Mutations in potassium channel Kir2.6 cause susceptibility to thyrotoxic hypokalemic periodic paralysis.

Thyrotoxic hypokalemic periodic paralysis (TPP) is characterized by acute attacks of weakness, hypokalemia, and thyrotoxicosis of various etiologies. These transient attacks resemble those of patients with familial hypokalemic periodic paralysis (hypoKPP) and resolve with treatment of the underlying hyperthyroidism. Because of the phenotypic similarity of these conditions, we hypothesized that TPP might also be a channelopathy. While sequencing candidate genes, we identified a previously unreported gene (not present in human sequence databases) that encodes an inwardly rectifying potassium (Kir) channel, Kir2.6. This channel, nearly identical to Kir2.2, is expressed in skeletal muscle and is transcriptionally regulated by thyroid hormone. Expression of Kir2.6 in mammalian cells revealed normal Kir currents in whole-cell and single-channel recordings. Kir2.6 mutations were present in up to 33% of the unrelated TPP patients in our collection. Some of these mutations clearly alter a variety of Kir2.6 properties, all altering muscle membrane excitability leading to paralysis.

Diabetes outcomes in specialist and general practitioner settings in Singapore: challenges of right-siting.

The Singapore public healthcare system has increasingly used the term "right-siting" to describe the principle that stable chronic disease patients should be managed in primary care rather than specialist settings. The majority of primary healthcare providers in Singapore are general practitioners (GPs). The aims of this paper were to measure the quality of diabetes care in specialist and GP settings, and assess right-siting efforts in a tertiary centre in Singapore. Three hundred eighty-three consecutive patients with type 2 diabetes referred to the Singapore General Hospital Diabetes Centre (SGH DBC) between January and March 2005 were analysed. At the first visit, 51 patients (13.3%) were classified as inappropriate referrals and discharged back to the referral source or to primary care. After 12 months, 136 patients (group A = 35.5%) remained on follow-up at SGH DBC. In these patients, significant improvements were seen in mean HbA1c but not blood pressure (BP) or low density lipoprotein-cholesterol (LDL-C). One hundred twenty-eight (group B = 33.4%) patients were discharged from DBC within the 12 months of the study period. Mean follow-up duration in group B was 5.5 months and HbA1c, blood pressure and LDL-cholesterol had improved significantly in these patients. Glycaemic control of group B patients at the time of discharge was significantly better than group A at 12 months (mean HbA1c = 7.15% vs 8.16%; P <0.001). More than half (55.6%) of group B patients achieved HbA1c targets compared to 32.4% from group A (P <0.001). Although mean BP and LDL-C levels fell in group B patients, the percentage of patients achieving BP and LDL-C targets did not improve significantly in both groups. From August 2005 to January 2008, GPs participating in SingHealth's Delivering on Target (DOT) programme enrolled 579 patients under their care for additional diabetic counselling by community nurse educators. Pre- and post-programme HbA1c results were submitted for 370 patients (64%). Mean HbA1c levels of these patients decreased from 8.23% to 7.32% (P <0.001). The proportion of patients who achieved HbA1c <7% increased from 26% to 51% (P <0.01). However, BP and LDL-C levels did not improve. It is difficult to base referral or discharge decisions solely on these indicators. Our studies show that both in the specialist and GP settings, significant improvements in HbA1c are seen. Results for BP and LDL-C, however, showed little improvement. Some degree of rightsiting was seen at SGH DBC with discharged patients showing greater improvements than patients who were retained. However, >30% of patients remained in SGH DBC despite achieving HbA1C targets. Our results indicate the need for better strategies to address the underlying obstacles to right-siting. Of greater concern, the lack of improvement in BP and LDL-C indicates a high degree of clinical inertia to these issues among specialists and GPs treating diabetes in Singapore.

Effects of genetic immunization of Swiss outbred mice with human thyroid stimulating hormone receptor cDNA plasmids harboring gain-of-function mutations.

Animal models of Graves' disease have been generated in recent years with various vaccination protocols using wild-type TSH receptor. In this study, we report the findings of genetic immunization of Swiss outbred mice with three different mutated human TSH receptor plasmids, each containing one constitutive activating mutation located at the ectodomain (S281N), exoloop (I486F), and transmembrane segment (D633H) respectively. Although the overall rate of thyrotoxicosis in the mice was < 10%, anti-TSH receptor antibodies could be detected in many animals by flow cytometry, radioreceptor assay, and functional bioassays using recombinant human TSH receptor. Mice injected with plasmids harboring activated mutants (S281N and D633H) showed production of predominantly stimulating antibodies, whilst those treated with wild-type receptor plasmids generated mainly blocking sera. Most of these antibodies displaced radiolabeled bovine TSH, and their epitopes, independent of functional characteristics, were mapped to the first 271 amino acids of the TSH receptor. This supports recent findings that binding of stimulatory or blocking antibodies lie in close proximity within the leucine-rich repeat region.

Detection of thyroid peroxidase mRNA and protein in orbital tissue.

OBJECTIVE: We have previously reported that the absence of thyroid peroxidase antibodies (TPOAb) in Graves' disease (GD) was associated with an increased risk of Graves' ophthalmopathy (GO). This observation raised the possibility that TPOAb could act as a protective factor. However, the presence of thyroid peroxidase (TPO) in the orbit has not been previously reported. The aim of this study was to confirm or exclude the presence of orbital TPO. METHODS AND DESIGN: Relative TPO mRNA expression from GO (n=6) and normal (n=5) orbital fat tissue was determined using real-time PCR technique. Orbital fat in the normal group from blepharoplasty represents extraconal (anterior) fat. mRNA expression in fibroblasts grown from these tissues before and after adipocyte differentiation was also documented. Finally, Western blotting was carried out to verify translation of TPO mRNA transcripts. RESULTS AND DISCUSSION: TPO transcripts were detected in the orbital fat tissue obtained from normal and GO subjects using the real-time PCR technique. TPO expression was increased in GO compared to normal (N) tissues. However, TPO expression in cultured fibroblasts was similar in both groups and adipogenesis did not appear to alter TPO expression. Protein was detected by Western blot analysis using the TPO MAB 47 (mAb 47). The predicted 110-kDa band was detected in orbital fat as well as in orbital fibroblasts. Our results suggest the presence of TPO in GO and N orbital tissues. We hypothesise that immune responses directed against orbital TPO might play a role in modulating the clinical expression of GO.