Functional analysis of monocarboxylate transporter 8 mutations identified in patients with X-linked psychomotor retardation and elevated serum triiodothyronine

CONTEXT

T(3) action in neurons is essential for brain development. Recent evidence indicates that monocarboxylate transporter 8 (MCT8) is important for neuronal T(3) uptake. Hemizygous mutations have been identified in the X-linked MCT8 gene in boys with severe psychomotor retardation and elevated serum T(3) levels.

OBJECTIVE

The objective of this study was to determine the functional consequences of MCT8 mutations regarding transport of T(3).

DESIGN

MCT8 function was studied in wild-type or mutant MCT8-transfected JEG3 cells by analyzing: 1) T(3) uptake, 2) T(3) metabolism in cells cotransfected with human type 3 deiodinase, 3) immunoblotting, and 4) immunocytochemistry.

RESULTS

The mutations identified in MCT8 comprise four deletions (24.5 kb, 2.4 kb, 14 bp, and 3 bp), three missense mutations (Ala224Val, Arg271His, and Leu471Pro), a nonsense mutation (Arg245stop), and a splice site mutation (94 amino acid deletion). All tested mutants were inactive in uptake and metabolism assays, except MCT8 Arg271His, which showed approximately 20% activity vs. wild-type MCT8.

CONCLUSION

These findings support the hypothesis that the severe psychomotor retardation and elevated serum T(3) levels in these patients are caused by inactivation of the MCT8 transporter, preventing action and metabolism of T(3) in central neurons.

Normal perioperative serum calcitonin levels in patients with advanced medullary thyroid carcinoma: case report and review of the literature

CONTEXT

Medullary thyroid carcinoma (MTC), a tumor of the parafollicular C cells of the gland, comprises 3-5% of all malignant thyroid neoplasms. Calcitonin, a polypeptidic hormone secreted by the neoplastic cells, is considered a very sensitive and specific MTC tumor marker. Patients with MTC usually present elevated serum calcitonin levels, which correlate with tumor burden and prognosis.

OBJECTIVES

To describe a case of advanced MTC with normal serum calcitonin and review the literature on this subject.

DESIGN

A case study was performed.

INTERVENTION

There were no interventions.

PATIENTS

A case of advanced MTC with normal serum calcitonin was studied.

RESULTS

Serum calcitonin was measured by two distinct assays, a chemiluminescent immunometric and an in-house two-site monoclonal antibody-based immunofluorometric assay. To rule out a "hook effect," or posttranslational modifications of calcitonin molecule, serum dilutions and tumor immunohistochemistry for calcitonin with the same antibodies used for serum calcitonin measurements were performed. Serum calcitonin levels were within the normal range in both assays, whereas the tumor stained strongly positive for calcitonin. These findings suggest that the tumor was able to produce but not to secrete the calcitonin protein. Five other cases of advanced MTC with normal serum calcitonin levels had been previously reported.

CONCLUSIONS

We present an unusual case of advanced MTC with normal serum calcitonin levels. Awareness of MTC cases presenting with normal serum calcitonin levels is important in clinical practice and is particularly relevant to centers that use this test for screening.

Prevalence and clinical features of celiac disease in patients with autoimmune thyroiditis: cross-sectional study

CONTEXT AND OBJECTIVE

Celiac disease is an autoimmune disorder with an average prevalence of 1% in Europe and the United States. Because of strong European ancestry in southern Brazil, this study aimed to evaluate the seroprevalence of celiac disease among autoimmune thyroiditis patients.

DESIGN AND SETTING

Cross-sectional study in a public university hospital.

METHODS

This cross-sectional prevalence study included autoimmune thyroiditis patients who were tested for anti-endomysial and anti-transglutaminase antibodies between August 2010 and July 2011.

RESULTS

Fifty-three patients with autoimmune thyroiditis were included; 92.5% were women, with mean age of 49.0 ± 13.5 years. Five patients (9.3%) were serologically positive for celiac disease: three of them (5.6%) were reactive for anti-endomysial antibodies and two (3.7%) for anti-transglutaminase. None of them exhibited anemia and one presented diarrhea. Endoscopy was performed on two patients: one with normal histology and the other with lymphocytic infiltrate and villous atrophy.

CONCLUSION

The prevalence of celiac disease among patients with autoimmune thyroid disease was 9.3%; one patient complained of diarrhea and none presented anemia. Among at-risk populations, like autoimmune thyroiditis patients, the presence of diarrhea or anemia should not be used as a criterion for indicating celiac disease investigation. This must be done for all autoimmune thyroiditis patients because of its high prevalence.

Prevalence and clinical features of celiac disease in patients with autoimmune thyroiditis: cross-sectional study

CONTEXT AND OBJECTIVE

Celiac disease is an autoimmune disorder with an average prevalence of 1% in Europe and the United States. Because of strong European ancestry in southern Brazil, this study aimed to evaluate the seroprevalence of celiac disease among autoimmune thyroiditis patients.

DESIGN AND SETTING

Cross-sectional study in a public university hospital.

METHODS

This cross-sectional prevalence study included autoimmune thyroiditis patients who were tested for anti-endomysial and anti-transglutaminase antibodies between August 2010 and July 2011.

RESULTS

Fifty-three patients with autoimmune thyroiditis were included; 92.5% were women, with mean age of 49.0 ± 13.5 years. Five patients (9.3%) were serologically positive for celiac disease: three of them (5.6%) were reactive for anti-endomysial antibodies and two (3.7%) for anti-transglutaminase. None of them exhibited anemia and one presented diarrhea. Endoscopy was performed on two patients: one with normal histology and the other with lymphocytic infiltrate and villous atrophy.

CONCLUSION

The prevalence of celiac disease among patients with autoimmune thyroid disease was 9.3%; one patient complained of diarrhea and none presented anemia. Among at-risk populations, like autoimmune thyroiditis patients, the presence of diarrhea or anemia should not be used as a criterion for indicating celiac disease investigation. This must be done for all autoimmune thyroiditis patients because of its high prevalence.