A case of exclusive dopamine-secreting paraganglioma

Pathogenic variants in TSC2 might cause premature ovarian insufficiency through activated mTOR induced hyperactivation of primordial follicles

OBJECTIVE

To investigate the role of tuberous sclerosis complex (TSC) genes, including TSC1 and TSC2, in the pathogenesis of human premature ovarian insufficiency (POI).

DESIGN

Genetic and functional study.

SETTING

University-based reproductive medical center.

PATIENT(S)

Six patients from a cohort of 1,030 cases with idiopathic POI.

INTERVENTION(S)

Variants in TSC1 and TSC2 were screened through the largest in-house database of whole exome sequencing performed in 1,030 patients with idiopathic POI. The pathogenic effects of the variants were further verified by functional studies.

MAIN OUTCOME MEASURE(S)

TSC1 or TSC2 variant and functional characteristics.

RESULT(S)

Five pathogenic heterozygous variants in TSC2 were identified in 6 patients with POI. Functional studies showed these variants impaired the repressive effect of TSC2 on mammalian target of rapamycin (mTOR) pathway by disrupting the formation of TSC complex or its GTPase-activating protein activity. Furthermore, in vitro ovarian culture assay showed that TSC2 p.R98Q led to hyperactivation of mTOR pathway thereby triggering primordial follicle activation.

CONCLUSION(S)

The present study identified pathogenic variants of TSC2 in patients with POI, firstly suggested defective TSC/mTOR pathway mediated hyperactivation of primordial follicle participating in the pathogenesis of POI, giving insights into new targets of genetic counseling and clinical prevention for POI. Considering the pivotal role of TSC2 variants in diagnosis of TSC syndrome, the present study also highlighted the importance of history collection and long-term follow-up for the TSC2 variants carriers.

Dopamine-Secreting Pheochromocytoma and Paraganglioma

Predominantly or exclusively dopamine-secreting pheochromocytoma and paraganglioma are very rare. We report a 64-year-old woman with an adrenal incidentaloma. She was normotensive and had no symptoms of catecholamine excess. The 24-hour urine catecholamine level showed normal norepinephrine (122.9 μg/day), normal epinephrine (24.3 μg/day), and markedly elevated dopamine (148 212.4 μg/day). ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphy revealed tumor uptake. After α-blockade as preoperative management, she successfully underwent laparoscopic left adrenalectomy and was finally diagnosed with an exclusively dopamine-secreting pheochromocytoma. The tumor was histologically comprised of small polygonal cells with high cellularity and was immunohistochemically positive for all 3 catecholamine-synthesizing enzymes: tyrosine hydroxylase (very weak), dopamine β-hydroxylase (heterogeneous), and phenylethanolamine N-methyltransferase (very weak). Electron microscopy revealed very few catecholamine-containing small vesicles with a few organelles, which reflected immature cells. No biochemical or imaging evidence of recurrence or metastasis were evident 1 year after the surgery. We conducted a literature search in the PubMed database. A total of 33 cases were collected. Our case had the second-highest 24-hour urinary dopamine excretion and was the first in which immunostaining for catecholamine synthase and electron microscopy were performed together. Histological findings in our case give a possible hypothesis that the mechanism underlying a dopamine-secreting pheochromocytoma is associated with immature catecholamine vesicles in which dopamine β-hydroxylase is localized, thus resulting in inhibited conversion from dopamine to norepinephrine. We also discuss the reasons for the lack of catecholamine excess symptoms, whether preoperative management of α-blockade is needed, and the association between the prognosis and genetic mutation, with an extensive literature review.

Dopamine-secreting carotid body paragangliomas-biochemical control with radiotherapy

Head and neck paragangliomas that are exclusively or predominantly dopamine-secreting are rare. Surgery and/or radiotherapy are modalities for locoregional tumoral control. Little is known about the efficacy of radiotherapy for biochemical control in such tumors. We report a 62-year-old Chinese man with bilateral carotid body tumors which were exclusively dopamine secreting. The left-sided tumor invaded the skull base and encased the left carotid artery. Surgery was not performed due to high risk of morbidity and mortality. The patient received external beam radiotherapy to bilateral neck regions. Progressive decline and eventual normalization of urinary dopamine excretion was seen together with a slight reduction in tumor size. This is the first report demonstrating the efficacy of radiotherapy for both biochemical and locoregional control of functioning carotid body paragangliomas.

R27X nonsense mutation of the SDHB gene in a patient with sporadic malignant paraganglioma

It has been estimated that approximately 10% of pheochromocytomas and paragangliomas are part of a hereditary syndrome. Recent studies, however, suggest that the genetic involvement in pheochromocytoma/paraganglioma is actually far more common. Here, we report a case of malignant paraganglioma with no apparent family history. A 59-year-old man was referred to our services because of multiple abdominal masses. Plasma and urine adrenalin and noradrenalin levels were slightly elevated, and plasma dopamine and urine vanillylmandelic acid levels were remarkably elevated. Abdominal and chest computed tomography revealed multiple masses in the para-aortic region and in both lungs. Although (131)I-meta iodobenzylguanidine scintigraphy did not show significant uptake in these tumors, a 6-[(18)F]fluorodeoxyglucose positron emission tomographic scanning study showed multiple areas of uptake corresponding to the tumors. Biopsy of the tumors revealed paraganglioma with chromogranin A-immunopositive cells. Genetic analysis indicated a nonsense mutation at codon 27 of the SDHB gene. As recently described, SDHB mutations may cause extra-adrenal and malignant paragangliomas, such as in the present case.