Rita Domingues

RET polymorphisms and sporadic medullary thyroid carcinoma in a Portuguese population.

The genetic basis of the sporadic form of medullary thyroid carcinoma, derived from “C” cells, is still poorly understood. Somatic mutations of RET proto-oncogene have been reported at a variable frequency ranging from 23% to 69%. The hypothesis that low penetrance factors, such as polymorphisms, might contribute to the phenotype of this neoplasm has been addressed in a few studies conducting to conflicting results. Herein, we studied 100 individuals (50 patients and 50 controls) aiming to compare the frequencies of G691S, L769L, S836S, and S904S RET polymorphisms observed in patients with respect to controls. Furthermore, metaanalysis of published studies including the present results was conducted. To test the contributory role of the above polymorphisms for the development of “C”-cell hyperplasia, we studied a group of 10 individuals selected for having a positive pentagastrin test despite the absence of a RET germline mutation. An over-representation of the G691S polymorphism, particularly in females, was observed in patients with respect to controls, although not reaching the level of significance. Allelic frequencies of the other three polymorphisms were not different in patients and controls. Results obtained in the admittedly small group of individuals with a positive pentagastrin test are unlikely to support a major influence of any polymorphism in the development of “C”-cell hyperplasia. The meta-analysis provided evidence for a significant association of the S691 allele with MTC (odds ratio 1.54, 95% confidence interval 1.12–2.12, p=0.008) and found no significant associations for the other polymorphisms.

The minisequencing method: a simple strategy for genetic screening of MEN 2 families

BackgroundMultiple endocrine neoplasia type 2 is an autosomal dominant disorder. MEN 2A is characterized by medullary thyroid carcinoma, pheochromocytoma and hyperparathyroidism; MEN 2B by medullary thyroid carcinoma, pheochromocytoma and characteristic stigmata. Activating germline mutations of the RET proto oncogene are responsible for this hereditary syndrome. Codon 634 mutations are the most common mutations occurring in MEN 2A families whereas a specific mutation at codon 918 is observed in the great majority of MEN 2B families. Analysis of these codons will provide a final diagnosis in the great majority of affected families making unnecessary further studies. To specifically study the codons 634 and 918 we used a minisequencing method as an alternative method to complete sequencing.ResultsUsing this mutation detection method we were able to reproduce in all cases, representative of 7 families, the information previously obtained by direct sequencing of PCR products. Depending on the number of primers used in the minisequencing reaction, we were able to interrogate either only one nucleotide of the target codon or the three nucleotides simultaneously.ConclusionsThis technique appears as a simple, rapid and efficient method for genetic screening of MEN 2 families. It can be utilized to seek for unknown mutations at specific codons or to screen for previously identified mutations and is therefore of interest to study index cases or individuals at risk. Results suggest that complete sequencing is unnecessary.

A novel variant in Serpina7 gene in a family with thyroxine-binding globulin deficiency

Thyroxine-binding globulin (TBG) carries approximately 75% of serum T4 and T3. This protein is encoded by serpina7 gene, formerly known as TBG gene, localized on X-chromosome (Xq22.2). A deficiency in TBG is suspected when abnormally low serum total T4 and T3 are encountered in clinically euthyroid subjects in the presence of normal serum TSH. This condition has been associated with different serpina7 gene mutations resulting in amino acid substitutions or truncations in the mature protein. Herein, we report a new serpina7 gene variant in three members of the same family. It results in the replacement of the normal asparagine 233 by isoleucine and, subsequently, in disruption of a glycosylation site. Co-segregation of this new variant with undetectable levels of TBG in the hemizygous man studied and failure to recognize the same variant in 100 alleles at random, made us to consider it as the underlying cause of the TBG deficiency.

Uncommon association of cerebral meningioma, parathyroid adenoma and papillary thyroid carcinoma in a patient harbouring a rare germline variant in the CDKN1B gene

Multiple endocrine neoplasia type 4 (MEN 4) is a novel form of multiple endocrine neoplasia caused by mutations in the CDKN1B gene. Its clinical presentation includes MEN 1-related tumours such as parathyroid and anterior pituitary tumours in possible association with gonadal, adrenal, renal and thyroid tumours as well as facial angiofibromas, colagenomas and meningiomas. We describe the case of a patient with meningioma, papillary thyroid carcinoma, parathyroid adenoma and, additionally, Hürthle cell adenoma, cholesteatoma and uterine leiomyomas. Considering that this association could represent a MEN 4-like phenotype, we looked for germline mutations in the CDKN1B gene. A rare heterozygous single nucleotide substitution c.397C>A was identified. Its role as a susceptibility factor remains to be established.

Homozygous Calcium-Sensing Receptor Polymorphism R544Q Presents as Hypocalcemic Hypoparathyroidism

Context Autosomal dominant hypocalcemia type 1 (ADH1) is caused by heterozygous activating mutations in the calcium-sensing receptor gene (CASR). Whether polymorphisms that are benign in the heterozygous state pathologically alter receptor function in the homozygous state is unknown. Objective To identify the genetic defect in an adolescent female with a history of surgery for bilateral cataracts and seizures. The patient has hypocalcemia, hyperphosphatemia, and low serum PTH level. The parents of the proband are healthy. Methods Mutation testing of PTH, GNA11, GCM2, and CASR was done on leukocyte DNA of the proband. Functional analysis in transfected cells was conducted on the gene variant identified. Public single nucleotide polymorphism (SNP) databases were searched for the presence of the variant allele. Results No mutations were identified in PTH, GNA11, and GCM2 in the proband. However, a germline homozygous variant (c.1631G>A; p.R544Q) in exon 6 of the CASR was identified. Both parents are heterozygous for the variant. The variant allele frequency was near 0.1% in SNP databases. By in vitro functional analysis, the variant was significantly more potent in stimulating both the Ca2+i and MAPK signaling pathways than wild type when transfected alone (P < 0.05) but not when transfected together with wild type. The overactivity of the mutant CaSR is due to loss of a critical structural cation-π interaction. Conclusions The patients hypoparathyroidism is due to homozygosity of a variant in the CASR that normally has weak or no phenotypic expression in heterozygosity. Although rare, this has important implications for genetic counseling and clinical management.

Clinical usefulness of 68Ga-DOTA-NOC PET/CT in staging a vagal paraganglioma associated with a novel SDHB mutation

Paragangliomas are rare tumours arising from the autonomic nervous system. Most are benign, however, a few are malignant. The diagnosis of malignancy is dependent on the evidence of metastases. Approximately, 40% of all paragangliomas/pheochromocytomas harbour a germ-line mutation in one of the susceptibility genes identified so far.1 We present a case of a 29-year-old Caucasian man, referred to us on suspicion of a neck paraganglioma based on CT findings. MRI confirmed a lesion (80×40×40 mm) within the right parapharyngeal space, slightly intense on T2 and posterior …