Analysis of GNAS1 and PRKAR1A gene mutations in human cardiac myxomas not associated with multiple endocrine disorders

Frequent protein kinase A regulatory subunit A1 mutations but no GNAS mutations as potential driver in sporadic cardiac myxomas

PURPOSE

Cardiac myxomas (CMs) are the second most common benign primary cardiac tumors, mainly originating within the left atrium. Approximately 5% of CM cases are associated with Carney Complex (CNC), an autosomal dominant multiple neoplasia syndrome often caused by germline mutations in the protein kinase A regulatory subunit 1A (PRKAR1A). Data concerning PRKAR1A alterations in sporadic myxomas are variable and sparse, with PRKAR1A mutations reported to range from 0% to 87%. Therefore, we investigated the frequency of PRKAR1A mutations in sporadic CM using next-generation sequencing (NGS). Additionally, we explored mutations in the catalytic domain of the Protein Kinase A complex (PRKACA) and examined the presence of GNAS mutations as another potential driver.

METHODS AND RESULTS

This study retrospectively collected histological and clinical data from 27 patients with CM. First, we ruled out the possibility of underlying CNC through clinical evaluations and standardized interviews for each patient. Second, we performed PRKAR1A immunohistochemistry (IHC) analysis and graded the reactivity of myxoma cells semi-quantitatively. NGS was then applied to analyze the coding regions of PRKAR1A, PRKACA, and GNAS in all 27 cases. Of the 27 sporadic CM cases, 13 (48%) harbored mutations in PRKAR1A. Among these 13 mutant cases, six displayed more than one mutation in PRKAR1A. Most of the identified mutations resulted in premature stop codons or affected splicing. In PRKAR1A mutant CM cases, the loss of PRKAR1A protein expression was significantly more common. In two cases with missense mutations, protein expression remained preserved. Furthermore, a single mutation was detected in the catalytic domain of the protein kinase A complex, while no GNAS mutations were found.

CONCLUSION

We identified a relatively high frequency of PRKAR1A mutations in sporadic CM. These PRKAR1A mutations may also represent an important oncogenic mechanism in sporadic myxomas, as already known in CM cases associated with CNC.

Somatic Mutation of PRKAR1A in Four Cases of Sporadic Cardiac Myxoma

BACKGROUND

Inactivating mutations of the protein kinase A regulatory subunit 1 alpha (PRKAR1A) gene have been reported in familial cardiac myxoma. However, the role of PRKAR1A mutation in sporadic cardiac myxoma remains unknown.

METHODS

Targeted next-generation sequencing (NGS) was performed to identify mutations with the PRKAR1A gene in seven cases of sporadic cardiac myxomas. Sanger sequencing of DNA from cardiac myxoma specimens and matched peripheral blood samples was performed to verify the identified mutations.

RESULTS

Targeted NGS of myxoma DNA revealed 232 single nucleotide variants in 141 genes and 38 insertion-deletion mutations in 13 genes. Six PRKAR1A mutations were identified in four of the seven cardiac myxoma cases, and thus, the PRKAR1A inactivating mutation rate was 57.2% (4/7, 95% CI=0.44-0.58, P<0.05). The PRKAR1A variants identified by Sanger sequencing analysis were consistent with those from the NGS analysis for the four myxoma specimens. All of the pathogenic PRKAR1A mutations led to premature termination of PRKAR1A, except for one synonymous mutation. Moreover, none of the nonsense and missense mutations found in the myxoma specimens were found in the matched peripheral blood samples.

CONCLUSION

Pathogenic mutations of the PRKAR1A gene were identified in tumor specimens from four cases of sporadic cardiac myxoma, and the absence of these mutations in peripheral blood samples demonstrated that they were somatic mutations.

Sudden death by massive systemic embolism from cardiac myxoma. Role of the clinical autopsy and review of literature

Cardiac myxoma is a rare benign neoplasm of the heart. Historically myxomas were incidental findings during autopsies, however improved imaging techniques made these diagnosis possible in living patients, making the surgical treatment of these neoplasms achievable. Cardiac myxomas may occur both sporadically and in a familial context, often in the clinico-pathological picture of the Carney complex. While familial myxomas occur in the context of well-known genetic mutations, the molecular etiology of sporadically occurring myxomas is still not completely clear. We must note however that many of the patients affected by myxomas are asymptomatic; when symptoms are present they are often nonspecific and hard to decipher, especially when referring to sporadically occurring heart myxomas. In this paper we describe a case of sudden death from the massive embolization of a left atrial cardiac myxoma. We also reviewed all the cases in the literature of sudden death from heart myxoma embolism. An accurate epidemiology of heart myxomas would be the key to outline the best treatment practices and the etiology of sporadic myxomas, nevertheless this target could only be pursued with a deep revaluation of the clinical autopsy as a fundamental diagnostic tool.

The curious case of Gαs gain-of-function in neoplasia

BACKGROUND

Mutations activating the α subunit of heterotrimeric Gs protein are associated with a number of highly specific pathological molecular phenotypes. One of the best characterized is the McCune Albright syndrome. The disease presents with an increased incidence of neoplasias in specific tissues.

MAIN BODY

A similar repertoire of neoplasms can develop whether mutations occur spontaneously in somatic tissues during fetal development or after birth. Glands are the most "permissive" tissues, recently found to include the entire gastrointestinal tract. High frequency of activating Gαs mutations is associated with precise diagnoses (e.g., IPMN, Pyloric gland adenoma, pituitary toxic adenoma). Typically, most neoplastic lesions, from thyroid to pancreas, remain well differentiated but may be a precursor to aggressive cancer.

CONCLUSIONS

Here we propose the possibility that gain-of-function mutations of Gαs interfere with signals in the microenvironment of permissive tissues and lead to a transversal neoplastic phenotype.

Microinsertions in PRKACA cause activation of the protein kinase A pathway in cardiac myxoma

Cardiac myxoma is the most common cardiac tumour. Most lesions occur sporadically, but occasional lesions develop in patients with Carney complex, a syndrome characterized by cardiac myxoma, spotty pigmentation, and endocrine overactivity. Two-thirds of patients with Carney complex harbour germline mutations in PRKAR1A, which encodes the type I regulatory subunit of protein kinase A (PKA). Most studies have not found a mutation in PRKAR1A in sporadic cardiac myxoma cases. Recent studies identified frequent mutations in PRKACA, which encodes the catalytic subunit of PKA, in cortisol-secreting adrenocortical adenoma cases. To determine whether the PRKACA mutation is involved in the tumourigenesis of cardiac myxoma, we performed Sanger sequencing of 41 specimens of sporadic cardiac myxoma to test for the presence of mutations in the coding regions and intron-exon boundaries of PRKACA. Mutations were identified in four cases (9.7%). In contrast to the point mutations identified in adrenocortical adenoma, all mutations were in-frame microinsertions of 18-33 bp clustered in exons 7 and 8. The mutated PRKACA proteins lost their ability to bind to PRKAR1A, and thereby lead to constitutive activation of the PKA pathway. Together with previous reports of PRKAR1A mutations in syndromic cardiac myxoma, our study demonstrates the importance of the PKA pathway in the tumourigenesis of cardiac myxoma. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

miR-218 suppresses cardiac myxoma proliferation by targeting myocyte enhancer factor 2D

Cardiac myxoma is the most common type of human heart tumor, yet the molecular mechanism is still poorly understood. In the present study, we found that the level of myocyte enhancer factor 2D (MEF2D), a key regulatory protein for cardiac development, was elevated in specimens of cardiac myxoma, and was positively associated with the proliferation of myxoma cells. MEF2D suppression reduced the proliferation of myxoma cells and its tumorigenicity. Cell cycle progression was also inhibited by MEF2D suppression. miR-218, which is downregulated in myxoma, suppressed MEF2D expression by targeting its mRNA 3'UTR. Altogether, we found that miR-218/MEF2D may be an effective target for myxoma treatment.

A case of comorbid myxoma and chronic lymphocytic leukemia: not just a coincidence?

Background. It is unclear why cardiac myxomas develop. We describe a case of comorbid myxoma and chronic lymphocytic leukemia (CLL) to offer insights into the tumor's pathophysiology. Case. A 56-year-old female with recurrent venous thromboembolism developed embolic stroke. Transesophageal echocardiogram showed a 1.7 × 1 cm sessile left atrial mass at the interatrial septum. Histopathology revealed myxoma with a B cell lymphocytic infiltrate suggestive of a low grade lymphoproliferative disorder. Bone marrow biopsy and flow cytometry of blood and the cardiac infiltrate supported the diagnosis of atypical CLL. She was followed clinically in the absence of symptoms, organ infiltration, or cytopenia. After eighteen months, she developed cervical and axillary lymphadenopathy. Biopsy confirmed B cell CLL/small lymphocytic lymphoma. She elected to undergo chemotherapy with fludarabine, cyclophosphamide, and rituximab, with clinical remission. Conclusions. The coexistence of two neoplastic processes may be coincidental, but the cumulative likelihood is estimated at 0.002 per billion people per year. A shared pathogenic mechanism is more likely. Possibilities include chronic inflammation, vascular endothelial growth factor A, shared genetic mutations, changes in posttranslational regulation, or alterations in other cellular signaling pathways. Additional studies could expand our current understanding of the molecular biology of both myxomas and CLL.

Recurrent left atrial myxomas in Carney complex: a genetic cause of multiple strokes that can be prevented

BACKGROUND

Intracardiac myxomas in Carney complex are significant causes of cardiovascular morbidity and mortality through embolic stroke and heart failure. The genetic, clinical, and laboratory characteristics of Carney complex-related strokes from atrial myxomas have not been described. The regulatory subunit (R1A) of the protein kinase gene (PRKAR1A) is mutated in >60% of patients with Carney complex.

METHODS

We studied patients with strokes and cardiac myxomas that were hospitalized in our institution and elsewhere; a total of 7 patients with 16 recurrent atrial myxomas and >14 episodes of strokes were identified.

RESULTS

Neurologic deficits were reported; in 1 patient, an aneurysm developed at the site of a previous stroke. All patients were females, were also diagnosed with Cushing syndrome, and all had additional tumors or other Carney complex manifestations. Other than gender, although there was a trend for patients being overweight and hypertensive, no other risk factors were identified. A total of 5 patients (71%) had a PRKAR1A mutation; all mutations (c418_419delCA, c.340delG/p.Val113fsX15, c.353_365del13/p.Ile118fsX6, c.491_492delTG/p.Val164fsX4, and c.177+1G>A) were located in exons 3 to 5 and introns 2 to 3, and all led to a non-sense PRKAR1A mRNA.

CONCLUSIONS

Female patients with Carney complex appear to be at a high risk for recurrent atrial myxomas that lead to multiple strokes. Early identification of a female patient with Carney complex is of paramount importance for the early diagnosis of atrial myxomas and the prevention of strokes.