Skeletal muscle is regarded as an endocrine and paracrine organ. Muscle-derived secretory proteins, referred to as myokines, mediate interactions between skeletal muscle mass and other organs such as the liver, adipose tissue, pancreas, bone, and the cardiovascular system. As individuals age, reduced levels of physical activity and sarcopenia (loss of skeletal muscle mass and strength) are associated with physical frailty and disability. Recently, several studies have suggested that the loss of skeletal muscle mass may contribute to metabolic disease. Therefore, herein, we focus on the relationships between skeletal muscle mass and metabolic diseases, including metabolic syndrome and non-alcoholic fatty liver disease.

In 2017, the first Korean nationwide data on serum thyroid stimulating hormone (TSH) levels, serum free thyroxine (fT4) levels, and urinary iodine concentration (UIC) were published based on a population of 7,061 Koreans who participated in the Korea National Health and Nutrition Examination Survey VI. The mean TSH level was 2.16 mIU/L, with a reference interval of 0.59 to 7.03 mIU/L (men 2.09 mIU/L, women 2.24 mIU/L, P<0.001). A U-shaped association was found between serum TSH levels and age. The mean fT4 level was 1.25 ng/dL, and its reference interval was 0.92 to 1.60 ng/dL (men 1.29 ng/dL, women 1.20 ng/dL, P<0.0001). Serum fT4 levels decreased with age (P for trend <0.0001). Serum thyroid peroxidase antibody (TPOAb) was detected in 7.30% of participants (men 4.33%, women 10.62%). TPOAb titers tended to increase with age, and were higher in women than in men. The median UIC was 294 μg/L, and UIC showed a U-shaped relationship with age. According to the World Health Organization recommendations, only 23% of participants were in the adequate range of iodine intake, while 65% were in the above requirements or excessive, and 12% in insufficient. The prevalence of overt hyperthyroidism and hypothyroidism in Koreans was 0.34% to 0.54% and 0.73% to 1.43%, respectively.

The increased incidence of thyroid cancer is a worldwide phenomenon; however, the issue of overdiagnosis has been most prominent in South Korea. The age-standardized mortality rate of thyroid cancer in Korea steeply increased from 1985 to 2004 (from 0.17 per 100,000 to 0.85 per 100,000), and then decreased until 2015 to 0.42 per 100,000, suggesting that early detection reduced mortality. However, early detection of thyroid cancer may be cost-ineffective, considering its very high prevalence and indolent course. Therefore, risk stratification and tailored management are vitally important, but many prognostic markers can only be evaluated postoperatively. Discovery of preoperative marker(s), especially for small cancers, is the most important unmet clinical need for thyroid cancer. Herein, we discuss some such factors that we recently discovered. Another unmet clinical need is better treatment of radioiodine-refractory (RAIR) differentiated thyroid cancer (DTC) and undifferentiated cancers. Although sorafenib and lenvatinib are available, better drugs are needed. We found that phosphoglycerate dehydrogenase, a critical enzyme for serine biosynthesis, could be a novel therapeutic target, and that the lymphocyte-to-monocyte ratio is a prognostic marker of survival in patients with anaplastic thyroid carcinoma or RAIR DTC. Deeper insights are needed into tumor-host interactions in thyroid cancer to improve treatment.

Adrenal masses are mainly detected unexpectedly by an imaging study performed for reasons unrelated to any suspect of adrenal diseases. Such masses are commonly defined as “adrenal incidentalomas” and represent a public health challenge because they are increasingly recognized in current medical practice. Management of adrenal incidentalomas is currently matter of debate. Although there is consensus on the need of a multidisciplinary expert team evaluation and surgical approach in patients with significant hormonal excess and/or radiological findings suspicious of malignancy demonstrated at the diagnosis or during follow-up, the inconsistency between official guidelines and the consequent diffuse uncertainty on management of small adrenal incidentalomas still represents a considerable problem in terms of clinical choices in real practice. The aim of the present work is to review the proposed strategies on how to manage patients with adrenal incidentalomas that are not candidates to immediate surgery. The recent European Society of Endocrinology/European Network for the Study of Adrenal Tumors guidelines have supported the view to avoid surveillance in patients with clear benign adrenal lesions <4 cm and/or without any hormonal secretion; however, newer prospective studies are needed to confirm safety of this strategy, in particular in younger patients.

Since the identification of succinate's receptor in 2004, studies supporting the involvement of succinate signaling through its receptor in various diseases have accumulated and most of these investigations have highlighted succinate's pro-inflammatory role. Taken with the fact that succinate is an intermediate metabolite in the center of mitochondrial activity, and considering its potential regulation of protein succinylation through succinyl-coenzyme A, a review on the overall multifaceted actions of succinate to discuss whether and how these actions relate to the cellular locations of succinate is much warranted. Mechanistically, it is important to consider the sources of succinate, which include somatic cellular released succinate and those produced by the microbiome, especially the gut microbiota, which is an equivalent, if not greater contributor of succinate levels in the body. Continue learning the critical roles of succinate signaling, known and unknown, in many pathophysiological conditions is important. Furthermore, studies to delineate the regulation of succinate levels and to determine how succinate elicits various types of signaling in a temporal and spatial manner are also required.

Anaplastic thyroid cancer (ATC) is a lethal human cancer with a 5-year survival rate of less than 10%. Recently, its genomic and transcriptomic characteristics have been extensively elucidated over 5 years owing to advance in high throughput sequencing. These efforts have extended molecular understandings into the progression mechanisms and therapeutic vulnerabilities of aggressive thyroid cancers. In this review, we provide an overview of genomic and transcriptomic alterations in ATC and poorly-differentiated thyroid cancer, which are distinguished from differentiated thyroid cancers. Clinically relevant genomic alterations and deregulated signaling pathways will be able to shed light on more effective prevention and stratified therapeutic interventions for affected patients.

Osteoporotic fracture (OF) is associated with high disability and morbidity rates. The burden of OF may be reduced by early identification of subjects who are vulnerable to fracture. Although the current fracture risk assessment model includes clinical risk factors (CRFs) and bone mineral density (BMD), its overall ability to identify individuals at high risk for fracture remains suboptimal. Efforts have therefore been made to identify potential biomarkers that can predict the risk of OF, independent of or combined with CRFs and BMD. This review highlights the emerging biomarkers of bone metabolism, including sphongosine-1-phosphate, leucine-rich repeat-containing 17, macrophage migration inhibitory factor, sclerostin, receptor activator of nuclear factor-κB ligand, and periostin, and the importance of biomarker risk score, generated by combining these markers, in enhancing the accuracy of fracture prediction.

Since parathyroid hormone (PTH) was first isolated and its gene (PTH) was sequenced, only eight PTH mutations have been discovered. The C18R mutation in PTH, discovered in 1990, was the first to be reported. This autosomal dominant mutation induces endoplasmic reticulum stress and subsequent apoptosis in parathyroid cells. The next mutation, which was reported in 1992, is associated with exon skipping. The substitution of G with C in the first nucleotide of the second intron results in the exclusion of the second exon; since this exon includes the initiation codon, translation initiation is prevented. An S23P mutation and an S23X mutation at the same residue were reported in 1999 and 2012, respectively. Both mutations resulted in hypoparathyroidism. In 2008, a somatic R83X mutation was detected in a parathyroid adenoma tissue sample collected from a patient with hyperparathyroidism. In 2013, a heterozygous p.Met1_Asp6del mutation was incidentally discovered in a case-control study. Two years later, the R56C mutation was reported; this is the only reported hypoparathyroidism-causing mutation in the mature bioactive part of PTH. In 2017, another heterozygous mutation, M14K, was detected. The discovery of these eight mutations in the PTH gene has provided insights into its function and broadened our understanding of the molecular mechanisms underlying mutation progression. Further attempts to detect other such mutations will help elucidate the functions of PTH in a more sophisticated manner.

Machine learning (ML) applications have received extensive attention in endocrinology research during the last decade. This review summarizes the basic concepts of ML and certain research topics in endocrinology and metabolism where ML principles have been actively deployed. Relevant studies are discussed to provide an overview of the methodology, main findings, and limitations of ML, with the goal of stimulating insights into future research directions. Clear, testable study hypotheses stem from unmet clinical needs, and the management of data quality (beyond a focus on quantity alone), open collaboration between clinical experts and ML engineers, the development of interpretable high-performance ML models beyond the black-box nature of some algorithms, and a creative environment are the core prerequisites for the foreseeable changes expected to be brought about by ML and artificial intelligence in the field of endocrinology and metabolism, with actual improvements in clinical practice beyond hype. Of note, endocrinologists will continue to play a central role in these developments as domain experts who can properly generate, refine, analyze, and interpret data with a combination of clinical expertise and scientific rigor.

Korea is currently an aged society and is on the cusp of becoming a superaged society in a few years. The health burden of cardiovascular diseases increases with age, and the increasing prevalence of cardiovascular risk factors, such as obesity, hypertension, diabetes mellitus, and dyslipidemia, may be linked to increased population-level cardiovascular risk. In 2018, the prevalence of obesity in Korea was 35.7% (men, 45.4%; women, 26.5%) according to the Obesity Fact Sheet 2019, based on National Health Insurance Corporation medical checkup data. In 2016, the prevalence of diabetes was 14.4% in Koreans older than 30 years according to the Diabetes Fact Sheet published by the Korean Diabetes Association, based on data from the Korean National Health and Nutrition Examination Survey. The prevalence of hypertension in the total population of Korea in 2018 was 28.3% according to the Korean Hypertension Fact Sheet produced by the Korean Society of Hypertension. Lastly, the prevalence of dyslipidemia in 2018 was 40.5% according to the Dyslipidemia Fact Sheet published by the Korean Society of Lipid and Atherosclerosis. In this article, I would like to review the prevalence and current management of cardiovascular risk factors in Korea according to the fact sheets released by various associations.