y474N).

Many aspects of this case are noteworthy. First, it represents an amalgamation of rare events. Both amyloid types would be considered rare, even if identified as a sole amyloid type. The Mayo Tissue Proteomics database of 49,114 amyloid specimens from various anatomic sites typed by mass spectrometry proteomics (LC-MS/MS) from January 2009 to May 2024 was queried. Although ATTRwt is a common form of cardiac amyloidosis, it primarily involves older individuals and is rare in patients less than 50 years of age (0.3% of all cardiac ATTRwt cases). Similarly, AGel is a rare amyloid type that usually causes corneal lattice dystrophy, cranial neuropathy, cutis laxa, and renal failure but seldom involves the heart (0.02% of all cardiac amyloid cases in our database). Interestingly, the 3 other cardiac AGel cases in our database all showed perivascular amyloid deposits. The PyP negativity is unusual in the setting of cardiac ATTRwt but is a well-known phenomenon in certain hereditary types of ATTR (eg p.F84L). The PyP features of cardiac AGel amyloidosis are not known, but it is possible that the AGel rather than the ATTR was the dominant component of the cardiac amyloidosis, thus resulting in a negative PyP scan. Furthermore, a novel variant was identified in the gelsolin gene (p.Y474N), which is inherently rare.

Second, the 2 amyloid types involve different anatomic compartments within a single organ. Differential LMD coupled with untargeted shotgun proteomics facilitated unbiased and unequivocal identification of AGel exclusively in cardiac vasculature and ATTRwt exclusively in cardiac interstitium. Although a recent case report described a 57-year-old man with dual amyloid diagnoses of AGel and ATTRv (transthyretin variant amyloidosis), the 2 amyloid types involved separate anatomic sites, with AGel in fat aspirate and descending colon and ATTRv in the heart.⁹ Other dual amyloid cases have been found to have a hybrid of 2 amyloid types within a single anatomic compartment.⁸

Third, a novel AGel mutation (p.Y474N) was present. In a recent case series of 15 patients with AGel, 14 had the recurrent p.Asp214Asn (p.Asp187Asn) together with cranial neuropathy, which is a classic manifestation of AGel. However, one patient, a 38-year-old woman diagnosed with AGel in breast tissue, had a different GSN amino acid change (p.Y474H [Y447H]), at the same position presented in this report. Both this patient and our patient had carpal tunnel syndrome but did not have the classic manifestations of AGel (ie corneal lattice dystrophy, cranial neuropathy, and cutis laxa).^9,10 Furthermore, the patient in the case report described above also had a novel gelsolin mutation (p.Ala578Pro). Although he had paresthesia in his hands, he lacked the slowly progressive cranial neuropathy characteristic of patients with classic AGel.⁹ These findings raise the possibility that novel AGel mutations may be associated with more diverse clinical phenotypes.

Conclusion

We report the first case of cardiac amyloidosis with 2 amyloid types involving separate anatomic compartments, hereditary AGel amyloidosis with a previously unreported mutation (p.Y474N) in blood vessels and ATTRwt amyloidosis in the interstitium. Unequivocal report of the 2 amyloid types was facilitated by advanced proteomic techniques, including LMD technology followed by mass spectrometry-based amyloid typing and state of the art bioinformatics analysis. Both diagnoses are vanishingly rare, cardiac AGel is exceptionally uncommon, especially when linked to a previously unrecognized mutation, and cardiac ATTRwt is highly unusual in patients less than 50 years of age. The co-existence of these 2 rare amyloid types in mutually exclusive anatomic compartments in the same biopsy raise the possibility that an unknown systemic factor may play a role in amyloidogenesis in dual amyloid cases. Additional studies to further investigate this intriguing concept are warranted.

Potential Competing Interests

The authors report no competing interests.