CONTEXT:The treatment of resistance to thyroid hormone β (RTHβ) is challenging because features of hyperthyroidism in some tissues coexist with a hormone-resistant, hypothyroid state in other organs. OBJECTIVE:To determine whether triiodothyroacetic acid (TRIAC) therapy alleviates hyperthyroid symptoms and changes circulating thyroid hormones, resting energy expenditure and metabolic parameters in RTHβ. DESIGN:Retrospective cohort study. SETTING:Referral center. PARTICIPANTS:Eight adult patients with RTHβ (mean age 41 years; 4 males, 4 females). MAIN OUTCOME MEASURES:Hyperthyroid Symptom Scale (HSS) score, serum free T4 and total T3, resting energy expenditure, sleeping heart rate, fasting lipids, and glucose and systemic insulin resistance. RESULTS:From abnormally elevated levels prior to treatment, TRIAC therapy lowered HSS scores (baseline 17.5 vs posttreatment 6; P = .0014), showed a reduced resting energy expenditure trend (baseline Z-score +1.3 vs posttreatment +0.89; P = .38) and normalized circulating free T4 (baseline free T4 30 pmol/L vs posttreatment 17 pmol/L; P = .007) and total T3 (baseline 2.5 nmol/L vs posttreatment 1.4 nmol/L; P = .001) concentrations in 7 out of 8 patients, without any rise in their serum TSH (baseline 2.1 mU/L vs posttreatment 1.7 mU/L; P = .65), total cholesterol (baseline 4.9 mmol/L vs posttreatment 4.8 mmol/L; P = .81), and triglyceride (baseline 1.3 mmol/L vs post-treatment 1.3 mmol/L; P = .44). Their mean sleeping heart rate (baseline 60 bpm vs posttreatment 58 bpm; P = .56) and plasma N-terminal pro-brain natriuretic peptide (baseline 55 ng/L vs posttreatment 54 ng/L) were unchanged. TRIAC treatment was well tolerated, with no side effects. CONCLUSION:TRIAC therapy in RTHβ relieves hyperthyroid symptoms and lowers resting energy expenditure and circulating thyroid hormones without worsening hepatic hormone resistance or exacerbating cardiac thyromimetic activity. Future clinical trials to determine whether TRIAC treatment alters adverse cardiovascular outcomes in this disorder are warranted.

Monocarboxylate transporter 8 (MCT8) deficiency, also known as Allan-Herndon-Dudley syndrome, is a rare, severely debilitating, and life-limiting genetic disorder caused by variants in the SLC16A2 gene that render the MCT8 thyroid hormone transporter partially or completely dysfunctional. MCT8 is highly expressed throughout the body, including the brain. Its deficiency disrupts thyroid hormone homeostasis and is associated with 2 distinct concomitant clinical presentations: persistent peripheral thyrotoxicosis resulting from elevated serum levels of triiodothyronine and neurodevelopmental impairment arising from low thyroid hormone levels in the brain. The disorder severely impacts quality of life and reduces life expectancy to a median of 35 years due to a range of clinical sequelae, with approximately 30% of affected individuals dying during childhood. Recognition and treatment of thyrotoxicosis are crucial to prevent associated symptoms and long-term sequelae.

Our immune system contains multiple checkpoints to prevent the activation of self-reactive lymphocytes. How some lymphocytes escape these constraints to cause autoimmune disease remains poorly understood. A long-standing hypothesis posits that somatic mutations in immune regulatory genes may enable self-reactive lymphocytes to bypass tolerance checkpoints1-3, but testing this has been challenging owing to technical limitations. Here we used whole-exome and targeted NanoSeq4,5, an accurate single-molecule DNA sequencing protocol, to comprehensively search for driver mutations in autoimmune thyroid disease. This showed many B cell clones convergently acquiring loss-of-function mutations in the key immune checkpoint genes TNFRSF14 (also known as HVEM) and CD274 (which encodes PD-L1), as well as less frequent mutations in other immune genes. In highly inflamed biopsies, we detected tens to hundreds of independent immune checkpoint mutant clones. Laser microdissection, methylation sequencing, spatial transcriptomics, immunostaining, single-nucleus DNA sequencing and antibody synthesis localized these mutations to B cells, confirmed some to be self-reactive and identified clones carrying multiple hits. We found widespread TNFRSF14 biallelic loss, and clones with as many as 4-6 driver mutations. While each clone accounts for a small fraction of cells (typically less than 1%), the myriad mutant clones in each donor amounted to a substantial fraction of B cells harbouring driver mutations. Our results support the hypothesis that somatic mutations in autoimmune lymphocytes may allow them to escape tolerance constraints through a polyclonal cascade of somatic evolution, providing insights into the molecular basis of autoimmune disease.

Abstract Free carnitine is essential to mitochondrial health by buffering the free acetyl-CoA pool and thereby maintaining energy production. It is also responsible for transporting long-chain fatty acids into the mitochondria for oxidation. Almost all the body’s carnitine is in muscle, and plasma concentrations do not reflect tissue content, but there are as yet no non-invasive techniques to assess muscle total or free carnitine. Here we describe a novel non-invasive postprocessing method, using standard 1 H magnetic resonance spectroscopy data, for quantifying muscle total and free carnitine concentrations, which includes an orientation-visibility and spectral fitting component, and consideration of interfering metabolites. We demonstrate the importance of the orientation correction even within one muscle group (accounting for up to 1.9-fold difference within one muscle group and 2.9-fold difference in signal between muscles), show its good reproducibility (CoV 8-12%), and validate the results with mass spectrometry measurements in muscle biopsy samples. We apply this method in a group of patients with genetic mitochondrial disease, to investigate the relationship between mitochondrial dysfunction and muscle lipid accumulation. As predicted muscle total and free carnitine were lower in patients with disease and correlated with the degree of mitochondrial dysfunction and lipid accumulation. Further, robust spatial correlations of total carnitine and muscle lipid imply heterogeneity in mitochondrial function. Our findings suggest that increasing muscle carnitine stores could ameliorate the metabolic effects of and disorders related to mitochondrial dysfunction. Furthermore, it has not usually been known in supplementation studies whether l-carnitine actually reached the target tissue. We suggest that this novel method has significant potential for informing on physiology and pathophysiology, and as a biomarker in monitoring treatment response, investigative drug discovery, and personalised medicine.

ObjectiveRestoration of euthyroidism in patients with thyrotoxicosis prior to thyroidectomy is recommended to decrease perioperative morbidity and thyroid storm risk. This is challenging when conventional anti-thyroid medication is contraindicated or ineffective. Iopanoic acid (IOPA), an iodinated contrast medium formerly used as an oral cholecystographic agent, may facilitate treatment of thyrotoxicosis, but limited manufacture precludes its use in the UK. We investigated the effectiveness and safety of IOPA for optimizing thyroid status in treatment-resistant thyrotoxicosis prior to thyroidectomy at a referral centre. MethodsWith prior permission of our Drug and Therapeutics Committee, we sourced laboratory-grade (>98% pure) IOPA and administered this orally to control ongoing, severe thyrotoxicosis prior to thyroidectomy in 12 patients with inadequate response to standard therapies. Underlying aetiologies included Graves’ disease, amiodarone-induced thyrotoxicosis, toxic multinodular goitre and resistance to thyroid hormone beta. Medical case notes were reviewed retrospectively to analyse clinical and biochemical outcomes. ResultsAll patients exhibited a decline and normalization/near-normalization of free T3 (FT3) levels (mean 55% decrease, SEM 4.5%), with minimal changes in FT4 levels. Eleven patients proceeded to uneventful thyroidectomy, and IOPA was well tolerated with no directly attributable side effects. ConclusionIOPA is a safe and effective agent for controlling biochemical thyrotoxicosis in preparation for thyroidectomy, including disease refractory to conventional medication. Highly pure, laboratory-grade iopanoic acid that is approved for human use is now available in the UK; consideration should be given to more widespread use for emergency treatment of life-threatening hyperthyroidism.

BACKGROUND:Heterologous schedules of booster vaccines for COVID-19 following initial doses of mRNA or adenoviral vector vaccines have been shown to be safe and immunogenic. There are few data on booster doses following initial doses of protein nanoparticle vaccines. METHODS:Participants of the phase 3 clinical trial of the COVID-19 vaccine NVX-CoV2373 (EudraCT 2020-004123-16) enroled between September 28 and November 28, 2020, who received 2 doses of NVX-CoV2373 administered 21 days apart were invited to receive a third dose booster vaccine of BNT162b2 (wild type mRNA vaccine) as a sub-study of the COV-BOOST clinical trial, and were followed up for assessment of safety, reactogenicity and immunogenicity to day 242 post-booster. RESULTS:The BNT162b2 booster following two doses of NVX-COV2373 was well-tolerated. Most adverse events were mild to moderate, with no serious vaccine-related adverse events reported. Immunogenicity analysis showed a significant increase in spike IgG titres and T-cell responses post-third dose booster. Specifically, IgG levels peaked at day 14 with a geometric mean concentration (GMC) of 216,255 ELISA laboratory units (ELU)/mL (95% CI 191,083-244,743). The geometric mean fold increase from baseline to day 28 post-boost was 168.6 (95% CI 117.5-241.8). Spike IgG titres were sustained above baseline levels at day 242 with a GMC of 58,686 ELU/mL (95% CI 48,954-74,652), with significant decay between days 28 and 84 (geometric mean ratio 0.58, 95% CI 0.53-0.63). T-cell responses also demonstrated enhancement post-booster, with a geometric mean fold increase of 5.1 (95% CI 2.9-9.0) at day 14 in fresh samples and 3.0 (95% CI 1.8-4.9) in frozen samples as measured by ELISpot. In an exploratory analysis, participants who received BNT162b2 after two doses of NVX-COV2373 exhibited higher anti-spike IgG at Day 28 than those who received homologous three doses of BNT162b2, with a GMR of 5.02 (95% CI: 3.17-7.94). This trend remained consistent across all time points, indicating a similar decay rate between the two schedules. CONCLUSIONS:A BNT162b2 third dose booster dose in individuals primed with two doses of NVX-COV2373 is safe and induces strong and durable immunogenic responses, higher than seen in other comparable studies. These findings support the use and investigation of heterologous booster strategies and early investigation of heterologous vaccine technology schedules should be a priority in the development of vaccines against new pathogens.

Purpose:People with resistance to thyroid hormone due to defective thyroid receptor β (RTHβ) exhibit adverse cardiovascular outcomes and premature mortality. Whether this reflects increased global cardiovascular disease (CVD) risk or hyperthyroxinemia-associated effects on cardiac rhythm and contractility is unknown. We determined CVD risk and plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) concentrations as a marker of reduced cardiac function in 99 individuals (mean age 41 years, 37% males) with RTHβ. Results:The mean (SD range) QRISK3 score for 82 participants was 2.0% (0.5-8.8%) vs 1.3% (0.3-5.0%) for age, sex, and ethnicity-matched healthy controls (P = .005). The QRISK3 heart age of RTHβ participants was 49.8 ± 14.5 years vs actual age 44.5 ± 12.4 years [difference 5.3 (95% confidence interval: 4.0, 6.5) years; P < .001]. The mean (SD range) plasma NT-proBNP in 79 RTHβ participants was 51 (18-142) pg/mL; 10.1% of values were above the age-specific 97.5th percentile of a large control sample. In multiple linear regression, age and female sex were significant independent predictors of NT-proBNP (P ≤ .001), but free T3, free T4, TSH, and QRISK3 10-year CVD risk were not. Conclusion:Elevated NT-proBNP concentrations, seen even in young people with RTHβ, suggest that myocardial dysfunction contributes to early adverse cardiovascular outcomes in this disorder, with increased atherosclerotic disease risk likely manifesting later in life. Measurement of NT-proBNP and assessment of cardiovascular risk should be considered at first presentation and periodically during follow-up of RTHβ.

OBJECTIVE:To assess determinants of dyslipidemia (specifically raised serum low-density lipoprotein cholesterol and triglycerides, and reduced high-density lipoprotein cholesterol) in individuals with Resistance to Thyroid Hormone β (RTHβ). METHODS:Multivariable linear regression analyses of cross-sectional fasting serum lipid profiles from 105 genetically-confirmed individuals with RTHβ (mean age 40.0 years, 40% males) were conducted, including candidate variables with plausible independent associations with the individual components of dyslipidemia such as indices of thyroid function, plasma non-esterified fatty acid concentrations, and insulin resistance assessed using the Homoeostasis Model Assessment equation. RESULTS:Age was positively related to both serum total and low-density lipoprotein-cholesterol concentrations (P < .001), while there were similar directional associations between body mass index and total:high-density lipoprotein-cholesterol ratio, and Homoeostasis Model Assessment-insulin resistance and serum triglycerides (P ≤ .007). Plasma non-esterified fatty acid concentrations were not associated with serum triglycerides. The only thyroid function measure revealed by the individual models was an inverse association between reverse triiodothyronine and serum triglycerides (P = .009). CONCLUSIONS:The dyslipidemia associated with RTHβ shares recognized contributory factors found in studies of the general population but appears independent of thyroid status. The reason for the significant inverse association between circulating reverse triiodothyronine and serum triglyceride concentrations is unclear and merits further investigation.

Predicting and quantifying phenotypic consequences of genetic variants in rare disorders is a major challenge, particularly pertinent for ‘actionable’ genes such as thyroid hormone transporter MCT8 (encoded by the X-linked SLC16A2 gene), where loss-of-function (LoF) variants cause a rare neurodevelopmental and (treatable) metabolic disorder in males. The combination of deep phenotyping data with functional and computational tests and with outcomes in population cohorts, enabled us to: (i) identify the genetic aetiology of divergent clinical phenotypes of MCT8 deficiency with genotype-phenotype relationships present across survival and 24 out of 32 disease features; (ii) demonstrate a mild phenocopy in ~400,000 individuals with common genetic variants in MCT8; (iii) assess therapeutic effectiveness, which did not differ among LoF-categories; (iv) advance structural insights in normal and mutated MCT8 by delineating seven critical functional domains; (v) create a pathogenicity-severity MCT8 variant classifier that accurately predicted pathogenicity (AUC:0.91) and severity (AUC:0.86) for 8151 variants. Our information-dense mapping provides a generalizable approach to advance multiple dimensions of rare genetic disorders.

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Liver X receptor-alpha (LXR alpha) regulates cellular cholesterol abundance and potently activates hepatic lipogenesis. Here we show that at least 1 in 450 people in the UK Biobank carry functionally impaired mutations in LXR alpha, which is associated with biochemical evidence of hepatic dysfunction. On a western diet, male and female mice homozygous for a dominant negative mutation in LXR alpha have elevated liver cholesterol, diffuse cholesterol crystal accumulation and develop severe hepatitis and fibrosis, despite reduced liver triglyceride and no steatosis. This phenotype does not occur on low-cholesterol diets and can be prevented by hepatocyte-specific overexpression of LXR alpha. LXR alpha knockout mice exhibit a milder phenotype with regional variation in cholesterol crystal deposition and inflammation inversely correlating with steatosis. In summary, LXR alpha is necessary for the maintenance of hepatocyte health, likely due to regulation of cellular cholesterol content. The inverse association between steatosis and both inflammation and cholesterol crystallization may represent a protective action of hepatic lipogenesis in the context of excess hepatic cholesterol. LXR alpha is highly expressed in hepatocytes, where it regulates cholesterol abundance and stimulates lipogenesis. The authors provide evidence in humans and mice that impaired LXR alpha signalling is hepatotoxic, despite its potent lipogenic actions.

Background Obesity rates have nearly tripled in the past 50 years, and by 2030 more than 1 billion individuals worldwide are projected to be obese. This creates a significant economic strain due to the associated non-communicable diseases. The root cause is an energy expenditure imbalance, owing to an interplay of lifestyle, environmental, and genetic factors. Obesity has a polygenic genetic architecture; however, single genetic variants with large effect size are etiological in a minority of cases. These variants allowed the discovery of novel genes and biology relevant to weight regulation and ultimately led to the development of novel specific treatments. Methods We used a case-control approach to determine metabolic differences between individuals homozygous for a loss-of-function genetic variant in the small integral membrane protein 1 (SMIM1) and the general population, leveraging data from five cohorts. Metabolic characterization of SMIM1−/− individuals was performed using plasma biochemistry, calorimetric chamber, and DXA scan. Findings We found that individuals homozygous for a loss-of-function genetic variant in SMIM1 gene, underlying the blood group Vel, display excess body weight, dyslipidemia, altered leptin to adiponectin ratio, increased liver enzymes, and lower thyroid hormone levels. This was accompanied by a reduction in resting energy expenditure. Conclusion This research identified a novel genetic predisposition to being overweight or obese. It highlights the need to investigate the genetic causes of obesity to select the most appropriate treatment given the large cost disparity between them. Funding This work was funded by the National Institute of Health Research, British Heart Foundation, and NHS Blood and Transplant.

To investigate changes in brain network organization and possible neurobehavioral similarities to attention-deficit hyperactivity disorder (ADHD), we measured changes in brain resting-state functional connectivity (rs-fMRI) and cognitive domains in patients with resistance to thyroid hormone β (RTHβ) and compared them with those in healthy control subjects. In this prospective case-control study, twenty-one participants with genetically confirmed RTHβ were matched with 21 healthy controls. The Adult ADHD Self-Report Scale (ASRS-v1.1) and ADHD Rating Scale-IV were used to assess self-reported symptoms of ADHD. A voxel-wise and atlas-based approach was used to identify changes in the brain networks. The RTHβ group reported behavioral symptoms similar to those of ADHD. We found evidence of weaker network integration of the lingual and fusiform gyri in the RTHβ group, which was mainly driven by weaker connectivity to the bilateral insula and supplementary motor cortex. Functional connectivity between regions of the default mode network (angular gyrus/middle temporal gyrus) and regions of the cognitive control network (bilateral middle frontal gyrus) was increased in RTHβ patients compared to healthy controls. Increased connectivity between regions of the default mode network and the dorsolateral prefrontal cortex is frequently reported in ADHD and is interpreted to be associated with deficits in attention. Our finding of weaker connectivity of the lingual gyrus to the bilateral insula (salience network) in RTHβ patients has also been reported previously in ADHD and may reflect decreased habituation to visual stimuli and increased distractibility. Overall, our observations support the notion of neuropsychological similarities between RTHβ and ADHD.

The nuclear receptor Liver X Receptor-α (LXRα) activates lipogenic gene expression in hepatocytes. Its inhibition has therefore been proposed as a strategy to treat metabolic-dysfunction-associated steatotic liver disease (MASLD). In order to understand the impact of reducing LXRα activity on human health we first examined the association between the carriage of rare loss of function mutations in NR1H3 (encoding LXRα) and metabolic and hepatic phenotypes. We identified 63 rare predicted damaging variants in the ligand binding domain of LXRα in 454,787 participants in UK Biobank. On functional characterisation, 42 of these were found to be severely impaired. Consistent with loss of the lipogenic actions of LXRα, carriers of damaging mutations in LXRα had reduced serum triglycerides (ß=-0.13 s.d. ±0.03, P=2.7x10-5, N(carriers)=971). Surprisingly, these carriers also had elevated concentrations of serum liver enzymes (e.g. ALT: ß=0.17s.d. ±0.03, P=1.1x10-8, N(carriers)=972) with a 35% increased risk of clinically significant elevations in ALT (OR=1.32, 95%CI:1.15-1.53, P=1.2x10-4, N(carriers)=972), suggestive of hepatotoxicity. We generated a knock-in mouse carrying one of the most severely damaging mutations ( Nr1h3 p.W441R) which we demonstrated to have dominant negative properties. Homozygous knock-in mice rapidly developed severe hepatitis and fibrotic liver injury following exposure to western diet despite markedly reduced steatosis, liver triglycerides and lipogenic gene expression. This phenotype was completely rescued by viral over-expression of wildtype LXRα specifically in hepatocytes, indicating a cell-autonomous effect of the mutant on hepatocyte health. While homozygous LXRα knockout mice showed some evidence of hepatocyte injury under similar dietary conditions, the phenotype of the LXRαW441R/W441R mouse was much more severe, suggesting that dominant negative mutations that actively co-repress target genes can result in pathological impacts significantly more severe than those seen with simple absence of the receptor. In summary, our results show that loss of function mutations in LXRα occur in at least 1/450 people and are associated with evidence of liver dysfunction. These findings implicate LXRα in the maintenance of human liver health, identify a new murine model of rapidly progressive fibrotic liver disease and caution against LXR antagonism as a therapeutic strategy for MASLD. ### Competing Interest Statement S.O. has undertaken remunerated consultancy work for Pfizer, Third Rock Ventures, AstraZeneca, NorthSea TherapeuAcs and Courage TherapeuAcs. SL parAcipates in paid consultancy for Eolas Medical. EJG and JRBP are employees of Insmed InnovaAon UK and holds stock/stock opAons in Insmed Inc. JRBP performs paid consultancy for WW InternaAonal and receives research funding from GSK. YZ is a UK University Worker of GSK. XJ, KRS and DP are current employees and/or stockholders of AstraZeneca.

A three-year-old girl with a history of recurrent tonsillitis was investigated for failure to thrive and global developmental delay. Clinically, she had a triangular face with low-set ears and intermittent tachycardia. She had growth failure with her weight under the third centile while her height was within normal limits. Other systemic examinations were unremarkable. The presence of an elevated free T4 (FT4) with an inappropriately high thyroid stimulating hormone (TSH) in this patient raised the clinical suspicion of Thyroid Hormone Resistance Syndrome. DNA sequencing confirmed the diagnosis, which showed R243W gene mutation in Thyroid Hormone Receptor-Beta1 (THRB1).