Browsing by Author "Sobrinho, L"
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- Clinical and Genetic Characterization of Portuguese Patients with Pseudohypoparathyroidism Type IbPublication . Cavaco, B; Tomaz, R; Fonseca, F; Mascarenhas, MR; Leite, V; Sobrinho, LPatients with pseudohypoparathyroidism type Ib (PHP-Ib) present hypocalcemia and hyperphosphatemia, as a consequence of a resistance to PTH action, through its G-protein-coupled receptor, in the renal tubules. This resistance results from tissue-specific silencing of the G-protein alpha-subunit (G(s)α), due to imprinting disruption of its encoding locus--GNAS. In familial PHP-Ib, maternally inherited deletions at the STX16 gene are associated to a regional GNAS methylation defect. In sporadic PHP-Ib, broad methylation changes at GNAS arise from unknown genetic causes. In this study, we describe the clinical presentation of PHP-Ib in four Portuguese patients (two of whom were siblings), and provide further insight for the management of patients with this disease. The diagnosis of PHP-Ib was made after detection of GNAS imprinting defects in each of the cases. In the siblings, a regional GNAS methylation change resulted from a known 3.0 kb STX16 deletion. In the other two patients, the broad methylation defects at GNAS, which were absent in their relatives, resulted from genetic alterations that remain to be identified. We report the first clinical and genetic study of Portuguese patients with PHP-Ib. The genetic identification of a hereditary form of this rare disease allowed an early diagnosis, and may prevent hypocalcemia-related complications.
- Identification of de Novo Germline Mutations in the HRPT2 Gene in Two Apparently Sporadic Cases with Challenging Parathyroid Tumor DiagnosesPublication . Cavaco, B; Santos, R; Félix, A; Carvalho, D; Lopes, JM; Domingues, R; Sirgado, M; Rei, N; Fonseca, F; Santos, J; Sobrinho, L; Leite, VThe diagnosis of parathyroid carcinomas is often difficult. HRPT2 mutations have been identified in familial [hyperparathyroidism-jaw tumor (HPT-JT) syndrome] and sporadic parathyroid carcinomas, supporting that HRPT2 mutations may confer a malignant potential to parathyroid tumors. In this study, we report the clinical, histopathological, and genetic investigation of two unrelated cases, whom had apparently sporadic malignant parathyroid tumors, initially diagnosed as adenomas. In one case, the differential diagnosis was complicated by cervical seeding of parathyroid tumor cells. Genetic studies identified de novo HRPT2 germline mutations in cases 1 (c.518_521delTGTC [p.Ser174LysfsX27]) and 2 (c.226 C > T [p.Arg76X]), unveiling the hereditary HPT-JT syndrome in both patients. Furthermore, the identification of somatic mutations in the patients‟ parathyroid tumors provided evidence for complete inactivation of the HRPT2 gene, which was consistent with the tumor malignant features. The sensitivity of parafibromin immunostaining to detect HRPT2 mutations was limited. The present data suggests that patients with apparently sporadic parathyroid carcinomas, or parathyroid tumors with atypical histological features, should undergo molecular genetic testing, as it may detect germline HRPT2 mutations. Establishing the diagnosis of hereditary HPT-JT syndrome is relevant for clinical counseling and management of the carriers and their relatives.