A case of Carney triad complicated by renal cell carcinoma and a germline SDHA pathogenic variant

Background

Succinate dehydrogenase (SDH) is a heterotetrameric enzyme with dual roles in the mitochondrial citric acid cycle and electron transport chain. Germline inactivating SDHB, SDHC, and SDHD pathogenic variants were implicated in the pathogenesis of paragangliomas (PGLs) and pheochromocytomas (PHEOs) in the early 2000s (1). In 2007, inherited gastrointestinal stromal tumors (GISTs) were additionally associated with SDHB, SDHC, and SDHD pathogenic variants in patients with Carney dyad (CD), a rare autosomal-dominant disorder with co-existing PGL and GISTs) (1). It wasn’t until 2010 that SDHA disease-causing variants were implicated in hereditary PHEOs/PGLs (2, 3).

Carney triad (OMIM# 604287) was originally described by Dr J. Aidan Carney in 1977 and is a distinct entity from CD, presenting as an association of PGLs, GISTs, and pulmonary chondromas (CHOs, Fig. 1) (4). PHEOs have also been associated with the disease, but are not considered part of the ‘triad’. Carney triad is sporadic with a female predilection and is typically diagnosed at a young age (median 18 years old) (5). The disease is predominantly associated with somatic DNA hypermethylation of SDHC as demonstrated in tumor tissue from these patients (6). However, in rare cases, SDHA, SDHB, SDHC, or SDHD (collectively referred to as SDHx) germline pathogenic variants have been reported in patients with Carney triad (2, 3). It is hypothesized that a predisposing germline disease-causing event in a non-SDHx gene is required for SDHx pathogenic variants to cause Carney triad (3).

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The presence of pulmonary chondromas discerns Carney triad and Carney dyad. (A) A diagnosis of Carney triad requires co-existing paraganglioma (PGL), pulmonary chondroma, and gastrointestinal stromal tumor (GIST) with either a germline pathogenic variant in SDHx or SDHC locus-specific hypermethylation. (B) In contrast, Carney dyad is the association of PGL and GIST with a germline pathogenic variant in SDHx.

Citation: Endocrinology, Diabetes & Metabolism Case Reports 2021, 1; 10.1530/EDM-20-0170

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Pathogenic variants in SDHx have since been associated with several neoplasia syndromes (7). The three-P association (3PAs), which includes co-existing pituitary adenomas, PGLs, and PHEOs, has been associated with an SDHx disease-causing variant in approximately 43% of cases; the incidence increases to 75% in cases where the patient has a family history of PHEOs/PGLs (8). Pathogenic variants in SDHD and SDHC have been implicated in Cowden syndrome, a multiple-neoplasia disorder characterized by benign and malignant breast, thyroid, and endometrial tumors (7, 9). In 1979, comorbid neuroblastoma, PHEO, and renal cell carcinoma (RCC) were reported in a single patient and later genetic analysis of affected family members implicated an SDHB pathogenic variant (10). It has since been estimated that 1-5% of patients with RCC harbor a disease-causing variant in SDHB or SDHD (9).

In a handful of cases, germline SDHA pathogenic variants have been reported in patients with RCC, including a case with a co-existing GIST (11). In the current case, we report a patient with a germline SDHA pathogenic variant in the setting of Carney triad complicated by RCC. The patient is one of the ten patients previously reported (patient number 4) in a review on SDHA-related metastatic PHEOs/PGLs (12).

Case presentation

A 57-year-old male diagnosed with hypertension at age 49, presented with a gradual increase in blood pressure over a period of 12 months. Additional past history included coronary artery disease, hyperlipidemia, and tobacco use. Family history included hypertension, premature coronary artery disease, stroke, and prostate cancer, however, there was no family history of other tumors or endocrinopathies. He was initially started on Candesartan 4 mg daily for treatment of hypertension, however, his hypertension persisted resulting in a gradual increase to 32 mg daily and the addition of hydrochlorothiazide (12.5 mg daily), with the eventual switch to telmisartan 40 mg daily and amlodipine 5 mg daily. For seven years following his diagnosis of hypertension, the patient experienced episodic increases in blood pressure, to a systolic pressure greater than 180 mmHg associated with a tight band sensation around his forehead lasting half a day. These episodes occurred every 1–2 months and required emergency care on two occasions. He was referred to an endocrinologist for further evaluation.

Investigation

Clinical and biochemical evaluation for endocrine causes of secondary hypertension was performed including for PHEO/PGL and primary aldosteronism, and revealed plasma metanephrines and 24-h urine catecholamines and metanephrines within the normal range. An elevated aldosterone-to-renin ratio (55) was noted and the patient underwent a saline suppression test which was not consistent with primary aldosteronism (4 h serum aldosterone <5 ng/dL). Without apparent signs of endocrine-related hypertension, the episodic blood pressure exacerbations were believed to be anxiety related. He also underwent a 1 mg overnight dexamethasone suppression test that was not consistent with hypercortisolemia (serum cortisol after dexamethasone <1.8 µg/dL).

Abdominal CT revealed a left adrenal adenoma, a 5.1 cm para-aortic mass (Fig. 2A), and a right renal superior pole lesion measuring 2.5 cm, which was suspicious for a carcinoma (Fig. 2B). ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG, arrow in Fig. 2C) and ¹⁸F-fluorodeoxyglucose-PET (¹⁸F-FDG-PET, arrow in Fig. 2D) scans were performed, which suggested the para-aortic mass to be consistent with a PGL. Additionally, ¹⁸F-FDG uptake was noted in the gastroesophageal region (dashed arrow in Fig. 2D). The left adrenal mass was not associated with ¹²³I-MIBG (Fig. 2C) or ¹⁸F-FDG activity (Fig. 2D) and was not suspected to be hormonally active per prior biochemical testing.

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In this figure, 57-year-old-male, axial images of contrast-enhanced CT (A and B) demonstrates a para-aortic mass (arrow, A) and right superior pole lesion (arrowhead, B). The anterior planar image of 123I-metaiodobenzylguanidine demonstrates uptake in para-aortic mass (arrow, C) which is also seen on the anterior maximum intensity projection of 18F-fluorodeoxyglucose (18F-FDG) PET scan (arrow, D). The 18F-FDG PET scan also demonstrates uptake in gastroesophageal lesion (dashed arrow, D).

Citation: Endocrinology, Diabetes & Metabolism Case Reports 2021, 1; 10.1530/EDM-20-0170

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Treatment

The patient underwent an uncomplicated surgical resection of the PGL and a partial right nephrectomy. The gastroesophogeal region where ¹⁸F-FDG uptake (dashed arrow in Fig. 2D) had been noted was inspected and two subcentimeter nodules were found on the wall of the stomach. A subsequent gastroscopy was performed to resect the nodule nearest the gastroesophogeal junction.

Outcome and follow-up

The resected PGL (arrows in Fig. 2A, B, C and D) measured 4.2 cm in length and immunohistochemisty (IHC) staining was performed for SDHA and SDHB, which was positive and negative, respectively. Plasma 3-methoxy-tyramine levels were performed prior to surgery and were not elevated (< 200 pmol/L). Pathology from the renal lesion was consistent with a 2.3 cm conventional clear cell renal carcinoma, and did not demonstrate eosinophilic cytoplasm or vacuolated cytoplasm which are typically associated with SDH-deficient RCC (13) (Fig. 3A, B, C and D). Of note, IHC staining was positive for both SDHB and SDHA for the RCC (Fig. 3C and D). SDHC hypermethylation was not detected in the PGL, GIST, or RCC. The ¹⁸F-FDG-avid nodule (dashed arrow, Fig. 2D) resected from the gastroesophogeal junction was consistent with a GIST, which stained positive for SDHA and negative for SDHB on IHC. A 3-month post-operative endoscopic ultrasound was remarkable for two submucosal lesions (1.2 cm and 5 mm) at the gastroesophogeal junction. Fine needle biopsies were taken and pathology was inconclusive for GISTs. Chest CT demonstrated a right middle lobe lung lesion suspicious for CHO, although no biopsy was performed.

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Hematoxylin and eosin stain sections show a classical renal cell carcinoma, clear cell type, low grade (ISUP nuclear/nucleolar grade 2, (A and B) 200× and 400× magnification, respectively). SDHA (C) and SDHB (D) immunohistochemical stains exhibit positive, granular, cytoplasmic staining (preserved expression, 400×).

Citation: Endocrinology, Diabetes & Metabolism Case Reports 2021, 1; 10.1530/EDM-20-0170

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The aforementioned findings led to a diagnosis of Carney triad. Initial genetic screening for SDHB, SDHC, and SDHD pathogenic variants was unremarkable, however, follow-up sequencing of SDHA revealed a germline heterozygous pathogenic variant (c.91 C>T, p.R31X). Whole-exome sequencing did not reveal pathogenic variants in other genes associated with RCC and chromosome analysis by comparative genomic hybridization (CGH) was normal. This variant has previously been reported in a patients with hereditary PHEO/PGL and results in loss of function of SDHA (14). DNA sequencing of the RCC, GIST, and PGL did not indicate loss of heterozygosity (LOH) at the variant region of interest. The patient’s daughter, who is in her third decade of life, has inherited the pathogenic variant in SDHA, however, she had no evidence of disease. She was counseled to undergo annual biochemical catecholamine and metanepherine screening and whole body scans for the appearance of Carney triad-related tumors.

The patient was advised to obtain bilateral renal ultrasound, esophagogastroduodenoscopies, alternating whole-body CT and MRI annually, and functional imaging every 2 years as surveillance for recurrence and appearance of tumors associated with Carney triad. Two years after surgical resection of the PGL, functional imaging revealed a mediastinal lesion on both ¹⁸F-FDG-PET/CT and ⁶⁸Ga-DOTATATE-PET/CT scans (Fig. 4A and B, dashed arrows), and a left carotid body tumor which was only detected on ⁶⁸Ga-DOTATATE (Fig. 4B, arrow). Both lesions remained stable at 4 years after initial surgery (Fig. 4C and D, ¹⁸F-FDG and ⁶⁸Ga-DOTATATE, respectively). His hypertension was well controlled with telmisartan 40 mg and amlodipine 5 mg combination daily.

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The follow-up functional imaging with 18F-FDG (A and C) and 68Ga-DOTATATE (B and D) PET imaging after 2 (A and B) and 4 (C and D) years of paraganglioma surgery demonstrates stable mediastinal lesion (dashed arrows, A, B, C and D) on both 18F-FDG and 68Ga-DOTATATE PET scans whereas left carotid body tumor only on 68Ga-DOTATATE (arrows, B and D). Both the lesions were not localized on anatomic imaging by MRI.

Citation: Endocrinology, Diabetes & Metabolism Case Reports 2021, 1; 10.1530/EDM-20-0170

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Discussion

Carney triad is a rare multiple neoplasia disorder characterized by comorbid PGLs, GISTs, and CHOs. Although not considered part of the ‘triad’, PHEOs have also been associated with the disease (1). SDH enzymatic activity was found to be decreased in tumors from these patients, however, SDHx pathogenic variants had not been reported (3). Further studies of SDH-deficient tumors from patients with Carney triad indicated SDHC locus-specific hypermethylation may be causative of diminished SDH enzymatic activity (15). Our group has reported differential DNA methylation of SDHB and SDHC, without notable methylation of SDHA or SDHD. Interestingly, while the methylation pattern of SDHC is sequence-specific for Carney triad and consistent between patients, methylation of SDHB when seen in the triad has no apparent pattern, and is similar to that seen in other SDH-deficient tumors (6). Thus, SDHC-sequence-specific methylation is considered the molecular signature for Carney triad and is used diagnostically in our laboratory.

Although the majority of Carney triad patients have site-specific SDHC methylation, approximately 10% of cases harbor pathogenic germline variants in SDHx (2). It is hypothesized a predisposing pathogenic germline event in a non-SDHx gene, in addition to the SDHx disease-causing variant, is required to cause the disease (3). Interestingly, half of the reported Carney triad patients with SDHx pathogenic variants were males, in contrast to the associated female predilection. No other phenotypic differences were noted. Additionally, the variants were inherited, although with incomplete penetrance (2). In our case, we report a male patient with an inactivating SDHA pathogenic variant, which was inherited by his daughter, who has not developed any manifestations of Carney triad to date. Considering the low penetrance of SDHA disease-causing variants, estimated at less than 5% in patients with PHEO/PGL’s, it is unclear if the patient’s daughter will develop tumors associated with Carney triad (16). Additionally, it is important to acknowledge we are unable to confirm the SDHA variant is causative of the patient’s phenotype. It is possible our testing failed to identify a variant in one of the other SDHx genes. Given the normal SDHA IHC and low penetrance of SDHA pathogenic variants, we hypothesize this variant may be only one of the SDHx drivers involved in the Carney triad phenotype.

The SDH enzyme is a membrane-associated mitochondrial protein complex that functions as a key component of the electron transport chain. Although impaired aerobic respiration has been consistently observed in neoplastic cells, it has largely been regarded as an association rather than a cause of disease. However, the implication of SDHx pathogenic variants in hereditary PHEOs/PGLs altered this notion and has led to the classification of SDHx as tumor suppressor genes (17). Both the PGL and GIST in our patient were SDH-deficient, as indicated by negative SDHB IHC staining, which is consistent with previous reports of Carney triad patients harboring SDHx pathogenic variants (2).

Both familial and sporadic RCC have been associated with SDHx pathogenic variants, most commonly affecting SDHB or SDHD (9, 18). IHC staining for SDHB is often used to screen for the presence of SDH-deficient tumors; the presence of SDHx pathogenic variants or SDH epigenetic alterations will result in diminished SDHB protein levels. Interestingly, in the present case, SDHB and SDHA staining were positive in the RCC in contrast to the other associated tumors which were SDHB negative. The preserved expression of SDHA and SDHB in conjunction with histological characteristics consistent with clear cell renal carcinoma indicates this tumor may be an incidental finding. In the patient harboring a pathogenic variant in SDHA reported by Jiang et al., IHC staining of the renal tumor was positive for SDHA and negative for SDHB. Additionally, LOH was not detected in the RCC which is in agreement with our findings. Our report provides further support to the increasing evidence that SDHx pathogenic variants may predispose patients to develop renal neoplasms (19), although the exact role of SDHA disease-causing variants in the pathogenesis of RCC remains unknown.

In conclusion, we report a novel presentation of a germline inactivating SDHA pathogenic variant in a patient with Carney triad complicated by RCC. Although we believe the SDHA disease-causing variant is one of the drivers of the patient’s Carney triad phenotype, it is unclear if this variant is causative of the RCC. A small number of cases have reported SDHA disease-causing variants co-existing with RCC, including in a patient with comorbid GIST (11). However, to the knowledge of the authors, none of the reported cases involved a patient with Carney triad.

Declaration of interest

Constantine Stratakis holds patents on the PRKAR1A, PDE11A, and the GPR101 genes and his laboratory is the recipient of past and ongoing research grant support from Pfizer, Inc. Karel Pacak and Constantine A. Stratakis are Senior Editors of Endocrinology, Diabetes and Metabolism Case Reports. Karel Pacak and Constantine A Stratakis were not involved in the review or editorial process for this paper, on which they are listed as authors.

Funding

This work was supported by the research project Z01-HD008920 (Principal Investigator: Constantine A Stratakis) of the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD), National Institutes of Health (NIH), Bethesda, MD, USA.

Patient consent

Written informed consent has been obtained from the patient for publication of the submitted article and accompanying images.

Author contribution statement

All co-authors contributed equally.