Abstract
Background
Cardiomyopathy is a significant cause of mortality in dystrophinopathy, and early detection and intervention are critical to reduce the disease burden. Currently, cardiomyopathy detection primarily relies on echocardiography and cardiac magnetic resonance imaging (CMR), which are inconvenient for paediatric patients and those in remote areas. Uric acid (UA) is associated with various heart diseases and serves as a biomarker of injury severity, but its level changes and connection with myocardial injury in dystrophic cardiomyopathy remain unclear. Therefore, we investigated the relationship between UA and cardiomyopathy in dystrophinopathy, as its early detection may offer a more straightforward method for monitoring cardiac health.
Method
A total of 71 dystrophinopathy patients underwent biochemical, genetic, and echocardiography assessments to correlate UA, gene mutations types, and cardiac parameters.
Result
Patients with hyperuricaemia showed larger atria and ventricles, and thicker left ventricular walls compared to those with normal UA levels. This was reflected in increased left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), left atrial diameter (LAD), right ventricular diameter (RVD), left ventricular posterior wall thickness (LVPWT), and interventricular septal thickness (IVST). Multivariate linear regression analysis revealed an independent positive correlation between UA and these echocardiographic parameters.
Conclusion
Elevated serum UA levels were independently associated with cardiac morphological changes, including cardiac dilation and left ventricular remodelling in dystrophinopathy patients. Consequently, UA may be considered as a potential biomarker for cardiomyopathy in dystrophinopathy.
Keywords: Dystrophinopathy, cardiomyopathy, uric acid, gene mutation, echocardiography
KEY MESSAGES
Serum UA levels has positive correlation with cardiac enlargement, as well as ventricular hypertrophy in dystrophinopathy.
UA can serve as a biomarker for cardiac changes of dystrophinopathy.
Introduction
Dystrophinopathy is a recessive X-linked hereditary disease with an incidence of 1 in 5,000 to 1 in 6,000 newborn males [1]. The gene responsible for dystrophinopathy is dystrophin gene (DMD), which encodes the dystrophy protein and contains 79 exons [2,3]. Affected individuals exhibit early-onset symptoms of progressive motor deficiency and ultimately die from respiratory or cardiac failure. With improvements of airway management and more effective respiratory support, cardiopathy now has a significant impact on disability and accounts for 30–50% of mortality [4,5]. Therefore, early detection and intervention of cardiopathy have become an important approach of reducing mortality.
Currently, early detection of cardiopathy mainly relies on echocardiography and cardiac magnetic resonance imaging (CMR) [6,7]. Since dystrophinopathies predominantly affect paediatric patients, it may be challenging to obtain their cooperation during both echocardiography and CMR examinations. The presence of chest wall deformities, spinal curvature and respiratory functional impairments further complicates the technical aspects of performing echocardiography and CMR examinations, thus limiting the diagnostic rate [8,9]. Additionally, the precise equipment required for these diagnostic methods raises challenges for remote areas and primary healthcare stations [10]. Apart from echocardiography and CMR, genetic testing emerges as a potential diagnostic approach, as specific mutations have been found to be associated with cardiopathy. Notably, deletions within exons 45–55 have been arousing wide research attention as they might lead to more prominent symptoms of cardiac dysfunction [11]. Nevertheless, deletions only constitute partial mutations in the DMD gene, with approximately 47% of these deletions occurring in exons 45–55 and the relationship between genotype and cardiopathy remains unclear [2,12]. Therefore, it is not practical to detect cardiopathy through genetic analysis. In short, it is essential to explore simpler and more convenient methods to identify cardiopathy in patients with dystrophinopathy to facilitate the selection of appropriate treatment methods.
Uric acid (UA) is closely associated with cardiac diseases [13,14]. Some clinical studies and meta-analyses found that the incidence of heart failure in patients with hyperuricaemia were significantly higher than that in normouricemic population [15,16]. Moreover, UA was known as an independent predictor of adverse cardiac events such as all-cause mortality, long-term survival and risk of hospitalization in heart failure patients [17,18]. In dilated cardiomyopathy, it was proved that UA level was an independent prognostic factor [19].
UA is the end-product of purine metabolism mediated by xanthine oxidase. The destruction of cardiomyocytes releases nucleotides, which, in addition to being metabolized into UA, also activate purinergic receptors [20]. In mouse models, activation of the purinergic P2X7 receptor pathway in Duchenne muscular dystrophy (DMD) can lead to muscle cell damage, along with increased inflammation creating a vicious cycle [21]. The increase in UA suggests cardiomyocyte damage and nucleotide release, which further contributes to cardiomyocyte injury through the activation of purinergic receptors.
UA itself may also promote cardiac damage. It has been associated with vascular inflammation, endothelial dysfunction, and oxidative stress, all of which contribute to the advancement of cardiovascular disease [22]. Studies suggest that UA increases the production of reactive oxygen species and stimulates the activation of the renin-angiotensin system [23]. The upregulation of inflammatory pathways leads to myocardial fibrosis and exacerbates heart dysfunction, while activation of the renin-angiotensin system contributes to ventricular remodelling. Xanthine oxidase inhibition in hyperuricemic congestive heart failure patients may provide survival benefits, and the use of drugs such as dapagliflozin could reduce UA while improving cardiac function and 5-year survival rate [24,25], highlighting deleterious effects of UA on cardiovascular health. These mechanisms may explain why UA can serve as a biomarker for cardiac diseases. However, the changes in UA concentration and its association with cardiac function in dystrophinopathy remains unknown. Considering that UA correlates with cardiac function, we suggest that UA might serve as a valuable indicator to conveniently assess cardiac function in dystrophinopathy.
There are several other known biomarkers for heart diseases. For instance, N-terminal pro B-type natriuretic peptide (NT-proBNP) is a standard biological marker for heart failure [26]. It is not sensitive enough in the early stages of cardiomyopathy because it is often elevated after heart failure has developed, while the majority of the patients included in our study had not yet exhibited significant heart dysfunction. Currently, creatine kinase (CK) is used as the primary laboratory marker for DMD to monitor muscle necrosis [27]. Elevated CK levels in dystrophinopathy mainly caused by peripheral skeletal muscle damage and can vary with age, physical activity, medication, and other factors, making it not always reliably correlated with cardiac MRI data. Therefore, CK is more reflective of the overall systemic condition. Creatine kinase-MB isoenzyme (CKMB), a subtype of CK, is considered a more specific marker of myocardial injury. However, its detection window is short, and while it is specific in acute myocardial infarction, it may not show significant changes in chronic heart failure or other conditions [28]. Thus, combining UA with these known biomarkers may provide a more comprehensive assessment of myocardial injury in dystrophinopathy patients, aiding early diagnosis and monitoring of heart function.
In this study, we investigated the UA levels in patient with dystrophinopathy and its relation with cardiac morphology and function assessed by echocardiography. Additionally, we explored the relationship between the genotype of exon 45–55 deletions and echocardiographic parameters. Our findings indicated that hyperuricaemia was associated with cardiac dilation and left ventricular remodelling. Therefore, UA could serve as a valuable biomarker for detection cardiopathy in dystrophinopathy.
Method
Participants
Seventy-one dystrophinopathy patients admitted to the Neuromuscular Department at Guangzhou First People’s Hospital and the First Affiliated Hospital of Sun Yat-sen University participated in the present study. Their diagnoses were confirmed by clinical manifestation, biochemical detection and molecular analysis. Patients exhibiting the following confounding factors were excluded from the study: (a) Patients with missing genotype results; (b) Patients taking uric acid-lowering or cardiac function-improving drugs, such as diuretics. The inpatients had mild to moderate mild conditions with the ejection fraction (EF) all greater than 50%. Thus, the majority of them had not developed significant heart failure and treated with related medications like diuretics. A small subset of patients using such medications were excluded from the study according to the exclusion criteria. Because the included patients were minors, written informed consent to participate in the study were obtained from parents or legal guardians of patients at admission. The assent process for children was not conducted in written form, but the guardians were asked to communicate with the child to make the final decision. All patients’ guardians agreed to participate in the study and signed the informed consent. The specific informed consent form template is provided in the supplementary material. At the same time, the patients’ condition should allow them to undergo venous blood sampling, lower limb motor function assessment, and echocardiographic examination. The study protocol was approved by the Bioethical Committee of Guangzhou First People’s Hospital and the First Affiliated Hospital of Sun Yat-sen University, and the clinical trial registration number is K-2021-196-02. The studies involving human participants were carried out in accordance with the Declaration of Helsinki.
All patients’ demographic and clinical data including age, height, weight and the genetic mutation were collected, and their body mass index (BMI) were calculated. The Vignos’s Scale [29], a scale of 0–10, was used to evaluate participants’ motor function, with higher scores indicating more severe lower limb motor function impairment.
Sample process and tools
Blood samples were collected from the antecubital vein after an overnight fasting. Routine biochemical parameters including UA, creatine kinase (CK), creatine kinase-MB isoenzyme (CKMB), lactate dehydrogenase (LDH), hydroxybutyrate dehydrogenase (HBDH), creatinine (CREA), brain natriuretic peptide (BNP), alanine transaminase (ALT) and aspartate transaminase (AST) were measured using standard methods. According to previous studies [30], hyperuricaemia was defined as a UA level greater than 323umol/L (5.5 mg/dL). The threshold for hyperuricaemia was also determined with reference to the cross-sectional study on UA levels in Chinese adolescents by Lu et al. [31]. The UA level of 323 µmol/L functioned as a cut-off value in dividing the participants into two groups, namely, hyperuricemic group and normouricemic group.
Meanwhile, 2 ml of blood from each patient was extracted and stored in separate test tubes for DMD gene mutation analysis. Multiplex ligation-dependent probe-amplification reactions were used to detect large sequence rearrangements, and next-generation sequencing, using an Illumina HiSeq 2000 system (Illumina Corporation, San Diego, CA, USA), was used to detect smaller scale mutations. The average sequencing depth was >200×. All patients underwent genetic testing and were classified into two categories based on DMD gene mutations, that is, deletions in exons 45–55 of the DMD gene and other mutation types.
Evaluation of cardiac function
All patients underwent trans thoracic echocardiography (TTE) with the Acuson Sequoia 256 Cardiac Ultrasound Machine (2,5e3.5 MHz probe) or EPIQ7C Philips Machine to their test cardiac morphology and function. Measurement was performed by two specialized echocardiographers blinded to this study following the guidelines from the American Society of Echocardiography [32]. Left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), left atrial diameter (LAD) and right ventricular diameter (RVD) were acquired from the 2-dimensional parasternal long axis view to evaluate the degree of cardiac chamber dilation, while left ventricular posterior wall thickness (LVPWT) and interventricular septal thickness (IVST) were used as indices of ventricular remodelling. Systolic function was evaluated as left ventricular ejection fraction (LVEF) obtained by biplane Simpson’s method and left ventricular fraction shortening (LVFS) calculated from LVEDD and LVESD.
Statistical analysis
Statistical analysis was performed with SPSS 20.0 (IBM, Armonk, United States). The Kolmogorov-Smirnov test was used to assess the normality of distribution. Descriptive statistical analysis for continuous variables were presented as mean ± standard deviation (SD) or median (IQR) based on the distribution, while categorical variables were presented as percentage (%). Specifically, UA was treated as a continuous variable. Heat maps were made using GraphPad Prism 8. Inferential statistical analyses such as independent t-test or Man–Whitney U test were conducted to make comparisons between groups when appropriate. The relations between echocardiographic parameters and various variables were evaluated by simple correlation. Then variables with p < 0.05 and the known risk factors were included in the multivariate linear regression analysis to identify the independent determinants. The concomitant probability of p value was considered statistically significant when it was lower than 0.05.
Result
The demographic and clinical features of the patients
The study enrolled 71 patients diagnosed with dystrophinopathy, with an average age of 8. All patients’ guardians agreed to participate in the study and signed the informed consent. Motor function assessments revealed a median Vignos’s Scale score of 2, and 7.04% of patients were unable to walk. All these patients had undergone genetic testing, and 30.99% of them had deletions in exons 45–55 of the DMD gene. The laboratory characteristics are presented in Table 1, showing a mean UA level of 280.85 ± 103.18 umol/L.
Table 1.
The demographic and clinical features of the patients.
| Characteristics | Mean ± SD/Median (IQR) | Number (%) | |
|---|---|---|---|
| Demographic characteristics | |||
| Age | 8 (6–9) | ||
| BMI (kg/m2) | 16.74 ± 2.08 | ||
| Functional assessment | |||
| Gait Impairment | 5 (7.04%) | ||
| Vignos’s Scale | 2 (2–3) | ||
| Genetic testing | |||
| Deletions in exons 45–55 | 22 (30.99%) | ||
| Other mutation types | 49 (69.01%) | ||
| Laboratory parameters | |||
| UA (μmol/L) | 280.85 ± 103.18 | ||
| CK (U/L) | 8497.97 ± 4014.44 | ||
| CKMB (U/L) | 302.76 ± 191.04 | ||
| LDH (U/L) | 882 (555–1260) | ||
| HBDH (U/L) | 738.41 ± 326.73 | ||
| CREA (μmol/L) | 17 (14-24.5) | ||
| BNP (pg/ml) | 81.62 ± 55.46 | ||
| ALT (U/L) | 238.32 ± 149.05 | ||
| AST (U/L) | 179.18 ± 89.38 | ||
| UA group | |||
| Normal UA | 227.56 ± 58.71 | 50 (70.42%) | |
| Hyperuricaemia | 407.71 ± 69.40 | 21 (29.58%) | |
Values are presented as mean ± SD, median (IQR) or number (%).
BMI, body mass index; UA uric acid; CK creatine kinase; CKMB, creatine kinase-MB isoenzyme; LDH, lactate dehydrogenase; HBDH, hydroxybutyrate dehydrogenase; CREA, creatinine; BNP, brain natriuretic peptide; ALT, alanine transaminase; AST, aspartate transaminase.
Comparisons of echocardiographic parameters between different UA groups
Based on a UA cut-off of 323 umol/L, patients were divided into hyperuricaemia and normouricemia groups, with average UA levels of 407.71 ± 69.40 and 227.56 ± 58.71umol/L (Table 1), respectively. Echocardiographic assessments revealed that patients in the hyperuricaemia group displayed larger LVEDD, LVESD and LAD compared with the normouricemia group, indicating an enlargement of both the left ventricle and the left atrium. Moreover, patients with hyperuricaemia exhibited thicker LVPWT and IVST, suggesting a propensity towards left ventricular hypertrophy. Although no statistical difference was detected, the RVD value tended to increase in the hyperuricaemia group. Yet no significant distinctions in LVEF and LVFS between the two groups could be explored (Table 2).
Table 2.
Comparisons of echocardiographic parameters between the hyperuricaemia and normouricemia groups.
| Echocardiographic parameters | Normal UA | Hyperuricaemia | t | P value |
|---|---|---|---|---|
| LVEDD (mm) | 37.62 ± 4.83 | 41.33 ± 5.49 | −2.84 | <0.01 |
| LVESD (mm) | 24.31 ± 4.13 | 26.96 ± 4.14 | −2.47 | 0.02 |
| LAD (mm) | 22.85 ± 4.68 | 25.81 ± 4.78 | −2.40 | 0.02 |
| RVD (mm) | 14.32 ± 2.84 | 15.52 ± 3.36 | −1.55 | 0.13 |
| LVPWT (mm) | 5.47 ± 1.24 | 6.81 ± 1.94 | −3.49 | <0.01 |
| IVST (mm) | 5.93 ± 1.14 | 7.14 ± 2.08 | −2.51 | 0.02 |
| LVEF (%) | 66.48 ± 5.86 | 65.48 ± 5.288 | 0.71 | 0.48 |
| LVFS (%) | 36.52 ± 4.73 | 35.64 ± 3.65 | 0.69 | 0.49 |
LVEDD, left ventricular end-diastolic diameter; LVESD, left ventricular end-systolic diameter; LAD, left atrial diameter; RVD, right ventricle diameter (LVEDD, LVESD, LAD and RVD reflect the degree of dilation of the heart cavity); LVPWT, left ventricular posterior wall thickness; IVST, interventricular septal thickness (LVPWT and IVST are the thickness of the ventricular wall, reflecting the degree of ventricular remodelling); LVEF, left ventricular ejection fraction; LVFS, left ventricular fraction shortening (LVEF and LVFS reflect the systolic function of the left ventricle).
Correlations between biochemical and echocardiographic parameters
Relations between clinical characteristics and echocardiographic parameters were evaluated by simple correlation analysis, and the correlation coefficients were visually represented by different colours in the heat map (Figure 1). Positive correlations were found among age, UA and CREA levels with various echocardiographic indicators.
Figure 1.
Simple correlations among clinical characteristics and echocardiographic parameters. The heatmap was generated based on the correlation coefficients between indices, with red indicating a positive correlation and blue signifying a negative correlation.
Notably, UA exhibited significant positive correlations with LVEDD, LVESD, LAD, RVD, LVPWT and IVST. However, no observable correlations were identified between LVEF and LVFS with UA. Detailed correlation coefficients were provided in Table S1.
Comparisons of echocardiographic parameters between different gene groups
Considering that exons 45–55 constitute a critical region associated with more prominent symptoms of cardiac dysfunction, patients were divided into two groups: one refers to the deletions specifically within exons 45–55, and the other comprising all other types of gene mutations. Our observations revealed a significant decrease in the thickness of LVPWT among patients with the deletion of exons 45–55, as compared to those with other mutations in the DMD gene. However, no difference was observed in other echocardiographic parameters between the two groups (Table 3).
Table 3.
Comparisons of echocardiographic parameters between two gene groups.
| Echocardiographic parameters | Deletion of exon 45–55 | Other gene types | t | P value |
|---|---|---|---|---|
| LVEDD (mm) | 38.50 ± 5.22 | 39.91 ± 5.70 | 0.81 | 0.42 |
| LVESD (mm) | 24.89 ± 4.29 | 26.19 ± 4.26 | 0.93 | 0.36 |
| LAD (mm) | 23.44 ± 4.77 | 25.27 ± 5.37 | 1.15 | 0.25 |
| RVD (mm) | 14.56 ± 3.04 | 15.27 ± 3.00 | 0.71 | 0.48 |
| LVPWT (mm) | 5.68 ± 1.51 | 6.91 ± 1.70 | 2.45 | 0.02 |
| IVST (mm) | 6.16 ± 1.37 | 7.00 ± 2.32 | 1.16 | 0.27 |
| LVEF (%) | 66.20 ± 5.76 | 66.09 ± 5.45 | −0.06 | 0.95 |
| LVFS (%) | 36.27 ± 4.65 | 35.74 ± 3.76 | −0.48 | 0.63 |
LVEDD, left ventricular end-diastolic diameter; LVESD, left ventricular end-systolic diameter; LAD, left atrial diameter; RVD, right ventricle diameter; LVPWT, left ventricular posterior wall thickness; IVST, interventricular septal thickness; LVEF, left ventricular ejection fraction; LVFS, left ventricular fraction shortening.
Subsequently, correlational analyses were conducted between genetic mutation types and echocardiographic parameters. No significant correlation between genetic mutation types and any of the echocardiographic parameters was detected (Table 4).
Table 4.
Correlations between genetic mutation types and echocardiographic parameters.
| Echocardiographic parameters | r | P value |
|---|---|---|
| LVEDD | 0.21 | 0.11 |
| LVESD | 0.21 | 0.10 |
| LAD | 0.15 | 0.28 |
| RVD | −0.07 | 0.59 |
| LVPWT | 0.17 | 0.20 |
| IVST | 0.12 | 0.38 |
| LVEF | −0.19 | 0.17 |
| LVFS | −0.18 | 0.38 |
LVEDD, left ventricular end-diastolic diameter; LVESD, left ventricular end-systolic diameter; LAD, left atrial diameter; RVD, right ventricle diameter; LVPWT, left ventricular posterior wall thickness; IVST, interventricular septal thickness; LVEF, left ventricular ejection fraction; LVFS, left ventricular fraction shortening.
Multiple linear regression analysis of echocardiographic parameters
Furthermore, multiple linear regression analysis was conducted to determine the independent determinants of echocardiographic parameters. After adjusting for potential confounders, UA level exhibited significant positive correlations with indices representing cardiac chambers dimensions and wall thickness: LVEDD (β = 0.01, p < 0.01), LAD (β = 0.26, p = 0.02), RVD (β = 0.30, p = 0.03), LVPWT (β = 0.34, p < 0.01) and IVST (β = 0.22, p = 0.02), respectively (Table 5).
Table 5.
Multiple correlations among echocardiographic parameters and clinical characteristics.
| β value | P value | F | Adjust R2 |
P value (the regression models) |
|
|---|---|---|---|---|---|
| LVEDD | 7.58 | 0.60 | <0.01 | ||
| Age | 0.25 | 0.42 | |||
| UA | 0.01 | <0.01 | |||
| ALT | −0.002 | 0.29 | |||
| LVESD | 9.37 | 0.31 | <0.01 | ||
| Age | 0.37 | <0.01 | |||
| UA | 0.25 | 0.05 | |||
| ALT | −0.25 | 0.03 | |||
| LAD | 16.23 | 0.45 | <0.01 | ||
| Age | 0.50 | <0.01 | |||
| UA | 0.26 | 0.02 | |||
| ALT | −0.19 | 0.07 | |||
| RVD | 7.90 | 0.31 | <0.01 | ||
| Age | 0.29 | 0.03 | |||
| UA | 0.30 | 0.03 | |||
| ALT | −0.22 | 0.06 | |||
| LVPWT | 12.16, | 0.44 | <0.01 | ||
| Age | 0.41 | <0.01 | |||
| UA | 0.34 | <0.01 | |||
| ALT | −0.21 | 0.04 | |||
| Gene type | 0.11 | 0.28 | |||
| IVST | 35.02 | 0.59 | <0.01 | ||
| Age | 0.56 | <0.01 | |||
| UA | 0.22 | 0.02 | |||
| ALT | −0.24 | <0.01 |
LVEDD, left ventricular end-diastolic diameter; LVESD, left ventricular end-systolic diameter; LAD, left atrial diameter; RVD, right ventricle diameter; LVPWT, left ventricular posterior wall thickness; IVST, interventricular septal thickness; UA uric acid; ALT, alanine transaminase.
Given the significant difference in LVPWT between the two groups with different gene mutations, an additional multiple linear regression analysis of LVPWT, including gene mutation types as independent variables, was conducted. However, no significant correlations were detected (Table 5). The regression models constructed for the LVEF and LVFS were not statistically significant (Table S2). Although deletions in exons 45–55 have been associated with less severe dystrophic phenotypes [11], this study does not show a clear connection between these deletions and specific cardiac outcomes.
Discussions
Our study found that hyperuricaemia is associated with cardiac morphological changes in dystrophinopathy, the increased chamber diameters and left ventricular remodelling. Whereas, the deletion of exons 45–55 in the DMD gene was not related with these cardiac pathologies.
UA is the end-product of purine metabolism mediated by xanthine oxidase which plays a crucial role in the oxygen radical-generating system contributing to endothelial dysfunction, metabolic impairment and inflammatory activation, among other features of cardiovascular pathophysiology [22,25]. Therefore, hyperuricaemia, reflecting increased xanthine oxidase activity, was commonly observed in cardiovascular diseases such as hypertension, coronary artery disease, and heart failure [13]. The destruction of cardiomyocytes releases nucleotides, which, in addition to being metabolized into UA, also activate purinergic receptors [20]. In mouse models, activation of the purinergic P2X7 receptor pathway in DMD can lead to muscle cell damage [21]. The increase in UA suggests cardiomyocyte damage and nucleotide release, which further contributes to cardiomyocyte injury through the activation of purinergic receptors. Clinical studies have also demonstrated that hyperuricaemia was related to increased incidence of cardiovascular disease, even in young individuals with fewer risk factors [33]. Kirsty McDowell et al. found that UA was an independent predictor of disease progression and death in patients with heart failure [24]. The risk of hospitalization and cardiovascular death of heart failure increased by 7 and 6%, respectively, per 1 mg/dl unit increase of UA. Additionally, elevated UA level was observed in children with DCM and might serve as a biomarker reflecting the disease severity [34], given its association with NYHA classification and echocardiographic parameters such as LVEDD, LVESD and LVEF. By following up with patients with non-ischemic DCM, Hyungseop Kim et al. found that hyperuricaemia was significantly associated with decreased event-free survival [19], indicating that serum UA level is an independent predictor of prognosis in DCM.
Deficiency and malfunction of dystrophin can involve myocardium in addition to skeletal muscle. With the advancement of nursing quality and the development of non-invasive respiratory management, early mortality related with respiratory complications has decreased, while the proportion of deaths due to heart failure has increased [2,4]. Due to myocardial cell injury and necrosis, as well as fibrous proliferation and lipid deposition in the interstitium, ventricular remodelling occurs and may eventually develop into cardiac morphological changes [35,36]. However, the relationship between UA and cardiac structure as well as the relationship between UA and cardiac function in dystrophinopathy have not been studied. In this study, we found that patients with hyperuricaemia had significantly larger LVEDD, LVESD, LAD and thicker LVPWT and IVST. Multiple regression analysis further revealed independent associations between UA and all these echocardiographic parameters. However, UA was not independently correlated with other echocardiographic parameters such as RVD, LVEF and LVFS, possibly due to the insufficient sample size and the inclusion of patients with mild conditions who had not progressed to the stage of cardiomyopathy. The present study provided the first evidence that UA might serve as a biomarker of cardiac enlargement and ventricular remodelling in dystrophinopathy, which is usually diagnosed by echocardiography. Although echocardiography is a relatively rapid and cost-effective imaging method, it may be technically challenging for dystrophinopathy patients due to chest wall deformity, scoliosis and respiratory dysfunction, thus limiting the diagnostic rate [8,9]. Furthermore, it is difficult to perform echocardiography examination in some remote areas and primary healthcare stations due to the lack of equipment [10]. As our study suggest, the elevated UA levels in dystrophinopathy patients correlated with significant cardiac changes, which highlights the potential utility of UA as an early indicator of cardiac damage in this patient population. Considering the difficulties in obtaining modern imaging technologies in distant regions, utilizing UA as a biomarker presents a more straightforward and economical option for regularly monitoring patients with dystrophinopathy.
Elevated UA levels are more likely to be considered the consequence of progression in dystrophinopathy. The lack of dystrophin in cardiomyocytes leads to membrane instability, making cells more susceptible to damage and death [2]. As cardiomyocytes break down, nucleic acids and purine compounds are released, which are metabolized into UA [37]. Changes in UA levels have also been observed in other forms of myocardial injury. In acute coronary syndrome, elevated UA levels associated with the incidence of acute heart failure and cardiogenic shock may result from increased purine degradation driven by hypoxia and tissue catabolism [16]. UA itself may also play a promoting role in the development of cardiovascular disease. It was found that using drugs such as allopurinol, atorvastatin and dapagliflozin to lower UA levels could improve cardiac systolic function and reduce hospitalization and mortality rates in heart failure patients [24,38,39]. The pathophysiology of the cardiac effects of UA is still uncertain, it may contribute to cardiac fibrosis, myocardial remodelling, and atherosclerosis through oxidative stress, endothelial dysfunction and vascular inflammation [22,40]. Studies suggest that UA increases the production of reactive oxygen species and stimulates the activation of the renin-angiotensin system [23]. The upregulation of inflammatory pathways leads to myocardial fibrosis and exacerbates heart dysfunction, while activation of the renin-angiotensin system contributes to ventricular remodelling. These mechanisms may play a role in the cardiac remodelling observed in dystrophinopathy, particularly in patients with elevated UA levels. Moreover, the potential for UA levels to be modulated through urate-lowering drugs offers a therapeutic option. Reducing UA may potentially mitigate heart damage, reduce myocardial remodelling, and ultimately improve the cardiac prognosis of dystrophinopathy patients. This could be particularly valuable in resource-constrained environments where other treatment options are limited.
It remains unclear whether UA is an independent risk factor or simply a biomarker of dystrophinopathy-related cardiomyopathy. Therefore, it is necessary for future studies to probe into the relationship between UA and the prognosis of cardiac in dystrophinopathy, as well as whether reducing UA can alleviate myocardial dilation and remodelling.
The DMD gene contains 79 exons. Due to allelic heterogeneity, different individuals have different mutation sites, which can cause various phenotypes [2]. Exons 45–55 are the most common mutation sites, harbouring 66% of large (≥1 exon) deletions, and are currently research hotspot for the DMD gene [12,41]. It was found that the deletion of exons 45–55 was commonly associated with asymptomatic to mild phenotypes [11], and thus, gene therapies such as multi-exon skipping have frequently targeted at this sequence [42]. Exons 45–55 encoded the protein-like repeat sequence R17-21 of dystrophin, and the absence of which was considered to be associated with severe cardiac complications and might lead to early-onset heart disease [11,43]. In the mdx mice model, Nalinda B Wasala found that mini-gene therapy, allowing the heart to express the muscular dystrophin-like repeat sequences 16–19 (R16-19) encoded by exons 45–50, improved hemodynamics and corrected the end-diastolic volume [35]. This suggested that the absence of these exons might alter the morphology and pumping function of the heart by directly affecting the sequences and functions of dystrophin in cardiac myocytes. Considering that the deletion of exons 45–55 may be associated with myocardial injury, the present study compared echocardiographic parameters among patients with different gene mutation types and investigated the relationship between gene mutation types and cardiac morphological changes. It was found that the deletion of exons 45–55 in the DMD gene was not related to cardiac pathology. Previous studies suggest that mutations at different sites within the exon 45–55 region have varying effects. Mutations in exon 48–49 of the dystrophin gene may be associated with the early onset of cardiomyopathy, whereas mutations in exon 51–52 may have a cardioprotective effect [20]. Research by Javier Poyatos-García et al. indicates that, in addition to mutation sites, patient phenotypes are also influenced by intronic breakpoint locations and modifying factors in DMD [11]. These factors may explain why the types of genetic mutations were not related to the echocardiographic parameters in this study.
Our study was the first to investigate the relationship between UA and heart disease in dystrophinopathy, and the results showed that hyperuricaemia was associated with morphologic changes in the heart, specifically the increase in the diameter of cardiac cavities and left ventricular thickness. Therefore, UA could serve as a biomarker to assess the degree of cardiac enlargement or remodelling in dystrophinopathy patients. Results of the present study might contribute to a better understanding of heart disease in dystrophinopathy and provide insights for the development of new therapeutic approaches.
The present study has some limitations. Firstly, the sample size was relatively small and the patients involved exhibited milder disease conditions. Therefore, further large sample size multicentre studies are necessary to be conducted to verifying these results. Secondly, as a cross-sectional study, no causal relationship between UA and cardiac morphological changes was confirmed in it. Hence, a longitudinal study is essential to verify that UA levels can be a biomarker varying with disease progression or treatment efficacy. Further interventional studies and follow-up of patients are also needed to detect whether lowering UA could alleviate the progression of heart disease and whether it might be an independent prognostic factor for cardiac complications in patients with dystrophinopathy.
Conclusion
Dystrophinopathy is a hereditary muscle disorder caused by the mutation of DMD gene, which can affect the myocardium, leading to cardiac complications and increased mortality. It is important to detect cardiac change early and conveniently. The current study showed patients in hyperuricaemia group showed larger atrial and ventricular diameters, as well as thicker left ventricular walls. And the elevated serum UA levels were independently associated with cardiac dilation and left ventricular remodelling, suggesting UA as a potential biomarker for detecting cardiopathy in dystrophinopathy. Further research should prioritize longitudinal studies to determine whether UA levels vary over time in relation to disease progression and whether improvements in echocardiographic parameters occur after reducing UA by interventions.
Supplementary Material
Acknowledgments
The authors acknowledge the Guangzhou First People’s Hospital and the First Affiliated Hospital of Sun Yat-sen University for the support that enabled the completion of this study. All authors have read and approved the submitted version of the manuscript.
Funding Statement
This study was supported by National Natural Science Foundation of China (No. 82001333).
Disclosure statement
No potential conflict of interest was reported by the author(s).
Ethical statement
The studies involving human participants were reviewed and approved by Guangzhou first people’s hospital ethics committee, with the identification number of K-2021-196-02. The studies on patients were carried out in accordance with the Declaration of Helsinki. Because the included patients were minors, written informed consent to participate in the study were provided by the patient’s parents or legal guardians.
Data availability statement
The raw data of this study are available from the corresponding authors on reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The raw data of this study are available from the corresponding authors on reasonable request.