Urate is produced in the liver by the degradation of purines from the diet and nucleotide turnover and excreted by the kidney and gut. The kidney is the major route of urate removal and has a pivotal role in the regulation of urate homeo- stasis. Approximately 10% of the glomerular filtered urate is excreted in the urine, and the remainder is reabsorbed by the proximal tubule. However, the transport of urate in the proximal tubule is bidirectional: reabsorption and secretion. Thus, an increase in reabsorption or a decrease in secretion may induce hyperuricemia. In contrast, a decrease in reabsorption or an increase in secretion may result in hyperuricosuria. In the proximal tubule, urate reabsorption is mainly mediated by apical URAT1(SLC22A12) and basolateral GLUT9(SLC2A9) transporter. OAT4 (SLC22A11) also acts in urate reabsorption in the apical membrane, and its poly- morphism is associated with the risk of hyperuricemia. Renal hypouricemia is cau- sed by SLC22A12 or SLC2A9 loss-of-function mutations, and it may be complicated by exercise-induced acute kidney injury. URAT1 and GLUT9 are also drug targets for uricosuric agents. Sodium-glucose cotransporter inhibitors may induce hyperuri- cosuria by inhibiting GLUT9b located in the apical plasma membrane. Urate secre- tion is mediated by basolateral OAT1 (SLC22A6) and OAT3 (SLC22A8) and apical ATP-binding cassette super-family G member 2 (ABCG2), NPT1 (SLC17A1), and NPT4 (SLC17A3) transporter in the proximal tubule. NPT1 and NPT4 may be key players in renal urate secretion in humans, and deletion of SLC22A6 and SLC22A8 in mice leads to decreased urate excretion. Dysfunctional variants of ABCG2 inhibit urate secretion from the gut and kidney and may cause gout. In summary, the net result of urate transport in the proximal tubule is determined by the dominance of trans- porters between reabsorption(URAT1, OAT4, and GLUT9) and secretion(ABCG2, NPT1, NPT4, OAT1, and OAT3).

• Gout
• Hyperuricosuria
• Hypouricemia
• Proximal tubule
• Uric acid transport

Hypokalemic periodic paralysis (hypoPP) is a disorder characterized by episodic, short-lived, and hypo-reflexive skeletal muscle weakness. HypoPP is a rare disease caused by genetic mutations related to expression of sodium or calcium ion chan- nels. Most mutations are associated with autosomal dominant inheritance, but some are found in patients with no relevant family history. A 28-year-old man who visited the emergency room for paralytic attack was assessed in this study. He exhibited motor weakness in four limbs. There was no previous medical history or family history. The initial electrocardiogram showed a flat T wave and QT prolongation. His blood test was delayed, and sudden hypotension and bradycardia were observed. The blood test showed severe hypokalemia. After correcting hypokalemia, his muscle paralysis recovered without any neurological deficits. The patient’s thyroid function and long exercise test results were normal. However, because of the history of high carbohydrate diet and exercise, hypoPP was suspected. Hence, next-generation sequencing (NGS) was performed, and a mutation of Arg669His was noted in the SCN4A gene. Although hypoPP is a rare disease, it can be suspected in patients with hypokalemic paralysis, and iden tification of this condition is important for preventing further attacks and improving patient outcomes. Diagnosing hypoPP through targeted NGS is a cost-effective and useful method.

• Hypokalemic periodic paralysis
• Genetic diseases
• Arrhythmia

A 44-year-old man with chronic alcoholism presented with seizure and loss of consciousness. He was diagnosed with alcoholic hepatic encephalopathy, and his neurologic symptoms recovered after lactulose enema treatment. His initial serum sodium level was 141 mEq/L. However, his mental state became confused after treatment with lactulose enema for five days, and his serum sodium level increased to 178 mEq/L. After five days of gradual correction of serum sodium level from 178 mEq/L to 140 mEq/L, the patient’s mental state recovered, but motor weakness in both limbs remained. Therefore, magnetic resonance imaging of the brain was performed. T2-weighted brain images showed bilateral symmetrical hyperintensities in the central pons, basal ganglia, thalami, hippocampi and unci, which were consistent with central pontine and extrapontine myelinolysis. We report a rare case of osmotic demyelination syndrome that occurred as a result of a rapid increase from a normal sodium level to hypernatremia caused by lactulose enema administered to treat alcoholic hepatic encephalopathy.

• Central pontine myelinolysis
• Extrapontine myelinolysis
• Lactulose
• Alcoholic
• Hepatic encephalopathy