First Somatic PRKAR1A Defect Associated With Mosaicism for Another PRKAR1A Mutation in a Patient With Cushing Syndrome

Abstract

Context: Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of ACTH-independent Cushing syndrome (CS) associated mostly with Carney complex (CNC), a rare autosomal dominant multiple neoplasia syndrome. More than two-thirds of familial cases and approximately one-third of sporadic cases of CNC harbor germline inactivating PRKAR1A defects. Increasingly sensitive technologies for the detection of genetic defects such as next-generation sequencing (NGS) have further highlighted the importance of mosaicism in human disease.

Case description: A 33-year-old woman was diagnosed with ACTH-independent CS with abdominal computed tomography showing bilateral micronodular adrenal hyperplasia with a left adrenal adenoma. She underwent left adrenalectomy with pathology demonstrating PPNAD with a 1.5-cm pigmented adenoma. DNA analysis by Sanger sequencing revealed 2 different PRKAR1A variants in the adenoma that were absent from DNA extracted from blood and saliva: c.682C > T and c.974-2A > G. "Deep" NGS revealed that 0.31% of DNA copies extracted from blood and saliva did in fact carry the c.682C > T variant, suggesting low-level mosaicism for this defect.

Conclusions: We present a case of PPNAD due to low-level mosaicism for a PRKAR1A defect which led to the formation of an adenoma due to a second, adrenal-specific, somatic PRKAR1A mutation. The identification of mosaicism for PRKAR1A, depending on the number and distribution of cells affected has implications for genetic counseling and tumor surveillance. This is the first recorded case of a patient with PRKAR1A mosaicism, PPNAD, and an adenoma forming due to complete inactivation of PRKAR1A in adrenal tissue from a second, somatic-only, PRKAR1A coding sequence mutation.

Keywords: Carney complex; Cushing syndrome; PRKAR1A; adrenocortical hyperplasia; mosaicism; primary pigmented nodular adrenocortical disease.

Figure 1.

Clinical features of Cushing syndrome. A, B, Central obesity with proximal muscle wasting; C, Bitemporal fat pads, facial rounding, acne, lanugo; D, Dorsocervical and supraclavicular fat deposition, alopecia; E, Wide, though faint, abdominal striae.

Figure 2.

Adrenal imaging. A, Computed tomography (CT) of the adrenal glands with intravenous contrast showing left micronodular adrenal hyperplasia with an adenoma; B, CT adrenal glands with intravenous contrast demonstrating right micronodular adrenal hyperplasia; C, Axial view of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) showing an abnormally hypermetabolic left adrenal mass; D, Coronal view of ¹⁸F-FDG PET fused to CT without intravenous contrast, showing the hypermetabolic left adrenal mass.

Figure 3.

Left adrenal gland pathology consistent with primary pigmented nodular adrenocortical hyperplasia with a macronodule. A, Left adrenal gland. Scanning magnification view shows multiple well-circumscribed unencapsulated hyperplastic adrenocortical nodules composed of large epithelioid cells with abundant eosinophilic cytoplasm partially separated by adrenocortical cells with pale staining cytoplasm (hematoxylin and eosin staining, 4× original magnification); B, Left adrenal gland hematoxylin. Intermediate magnification view shows one of the hyperplastic nodules composed of large epithelioid cells with abundant eosinophilic cytoplasm and surrounding adrenocortical cells with pale staining cytoplasm (hematoxylin and eosin staining, 10× original magnification); C, Left adrenal gland. High magnification view revealed intracytoplasmic melanin pigments within large epithelioid cells of hyperplastic nodule (hematoxylin and eosin staining, 4× original magnification); D, Left adrenal gland. Lesional cells of the hyperplastic nodule are mostly negative for HMB-45. The adjacent adrenal cortical epithelium shows focal weak staining by HMB-45 immunohistochemistry, ×10 magnification; E, Left adrenal gland. Lesional cells of the hyperplastic nodule show strong cytoplasmic staining by melan-A immunohistochemistry, 10× original magnification; F, Left adrenal gland. Lesional cells of the hyperplastic nodule show strong and diffuse staining by synaptophysin immunohistochemistry, 10× original magnification.

Figure 4.

PRKAR1A DNA analysis. A, Electropherogram showing the 2 PRKAR1A variants found in the DNA extracted from the patient’s adrenocortical adenoma. Red rectangles show the location of the mutation; B, Integrative genome viewer (IGV) raw data analysis showing the presence of the variant in high frequency only at the tumor level.

Figure 5.

PRKAR1A RNA splice analysis. A, c.974-2A>G was identified at the cDNA level where a new acceptor site was created before the regular one. The presence of this change generated a new acceptor site 67 bases before the beginning of the normal exon 11; B, This new sequence created a new exon 12.