The clinical and genetic features in a cohort of mainland Chinese patients with thyrotoxic periodic paralysis

Periodic paralysis

Periodic paralysis is a rare, dominantly inherited disorder of skeletal muscle in which episodic attacks of weakness are caused by a transient impairment of fiber excitability. Attacks of weakness are often elicited by characteristic environmental triggers, which were the basis for clinically delineating subtypes of periodic paralysis and are an important distinction for optimal disease management. All forms of familial periodic paralysis are caused by mutations of ion channels, often selectively expressed in skeletal muscle, that destabilize the resting potential. The missense mutations usually alter channel function through gain-of-function changes rather than producing a complete loss-of-function null. The knowledge of which channel gene harbors a variant, whether that variant is expected to (or known to) alter function, and how altered function impairs fiber excitability aides in the interpretation of patient signs and symptoms, the interpretation of gene test results, and how to optimize therapeutic intervention for symptom management and improve quality of life.

Gene panel analysis of 119 index patients with suspected periodic paralysis in Japan

Introduction

Genetic factors are recognized as the major reason for patients with periodic paralysis. The goal of this study was to determine the genetic causes of periodic paralysis in Japan.

Methods

We obtained a Japanese nationwide case series of 119 index patients (108 men and 11 women) clinically suspected of periodic paralysis, and a gene panel analysis, targeting CACNA1S, SCN4A, and KCNJ2 genes, was conducted.

Results

From 34 cases, 25 pathogenic/likely pathogenic/unknown significance variants were detected in CACNA1S (nine cases), SCN4A (19 cases), or KCNJ2 (six cases), generating a molecular diagnostic rate of 28.6%. In total, seven variants have yet been found linked to periodic paralysis previously. The diagnostic yield of patients with hypokalemic and hyperkalemic periodic paralyzes was 26.2 (17/65) and 32.7% (17/52), respectively. A considerably higher yield was procured from patients with than without positive family history (18/25 vs. 16/94), onset age ≤20 years (24/57 vs. 9/59), or recurrent paralytic attacks (31/94 vs. 3/25).

Discussion

The low molecular diagnostic rate and specific genetic proportion of the present study highlight the etiological complexity of patients with periodic paralysis in Japan.

Ion Channel Gene Mutations Causing Skeletal Muscle Disorders: Pathomechanisms and Opportunities for Therapy

Skeletal muscle ion channelopathies (SMICs) are a large heterogeneous group of rare genetic disorders caused by mutations in genes encoding ion channel subunits in the skeletal muscle mainly characterized by myotonia or periodic paralysis, potentially resulting in long-term disabilities. However, with the development of new molecular technologies, new genes and new phenotypes, including progressive myopathies, have been recently discovered, markedly increasing the complexity in the field. In this regard, new advances in SMICs show a less conventional role of ion channels in muscle cell division, proliferation, differentiation, and survival. Hence, SMICs represent an expanding and exciting field. Here, we review current knowledge of SMICs, with a description of their clinical phenotypes, cellular and molecular pathomechanisms, and available treatments.

Impact of first-line treatment choice on long-term outcomes of hyperthyroid Graves' disease patients with thyrotoxic periodic paralysis

Background

Thyrotoxic periodic paralysis (TPP) is a unique manifestation of Graves’ disease. While it is uncommon in Asian, it is extremely rare in Caucasian patients (0.1–0.2%). Previous studies suggested that TPP indicate more severity of Graves’ disease and definitive treatments should be used to prevent relapses.

Aim

To describe clinical features and impact of first-line treatment on long-term outcomes of TPP patients.

Method

A retrospective cohort study over 35 years (1985–2019) of TPP from Graves’ disease patients was conducted. All cases were analyzed and their clinical courses were compared between those who received anti-thyroid drugs (ATD) versus radioactive iodine (RAI) as a primary treatment. None of them underwent surgery.

Results

A total of 2964 hyperthyroid Graves’ disease patients were treated and followed-up at least 3 months over the study period. TPP was identified in 63 cases (2.1%) of all patients. There were 60 males and only 3 females with age at presentation of 35.0 ± 8.2 years. TPP was the first presentation of hyperthyroid Graves’ disease in 82.5% of them. During the acute attack of TPP, all patients presented with bilateral lower limb flaccid weaknesses with median serum potassium of 2.1 mmol/L. No fatal TPP cases were found. RAI was selected as primary treatment in 27 patients (42.9%). Nearly all RAI-treated patients rendered hypothyroidism with the median RAI dose at 15 mCi. No patients who were in remission after RAI treatment developed recurrent attack of TPP. In the remaining 36 ATD-treated patients with mean follow-up time at 9.1 years, relapse was found in 10 patients (27.8%) after the drug discontinuation and 6 patients suffered recurrent TPP. Only 8 ATD-treated TPP patients (22.2%) went into remission.

Conclusions

TPP is a rare complication of hyperthyroid Graves’ disease. Definitive treatment with RAI or thyroidectomy should be employed to prevent relapse and further attacks of TPP.

Analysis of the genetic background associated with sporadic periodic paralysis in Japanese patients

Periodic paralysis (PP) is a rare disease caused by abnormal excitability of the sarcolemma, resulting in the episodic weakness in extremities. Two major subtypes have been identified: primary/familial PP showing Mendelian inheritance of a mutation in the ion channel genes expressed in skeletal muscle, and secondary/sporadic PP which does not show Mendelian inheritance. Thyrotoxic periodic paralysis (TPP) contributes to the majority of secondary PP cases in Asians and Latin Americans, suggesting that genetic factors may underlie the pathogenesis. In contrast, sporadic periodic paralysis (SPP) has no familial history and no secondary factors. The genetic features associated with SPP in Japanese patients remain unexplored. Here, we investigate whether nine single nucleotide variants (SNVs), rs623011, rs312691, rs393743, rs312692, rs312736, rs992072, rs312732, rs723498, and rs312707, found in TPP and/or SPP in other Asian populations are also associated with Japanese SPP cases. The study cohort included 43 Japanese periodic paralysis patients with no mutations in causative genes (SCN4A, CACNA1S, and KCNJ2), no myotonia, and with euthyroid function. The results showed disease susceptibility for all nine SNVs in our Japanese SPP cohort. One of them, rs312691, was newly confirmed to show susceptibility to SPP. Our results suggest the genetic background underlies periodic paralysis.

Thyrotoxic hypokalemic periodic paralysis due to Graves' disease in 2 adolescents

Thyrotoxic periodic paralysis (TPP) is a notable and potentially lethal complication of thyrotoxicosis, and Graves' disease is the most common cause of TPP. TPP is commonly reported in Asian males between 20-40 years of age, but it is rare in children and adolescents. We report 2 Korean adolescents (a 16-year-old male and a 14-year-old female) with episodes of TPP who were previously diagnosed with Graves' disease. These 2 patients presented with lower leg weakness in the morning after waking up. They were diagnosed with TPP-associated with thyrotoxicosis due to Graves' disease. After they were initially treated with potassium chloride and antithyroid drugs, muscle paralysis improved and an euthyroid state without muscle paralytic events was maintained during follow-up. Therefore, clinicians should consider TPP when patients have sudden paralysis and thyrotoxic symptoms such as goiter, tachycardia, and hypertension.

Evaluation of the Saline Infusion Test and the Captopril Challenge Test in Chinese Patients With Primary Aldosteronism

CONTEXT

The aim of this study was to determine whether the diagnosis cutoff values associated with the saline infusion test (SIT) and captopril challenge test (CCT) in the Endocrine Society guidelines are applicable to Chinese subjects.

OBJECTIVE AND DESIGN

We performed a head-to-head comparison of the SIT and CCT among Chinese subjects with primary aldosteronism (PA) and essential hypertension (EH).

PARTICIPANTS AND SETTING

One hundred sixty-four hypertensive patients were enrolled.

INTERVENTION

All participants underwent both the SIT and CCT.

MAIN OUTCOME MEASURES

The plasma aldosterone concentration (PAC) and plasma renin activity were measured before and after the SIT and CCT. The degree of PAC decline after CCT was calculated.

RESULTS

This study included 115 PA and 49 EH subjects. The prevalence of hypokalemia was 74.8% in the PA group. Supine PACs in the EH and PA groups were 15.1 ± 4.7 mmol/L and 30.4 ± 12.1 mmol/L. Post-SIT PACs were 8.8 ± 1.7 ng/dL and 22.7 ± 10.2 ng/dL in the EH and PA groups. The degree of PAC decline after CCT was 17.7% and 14.2% in the EH and PA groups; post-CCT PACs were 11.7 ± 3.3 ng/dL and 25.9 ± 10.6 ng/dL. PAC values of 11.2 ng/dL and 16.7 ng/dL after the SIT and CCT represented the optimal cutoff values for PA diagnosis. The post-SIT and post-CCT area under the receiver operating characteristic curve values were 0.972 [95% confidence interval (CI) = 0.934 to 0.991] and 0.933 (95% CI = 0.883 to 0.966).

CONCLUSIONS

Post-SIT and post-CCT PACs, but not the degree of PAC suppression, were both reliable for PA diagnosis. However, the optimal cutoffs were slightly higher in Chinese subjects than those recommended by the Endocrine Society.

Long Exercise Test in the Interattack Period of Periodic Paralysis: A Useful and Sensitive Diagnostic Tool

PURPOSE

The reference values of long exercise test are inconsistent in previous studies. Our research aims to determine the reference values and improve diagnostic efficiency of long exercise test in periodic paralysis.

METHODS

In this study, 100 healthy controls, 35 non-periodic paralysis patients, and 47 patients with periodic paralysis were recruited. The procedures of long exercise test were conducted following McMannis(1986) method.

RESULTS

The decrease rate in compound muscle action potential amplitudes was correlated with gender, and it was not influenced by age, height, weight, and exercise. After analyzing receiver operating characteristic curves, the compound muscle action potential amplitude decrease rate was stratified by sex. The mean area under the curve, sensitivity, and specificity were higher in male and female than all pooled subjects. The reference values of compound muscle action potential amplitude decrease rate were 46.8% in male and 26.9% in female, respectively.

CONCLUSIONS

The long exercise test is a useful and sensitive diagnostic tool for primary periodic paralysis and thyrotoxic periodic paralysis. However, the reference values should be set by sex, which has better diagnostic performance, sensitivity, and specificity.

Whole genome and exome sequencing realignment supports the assignment of KCNJ12, KCNJ17, and KCNJ18 paralogous genes in thyrotoxic periodic paralysis locus: functional characterization of two polymorphic Kir2.6 isoforms

Next-generation sequencing (NGS) has enriched the understanding of the human genome. However, homologous or repetitive sequences shared among genes frequently produce dubious alignments and can puzzle NGS mutation analysis, especially for paralogous potassium channels. Potassium inward rectifier (Kir) channels are important to establish the resting membrane potential and regulating the muscle excitability. Mutations in Kir channels cause disorders affecting the heart and skeletal muscle, such as arrhythmia and periodic paralysis. Recently, a susceptibility muscle channelopathy-thyrotoxic periodic paralysis (TPP)-has been related to Kir2.6 channel (KCNJ18 gene). Due to their high nucleotide sequence homology, variants found in the potassium channels Kir2.6 and Kir2.5 have been mistakenly attributable to Kir2.2 polymorphisms or mutations. We aimed at elucidating nucleotide misalignments by performing realignment of whole exome sequencing (WES) and whole genome sequencing (WGS) reads to specific Kir2.2, Kir2.5, and Kir2.6 cDNA sequences using BWA-MEM/GATK pipeline. WES/WGS reads correctly aligned 26.9/43.2, 37.6/31.0, and 35.4/25.8 % to Kir2.2, Kir2.5, and Kir2.6, respectively. Realignment was able to reduce over 94 % of misalignments. No putative mutations of Kir2.6 were identified for the three TPP patients included in the cohort of 36 healthy controls using either WES or WGS. We also distinguished sequences for a single Kir2.2, a single Kir2.5 sequence, and two Kir2.6 isoforms, which haplotypes were named RRAI and QHEV, based on changes at 39, 40, 56, and 249 residues. Electrophysiology records on both Kir2.6_RRAI and _QHEV showed typical rectifying currents. In our study, the reduction of misalignments allowed the elucidation of paralogous gene sequences and two distinct Kir2.6 haplotypes, and pointed the need for checking the frequency of these polymorphisms in other populations with different genetic background.

A novel Kir2.6 mutation associated with hypokalemic periodic paralysis

BACKGROUND AND OBJECTIVE

Mutations in KCNJ18, which encodes the inwardly rectifying potassium channel Kir2.6, have rarely been reported in hypokalemic periodic paralysis. We describe the clinical phenotype of a novel KCNJ18 gene mutation and perform functional characterization of this mutant Kir2.6.

METHODS

A long-term exercise test (ET) was conducted based on the McManis method. Whole-cell currents were recorded using patch clamp, and the HEK293 cells were transfected with wild-type or/and mutant Kir2.6 cDNA.

RESULTS

A de novo conserved heterozygous mutation in Kir2.6, G169R, was found in a hypokalemic periodic paralysis patient. ET led to a decrease in the amplitude of compound muscle action potential (CMAP) by 64%. Patch clamp results showed that the potassium inward and outward current densities of the G169R mutant were, respectively, reduced by 65.6% and 84.7%; for co-expression with wild type, which more closely resembles the physiological conditions in vitro, the inward and outward current densities decreased, respectively, by 48.2% and 47.4%.

CONCLUSIONS

A novel KCNJ18 mutation, G169R, was first reported to be associated with hypokalemic periodic paralysis without hyperthyroidism. Electrophysiological results demonstrated a significant functional defect of this mutant, which may predispose patients with this mutation to paralysis.

SIGNIFICANCE

This new G169R mutation of the potassium channel Kir2.6 provides insight into the pathogenic mechanisms of hypokalemic periodic paralysis.

Novel susceptibility gene for nonfamilial hypokalemic periodic paralysis

OBJECTIVE

To identify susceptibility genes to nonfamilial hypokalemic periodic paralysis (hypoKPP) consisting of thyrotoxic periodic paralysis (TPP) and sporadic periodic paralysis (SPP) and explore the potential pathogenic mechanisms.

METHODS

We enrolled patients with nonfamilial hypoKPP not carrying mutations in CACNA1S, SCN4A, KCNJ18, or KCNJ2 and conducted genome-wide association analyses comparing 77 patients with TPP and 32 patients with SPP with 1,730 controls in a Han Chinese population in Taiwan. Replication was performed using an independent Han Chinese cohort of 50 patients with TPP, 22 patients with SPP, and 376 controls.

RESULTS

We identified 4 single nucleotide polymorphisms (rs312692, rs312736, rs992072, rs393743) located about 100 Kb downstream of KCNJ2 on chromosome 17q24.3 associated with both TPP and SPP reaching genome-wide significance (p < 9 × 10(-8)). rs312736 was mapped to CTD-2378E21.1, a lincRNA, and direct sequencing revealed an exon variant rs312732 (risk allele A) highly associated with both TPP (p = 1.81 × 10(-12); odds ratio [OR] 3.22 [95% confidence interval (CI) 2.36-4.40]) and SPP (p = 8.6 × 10(-12); OR 5.4 [95% CI 3.17-9.18]). Overexpression of C (normal allele) CTD-2378E21.1 in C2C12 skeletal muscle cell, but not A (risk allele) CTD-2378E21.1, showed significantly decreased Kcnj2 expression, indicating A-type CTD-2378E21.1 has lost the ability to regulate Kcnj2.

CONCLUSIONS

Our study reveals a shared genetic predisposition between TPP and SPP. CTD-2378E21.1 is a novel disease-associated gene for both TPP and SPP and may negatively regulate KCNJ2 expression. These findings provide new insights into the pathogenesis of nonfamilial hypoKPP.

Periodic Paralysis as a New Phenotype of Resistance to Thyroid Hormone Syndrome in a Chinese Male Adult

CONTEXT

A majority of patients with resistance to thyroid hormone (RTH) are asymptomatic, whereas some patients show signs of hyperthyroidism, or hypothyroidism, or both. Thyrotoxic periodic paralysis is the most common form of acquired periodic paralysis. However, it has not been reported in a patient with RTH up to now.

OBJECTIVE

We evaluated a 36-year-old male patient from China with elevated serum free T4 and free T3 and inappropriately high TSH who presented with periodic paralysis.

STUDY DESIGN

Clinical, biochemical, and radiological assessments, as well as DNA sequencing, were performed.

RESULTS

The patient's laboratory tests revealed the following: TSH, 6.14 mIU/L (0.27-4.2 mIU/L); free T3, 12.85 pmol/L (2.8-7.1 pmol/L); free T4, 33.62 pmol/L (9.05-25.5 pmol/L); and serum SHBG, 19.4 nmol/L (18.3-54.1 nmol/L). No significant suppression of TSH was observed in the rapid TSH suppression test with somatostatin analogs. Compound muscle action potential after exercise of the patient was reduced by 58%. Sequencing of thyroid hormone receptor genes confirmed a C446S mutation in the THRβ gene.

CONCLUSIONS

This is the first report of periodic paralysis as a new phenotype of RTH syndrome.