Distribution of creatine kinase in the general population: implications for statin therapy

Deep characterization of females with heterozygous Duchenne muscular dystrophy mutations

OBJECTIVE

Duchenne muscular dystrophy (DMD) is an X-linked muscular dystrophy due to null mutations in the DMD gene that predominantly affects males, while heterozygous females are usually asymptomatic carriers. In approximately 10-20% of cases, they may present with muscle weakness and/or cardiomyopathy. We aimed to describe clinical and molecular characteristics of DMD heterozygous females.

METHODS

A monocentric, observational, and cross-sectional study was designed. Clinical and molecular data were collected along with, when available, muscle biopsies. The pattern of X inactivation was determined in peripheral blood and the genotypes at SPP1, LTBP4 and CD40 modifier genes were established.

RESULTS

We recruited 47 participants: 27 (57%) were asymptomatic and 20 (43%) manifested symptoms. Proximal muscles were prominently involved, as in male dystrophinopathies. Twenty % of carriers showed cardiac involvement. Creatine kinase (CK) values were in the normal range in ~ 20% of symptomatic and ~ 46% asymptomatic patients. In all muscle biopsies, a mosaic of dystrophin positive and negative fibers was observed that only marginally correlated to dystrophin amount. No correlation was found between X chromosome inactivation pattern and the severity of muscular involvement, nor any association with cardiomyopathy. No genotype-phenotype correlations were identified.

INTERPRETATION

Genotype/phenotype correlations in females heterozygous for DMD mutations are influenced by multiple mechanisms, of which better understanding will be crucial for future dystrophin gene replacement therapies. An earlier molecular identification is essential to lead to greater awareness of the potential cardiac complications, and hence the reinforcement of  appropriate cardiac follow-up.

Ptosis in human immunodeficiency virus-infected patients under long-term antiretroviral treatment

OBJECTIVE

To present cases of ptosis in HIV-1 patients on long-term antiretroviral therapy (ART) and review the existing literature.

METHODS

Five HIV-1-positive patients with slowly progressive bilateral ptosis underwent a comprehensive diagnostic evaluation, including imaging studies, neurophysiological testing, muscle biopsy, and genetic analysis. A literature review was conducted.

RESULTS

On clinical examination, all patients presented with bilateral symmetrical non-fatigable ptosis, three exhibited facial lipoatrophy and two also had mild multidirectional ophthalmoparesis and all had ocular abnormalities in Hess screen test. Additionally, one patient displayed proptosis, three had floppy lower eyelids, and four presented with exotropia. Anti-acetylcholine receptor antibodies were negative in all patients. Brain magnetic resonance imaging (MRI), motor unit potential analysis, and single-fiber electromyography were unremarkable. Orbital MRI revealed introrbital fat expansion in one patient, and limb muscle biopsies were inconclusive in two cases. Blood genetic testing for chronic progressive external ophthalmoplegia was negative in all patients. A total of 30 similar cases have been documented in the literature, with some studies reporting key findings such as muscle histology indicative of mitochondrial myopathy, MRI revealing patchy extraocular muscle hyperintensity, and muscle genetic testing identifying mitochondrial deoxyribonucleic acid (DNA) deletions. Ptosis surgical repair appears to be the most effective treatment.

CONCLUSION

HIV patients on long-term ART may develop ocular muscle involvement due to mitochondrial dysfunction, with bilateral ptosis being the primary manifestation. Diagnosis is challenging and requires the exclusion of other conditions. Ptosis surgery can significantly improve quality of life.

Asymptomatic HyperCKemia in the Pediatric Population: A Prospective Study Utilizing Next-Generation Sequencing and Ancillary Tests

BACKGROUND AND OBJECTIVES

Persistent elevation of serum creatine kinase levels (hyperCKemia) as an isolated manifestation presents a diagnostic challenge. Genetic myopathies are frequently involved; however, studies using next-generation sequencing (NGS) in pediatric patients are lacking, and the significance of genetic aberrations remains poorly understood. This study, therefore, aimed to investigate the relevance of NGS and the support of contemporary diagnostic tools in the diagnosis of pediatric asymptomatic hyperCKemia.

METHODS

This was a prospective cohort study enrolling pediatric (0-18 years old) patients meeting the predefined criteria for asymptomatic/paucisymptomatic hyperCKemia, excluding DMD gene deletion/duplication, recruited from a referral center. NGS, muscle MRI, EMG, and muscle biopsies with immunolabeling and inflammatory markers were performed according to a prespecified protocol. Data analysis was performed using descriptive/univariate statistics and Bayesian logistic regression.

RESULTS

The series comprised 65 patients (78% male). NGS diagnosis was achieved in 55% of the cohort, with 70% of the pathogenic variants involving 7 genes (DMD, CAPN3, ANO5, DYSF, RYR1, GAA, and CAV3). The diagnostic rate was similar across all age groups; however, the gene profiles varied between the childhood and juvenile groups. EMG yielded myopathic features in 48% of the investigated cases, being predictive for diagnosis (p < 0.05; odds ratio [OR] 13.484, 95% CI 1.358-705.297). MRI showed normal (64%), focal fatty change (26%), or short-tau inversion recovery hyperintensity (10%) profiles, which were not predictive of diagnosis but supported muscle biopsy indications. Muscle biopsy provided a significant diagnostic effect (p < 0.05; OR 0.028, 95% CI 0.001-0.238), contributing to myopathologic features clarifying the variant pathogenicity and identifying inflammatory myopathies. The diagnoses remained inconclusive and unresolved in 14% and 29% of the cohorts, respectively. The diagnostic rate for patients with CK levels below the threshold of 3× was 42%. In multivariate analysis, NGS was the only variable achieving a significant diagnostic effect (β = 9.85, 95% CI 4.65-16.09).

DISCUSSION

NGS, as the primary diagnostic tool for investigating hyperCKemia in the pediatric population, yielded a higher diagnostic rate. However, muscle biopsies are necessary to define variants of uncertain pathogenicity and aid in identifying inflammatory myopathies. EMG and MRI may play a role in hyperCKemia characterization, guiding the decision to perform muscle biopsy. The primary limitation of this study was that not all ancillary tests were performed in all recruited patients owing to ethical restrictions, which lowered the power of the predictive analysis.

A Neuropathy Mimic: Statin-Induced Myopathy Presenting as Guillain-Barré Syndrome

Statins are widely used to manage dyslipidemia and prevent cardiovascular diseases due to their effectiveness and general safety profile. However, they can sometimes cause severe muscle-related adverse effects, presenting diagnostic challenges when symptoms overlap with other conditions. This case report describes a middle-aged woman who presented to the emergency department with bilateral lower limb weakness, initially suggesting Guillain-Barré syndrome (GBS). Despite her history of low-grade fever and diarrhea, primary and secondary surveys, including electrocardiogram, blood gas analysis, and nerve conduction studies, showed no definitive signs of GBS. The patient had a recent history of percutaneous transluminal coronary angioplasty and was on dual antiplatelet therapy and rosuvastatin. Elevated creatine kinase levels and exclusion of other differential diagnoses led to the diagnosis of statin-induced myopathy, a rare but severe adverse effect of statins. The patient was treated with intravenous fluids, cessation of statins, and sessions of hemodialysis and plasmapheresis, resulting in significant improvement and eventual recovery of muscle power and neurological function. This case highlights the importance of recognizing statin-induced myopathy in patients with muscle weakness and emphasizes the need for thorough clinical evaluation to differentiate it from other conditions such as GBS. Further research is warranted to understand the pathophysiology of statin myopathy and identify at-risk populations.

International Migration and Cardiovascular Health: Unraveling the Disease Burden Among Migrants to North America and Europe

Europe and North America are the 2 largest recipients of international migrants from low-resource regions in the world. Here, large differences in cardiovascular disease (CVD) morbidity and death exist between migrants and the host populations. This review discusses the CVD burden and its most important contributors among the largest migrant groups in Europe and North America as well as the consequences of migration to high-income countries on CVD diagnosis and therapy. The available evidence indicates that migrants in Europe and North America generally have a higher CVD risk compared with the host populations. Cardiometabolic, behavioral, and psychosocial factors are important contributors to their increased CVD risk. However, despite these common denominators, there are important ethnic differences in the propensity to develop CVD that relate to pre- and postmigration factors, such as socioeconomic status, cultural factors, lifestyle, psychosocial stress, access to health care and health care usage. Some of these pre- and postmigration environmental factors may interact with genetic (epigenetics) and microbial factors, which further influence their CVD risk. The limited number of prospective cohorts and clinical trials in migrant populations remains an important culprit for better understanding pathophysiological mechanism driving health differences and for developing ethnic-specific CVD risk prediction and care. Only by improved understanding of the complex interaction among human biology, migration-related factors, and sociocultural determinants of health influencing CVD risk will we be able to mitigate these differences and truly make inclusive personalized treatment possible.

Safety monitoring of drug-induced muscle injury and rhabdomyolysis: a biomarker-guided approach for clinical practice and drug trials

Skeletal muscle tissue (SKM) may be damaged due to mechanical, metabolic, and exertional causes. However, drug-induced myopathy is among the most frequent causes of muscle disease. The clinical picture of drug-induced myopathies may be highly variable. It may present as asymptomatic or mild myalgias, with or without muscle weakness, which are likely underreported. However, it may also appear as chronic myopathy with severe weakness and, rarely, even as massive rhabdomyolysis with acute kidney injury (AKI). Unfortunately, the available biomarkers for SKM injury do not fully meet the needs for satisfactory detection of drug-induced damage, both in clinical and research settings, mainly due to their low sensitivity and specificity. Therefore, the present study proposes a strategy for drug safety monitoring using the available biomarkers of SKM injury. Moreover, we will discuss mechanisms of drug-induced SKM injury, traditional laboratory testing for SKM injury, and novel skeletal myocyte biomarkers under investigation. This can be incredibly useful in both clinical practice and for de-challenge/re-challenge investigational trials where the risk of drug-induced SKM injury is present.

Factors Influencing Creatine Kinase-MM Concentrations in Newborns and Implications for Newborn Screening for Duchenne Muscular Dystrophy

INTRODUCTION

Newborn screening for Duchenne muscular dystrophy can be performed via a first-tier creatine kinase-MM measurement followed by reflex testing to second-tier molecular analysis of the DMD gene. In order to establish appropriate cut-offs for the creatine kinase-MM screen, factors that influence creatine kinase-MM in newborns were investigated.

MATERIALS AND METHODS

Creatine kinase-MM data from a consented pilot study in New York State were collected over a two-year period and combined with de-identified validation data and analyzed. Univariate analysis and multiple linear regression analysis were performed.

RESULTS

The analysis indicated that age of newborn at specimen collection, gestational age and birth weight were significant influencers of CK-MM levels in newborns. In addition, to a lesser extent, sex, race/ethnicity and seasonal temperature also affect CK-MM levels in newborns.

CONCLUSIONS

To reduce false positive and false negative cases, newborn screening programs should be cognizant of factors that influence CK-MM when determining cut-offs for the assay. Variability based on age at specimen collection and birth weight are primarily observed within the first week of life. Therefore, particularly during this time period, multi-tiered cut-offs based on age of collection and lower cut-offs for premature and low birth weight babies are recommended. Other cut-off determinants may include sex, race/ethnicity and seasonal temperature.

Assessment and management of statin-associated muscle symptoms (SAMS): A clinical perspective from the National Lipid Association

Statin-associated muscle symptoms (SAMS) are the most common form of statin intolerance and are associated with increased risk of cardiovascular events that manifest from statin underutilization and discontinuation. The reported frequencies of SAMS are divergent in the literature. The writing group estimates the prevalence of SAMS, namely all muscle symptoms temporally related to statin use but without regard to causality, to be about 10% (range 5% to 25%), and the prevalence of pharmacological SAMS, specifically muscle symptoms resulting from pharmacological properties of the statin, to be about 1-2% (range 0.5% to 4%). In clinical practice, SAMS are likely to result from a combination of pharmacological and nonpharmacological effects, however this does not make the symptoms any less clinically relevant. Regardless of the etiology, SAMS need to be addressed in accordance with patients' preferences and experiences. This clinical perspective reviews the epidemiology and underlying pathophysiology of SAMS, and the cardiovascular consequences resulting from statin discontinuation. We present patient-centered clinical and communication strategies to mitigate SAMS and improve medication adherence and outcomes among statin users. Treatment strategies include 1) optimizing lifestyle interventions, 2) modulating risk factors that may contribute to muscle symptoms, 3) optimizing statin tolerability by dose reduction, decreased dosing frequency, or use of an alternate statin with more favorable pharmacokinetic properties, and 4) use of non-statins, emphasizing those with evidence for atherosclerotic risk reduction, either in combination with or in place of statin therapy depending on the patient's circumstances. The focus of this clinical perspective is sustainable lipoprotein goal achievement, which is important for cardiovascular risk reduction.

Causes of HyperCKemia in Children: A Retrospective Cohort Study

Background and Objectives: Creatine kinase (CK) is a commonly used screening test for neuromuscular disorders (NMDs). However, hyperCKemia can result from several pathologic and physiologic causes. We analyzed neuromuscular disorders in noninfant children with hyperCKemia including those with no weakness and mild CK elevations (<5 times the upper limit of normal). We hypothesized that children with mild CK elevation and no weakness would be unlikely to have neuromuscular disorders and require additional evaluation. Methods: We retrospectively evaluated patients between 1 and 18 years of age seen at a single children's hospital over a 3-calendar-year period with initial total CK values greater than the upper limit of normal with at least 2 years of follow-up data. Final diagnoses were analyzed and associations with possible risk factors assessed. Receiver operating characteristic curves were generated to assess altering CK cutoff values. Results: Of 260 subjects with hyperCKemia, 18 had a neuromuscular disorder (6.9%, 95% confidence interval [CI] 4.2%-10.9%). Of 166 subjects with CK <5 times the upper limit of normal and no weakness, 8 had a neuromuscular disorder (4.8%, 95% CI 2.3%-9.6%). Weakness (odds ratio [OR] 32.5, 95% CI 4-385, P = .0002), and family history of neuromuscular disorders (OR not calculable, P = .0003) were associated with neuromuscular disorders. An optimal CK threshold of 777 was identified on receiver operating characteristic curve analysis (sensitivity of 72% and specificity of 64%). The most commonly identified neuromuscular disorders were muscular dystrophies, inflammatory myopathies, and metabolic myopathies. Conclusion: Most children with hyperCKemia will not be diagnosed with a neuromuscular disorder, but a significant minority even with mild hyperCKemia and without weakness may warrant additional evaluation.

Creatine Kinase Is Associated With Recurrent Stroke and Functional Outcomes of Ischemic Stroke or Transient Ischemic Attack

Background

Many patients after stroke are found to have elevated serum creatine kinase (CK). This study aimed to investigate the associations between serum CK levels and clinical outcomes in patients with acute ischemic stroke or transient ischemic attack.

Methods and Results

The study included 8910 patients with acute ischemic stroke or transient ischemic attack from the CNSR‐III (Third China National Stroke Registry). Baseline serum CK levels after admission were measured. The associations between CK and clinical outcomes (stroke recurrence, death, and disability, defined as modified Rankin scale score 3–6 or 2–6) were analyzed. Patients with elevated CK levels had higher risks of recurrent stroke (hazard ratio [HR], 1.53; 95% CI, 1.21–1.93), death (HR, 1.68; 95% CI, 1.10–2.58), and disability (modified Rankin scale score, 3–6; odds ratio, 1.57; 95% CI, 1.29–1.90) at 3 months after adjusting confounding factors. Similar results were found at 1 year. The effects of CK on death and disability were more significant in male patients than female patients (P value for interaction <0.05). Elevated CK‐MB levels were not associated with clinical outcomes in this study.

Conclusions

Elevated serum CK after ischemic stroke or transient ischemic attack is associated with higher risks of recurrent stroke, death, and disability at 3 months and 1 year. Serum CK may act as a useful predictor for recurrent stroke and poor functional outcomes in patients with acute ischemic stroke or transient ischemic attack. Sex modifies the relationship between elevated CK and disability or death.

The Effect of Years-Long Exposure to Low-Dose Colchicine on Renal and Liver Function and Blood Creatine Kinase Levels: Safety Insights from the Low-Dose Colchicine 2 (LoDoCo2) Trial

BACKGROUND AND OBJECTIVE

The Low-Dose Colchicine-2 (LoDoCo2) trial showed that 2-4 years exposure to colchicine 0.5 mg once daily reduced the risk of cardiovascular events in patients with chronic coronary artery disease. The potential effect of years-long exposure to colchicine on renal or liver function and creatine kinase (CK) has not been systematically evaluated and was investigated in this LoDoCo2 substudy.

METHODS

Blood samples drawn from 1776 participants at the close-out visit of the LoDoCo2 trial were used to measure markers of renal function (creatinine, blood urea nitrogen [BUN]), liver function (alanine aminotransferase [ALT], γ-glutamyl transferase [GGT], bilirubin and albumin), and CK. Renal and liver function as well as hyperCKemia (elevated CK) were categorized to the degree of elevation biomarkers as mild, mild/moderate, moderate/severe, and marked elevations.

RESULTS

In total, 1776 participants (mean age 66.5 years, 72% male) contributed to this analysis, with a median exposure to trial medication of 32.7 months. Compared with placebo, colchicine was not associated with changes in creatinine and BUN but was associated with elevations in ALT (30 U/L vs. 26 U/L; p < 0.01) and CK (123 U/L vs. 110 U/L; p < 0.01). Most elevations in ALT and CK were mild in both treatment groups. There were no moderate to marked ALT elevations (> 5-10 × upper limit of normal [ULN]) in both treatment groups, and 6 (0.7%) colchicine-treated vs. 2 (0.2%) placebo-treated participants had moderate to marked CK elevations (> 5-10 × ULN).

CONCLUSION

In chronic coronary artery disease, 2-4 years of exposure to colchicine 0.5 mg once daily was associated with small elevations in ALT and CK, but was not associated with changes in renal function.

TRIAL REGISTRATION

https://www.anzctr.org.au ; ACTRN12614000093684, 24 January 2014.

Pearl lecture: Biological normalcy: A new framework for biocultural analysis of human population variation

Biological normalcy is a new analytical framework for understanding the bi-directional relationships between the biology of populations and cultural norms. Populations are characterized by statistical distributions-that is, measures of central tendency and variance-for biological traits, and these co-exist in societies with ideas about what constitutes "normal" human bodies, that is, normative views about what bodies "should" be like. While statistical norms may carry no explicit evaluative weight, the question is how they are related to judgments about what is "normal" or "abnormal." In a 1947 paper, Margaret Mead recognized their potential relationship: "normal…may refer to the statistically usual in the culture-usually without any recognition that this is culturally relative-so that the statistically usual is identified with the basically human…." Despite her observations over 70 years ago, little has been done on this topic, yet such work promises new insights into the relationship between culture and biology, here described at the population level, rather than as individual genetic characteristics. Using examples of sex/gender, race/ethnicity, age, and my work on human variation in the ability to drink milk, I outline the ways in which statistical norms may: influence individuals' perceptions of what is "normal" (Mead's "basically human"); lead to normative judgments about what human biology "should" be ("ethno-biocentrism") that are reinforced by biases in discourse about human variation; and potentially feedback to mold the biological characteristics of a population.

RYR1-related rhabdomyolysis: a spectrum of hypermetabolic states due to ryanodine receptor dysfunction

Variants in the ryanodine receptor-1 gene (RYR1) have been associated with a wide range of neuromuscular conditions, including various congenital myopathies and malignant hyperthermia (MH). More recently, a number of RYR1 variants, mostly MH-associated, have been demonstrated to contribute to rhabdomyolysis events not directly related to anesthesia in otherwise healthy individuals. This review focuses on RYR1-related rhabdomyolysis, in the context of several clinical presentations (i.e., exertional rhabdomyolysis, exertional heat illnesses and MH), and conditions involving a similar hypermetabolic state, in which RYR1 variants may be present (i.e., neuroleptic malignant syndrome and serotonin syndrome). The variety of triggers that can evoke rhabdomyolysis, on their own or in combination, as well as the number of potentially associated complications, illustrates that this is a condition relevant to several medical disciplines. External triggers include but are not limited to strenuous physical exercise, especially if unaccustomed or performed under challenging environmental conditions (e.g., high ambient temperature or humidity), alcohol/illicit drugs, prescription medication (in particular statins, other anti-lipid agents, antipsychotics and antidepressants) infection, or heat. Amongst all patients presenting with rhabdomyolysis, a genetic susceptibility is present in a proportion, with RYR1 being one of the most common genetic causes. Clinical clues for a genetic susceptibility include recurrent rhabdomyolysis, creatine kinase (CK) levels above 50 times the upper limit of normal, hyperCKemia lasting for 8 weeks or longer, drug/medication doses insufficient to explain the rhabdomyolysis event, and a positive family history. For the treatment or prevention of RYR1-related rhabdomyolysis, the RYR1 antagonist dantrolene can be administered, both in the acute phase, or prophylactically in patients with a history of muscle cramps and/or recurrent rhabdomyolysis events. Aside from dantrolene, several other drugs are being investigated for their potential therapeutic use in RYR1-related disorders. These findings offer further therapeutic perspectives for humans, suggesting an important area for future research.

Characterization of Creatine Kinase Levels in Tofacitinib-Treated Patients with Ulcerative Colitis: Results from Clinical Trials

BACKGROUND

Tofacitinib is an oral, small-molecule JAK inhibitor for the treatment of ulcerative colitis (UC). Creatine kinase (CK) levels and CK-related adverse events (AEs) in tofacitinib-treated patients with UC were evaluated.

METHODS

Data were analyzed for three UC cohorts: Induction (phase 2 and 3 induction studies); Maintenance (phase 3 maintenance study); Overall [patients who received tofacitinib 5 or 10 mg twice daily (b.d.) in phase 2, phase 3, or open-label, long-term extension studies; data at November 2017]. Clinical trial data for tofacitinib-treated patients with rheumatoid arthritis, psoriasis, and psoriatic arthritis are presented for contextualization.

RESULTS

Week 8 mean change from baseline CK with tofacitinib 10 mg b.d. induction therapy was 91.1 U/L (95% CI, 48.1-134.1) versus 19.2 U/L (8.5-29.9) with placebo. Among patients completing induction with 10 mg b.d. and re-randomized to 52 weeks of maintenance therapy, mean increases from induction baseline to the end of maintenance were 35.9 (8.1-63.7), 90.3 (51.9-128.7), and 115.6 U/L (91.6-139.7), with placebo, 5 and 10 mg b.d., respectively. The incidence rate (unique patients with events per 100 patient-years) for AEs of CK elevation in the tofacitinib-treated UC Overall cohort was 6.6 versus 2.2, 6.5, and 3.7 for tofacitinib-treated patients with rheumatoid arthritis, psoriasis, and psoriatic arthritis, respectively. No serious AEs of CK elevation or AEs of myopathy occurred in UC studies.

CONCLUSIONS

In patients with UC, CK elevations with tofacitinib appeared reversible and not associated with clinically significant AEs. UC findings were consistent with tofacitinib use in other inflammatory diseases.

TRIAL REGISTRATION

NCT00787202; NCT01465763; NCT01458951; NCT01458574; NCT01470612; NCT01262118; NCT01484561; NCT00147498; NCT00413660; NCT00550446; NCT00603512; NCT00687193; NCT01059864; NCT01164579; NCT00976599; NCT01359150; NCT02147587; NCT00960440; NCT00847613; NCT00814307; NCT00856544; NCT00853385; NCT01039688; NCT02187055; NCT00413699; NCT00661661; NCT01710046; NCT00678210; NCT01276639; NCT01309737; NCT01241591; NCT01186744; NCT01163253; NCT01877668; NCT01882439; NCT01976364.

Creatine kinase is associated with bleeding after myocardial infarction

BACKGROUND

The ADP-scavenging enzyme creatine kinase (CK) is reported to reduce ADP-dependent platelet activation. Therefore, we studied whether highly elevated CK after ST-elevation myocardial infarction (STEMI) is associated with bleeding.

METHODS

Data of the Thrombolysis in Myocardial Infarction Study Group phase II trial on the efficacy of angioplasty, following intravenous recombinant tissue-type plasminogen activator (rt-PA), are used to assess whether peak plasma CK (CKmax) is independently associated with adjudicated fatal or non-fatal bleeding (primary) and combined bleeding/all-cause mortality (secondary) in multivariable binomial logistic regression analysis, adjusting for baseline and treatment allocation covariates.

RESULTS

The included patients (n=3339, 82% men, 88% white, mean age 57 years, SE 0.2) had a history of angina pectoris (55%), hypertension (38%) and/or diabetes mellitus (13%). CKmax ranged from 16 to 55 890 IU/L (mean 2389 IU/L, SE 41), reached within 8 hours in 51% of the patients (93% within 24 hours). Adjudicated fatal/non-fatal bleeding occurred in 30% of the patients (respectively 26% in the low vs 34% in the high CK tertile), and bleeding/all-cause mortality in 35% (29% in the low vs 40% in the high CK tertile). In multivariable regression analysis, the adjusted OR for fatal/non-fatal bleeding (vs not bleeding and survival) was 2.6 (95% CI 1.8 to 3.7)/log CKmax increase, and 3.1 (2.2 to 4.4) for bleeding/all-cause mortality.

CONCLUSION

Highly elevated plasma CK after myocardial infarction might be an independent predictor of bleeding and haemorrhagic death. This biologically plausible association warrants further prospective study of the potential role of extracellular CK in ADP-dependent platelet activation and bleeding.

Primary mitochondrial myopathy: Clinical features and outcome measures in 118 cases from Italy

Objective

To determine whether a set of functional tests, clinical scales, patient-reported questionnaires, and specific biomarkers can be considered reliable outcome measures in patients with primary mitochondrial myopathy (PMM), we analyzed a cohort of Italian patients.

Methods

Baseline data were collected from 118 patients with PMM, followed by centers of the Italian network for mitochondrial diseases. We used the 6-Minute Walk Test (6MWT), Timed Up-and-Go Test (x3) (3TUG), Five-Times Sit-To-Stand Test (5XSST), Timed Water Swallow Test (TWST), and Test of Masticating and Swallowing Solids (TOMASS) as functional outcome measures; the Fatigue Severity Scale and West Haven-Yale Multidimensional Pain Inventory as patient-reported outcome measures; and FGF21, GDF15, lactate, and creatine kinase (CK) as biomarkers.

Results

A total of 118 PMM cases were included. Functional outcome measures (6MWT, 3TUG, 5XSST, TWST, and TOMASS) and biomarkers significantly differed from healthy reference values and controls. Moreover, functional measures correlated with patients' perceived fatigue and pain severity. Patients with either mitochondrial or nuclear DNA point mutations performed worse in functional measures than patients harboring single deletion, even if the latter had an earlier age at onset but similar disease duration. Both the biomarkers FGF21 and GDF15 were significantly higher in the patients compared with a matched control population; however, there was no relation with severity of disease.

Conclusions

We characterized a large cohort of PMM by evaluating baseline mitochondrial biomarkers and functional scales that represent potential outcome measures to monitor the efficacy of treatment in clinical trials; these outcome measures will be further reinvestigated longitudinally to define the natural history of PMM.

Establishing reference intervals of 20 biochemical markers for children in Southwestern Fujian, China based on the UniCel DxC 800 system

BACKGROUND

To date, China has no industry standard for reference intervals of paediatric blood biochemical markers. This study aimed to evaluate changes in biochemical markers in the venous blood of healthy children aged 29 days to 12 years, derived from the UniCel DxC 800 system, and establish appropriate reference intervals.

METHODS

We analysed venous blood from 1980 healthy children for 20 biochemical markers. Reference intervals were established according to the Clinical and Laboratory Standards Institute C28-A3c guideline and compared with those of adults in China.

RESULTS

All markers except for sodium and chlorine required partitioning by age, but not by sex. The reference intervals of total protein, albumin, globulin, carbon dioxide, urea nitrogen, creatinine and uric acid consistently increased with age in children, but were always lower than those of adults. Children aged 29 days to 12 years had a single combined RI for sodium and chloride, respectively; although the reference intervals in children were similar to those of adults, their upper limits were lower. The reference intervals of direct bilirubin, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, potassium, calcium, magnesium, and phosphorus continued to decline with age. The reference intervals of total bilirubin, indirect bilirubin, and gamma-glutamyl transpeptidase initially declined followed by a slight rebound.

CONCLUSIONS

While establishing reference intervals, most markers required partitioning by age (aged 29 days to 12 years); the partitioning scheme differed for each marker, and paediatric reference intervals differed from those for adults. It is therefore necessary to establish separate paediatric reference intervals.

Population-Wide Duchenne Muscular Dystrophy Carrier Detection by CK and Molecular Testing

Carrier screening of Duchenne muscular dystrophy (DMD) has not been widely evaluated. To identify definite DMD female carriers prior to or in early pregnancy, we studied a large population of reproductive age females and provided informed reproductive options to DMD carriers. 37268 females were recruited from the Hangzhou Family Planning Publicity and Technology Guidance Station/Hangzhou Health Service Center for Children and Women, Hangzhou, China, between October 10, 2017, and December 16, 2018. CK activity was measured with follow-up serum DMD genetic testing in subjects with hyperCKemia, defined as CK > 200 U/L. The calculated upper reference limit (97.5^th percentile) of serum creatine kinase (CK) for females aged 20-50 years in this study was near the reference limit recommended by the manufacturer (200 U/L), above which was defined as hyperCKemia. 427 females (1.2%) harbored initially elevated CK, among which 281 females (response rate of 65.8%) accepted CK retesting. DMD genetic testing was conducted on 62 subjects with sustained serum CK > 200 U/L and 16 females with a family history of DMD. Finally, 6 subjects were confirmed to be DMD definite carriers. The estimated DMD female carrier rate in this study was 1 : 4088 (adjusting for response rate), an underestimated rate, since only 50% to 70% of DMD female carriers manifest elevated serum CK, and carriers in this study may have been missed due to lack of follow-up or inability to detect all DMD pathogenic variants by current genetic testing.

Extracellular creatine kinase may modulate purinergic signalling

Extracellular purine nucleotides and nucleosides including ADP and ATP regulate a wide array of physiological processes including platelet aggregation, vasomotor responses and inflammation through specific purinergic receptors. In the recent years, a strong association has been reported between circulating cytoplasmic-type creatine kinase and adverse clinical outcomes such as major bleeding, hypertension and obesity. Therefore, it is proposed that extracellular CK may modulate purinergic signalling through its ADP binding and/or ATP-generating effect.

CK (Creatine Kinase) Is Associated With Cardiovascular Hemodynamics: The HELIUS Study

The ATP-regenerating enzyme CK (creatine kinase) is strongly associated with blood pressure, which lowers upon experimental CK inhibition. The enzyme is thought to affect cardiovascular hemodynamics through enhanced systemic vascular resistance, stroke volume, and cardiac contractility, but data on these parameters are lacking. We hereby report hemodynamics by CK levels in the multiethnic, cross-sectional HELIUS study (Healthy Life in an Urban Setting). Physical examination included sitting brachial blood pressure and noninvasively assessed supine systemic vascular resistance, stroke volume, cardiac output, and cardiac contractility, which we associated with resting plasma CK. Data from 14 937 men and women (mean age, 43.3; SD, 12.9) indicated that per log CK increase, blood pressure increased with 20.2 (18.9-21.4) mm Hg systolic/13.0 (12.2-13.7) diastolic, an odds ratio for hypertension of 6.1 (5.1-7.2). Outcomes were similar by sex, body mass index, and ancestry, although higher blood pressures in men, with overweight/obesity, and West-African ancestry were partially explained by higher CK, with an adjusted increase in systolic/diastolic pressure of 10.5 (10.0-10.9)/6.4 (6.0-6.7) mm Hg per log CK increase. Systemic vascular resistance, stroke volume, cardiac output, and cardiac contractility (n=7876), increased by respectively 20%, 39%, 14%, and 23% SD per log CK increase. This study indicates that the association of CK with blood pressure likely results from an increase in systemic vascular resistance and stroke volume. These data expand the knowledge on the nature of hypertension associated with CK and may inform further experiments on CK inhibition as a means to lower blood pressure.

A Possible Antioxidant Role for Vitamin D in Soccer Players: A Retrospective Analysis of Psychophysical Stress Markers in a Professional Team

The health benefits of physical activity are recognized, however, high levels of exercise may lead to metabolic pathway imbalances that could evolve into pathological conditions like the increased risk of neurological disease observed in professional athletes. We analyzed the plasma/serum levels of 29 athletes from a professional soccer team playing in the Italian first league and tested the levels of psychophysical stress markers (vitamin D, creatine kinase, reactive oxygen species (ROS) and testosterone/cortisol ratio) during a period of 13 months. The testosterone/cortisol ratio was consistent with an appropriate training program. However, most of the athletes showed high levels of creatine kinase and ROS. Despite the large outdoor activity, vitamin D values were often below the sufficiency level and, during the "vitamin D winter", comparable with those of the general population. Interestingly, high vitamin D values seemed to be associated to low levels of ROS. Based on the results of our study we proposed a vitamin D supplementation as a general practice for people who perform high levels of physical exercise. Beside the known effect on calcium and phosphate homeostasis, vitamin D supplementation should mitigate the high reactivity of ROS which might be correlated to higher risk of neurodegenerative diseases observed in professional athletes.

Age- and Sex-Specific Reference Intervals for Myocardial Enzyme Activity in Healthy Chinese Han Population Aged 1∼<18 years

Age- and sex-specific reference intervals (RIs) for myocardial enzyme activity of children and adolescents are not available in China. Our study aimed to establish age- and gender-related RIs for AST, LDH, CK, and CKMB activity in healthy Chinese Han population aged 1∼<18 years. Healthy Han children and adolescents (n = 6322, 1∼<18 years old) were assessed from completed questionnaires and defined criteria from communities and schools in 5 administrative districts of Jilin Province from September 2017 to December 2018. Measurements of AST, LDH, CK, and CKMB activity were performed on the VITROS 5600 Integrated System. Percentiles of enzyme activity were completed by LMS. RIs were established by Medcalc according to the EP28-A3c guidelines issued by the Clinical and Laboratory Standards Institute. AST declined rapidly during 1∼<6 years and had been subsided during 11∼<18 years, though LDH decreased at a steady rate. CK activity stabilized while CKMB showed a downward trend. Sex differences started after age 12 when males presented higher results. There were significant differences comparing with domestic and other countries' experiments which applied similar methodologies. Enzymes were associated with age and sex, while age had greater impact. We established age- and sex-specific RIs of serum AST, LDH, CK, and CKMB activities for Chinese children and adolescents using the VITROS 5600 Integrated System for the first time. These data will lay the groundwork for the next horizon in pediatric RIs as well as improve test result interpretation for pediatric illness.

Panel-Based Exome Sequencing for Neuromuscular Disorders as a Diagnostic Service

BACKGROUND

Neuromuscular disorders (NMDs) are clinically and genetically heterogeneous. Accurate molecular genetic diagnosis can improve clinical management, provides appropriate genetic counseling and testing of relatives, and allows potential therapeutic trials.

OBJECTIVE

To establish the clinical utility of panel-based whole exome sequencing (WES) in NMDs in a population with children and adults with various neuromuscular symptoms.

METHODS

Clinical exome sequencing, followed by diagnostic interpretation of variants in genes associated with NMDs, was performed in a cohort of 396 patients suspected of having a genetic cause with a variable age of onset, neuromuscular phenotype, and inheritance pattern. Many had previously undergone targeted gene testing without results.

RESULTS

Disease-causing variants were identified in 75/396 patients (19%), with variants in the three COL6-genes (COL6A1, COL6A2 and COL6A3) as the most common cause of the identified muscle disorder, followed by variants in the RYR1 gene. Together, these four genes account for almost 25% of cases in whom a definite genetic cause was identified. Furthermore, likely pathogenic variants and/or variants of uncertain significance were identified in 95 of the patients (24%), in whom functional and/or segregation analysis should be used to confirm or reject the pathogenicity. In 18% of the cases with a disease-causing variant of which we received additional clinical information, we identified a genetic cause in genes of which the associated phenotypes did not match that of the patients. Hence, the advantage of panel-based WES is its unbiased approach.

CONCLUSION

Whole exome sequencing, followed by filtering for NMD genes, offers an unbiased approach for the genetic diagnostics of NMD patients. This approach could be used as a first-tier test in neuromuscular disorders with a high suspicion of a genetic cause. With uncertain results, functional testing and segregation analysis are needed to complete the evidence.

Creatine-kinase reference intervals at rest and after maximal exercise in Standardbred racehorses

Due to the high variability of data drawn from the literature, aim of the study was to evaluate the effects of exercise on creatine-kinase (CK) serum activity and to determine CK reference intervals (RIs) at rest and post-exercise in healthy Standardbred racehorses. Data concerning history, physical examination, laboratory evaluation and ECG were collected retrospectively from a population of 258 Standardbred racehorses in training that underwent an incremental-maximal treadmill exercise. Those subjects with alterations potentially influencing CK serum activity were excluded. Finally, a reference sample of 194 horses was selected. Blood samples were collected 1 hour before exercise and 6 hour post-exercise and analysed with a spectrophotometric method. Values were compared by Wilcoxon test for paired samples. The effect of age and sex was evaluated by Kruskal-Wallis and Dunn post-test. Statistical significance was set at P<0.05. RIs were determined following Clinical and Laboratory Standard Institute guidelines (CLSI), approved by the American Society for Veterinary Clinical Pathology. Using a macroinstruction set for Microsoft Excel (RefValAdv), RIs were determined with a non-parametric method. A significant increase (P<0.0001) in CK activity post-exercise was observed. Partition by sex and age did not show any statistical difference, either at rest or post-exercise. In RIs determination no outliers were identified. RIs ranged from 25 to 394 U/l at rest and from 44 to 735 U/l post-exercise. To our knowledge, this is the first study considering CK post-exercise RIs in racehorses using CLSI’s guidelines and specific CK-related exclusion criteria. These RIs could be useful to discriminate between physiological and pathological CK post-exercise increase.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

European Federation of Neurological Societies cutoff values significantly reduce creatine kinase sensitivity for diagnosing neuromuscular disorders

INTRODUCTION

Elevated creatine kinase (CK) level was redefined by the European Federation of Neurological Societies)EFNS(as 1.5 times the upper limit of normal. In the current study we sought to determine the sensitivity and specificity of CK testing for the diagnosis of neuromuscular disorders.

METHODS

Demographics and CK levels were retrospectively extracted from an electronic database for 234 patients with neuromuscular disorders. Sensitivity, specificity, and likelihood ratios and the area under curve were determined for each diagnosis and different cutoff CK values.

RESULTS

Using the EFNS cutoff values significantly reduced CK test sensitivity. Creatine kinase values >1000 IU/L showed a high likelihood (11.04) for myopathies and a low likelihood for polyneuropathies (0).

DISCUSSION

European Federation of Neurological Societies cutoff values significantly reduce CK sensitivity for diagnosing neuromuscular disorders. While low CK values cannot exclude a neuromuscular disease, values >1000 IU/L are associated with a high likelihood of myopathy.

Cytidine Diphosphate-Ribitol Analysis for Diagnostics and Treatment Monitoring of Cytidine Diphosphate-l-Ribitol Pyrophosphorylase A Muscular Dystrophy

BACKGROUND

Many muscular dystrophies currently remain untreatable. Recently, dietary ribitol has been suggested as a treatment for cytidine diphosphate (CDP)-l-ribitol pyrophosphorylase A (CRPPA, ISPD), fukutin (FKTN), and fukutin-related protein (FKRP) myopathy, by raising CDP-ribitol concentrations. Thus, to facilitate fast diagnosis, treatment development, and treatment monitoring, sensitive detection of CDP-ribitol is required.

METHODS

An LC-MS method was optimized for CDP-ribitol in human and mice cells and tissues.

RESULTS

CDP-ribitol, the product of CRPPA, was detected in all major human and mouse tissues. Moreover, CDP-ribitol concentrations were reduced in fibroblasts and skeletal muscle biopsies from patients with CRPPA myopathy, showing that CDP-ribitol could serve as a diagnostic marker to identify patients with CRPPA with severe Walker-Warburg syndrome and mild limb-girdle muscular dystrophy (LGMD) phenotypes. A screen for potentially therapeutic monosaccharides revealed that ribose, in addition to ribitol, restored CDP-ribitol concentrations and the associated O-glycosylation defect of α-dystroglycan. As the effect occurred in a mutation-dependent manner, we established a CDP-ribitol blood test to facilitate diagnosis and predict individualized treatment response. Ex vivo incubation of blood cells with ribose or ribitol restored CDP-ribitol concentrations in a patient with CRPPA LGMD.

CONCLUSIONS

Sensitive detection of CDP-ribitol with LC-MS allows fast diagnosis of patients with severe and mild CRPPA myopathy. Ribose offers a readily testable dietary therapy for CRPPA myopathy, with possible applicability for patients with FKRP and FKTN myopathy. Evaluation of CDP-ribitol in blood is a promising tool for the evaluation and monitoring of dietary therapies for CRPPA myopathy in a patient-specific manner.

Serum Creatine Kinase in Patients with Neuromyelitis Optica Spectrum Disorder

OBJECTIVES

There have been reports of elevated serum creatine kinase (CK) and myopathy in patients with Neuromyelitis Optica Spectrum Disorder (NMOSD). Such findings have raised the possibility that myopathies may be a part of the spectrum of NMOSD. The incidence of elevated CK in NMOSD remains unknown. We sought to assess the potential association between hyperCKemia, myopathy, and NMOSD, and the potential role of screening for muscle involvement using serum CK.

METHODS

We reviewed records of all aquaporin 4 (AQP4) antibody-seropositive and seronegative NMOSD patients who had CK levels evaluated at two major academic medical centers.

RESULTS

Of 199 total NMOSD patients, CK levels were checked in 43, and elevated, on at least one occasion, in 4. In 1 patient, CK was elevated during an NMO exacerbation. A myopathic process occurring with NMOSD was suggested in 2 of 4 patients in the form of symptomatic complaint of myalgias and associated MRI signal change.

DISCUSSION

Unexplained hyperCKemia was found on one or more occasion in 4 of 43 tested NMOSD patients. Testing NMOSD patients for serum CK may reveal otherwise unsuspected myopathy. More formally powered, prospective assessment of the incidence and utility of CK in NMOSD is needed.

Evidence of Clinical Pathology Abnormalities in People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) from an Analytic Cross-Sectional Study

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease presenting with extreme fatigue, post-exertional malaise, and other symptoms. In the absence of a diagnostic biomarker, ME/CFS is diagnosed clinically, although laboratory tests are routinely used to exclude alternative diagnoses. In this analytical cross-sectional study, we aimed to explore potential haematological and biochemical markers for ME/CFS, and disease severity. We reviewed laboratory test results from 272 people with ME/CFS and 136 healthy controls participating in the UK ME/CFS Biobank (UKMEB). After corrections for multiple comparisons, most results were within the normal range, but people with severe ME/CFS presented with lower median values (p < 0.001) of serum creatine kinase (CK; median = 54 U/L), compared to healthy controls (HCs; median = 101.5 U/L) and non-severe ME/CFS (median = 84 U/L). The differences in CK concentrations persisted after adjusting for sex, age, body mass index, muscle mass, disease duration, and activity levels (odds ratio (OR) for being a severe case = 0.05 (95% confidence interval (CI) = 0.02-0.15) compared to controls, and OR = 0.16 (95% CI = 0.07-0.40), compared to mild cases). This is the first report that serum CK concentrations are markedly reduced in severe ME/CFS, and these results suggest that serum CK merits further investigation as a biomarker for severe ME/CFS.

Creatine Kinase and Blood Pressure: A Systematic Review

Background: Hypertension is a main risk factor for premature death. Although blood pressure is a complex trait, we have shown that the activity of the ATP-generating enzyme creatine kinase (CK) is a significant predictor of blood pressure and of failure of antihypertensive drug therapy in the general population. In this report, we systematically review the evidence on the association between this new risk factor CK and blood pressure outcomes. Method: We used a narrative synthesis approach and conducted a systematic search to include studies on non-pregnant adult humans that address the association between plasma CK and blood pressure outcomes. We searched electronic databases and performed a hand search without language restriction. We extracted data in duplo. The main outcome was the association between CK and blood pressure as continuous measures. Other outcomes included the association between CK and blood pressure categories (normotension and hypertension, subdivided in treated controlled, treated uncontrolled, and untreated hypertension). Results: We retrieved 139 reports and included 11 papers from 10 studies assessing CK in 34,578 participants, men and women, of African, Asian, and European ancestry, aged 18 to 87 years. In 9 reports, CK was associated with blood pressure levels, hypertension (vs. normotension), and/or treatment failure. The adjusted increase in systolic blood pressure (mmHg/log CK increase) was reported between 3.3 [1.4 to 5.2] and 8.0 [3.3 to 12.7] and the odds ratio of hypertension with high vs. low CK ranged between 1.2 and 3.9. In addition, CK was a strong predictor of treatment failure in the general population, with an adjusted odds ratio of 3.7 [1.2 to 10.9]. Discussion: This systematic review largely confirms earlier reports that CK is associated with blood pressure and failure of antihypertensive therapy. Further work is needed to address whether this new risk factor is useful in clinical medicine.

Creatine kinase and blood pressure in women with a history of early-onset preeclampsia

OBJECTIVES

High plasma creatine kinase (CK) activity is associated with hypertension in the general and pregnant population. We hypothesize that women with a history of early-onset preeclampsia are prone to hypertension due to a high CK activity level.

STUDY DESIGN

Nine to 16 years after pregnancy, serum CK activity and blood pressure were measured in 117 women with a history of early-onset preeclampsia and 50 women with a history of an uncomplicated pregnancy.

MAIN OUTCOME MEASURES

CK activity levels of the two groups were compared using the Mann-Whitney U test. The association between CK activity and blood pressure was evaluated by means of multivariable regression analysis.

RESULTS

There was no significant difference in median (interquartile range) CK activity between women with a history of early-onset preeclampsia and an uncomplicated pregnancy (59.00 [47.00-85.00] vs. 58.00 [46.50-75.25], respectively, p = 0.774). The association between CK and systolic blood pressure was significant in women with a pregnancy history of early-onset preeclampsia (regression coefficient [95% confidence interval]: 0.123 mmHg [0.020-0.226], p = 0.019), and a trend was found for diastolic blood pressure (p = 0.069). CK and blood pressure were not significantly associated in women with a history of an uncomplicated pregnancy.

CONCLUSIONS

Median CK did not significantly differ between the two groups. Serum CK activity was significantly associated with systolic blood pressure in women with a history of early-onset preeclampsia. These data suggest that CK is not a predominant factor in the increased risk of hypertension in women with a history of early-onset preeclampsia.

Strategy for suspected myositis

Skeletal muscle inflammation is the feature shared by all forms of myositis. However, the muscle damage ranges in severity from asymptomatic to responsible for severe weakness. In addition, myositis usually occurs as a systemic disease that affects multiple organs. More specifically myositis should be considered in patients with muscular, cutaneous, pulmonary, and articular manifestations. The definitive diagnosis and classification of myositis has benefited considerably in recent years from the identification of characteristic autoantibodies. Nonetheless, a muscle biopsy is often necessary to confirm the diagnosis, and the differential diagnoses may raise challenges that require evaluation at a myositis referral center. The management depends on the type of myositis. Treatments should be provided for both the systemic complications (involving the lungs, heart, gastrointestinal tract, and/or joints) and the comorbidities (cancer and risks factors for cardiovascular disease, thromboembolism, and fractures), which together determine the prognosis. Many drugs are available for treating myositis. Findings from randomized controlled trials will help to use them optimally.

Pediatric reference intervals for clinical chemistry assays on Siemens ADVIA XPT/1800 and Dimension EXL in the CALIPER cohort of healthy children and adolescents

INTRODUCTION

Accurate reference intervals (RIs) are essential for clinical interpretation of laboratory test results; however, major gaps exist in pediatric RIs. The Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) has established age- and sex-specific pediatric RIs on various analytical platforms. The current study expands the CALIPER database by establishing age- and sex-specific RIs for biochemical assays on Siemens ADVIA XPT/1800 and Dimension EXL Systems.

METHODS

Serum samples from a total of 909 and 867 healthy children and adolescents (ages 0-<19 y) were tested on ADVIA XPT/1800 and Dimension EXL systems, respectively. Age- and/or sex-specific RIs were calculated for a total of 54 biochemical assays.

RESULTS

Serum concentrations of several biomarkers remained relatively constant across the pediatric age range and similar between sexes, including sodium and triglycerides. Other biomarkers, such as alkaline phosphatase and creatinine showed both age and sex differences. Furthermore, immunoglobulin A and iron showed only age differences.

DISCUSSION

We established RIs for creatine kinase, random glucose, total iron binding capacity, and several electrolytes for the first time using the CALIPER cohort. Overall, pediatric RIs established in the current study will allow for more accurate laboratory test interpretation worldwide using Siemens chemistry assays.

Creatine kinase, energy reserve, and hypertension: from bench to bedside

We hypothesized that human variation in the activity of the ATP regenerating enzyme creatine kinase (CK) activity affects hypertension and cardiovascular disease risk. CK is tightly bound close to ATP-utilizing enzymes including Ca2+-ATPase, myosin ATPase, and Na+/K+-ATPase, where it rapidly regenerates ATP from ADP, H+, and phosphocreatine. Thus, relatively high CK was thought to enhance ATP-demanding processes including resistance artery contractility and sodium retention, and reduce ADP-dependent functions. In a series of studies of our group and others, CK was linked to hypertension and bleeding risk. Plasma CK after rest, used as a surrogate measure for tissue CK, was associated with high blood pressure and failure of antihypertensive therapy in case-control and population studies. Importantly, high tissue CK preceded hypertension in animal models and in humans, and human vascular tissue CK gene expression was strongly associated with clinical blood pressure. In line with this, CK inhibition substantially reduced the contractility of human resistance arteries ex vivo. We also presented evidence that plasma CK reduced ADP-dependent platelet aggregation. In subsequent intervention studies, the oral competitive CK inhibitor beta-guanidinopropionic acid (GPA) reduced blood pressure in spontaneously hypertensive rats (SHRs), and a 1-week trial of sub-therapeutic dose GPA in healthy men was uneventful. Thus, based on theoretical concepts, evidence was gathered in laboratory, case-control, and population studies that high CK is associated with hypertension and with bleeding risk, potentially leading to a new mode of cardiovascular risk reduction with CK inhibition.

Biological variables influencing the estimation of reference limits

Reference limits (RLs) are required to evaluate laboratory results for medical decisions. The establishment of RL depends on the pre-analytical and the analytical conditions. Furthermore, biological characteristics of the sub-population chosen to provide the reference samples may influence the RL. The most important biological preconditions are gender, age, chronobiological influences, posture, regional and ethnic effects. The influence of these components varies and is often neglected. Therefore, a list of biological variables is collected from the literature and their influence on the estimation of RL is discussed. Biological preconditions must be specified if RL are reported as well for directly as for indirectly estimated RL. The influence of biological variables is especially important if RL established by direct methods are compared with those derived from indirect techniques. Even if these factors are not incorporated into the estimation of RL, their understanding can assist the interpretation of laboratory results of an individual.

Spectrum of Neuromuscular Disorders With HyperCKemia From a Tertiary Care Pediatric Neuromuscular Center

Elevated creatine kinase is a useful screening test in the diagnostic workup of patients with neuromuscular disorders. We did a retrospective study of children with hyperCKemia (>175 IU/L) who were followed in the neuromuscular program of a tertiary care pediatric center from 2005 to 2016. Patients with hyperCKemia were divided into 2 groups: myopathic and nonmyopathic. Within the myopathic group, there were 3 arbitrary subgroups based on creatine kinase values: A (creatine kinase >10 times normal), B (creatine kinase 5-10 times normal), and C (creatine kinase 1-5 times normal). The 3 major categories of myopathies across all the subgroups were muscular dystrophies (commonest) followed by metabolic myopathies and inflammatory myopathies. Among the nonmyopathic causes of hyperCKemia, spinal muscular atrophy was the commonest. Muscular dystrophies should be considered in children with hyperCKemia, muscle weakness, or calf hypertrophy, and metabolic myopathies to be considered in children with recurrent rhabdomyolysis.

Is it necessary to adjust current creatine kinase reference ranges to reflect levels found in professional footballers?

Objective

We aimed to explore the validity of applying current reference ranges of the enzyme creatine kinase (CK) when analysing the medical status of professional footballers and to offer a more functional CK reference range for professional footballers.

Methods

A sample of 27 professional male footballers competing in The Football League Championship was analysed. The single sample Wilcoxon signed-rank test was used to compare the CK distribution of the study group with that of a control group of military personnel reported in the literature.

Results

The median values for study group and the published control group were 284 U/L and 124 U/L, respectively (P<0.001) suggesting that the average CK activity of professional footballers is higher than that of the normal healthy military population.

Conclusion

Ethnicity, sex, age and physical exercise are factors that likely influence CK levels among various populations. From our analysis, we recommend a new 95% reference interval of 64.9 U/L to 1971.7 U/L for professional footballers.

Creatine kinase and renal sodium excretion in African and European men on a high sodium diet

Creatine kinase (CK) rapidly regenerates ATP for Na⁺ /K⁺ -ATPase driven sodium retention throughout the kidney. Therefore, we assessed whether resting plasma CK is associated with sodium retention after a high sodium diet. Sixty healthy men (29 European and 31 African ancestry) with a mean age of 37.2 years (SE 1.2) were assigned to low sodium intake (< 50 mmol/d) during 7 days, followed by 3 days of high sodium intake (> 200 mmol/d). Sodium excretion (mmol/24-h) after high sodium was 260.4 (28.3) in the high CK tertile versus 415.2 (26.3) mmol/24-h in the low CK tertile (P < .001), with a decrease in urinary sodium excretion of 98.4 mmol/24-h for each increase in log CK, adjusted for age and African ancestry. These preliminary results are in line with the energy buffering function of the CK system, but more direct assessments of kidney CK will be needed to further establish whether this enzyme enhances sodium sensitivity.

The acute effect of beta-guanidinopropionic acid versus creatine or placebo in healthy men (ABC-Trial): A randomized controlled first-in-human trial

Aims

Increasing evidence indicates that the ATP‐generating enzyme creatine kinase (CK) is involved in hypertension. CK rapidly regenerates ATP from creatine phosphate and ADP. Recently, it has been shown that beta‐guanidinopropionic acid (GPA), a kidney‐synthesized creatine analogue and competitive CK inhibitor, reduced blood pressure in spontaneously hypertensive rats. To further develop the substance as a potential blood pressure‐lowering agent, we assessed the tolerability of a sub‐therapeutic GPA dose in healthy men.

Methods

In this active and placebo‐controlled, triple‐blind, single‐centre trial, we recruited 24 healthy men (18–50 years old, BMI 18.5–29.9 kg m⁻²) in the Netherlands. Participants were randomized (1:1:1) to one week daily oral administration of GPA 100 mg, creatine 5 g, or matching placebo. The primary outcome was the tolerability of GPA, in an intent‐to‐treat analysis.

Results

Twenty‐four randomized participants received the allocated intervention and 23 completed the study. One participant in the placebo arm dropped out for personal reasons. GPA was well tolerated, without serious or severe adverse events. No abnormalities were reported with GPA use in clinical safety parameters, including physical examination, laboratory studies, or 12‐Lead ECG. At day 8, mean plasma GPA was 213.88 (SE 0.07) in the GPA arm vs. 32.75 (0.00) nmol l⁻¹ in the placebo arm, a mean difference of 181.13 (95% CI 26.53–335.72).

Conclusion

In this first‐in‐human trial, low‐dose GPA was safe and well‐tolerated when used during 1 week in healthy men. Subsequent studies should focus on human pharmacokinetic and pharmacodynamic assessments with different doses.