Case report: Obstructive azoospermia as the first presentation of Von Hippel-Lindau disease.

We report the case of a 38-year-old man whose diagnostic workup for primary infertility led to the discovery of obstructive azoospermia due to bilateral papillary cystadenoma of the epididymis (PCE). Given the rarity of this finding and because PCE could be a manifestation of Von Hippel-Lindau disease (VHL), although the patient had no family or personal history of VHL, the VHL gene was tested, and a known pathogenetic variant (c.464-1G>A; p.)? was found. Screening for other Von Hippel-Lindau disease-associated neoplasms revealed bilateral retinal capillary hemangioblastomas, clear cell renal cell carcinoma, and multiple pancreatic cysts. In this case, an accurate diagnostic workup for male infertility allowed the detection of a rare life-threatening syndrome, already presenting with several silent neoplasms. For this reason, this case report may be useful for reproductive medicine specialists in the management of male infertility.

Hyper-reflective retinal foci as possible in vivo imaging biomarker of microglia activation in von Hippel-Lindau disease.

PURPOSE: von Hippel-Lindau (VHL) disease is caused by a mutation of the VHL gene and characterized by the development of retinal hemangioblastomas (RH). Current pathophysiologic mechanisms of RH development and progression are still insufficient to predict RH behavior. VHL gene is involved in the cellular response to hypoxia and in many intracellular signaling pathways expressed both in angiogenesis and inflammation. Optical coherence tomography (OCT) allows to identify hyper-reflective retinal foci (HRF) known as aggregates of activated microglial cells as possible in vivo biomarker of local inflammation. The aim of the present study was to investigate the presence of HRF in patients with genetically confirmed VHL disease. METHODS: In this cross-sectional study, patients with VHL underwent complete ophthalmological examination and OCT with HRA + OCT Spectralis. HRF were manually identified and calculated in inner (IR), outer (OR) and full retina. Age-matched healthy subjects were enrolled as controls. RESULTS: 113 eyes of 63 VHL patients and 56 eyes of 28 healthy subjects were evaluated. HRF number was significantly higher in VHL than in controls in IR (28.06 ± 7.50 vs 25.25 ± 6.64, p = 0.042). No difference was observed in OR and in full retina (OR: 7.73 ± 2.59 vs 7.95 ± 2.51, p = 0.599; full retina: 35.79 ± 8.77 vs 33.20 ± 7.47, p = 0.093). CONCLUSION: The increase of HRF, which mirror retinal microglial activation, characterizes VHL eyes. The role of activated microglia in the retina of VHL eyes needs to be better investigated, mainly considering local VHL disease manifestations.

Overexpression of miR-375 and L-type Amino Acid Transporter 1 in Pheochromocytoma and Their Molecular and Functional Implications.

Pheochromocytoma (Pheo) is a tumor derived from chromaffin cells. It can be studied using 18F-dihydroxyphenylalanine (DOPA)-positron emission tomography (PET) due to its overexpression of L-type amino acid transporters (LAT1 and LAT2). The oncogenic pathways involved are still poorly understood. This study examined the relationship between 18F-DOPA-PET uptake and LAT1 expression, and we explored the role of miR-375 and putative target genes. A consecutive series of 58 Pheo patients were retrospectively analyzed, performing 18F-DOPA-PET in 32/58 patients. Real-time quantitative PCR was used to assess the expression of LAT1, LAT2, phenylethanolamine N-methyltransferase (PNMT), miR-375, and the major components of the Hippo and Wingless/Integrated pathways. Principal germline mutations associated with hereditary Pheo were also studied. Pheo tissues had significantly higher LAT1, LAT2, and PNMT mRNA levels than normal adrenal tissues. MiR-375 was strongly overexpressed. Yes-associated protein 1 and tankyrase 1 were upregulated, while beta-catenin, axin2, monocarboxylate transporter 8, and Frizzled 8 were downregulated. A positive relationship was found between 18F-DOPA-PET SUV mean and LAT1 gene expression and for 24 h-urinary norepinephrine and LAT1. This is the first experimental evidence of 18F-DOPA uptake correlating with LAT1 overexpression. We also demonstrated miR-375 overexpression and downregulated (Wnt) signaling and identified the Hippo pathway as a new potentially oncogenic feature of Pheo.

A Multicenter Epidemiological Study on Second Malignancy in Non-Syndromic Pheochromocytoma/Paraganglioma Patients in Italy.

No studies have carried out an extensive analysis of the possible association between non-syndromic pheochromocytomas and paragangliomas (PPGLs) and other malignancies. To assess >the risk of additional malignancy in PPGL, we retrospectively evaluated 741 patients with PPGLs followed-up in twelve referral centers in Italy. Incidence of second malignant tumors was compared between this cohort and Italian patients with two subsequent malignancies. Among our patients, 95 (12.8%) developed a second malignant tumor, which were mainly prostate, colorectal and lung/bronchial cancers in males, breast cancer, differentiated thyroid cancer and melanoma in females. The standardized incidence ratio was 9.59 (95% CI 5.46-15.71) in males and 13.21 (95% CI 7.52-21.63) in females. At multivariable analysis, the risk of developing a second malignant tumor increased with age at diagnosis (HR 2.50, 95% CI 1.15-5.44, p = 0.021 for 50-59 vs. <50-year category; HR 3.46, 95% CI 1.67-7.15, p < 0.001 for >60- vs. <50-year). In patients with available genetic evaluation, a positive genetic test was inversely associated with the risk of developing a second tumor (HR 0.25, 95% CI 0.10-0.63, p = 0.003). In conclusion, PPGLs patients have higher incidence of additional malignant tumors compared to the general population who had a first malignancy, which could have an impact on the surveillance strategy.

Structural and microvascular changes of the peripapillary retinal nerve fiber layer in Von Hippel-Lindau disease: an OCT and OCT angiography study.

Von Hippel-Lindau (VHL) disease is an autosomal dominant genetic disease caused by VHL gene mutation. Retinal hemangioblastomas (RH) are vascularized tumors and represent the main ocular manifestation of the disease. Histopathologically, RH are composed of capillary vessels and stromal cells, the neoplastic population of the lesion. The origin of these stromal cells remains controversial, even if they are hypothesized to be glial cells. The aim of the present study was to investigate neuronal and microvascular changes of the peripapillary retinal nerve fiber layer, in which glial cells, neurons and capillaries (the radial peripapillary capillary plexus) interact. VHL patients with or without peripheral RH were enrolled and compared to healthy controls. Mean peripapillary retinal nerve fiber layer (pRNFL) thickness was measured by means of optical coherence tomography (OCT). The following vascular parameters of the radial peripapillary capillary plexus were quantified using OCT angiography: Vessel Area Density,Vessel Length Fraction, Vessel Diameter Index and Fractal Dimension. One hundred and nine eyes of 61 patients, and 56 eyes of 28 controls were consecutively studied. Mean pRNFL was significantly thinner in VHL eyes without RH versus eyes with RH and controls. Mean pRNFL thickness did not differ between VHL eyes with RH and controls. All OCTA vascular parameters were reduced in VHL eyes with or without RH versus controls, with significative difference for Vessel Diameter Index. The same OCTA parameters did not significantly differ between VHL eyes with or without RH. In VHL eyes without RH, pRNFL thinning may be the consequence of impaired perfusion of the radial peripapillary capillary plexus, while the increase of pRNFL thickness in VHL eyes with RH may depend on possible activation and proliferation of the other RNFL resident cells, the glial cells.

Retinal Glial Cells in Von Hippel-Lindau Disease: A Novel Approach in the Pathophysiology of Retinal Hemangioblastoma.

BACKGROUND: Von Hippel-Lindau (VHL) disease is a neoplastic syndrome caused by a mutation of the VHL tumor suppressor gene. Retinal hemangioblastoma (RH) is a vascularized tumor and represents the most common ocular manifestation of this disease. At the retinal level, VHL protein is able to regulate tumor growth, angiogenic factors, and neuroinflammation, probably stimulating retinal glial cells. The aim of the present study was to analyze in vivo the optical coherence tomography (OCT) biomarkers of retinal macroglia and microglia in a cohort of VHL patients. METHODS: The mean thicknesses of macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL), and peripapillary retinal nerve fiber layer (pRNFL) were measured with OCT as biomarkers of retinal macroglia. OCT images were also analyzed to detect and quantify hyperreflective retinal foci (HRF), a biomarker of retinal activated microglia. RESULTS: 61 eyes of 61 VHL patients (22 eyes (36.07%) with peripheral RH and 39 eyes (63.93%) without RH) and 28 eyes of 28 controls were evaluated. pRNFL was thinner in VHL patients (p < 0.05) and in VHL without RH (p < 0.01) compared to controls, and thicker in VHL patients with RH than in those without RH (p < 0.05). The thickness of mRNFL (p < 0.0001) and GCL (p < 0.05) was reduced in VHL patients and in VHL without RH compared to controls, whereas mRNFL (p < 0.0001) and GCL (p < 0.05) were increased in VHL patients with RH compared to those without RH. HRF were significantly higher in number in VHL patients and in VHL without RH, than in controls, and significantly lower (p < 0.05) in the eyes of VHL patients with RH, than in those without RH. CONCLUSIONS: The OCT analysis, which detects and allows to quantify the biomarkers of retinal microglia (HRF) and macroglia (pRNFL, mRNFL and GCL), showed a different behavior of these two retinal glial cells populations in VHL patients, related to the presence or absence of peripheral RH. These data allow to hypothesize a novel pathophysiologic pathway of retinal hemangioblastoma in VHL disease.

Macular Perfusion Impairment in Von Hippel-Lindau Disease Suggests a Generalized Retinal Vessel Alteration.

BACKGROUND: To evaluate macular perfusion in patients with Von Hippel-Lindau (VHL) disease. METHODS: VHL patients with or without peripheral retinal hemangioblastomas (RHs) were consecutively enrolled. A group of healthy subjects served as controls. Macular perfusion was analyzed by means of OCT angiography (OCTA) in the superficial vascular plexus (SVP), and in the intermediate (ICP) and deep retinal capillary (DCP) plexuses. The following OCTA parameters were measured: Vessel Area Density (VAD), Vessel Length Fraction (VLF), Vessel Diameter Index (VDI) and Fractal Dimension (FD). RESULTS: Sixty-three VHL patients (113 eyes) and 28 healthy controls (56 eyes) were enrolled. All OCTA quantitative parameters were reduced in VHL patients vs. controls, reaching statistical significance for VAD of the SVP (0.348 ± 0.07 vs. 0.369 ± 0.06, p = 0.0368) and VDI of all plexuses (p < 0.03 for all). No significant differences were detected between eyes without or with peripheral RHs. CONCLUSIONS: Macular perfusion is reduced in VHL patients demonstrating retinal vessel changes that are independent of the presence of peripheral RHs. VHL gene mutations disrupt the hypoxia-induced (HIF)/vascular endothelium growth factors (VEGF) pathway and the Notch signaling, both essential for the normal retinal vasculogenesis and angiogenesis. Therefore, an anomalous generalized retinal vascular development may be hypothesized in VHL disease.

Comparison of Pheochromocytoma-Specific Morbidity and Mortality Among Adults With Bilateral Pheochromocytomas Undergoing Total Adrenalectomy vs Cortical-Sparing Adrenalectomy.

Importance: Large studies investigating long-term outcomes of patients with bilateral pheochromocytomas treated with either total or cortical-sparing adrenalectomies are needed to inform clinical management. Objective: To determine the association of total vs cortical-sparing adrenalectomy with pheochromocytoma-specific mortality, the burden of primary adrenal insufficiency after bilateral adrenalectomy, and the risk of pheochromocytoma recurrence. Design, Setting, and Participants: This cohort study used data from a multicenter consortium-based registry for 625 patients treated for bilateral pheochromocytomas between 1950 and 2018. Data were analyzed from September 1, 2018, to June 1, 2019. Exposures: Total or cortical-sparing adrenalectomy. Main Outcomes and Measures: Primary adrenal insufficiency, recurrent pheochromocytoma, and mortality. Results: Of 625 patients (300 [48%] female) with a median (interquartile range [IQR]) age of 30 (22-40) years at diagnosis, 401 (64%) were diagnosed with synchronous bilateral pheochromocytomas and 224 (36%) were diagnosed with metachronous pheochromocytomas (median [IQR] interval to second adrenalectomy, 6 [1-13] years). In 505 of 526 tested patients (96%), germline mutations were detected in the genes RET (282 patients [54%]), VHL (184 patients [35%]), and other genes (39 patients [7%]). Of 849 adrenalectomies performed in 625 patients, 324 (52%) were planned as cortical sparing and were successful in 248 of 324 patients (76.5%). Primary adrenal insufficiency occurred in all patients treated with total adrenalectomy but only in 23.5% of patients treated with attempted cortical-sparing adrenalectomy. A third of patients with adrenal insufficiency developed complications, such as adrenal crisis or iatrogenic Cushing syndrome. Of 377 patients who became steroid dependent, 67 (18%) developed at least 1 adrenal crisis and 50 (13%) developed iatrogenic Cushing syndrome during median (IQR) follow-up of 8 (3-25) years. Two patients developed recurrent pheochromocytoma in the adrenal bed despite total adrenalectomy. In contrast, 33 patients (13%) treated with successful cortical-sparing adrenalectomy developed another pheochromocytoma within the remnant adrenal after a median (IQR) of 8 (4-13) years, all of which were successfully treated with another surgery. Cortical-sparing surgery was not associated with survival. Overall survival was associated with comorbidities unrelated to pheochromocytoma: of 63 patients who died, only 3 (5%) died of metastatic pheochromocytoma. Conclusions and Relevance: Patients undergoing cortical-sparing adrenalectomy did not demonstrate decreased survival, despite development of recurrent pheochromocytoma in 13%. Cortical-sparing adrenalectomy should be considered in all patients with hereditary pheochromocytoma.

A Novel Thyroid Hormone Receptor Beta Mutation (G357R) in a Family with Resistance to Thyroid Hormone Beta: Extending the Borders of the "Hot" Region in the THRB Gene.

Resistance to thyroid hormone beta (RTHß) is a syndrome characterized by high serum levels of thyroid hormone and unsuppressed serum thyrotropin concentrations. RTHß is caused by mutations in the thyroid hormone receptor beta (THRB) gene, which are mostly clustered in three "hot" regions along the gene. Here, a report is given on a family with RTHß caused by a novel mutation in the THRB gene (c.1069 G>C, p.G357R) occurring outside the historically known "hot" regions.

Preventive medicine of von Hippel-Lindau disease-associated pancreatic neuroendocrine tumors.

Pancreatic neuroendocrine tumors (PanNETs) are rare in von Hippel-Lindau disease (VHL) but cause serious morbidity and mortality. Management guidelines for VHL-PanNETs continue to be based on limited evidence, and survival data to guide surgical management are lacking. We established the European-American-Asian-VHL-PanNET-Registry to assess data for risks for metastases, survival and long-term outcomes to provide best management recommendations. Of 2330 VHL patients, 273 had a total of 484 PanNETs. Median age at diagnosis of PanNET was 35 years (range 10-75). Fifty-five (20%) patients had metastatic PanNETs. Metastatic PanNETs were significantly larger (median size 5 vs 2 cm; P < 0.001) and tumor volume doubling time (TVDT) was faster (22 vs 126 months; P = 0.001). All metastatic tumors were ≥2.8 cm. Codons 161 and 167 were hotspots for VHL germline mutations with enhanced risk for metastatic PanNETs. Multivariate prediction modeling disclosed maximum tumor diameter and TVDT as significant predictors for metastatic disease (positive and negative predictive values of 51% and 100% for diameter cut-off ≥2.8 cm, 44% and 91% for TVDT cut-off of ≤24 months). In 117 of 273 patients, PanNETs >1.5 cm in diameter were operated. Ten-year survival was significantly longer in operated vs non-operated patients, in particular for PanNETs <2.8 cm vs ≥2.8 cm (94% vs 85% by 10 years; P = 0.020; 80% vs 50% at 10 years; P = 0.030). This study demonstrates that patients with PanNET approaching the cut-off diameter of 2.8 cm should be operated. Mutations in exon 3, especially of codons 161/167 are at enhanced risk for metastatic PanNETs. Survival is significantly longer in operated non-metastatic VHL-PanNETs.

Coexistence of VHL Disease and CPT2 Deficiency: A Case Report.

von Hippel-Lindau (VHL) disease is an inherited syndrome manifesting with benign and malignant tumors. Deficiency of carnitine palmitoyltransferase type II (CPT2) is a disorder of lipid metabolism that, in the muscle form, manifests with recurrent attacks of myalgias often associated with myoglobinuria. Rhabdomyolytic episodes may be complicated by life-threatening events, including acute renal failure (ARF). We report on a male patient who was tested, at 10 years of age, for VHL disease because of family history of VHL. He was diagnosed with VHL but without VHL-related manifestation at the time of diagnosis. During childhood, the patient was hospitalized several times for diffuse muscular pain, muscle weakness, and dark urine. These recurrent attacks of rhabdomyolysis were never accompanied by ARF. The patient was found to be homozygous for the mutation p.S113L of the CPT2 gene. To the best of our knowledge, this is the first report of the coexistence of VHL disease and CPT2 deficiency in the same individual. Based on findings from animal models, the case illustrates that mutations in the VHL gene might protect against renal damage caused by CPT2 gene mutations.

Inherited defects of thyroxine-binding proteins.

Thyroid hormones (TH) are bound to three major serum transport proteins, thyroxine-binding globulin (TBG), transthyretin (TTR) and human serum albumin (HSA). TBG has the strongest affinity for TH, whereas HSA is the most abundant protein in plasma. Individuals harboring genetic variations in TH transport proteins present with altered thyroid function tests, but are clinically euthyroid and do not require treatment. Clinical awareness and early recognition of these conditions are important to prevent unnecessary therapy with possible untoward effects. This review summarizes the gene, molecular structure and properties of these TH transport proteins and provides an overview of their inherited abnormalities, clinical presentation, genetic background and pathophysiologic mechanisms.

The Thyroid Hormone Analog DITPA Ameliorates Metabolic Parameters of Male Mice With Mct8 Deficiency.

Mutations in the gene encoding the thyroid hormone (TH) transporter, monocarboxylate transporter 8 (MCT8), cause mental retardation in humans associated with a specific thyroid hormone phenotype manifesting high serum T3 and low T4 and rT3 levels. Moreover, these patients have failure to thrive, and physiological changes compatible with thyrotoxicosis. Recent studies in Mct8-deficient (Mct8KO) mice revealed that the high serum T3 causes increased energy expenditure. The TH analog, diiodothyropropionic acid (DITPA), enters cells independently of Mct8 transport and shows thyromimetic action but with a lower metabolic activity than TH. In this study DITPA was given daily ip to adult Mct8KO mice to determine its effect on thyroid tests in serum and metabolism (total energy expenditure, respiratory exchange rate, and food and water intake). In addition, we measured the expression of TH-responsive genes in the brain, liver, and muscles to assess the thyromimetic effects of DITPA. Administration of 0.3 mg DITPA per 100 g body weight to Mct8KO mice brought serum T3 levels and the metabolic parameters studied to levels observed in untreated Wt animals. Analysis of TH target genes revealed amelioration of the thyrotoxic state in liver, somewhat in the soleus, but there was no amelioration of the brain hypothyroidism. In conclusion, at the dose used, DITPA mainly ameliorated the hypermetabolism of Mct8KO mice. This thyroid hormone analog is suitable for the treatment of the hypermetabolism in patients with MCT8 deficiency, as suggested in limited preliminary human trials.

A novel mechanism of inherited TBG deficiency: mutation in a liver-specific enhancer.

CONTEXT: T4-binding globulin (TBG), a protein secreted by the liver, is the main thyroid hormone (TH) transporter in human serum. TBG deficiency is characterized by reduced serum TH levels, but normal free TH and TSH and absent clinical manifestations. The inherited form of TBG deficiency is usually due to a mutation in the TBG gene located on the X-chromosome. OBJECTIVE: Among the 75 families with X-chromosome-linked TBG deficiency identified in our laboratory, no mutations in the TBG gene were found in four families. The aim of the study was to identify the mechanism of TBG deficiency in these four families using biochemical and genetic studies. DESIGN: Observational cohort, prospective. SETTING: University research center. PATIENTS: Four families with inherited TBG deficiency and no mutations in the TBG gene. INTERVENTION: Clinical evaluation, thyroid function tests, and targeted resequencing of 1 Mb of the X-chromosome. RESULTS: Next-generation sequencing identified a novel G to A variant 20 kb downstream of the TBG gene in all four families. In silico analysis predicted that the variant resides within a liver-specific enhancer. In vitro studies confirmed the enhancer activity of a 2.2-kb fragment of genomic DNA containing the novel variant and showed that the mutation reduces the activity of this enhancer. The affected subjects share a haplotype of 8 Mb surrounding the mutation, and the most recent common ancestor among the four families was estimated to be 19.5 generations ago (95% confidence intervals, 10.4-37). CONCLUSIONS: To our knowledge, the present study is the first report of an inherited endocrine disorder caused by a mutation in an enhancer region.

Placenta passage of the thyroid hormone analog DITPA to male wild-type and Mct8-deficient mice.

Monocarboxylate transporter 8 (MCT8) deficiency causes severe X-linked intellectual and neuropsychological impairment associated with abnormal thyroid function tests (TFTs) producing thyroid hormone (TH) deprivation in brain and excess in peripheral tissues. The TH analog diiodothyropropionic acid (DITPA) corrected the TFTs abnormalities and hypermetabolism of MCT8-deficient children but did not improve the neurological phenotype. The latter result was attributed to the late initiation of treatment. Therefore, we gave DITPA to pregnant mice carrying Mct8-deficient embryos to determine whether DITPA, when given prenatally, crosses the placenta and affects the serum TFTs and cerebral cortex of embryos. After depletion of the endogenous TH, Mct8-heterozygous pregnant dams carrying both wild-type (Wt) and Mct8-deficient (Mct8KO) male embryos were given DITPA. Effects were compared with those treated with levothyroxine (L-T4). With DITPA treatment, serum DITPA concentration was not different in the two genotypes, which produced equal effect on serum TSH levels in both groups of pups. In contrast, with L-T4 treatment, TSH did not normalize in Mct8KO pups whereas it did in the Wt littermates and dams despite higher concentration of serum T4. Finally, both treatments similarly modulated the expression of the TH-dependent genes Shh, Klf9, and Aldh1a3 in brain. Thus, the ability of DITPA to cross the placenta, its thyromimetic action on the expression of TH-dependent genes in brain, and its better accessibility to the pituitary than L-T4, as assessed by serum TSH, make DITPA a candidate for the prenatal treatment of MCT8 deficiency.

A novel mutation in the Albumin gene (R218S) causing familial dysalbuminemic hyperthyroxinemia in a family of Bangladeshi extraction.

BACKGROUND: Familial dysalbuminemic hyperthyroxinemia (FDH) is a common cause of euthyroid hyperthyroxinemia. Clinical recognition of FDH is crucial for preventing unnecessary therapy in clinically euthyroid patients with abnormal thyroid function tests. Our goal was to identify the cause of abnormal serum tests of thyroid function in a Canadian family of Bangladeshi extraction. PATIENTS: The proposita was found to have elevated free thyroxine (fT4) and free triiodothyronine (fT3) with nonsuppressed thyrotropin (TSH) on screening blood work. After detailed studies excluding hyperthyroidism and resistance to thyroid hormone, blood was obtained from all members of her immediate family for further investigation. METHODS: We conducted laboratory analyses and sequencing of candidate genes. RESULTS: Two members of this family have FDH, caused by a not previously identified mutation in the albumin gene. This mutation, located in exon 7 of the gene (652A>C), produces a single amino acid substitution in the protein molecule (R218S). The mutant albumin is associated with a ninefold increase in serum total T4 and a twofold increase in serum total reverse T3 compared to patients with normal albumin. Modeling data for the R218S variant are compatible with the increased binding affinity of this variant albumin for T4. CONCLUSIONS: The R218S substitution reported here causes FDH that, in terms of the magnitude of serum iodothyronine elevation, is intermediate to the two previously reported mutations at codon 218 FDH: R218H being more mild and R218P more severe.

Mct8-deficient mice have increased energy expenditure and reduced fat mass that is abrogated by normalization of serum T3 levels.

Children with monocarboxylate transporter 8 (MCT8) deficiency lose weight, even when adequately nourished. Changes in serum markers of thyroid hormone (TH) action compatible with thyrotoxicosis suggested that this might be due to T3 excess in peripheral tissues. Mct8-deficient mice (Mct8KO) replicate the human thyroid phenotype and are thus suitable for metabolic studies so far unavailable in humans. In the current work, compared with wild-type (Wt) mice, Mct8KO mice were leaner due to reduced fat mass. They tended to use more carbohydrates and fewer lipids during the dark phase. Mct8KO mice had increased total energy expenditure (TEE) and food and water intake, with normal total activity, indicating hypermetabolism. To determine whether this is due to the high serum T3, we studied mice deficient in both Mct8 and deiodinase 1 (Mct8D1KO) with serum T3 similar to Wt mice and Wt mice given L-T3 to raise their serum T3 to the level of Mct8KO mice. Contrary to Mct8KO, Mct8D1KO mice had similar fat mass, TEE, and food intake as their D1KO littermates, whereas T3-treated Wt mice showed increased food intake and TEE, similar to Mct8KO mice. In skeletal muscle, Mct8KO mice had increased T3 content and TH action and increased glucose metabolism, which improved in Mct8D1KO mice. These studies indicate that the high serum T3 in MCT8 deficiency increases the TEE and fails to maintain weight despite adequate calorie intake. This is mediated by tissues that are not predominantly MCT8 dependent for TH transport, including skeletal muscle. Normalizing serum T3 level by deleting deiodinase 1 corrects body composition and the metabolic alterations caused by the MCT8 deficiency.

Coexistence of THRB and TBG gene mutations in a Turkish family.

OBJECTIVE: Resistance to thyroid hormone is a syndrome characterized by high serum free T4 levels and unsuppressed serum TSH concentration. Thyroxine-binding globulin complete deficiency manifests with low serum total T4 and T3 levels and normal serum TSH concentration. Our objective is to describe a family with the coexistence of resistance to thyroid hormone and thyroxine-binding globulin complete deficiency. METHODS: We conducted clinical studies and genetic analyses. RESULTS: The proband presented with mental retardation, hearing loss, and recurrent upper respiratory tract infections accompanied by high serum levels of TSH, T3, T4, and high thyroglobulin antibody titers. His elder sister presented with normal TSH and T3 and high serum T4 levels. Both patients were found to be heterozygous for the mutation P453A in the thyroid hormone receptor beta (THRB) gene. One of the proband's brothers had low serum total T3 and T4 and normal TSH concentrations, without any clinical manifestations. He was hemizygous for the mutation P50fs51X in the TBG gene. The proband's mother showed slightly elevated TSH, normal total T3 and T4, and elevated titers of thyroperoxidase antibodies and thyroglobulin antibodies. She was heterozygous for both THRB and TBG genes mutations. CONCLUSIONS: To our knowledge, this is the first report of the coexistence of THRB and TBG gene mutations in the same individual (mother of the proband), whereas other affected family members had only 1 of the 2 genes mutated. The case illustrates the difficulty that might be encountered in the interpretation of thyroid function tests when different genetic defects affecting thyroid function coexist.

Changes in thyroid status during perinatal development of MCT8-deficient male mice.

Patients with the monocarboxylate transporter 8 (MCT8) deficiency syndrome present with a severe psychomotor retardation and abnormal serum thyroid hormone (TH) levels, consisting of high T(3) and low T(4) and rT(3). Mice deficient in Mct8 replicate the thyroid phenotype of patients with the MCT8 gene mutations. We analyzed the serum TH levels and action in the cerebral cortex and in the liver during the perinatal period of mice deficient in Mct8 to assess how the thyroid abnormalities of Mct8 deficiency develop and to study the thyroidal status of specific tissues. During perinatal life, the thyroid phenotype of Mct8-deficient mice is different from that of adult mice. They manifest hyperthyroxinemia at embryonic day 18 and postnatal day 0. This perinatal hyperthyroxinemia is accompanied by manifestations of TH excess as evidenced by a relative increase in the expression of genes positively regulated by T3 in both the cerebral cortex and liver. An increased tissue accumulation of T(4) and T(3) and the expression of TH alternative transporters, including Lat1, Lat2, Oatp1c1, and Oatp3a1 in the cortex and Lat2 and Oatp1b2 in the liver, suggested that Mct8 deficiency either directly interferes with tissue efflux of TH or indirectly activates other transporters to increase TH uptake. This report is the first to identify that the ontogenesis of TH abnormalities in Mct8-deficient mice manifests with TH excess in the perinatal period.