Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet): case definition in surveillance for childhood-onset Duchenne/Becker muscular dystrophy

Prophylactic use of cardiac medications for delay of left ventricular dysfunction in Duchenne muscular dystrophy

BACKGROUND

Epidemiological support for prophylactic treatment of left ventricular dysfunction (LVD) in Duchenne muscular dystrophy is limited. We used retrospective, population-based surveillance data from the Muscular Dystrophy Surveillance, Tracking and Research Network to evaluate whether prophylaxis delays LVD onset.

METHODS

We analyzed 455 males born during 1982-2009. Age at first abnormal echocardiogram (ejection fraction <55% or shortening fraction <28%) determined LVD onset. Prophylaxis was defined as cardiac medication use at least 1 year prior to LVD. Corticosteroid use was also coded. Kaplan-Meier curve estimation and Cox Proportional Hazard modeling with time-varying covariates describe associations.

RESULTS

LVD was identified among 40.7%; average onset age was 14.2 years. Prophylaxis was identified for 20.2% and corticosteroids for 57.4%. Prophylaxis showed delayed LVD onset (p < .001) and lower hazard of dysfunction (adjusted hazard ratio [aHR] = 0.39, 95%CL = 0.22, 0.65) compared to untreated. Compared to no treatment, continuous corticosteroids only (aHR = 1.01, 95%CL = 0.66, 1.53) and prophylaxis only (aHR = 0.67, 95%CL = 0.25, 1.50) were not cardioprotective, but prophylaxis plus continuous corticosteroids were associated with lower hazard of dysfunction (aHR = 0.37, 95%CL = 0.15, 0.80).

CONCLUSIONS

Proactive cardiac treatment and monitoring are critical aspects of managing Duchenne muscular dystrophy. Consistent with clinical care guidelines, this study supports clinical benefit from cardiac medications initiated prior to documented LVD and suggests further benefit when combined with corticosteroids.

Sources of variation in estimates of Duchenne and Becker muscular dystrophy prevalence in the United States

BACKGROUND

Direct estimates of rare disease prevalence from public health surveillance may only be available in a few catchment areas. Understanding variation among observed prevalence can inform estimates of prevalence in other locations. The Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) conducts population-based surveillance of major muscular dystrophies in selected areas of the United States. We identified sources of variation in prevalence estimates of Duchenne and Becker muscular dystrophy (DBMD) within MD STARnet from published literature and a survey of MD STARnet investigators, then developed a logic model of the relationships between the sources of variation and estimated prevalence.

RESULTS

The 17 identified sources of variability fell into four categories: (1) inherent in surveillance systems, (2) particular to rare diseases, (3) particular to medical-records-based surveillance, and (4) resulting from extrapolation. For the sources of uncertainty measured by MD STARnet, we estimated each source's contribution to the total variance in DBMD prevalence. Based on the logic model we fit a multivariable Poisson regression model to 96 age-site-race/ethnicity strata. Age accounted for 74% of the variation between strata, surveillance site for 6%, race/ethnicity for 3%, and 17% remained unexplained.

CONCLUSION

Variation in estimates derived from a non-random sample of states or counties may not be explained by demographic differences alone. Applying these estimates to other populations requires caution.

Time to diagnosis of Duchenne muscular dystrophy remains unchanged: Findings from the Muscular Dystrophy Surveillance, Tracking, and Research Network, 2000-2015

INTRODUCTION/AIMS

With current and anticipated disease-modifying treatments, including gene therapy, an early diagnosis for Duchenne muscular dystrophy (DMD) is crucial to assure maximum benefit. In 2009, a study from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) showed an average diagnosis age of 5 years among males with DMD born from January 1, 1982 to December 31, 2000. Initiatives were implemented by the US Centers for Disease Control and Prevention (CDC) and patient organizations to reduce time to diagnosis. We conducted a follow-up study in a surveillance cohort born after January 1, 2000 to determine whether there has been an improvement in time to diagnosis.

METHODS

We assessed the age of diagnosis among males with DMD born from January 1, 2000 to December 31, 2015 using data collected by six US MD STARnet surveillance sites (Colorado, Iowa, western New York State, the Piedmont region of North Carolina, South Carolina, and Utah). The analytic cohort included 221 males with definite or probable DMD diagnosis without a documented family history. We computed frequency count and percentage for categorical variables, and mean, median, and standard deviation (SD) for continuous variables.

RESULTS

The mean [median] ages in years of diagnostic milestones were: first signs, 2.7 [2.0]; first creatine kinase (CK), 4.6 [4.6]; DNA/muscle biopsy testing, 4.9 [4.8]; and time from first signs to diagnostic confirmation, 2.2 [1.4].

DISCUSSION

The time interval between first signs of DMD and diagnosis remains unchanged at 2.2 years. This results in lost opportunities for timely genetic counseling, implementation of standards of care, initiation of glucocorticoids, and participation in clinical trials.

Evaluation of effects of continued corticosteroid treatment on cardiac and pulmonary function in non-ambulatory males with Duchenne muscular dystrophy from MD STARnet

INTRODUCTION/AIMS

Corticosteroids have been shown to improve muscle strength and delay loss of ambulation (LOA) in Duchenne muscular dystrophy (DMD) and are considered standard of care despite significant side-effects. The objective of this study is to evaluate whether corticosteroid treatment after LOA is beneficial for cardiac or pulmonary functions among boys with DMD.

METHODS

We used the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) to characterize associations between corticosteroid use and onset of abnormal left ventricular (LV) function or abnormal percent predicted forced vital capacity (ppFVC) among 398 non-ambulatory boys with DMD. Kaplan-Meier curve estimation was used to compare time to onset by corticosteroid use groups; Cox proportional hazards modeling was used to estimate hazard ratios (HRs) and corresponding 95% confidence intervals.

RESULTS

We found no differences in time to onset of abnormal LV function by corticosteroid use groups. We observed a longer time from LOA to first abnormal ppFVC in boys that were treated with corticosteroid ≥1 y beyond LOA compared with those with no corticosteroid use or those who stopped corticosteroid use within 1 y of LOA.

DISCUSSION

Our findings show no association of corticosteroid use beyond LOA with the onset of abnormal LV function, but a significant association with a delay in onset of abnormal ppFVC. Prospective studies of corticosteroid use in boys with DMD who have lost ambulation may identify benefits and can better elucidate risks, allowing for more effective counseling of patients on continuing treatment after LOA.

Selected clinical and demographic factors and all-cause mortality among individuals with Duchenne muscular dystrophy in the Muscular Dystrophy Surveillance, Tracking, and Research Network

Population-based estimates of survival among individuals with Duchenne muscular dystrophy (DMD) living in the United States are lacking. It is also unclear whether the association between glucocorticoid use and all-cause mortality persists in the context of other common treatments (cardiac medication, cough-assist, bilevel positive airway pressure, and scoliosis surgery) observed to delay mortality. Among 526 individuals identified by the Muscular Dystrophy Surveillance, Tracking, and Research Network, the estimated median survival time from birth was 23.7 years. Current glucocorticoid users had a lower hazard of mortality than non-users. Individuals who ever had scoliosis surgery had a lower hazard of mortality than individuals who did not have scoliosis surgery. Individuals who ever used cough assist had a lower hazard of mortality than individuals who never used cough assist. Non-Hispanic Black individuals had a higher hazard of mortality than non-Hispanic White individuals. No differences in hazards of mortality were observed between ever versus never use of cardiac medication and ever versus never use of bilevel positive airway pressure. The glucocorticoid observation is consistent with the 2018 Care Considerations statement that glucocorticoid use continues in the non-ambulatory phase. Our observations may inform the clinical care of individuals living with DMD.

A population-based study of scoliosis among males diagnosed with a dystrophinopathy identified by the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet)

INTRODUCTION/AIMS

Scoliosis is a common comorbidity among individuals diagnosed with a dystrophinopathy. We examined associations between clinical predictors and scoliosis in childhood-onset dystrophinopathy.

METHODS

The progression and treatment of scoliosis were obtained from data collected by the US population-based Muscular Dystrophy Surveillance, Tracking, and Research Network. Associations between loss of independent ambulation (LoA) and corticosteroid use and scoliosis outcomes (ages at or exceeding Cobb angle thresholds [10°, 20°, 30°]; surgery) were estimated using Kaplan-Meier curve estimation and extended Cox regression modeling.

RESULTS

We analyzed curvature data for 513 of 1054 individuals ascertained. Overall, approximately one-half had at least one radiograph and one-quarter had a curvature of at least 20°. The average maximum curvature was 25.0° (SD = 21.5°) among all individuals and 42.8° (SD = 18.8°) among those recommended for surgery. Higher adjusted hazards ratio of curvature (aHR(curvature) [95% confidence interval]) were found among individuals with LoA compared to those without LoA (aHR(10)  = 6.2 [4.4, 8.7], aHR(20)  = 15.3 [7.4, 31.7], aHR(30)  = 31.6 [7.7, 128.9]), among individuals who did not use corticosteroids compared to those who did (aHR(10)  = 1.2 [0.9, 1.7], aHR(20)  = 1.8 [1.1, 2.7], aHR(30)  = 2.3 [1.3, 4.0]), and among non-ambulatory individuals who used corticosteroids after LoA compared to those who did not (aHR(10)  = 1.8 [1.2, 2.8], aHR(20)  = 1.6 [1.0, 2.6], aHR(30)  = 3.6 [1.6, 7.9]). Scoliosis surgery among individuals with LoA who did not use corticosteroids was more than double compared to those who used (aHR = 2.3 [1.3, 4.2]).

DISCUSSION

Our retrospective observational study suggests corticosteroids may delay spinal curvature progression and need for scoliosis surgery. Continuing corticosteroids after LoA also showed potential benefits of delaying curvature progression, additional studies are needed to confirm this finding or address the magnitude of benefit.

Role Attainment in Emerging Adulthood: Subjective Evaluation by Male Adolescents and Adults with Duchenne and Becker Muscular Dystrophy

BACKGROUND

Youth with Duchenne and Becker muscular dystrophy (DBMD) experience challenges in attaining adult roles, which may impact quality of life. New interventions and treatments may facilitate adult role attainment through improved function. Historical data on adult role attainment is important to assess the impact of new interventions on teens and young adults with DBMD. This study assesses medical knowledge, independence and employment, and relationships among adolescents and young adults with DBMD.

METHODS

This study uses data from a 2013 Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) survey on adult transition. Males with DBMD aged 16-30 years were included.

RESULTS

Sixty-five of 258 eligible males participated; we report results on 60 participants with an MD STARnet case definition of DMD or BMD. Individuals with BMD reported higher rates than those with DMD of frequently staying home without supervision (50% BMD; 14% DMD), independently performing daily physical needs (93% BMD; 7% DMD) and being employed full or part time (33% BMD; 4% DMD). Most participants understood medication and physical therapy goals; less than half indicated being often or always responsible for scheduling DMBD-related management and refilling medications. Most had not been in a romantic relationship but reported desiring such relationships.

CONCLUSIONS

Our data reinforce the impact of DMD (and to a lesser extent, BMD) on transition to adult roles. These results provide an important historical comparator for teen and adult patients who are trying new interventions and therapies. Such data are important for assessing the quality-of-life impact of new treatments and to inform support and training programs for people with DBMD as they transition to new adult roles and responsibilities.

Differentiation of Pediatric-Onset Duchenne and Becker Muscular Dystrophy Subphenotypes Using Data from the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet)

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) phenotypes are used to describe disease progression in affected individuals. However, considerable heterogeneity has been observed across and within these two phenotypes, suggesting a spectrum of severity rather than distinct conditions. Characterizing the phenotypes and subphenotypes aids researchers in the design of clinical studies and clinicians in providing anticipatory guidance to affected individuals and their families. Using data from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet), we used K-means cluster analysis to group phenotypically similar males with pediatric-onset dystrophinopathy. We identified four dystrophinopathy clusters: Classical BMD, Classical DMD, late ambulatory DMD, and severe DMD. The clusters that we identified align with both 'classical' and 'non-classical' dystrophinopathy described in the literature. Individuals with dystrophinopathies have heterogenous clinical presentations that cluster into phenotypically similar groups. Use of clinically-derived phenotyping may provide a clearer understanding of disease trajectories, reduce variability in study results, and prevent exclusion of certain cohorts from analysis. Findings from studying subphenotypes may ultimately improve our ability to predict disease progression.

Health Profile of Preterm Males With Duchenne Muscular Dystrophy

In this retrospective cohort study, we characterize the health profile of preterm males with Duchenne muscular dystrophy. Major clinical milestones (ambulation cessation, assisted ventilation use, and onset of left ventricular dysfunction) and corticosteroids use in males with Duchenne muscular dystrophy identified through a population-based surveillance system were analyzed using Kaplan-Meier survival curves and Cox proportional hazards modeling. The adjusted risk of receiving any respiratory intervention among preterm males with Duchenne muscular dystrophy was 87% higher than among the corresponding full-term males with Duchenne muscular dystrophy. The adjusted risks for ambulation cessation and left ventricular dysfunction were modestly elevated among preterm compared to full-term males, but the 95% confidence intervals contained the null. No difference in the start of corticosteroid use between preterm and full-term Duchenne muscular dystrophy males was observed. Overall, the disease course seems to be similar between preterm and full-term males with Duchenne muscular dystrophy; however, pulmonary function seems to be affected earlier among preterm males with Duchenne muscular dystrophy.

Characteristics of Clinical Trial Participants with Duchenne Muscular Dystrophy: Data from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet)

BACKGROUND

Therapeutic trials are critical to improving outcomes for individuals diagnosed with Duchenne muscular dystrophy (DMD). Understanding predictors of clinical trial participation could maximize enrollment.

METHODS

Data from six sites (Colorado, Iowa, Piedmont region North Carolina, South Carolina, Utah, and western New York) of the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) were analyzed. Clinical trial participation and individual-level clinical and sociodemographic characteristics were obtained from medical records for the 2000-2015 calendar years. County-level characteristics were determined from linkage of the most recent county of residence identified from medical records and publicly available federal datasets. Fisher's exact and Wilcoxon two-sample tests were used with statistical significance set at one-sided p-value (<0.05) based on the hypothesis that nonparticipants had fewer resources.

RESULTS

Clinical trial participation was identified among 17.9% (MD STARnet site: 3.7-27.3%) of 358 individuals with DMD. Corticosteroids, tadalafil, and ataluren (PTC124) were the most common trial medications recorded. Fewer non-Hispanic blacks or Hispanics than non-Hispanic whites participated in clinical trials. Trial participants tended to reside in counties with lower percentages of non-Hispanic blacks. Conclusion: Understanding characteristics associated with clinical trial participation is critical for identifying participation barriers and generalizability of trial results. MD STARnet is uniquely able to track clinical trial participation through surveillance and describe patterns of participation.

Duchenne and Becker Muscular Dystrophies' Prevalence in MD STARnet Surveillance Sites: An Examination of Racial and Ethnic Differences

INTRODUCTION

Previous studies indicated variability in the prevalence of Duchenne and Becker muscular dystrophies (DBMD) by racial/ethnic groups. The Centers for Disease Control and Prevention's (CDC) Muscular Dystrophy Surveillance, Tracking, and Research network (MD STARnet) conducts muscular dystrophy surveillance in multiple geographic areas of the USA and continues to enroll new cases. This provides an opportunity to continue investigating differences in DBMD prevalence by race and ethnicity and to compare the impact of using varying approaches for estimating prevalence.

OBJECTIVE

To estimate overall and race/ethnicity-specific prevalence of DBMD among males aged 5-9 years and compare the performance of three prevalence estimation methods.

METHODS

The overall and race/ethnicity-specific 5-year period prevalence rates were estimated with MD STARnet data using three methods. Method 1 used the median of 5-year prevalence, and methods 2 and 3 calculated prevalence directly with different birth cohorts. To compare prevalence between racial/ethnic groups, Poisson modeling was used to estimate prevalence ratios (PRs) with non-Hispanic (NH) whites as the referent group. Comparison between methods was also conducted.

RESULTS

In the final population-based sample of 1,164 DBMD males, the overall 5-year prevalence for DBMD among 5-9 years of age ranged from 1.92 to 2.48 per 10,000 males, 0.74-1.26 for NH blacks, 1.78-2.26 for NH whites, 2.24-4.02 for Hispanics, and 0.61-1.83 for NH American Indian or Alaska Native and Asian or Native Hawaiian or Pacific Islander (AIAN/API). The PRs for NH blacks/NH whites, Hispanics/NH whites, and NH AIAN/API/NH whites were 0.46 (95% CI: 0.36-0.59), 1.37 (1.17-1.61), and 0.61 (0.40-0.93), respectively.

CONCLUSIONS

In males aged 5-9 years, compared to the prevalence of DBMD in NH whites, prevalence in NH blacks and NH AIAN/API was lower and higher in Hispanics. All methods produced similar prevalence estimates; however, method 1 produced narrower confidence intervals and method 2 produced fewer zero prevalence estimates than the other two methods.

Association of genetic mutations and loss of ambulation in childhood-onset dystrophinopathy

BACKGROUND

Quantifying associations between genetic mutations and loss of ambulation (LoA) among males diagnosed with childhood-onset dystrophinopathy is important for understanding variation in disease progression and may be useful in clinical trial design.

METHODS

Genetic and clinical data from the Muscular Dystrophy Surveillance, Tracking, and Research Network for 358 males born and diagnosed from 1982 to 2011 were analyzed. LoA was defined as the age at which independent ambulation ceased. Genetic mutations were defined by overall type (deletion/duplication/point mutation) and among deletions, those amenable to exon-skipping therapy (exons 8, 20, 44-46, 51-53) and another group. Cox proportional hazards regression modeling was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Mutation type did not predict time to LoA. Controlling for corticosteroids, Exons 8 (HR = 0.22; 95% CI = 0.08, 0.63) and 44 (HR = 0.30; 95% CI = 0.12, 0.78) were associated with delayed LoA compared to other exon deletions.

CONCLUSIONS

Delayed LoA in males with mutations amenable to exon-skipping therapy is consistent with previous studies. These findings suggest that clinical trials including exon 8 and 44 skippable males should consider mutation information prior to randomization.

Characterization of individuals with selected muscular dystrophies from the expanded pilot of the Muscular Dystrophy Surveillance, Tracking and Research Network (MD STARnet) in the United States

INTRODUCTION

Data on muscular dystrophies (MDs), a heterogeneous group of heritable diseases hallmarked by progressive muscle deterioration, are scarce.

OBJECTIVE

We describe cross-sectional sociodemographic and clinical characteristics of individuals with congenital, distal, Emery-Dreifuss, facioscapulohumeral, limb-girdle, myotonic, or oculopharyngeal MD.

METHODS

The study was conducted in four sites (Arizona, Colorado, Iowa, and 12 western New York counties) as a pilot expansion of the Muscular Dystrophy Surveillance, Tracking and Research Network, funded by the Centers for Disease Control and Prevention. MDs were detected in healthcare facilities and administrative data sources using International Classification of Disease codes. Our sample contains 1,723 individuals with a MD diagnosis and a healthcare encounter between January 1, 2007 and December 31, 2011.

RESULTS AND CONCLUSIONS

Individuals were mostly non-Hispanic and white. Median ages ranged from 9.2 to 66.0 years. Most (98%) had health insurance. The proportion of individuals who were disabled or unable to work increased with age (range: 8.6-46.4%). People with limb-girdle MD aged ≥18 years were more likely to be nonambulatory (range: 24.5-44.7%). The percentages of individuals with documented clinical interventions during the surveillance period were low. The most common cause of death was respiratory causes (46.3-57.1%); an ICD-10 code for MD (G71.1 or G71.0) was reported for nearly one-half. Our findings show wide variability in sociodemographic and clinical characteristics across MDs.

Left ventricular dysfunction in Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy is associated with progressive cardiorespiratory failure, including left ventricular dysfunction.

METHODS AND RESULTS

Males with probable or definite diagnosis of Duchenne muscular dystrophy, diagnosed between 1 January, 1982 and 31 December, 2011, were identified from the Muscular Dystrophy Surveillance Tracking and Research Network database. Two non-mutually exclusive groups were created: patients with ≥2 echocardiograms and non-invasive positive pressure ventilation-compliant patients with ≥1 recorded ejection fraction. Quantitative left ventricular dysfunction was defined as an ejection fraction <55%. Qualitative dysfunction was defined as mild, moderate, or severe. Progression of quantitative left ventricular dysfunction was modelled as a continuous time-varying outcome. Change in qualitative left ventricle function was assessed by the percentage of patients within each category at each age. Forty-one percent (n = 403) had ≥2 ejection fractions containing 998 qualitative assessments with a mean age at first echo of 10.8 ± 4.6 years, with an average first ejection fraction of 63.1 ± 12.6%. Mean age at first echo with an ejection fraction <55 was 15.2 ± 3.9 years. Thirty-five percent (140/403) were non-invasive positive pressure ventilation-compliant and had ejection fraction information. The estimated rate of decline in ejection fraction from first ejection fraction was 1.6% per year and initiation of non-invasive positive pressure ventilation did not change this rate.

CONCLUSIONS

In our cohort, we observed that left ventricle function in patients with Duchenne muscular dystrophy declined over time, independent of non-invasive positive pressure ventilation use. Future studies are needed to examine the impact of respiratory support on cardiac function.

Predictive validity of developmental milestones for detecting limited intellectual functioning

Developmental milestones are commonly used in child health care, although from many milestones the predictive validity has not been adequately assessed. We aimed to determine the predictive validity of 75 developmental milestones for detecting limited intellectual functioning that can be obtained before the age of 4 years. We performed a case-control study with 148 children aged 5–10 years with limited intellectual functioning (IQ 50–69), who were in special education (cases) and a random sample of 300 children aged 5–10 years who were in regular elementary education (controls). Developmental milestones scores were retrieved from Child Healthcare files. We calculated sensitivity, specificity, positive likelihood ratios (LR+) and diagnostic odds ratios (DOR) for limited intellectual functioning. The LR+ determines whether a test result changes the probability that a condition exists. Given the prevalence of intellectual disability (1–3%), we considered that an LR+ > 10 would be clinically useful, as it increases the a priori probability of limited intellectual functioning from 2% to a posteriori probability of at least 17%. Out of 75 assessed milestones, 50 were included in the analysis. We found nine milestones to have a significant adjusted (for socio-economic status and prematurity) DOR > 1 and a significant LR+ > 10 (assessment age in months between brackets): ‘says "dada-baba‴ (9), ‘balances head well while sitting’ (9), ‘sits on buttocks while legs stretched’ (9), ‘babbles while playing’ (12), ‘sits in stable position without support’ (12), ‘walks well alone’ (24), ‘says "sentences" of 3 or more words’ (36), ‘places 3 forms in form-box’ (36) and ‘copies circle’ (48). Sensitivities of these 9 milestones varied from 8–54%, specificities of these 9 milestones varied from 95–100%. Combining these milestones at 9, 12, and 36 months respectively resulted in sensitivities of 27–60% and specificities of 94–99%. These nine developmental milestones have substantial predictive validity for limited intellectual functioning.

Needs management in families affected by childhood-onset dystrophinopathies

Purpose

To collect information about the needs of families affected by childhood-onset dystrophinopathies residing in the United States.

Methods

Individuals with an eligible dystrophinopathy were identified by the Muscular Dystrophy Surveillance, Tracking, and Research network. Between September 2008 and December 2012, 272 caregivers completed a 48-item survey about needs related to information, healthcare services, psychosocial issues, finances, caregiver demographics, and the individual's functioning.

Results

Overall, at least 80% of the survey items were identified as needs for more than one-half of caregivers. Among the needs identified, physical health and access to information were currently managed for most caregivers. Items identified as needed but managed less consistently were funding for needs not covered by insurance and psychosocial support.

Conclusions

Healthcare providers, public health practitioners, and policymakers should be aware of the many needs reported by caregivers, and focus on addressing gaps in provision of needed financial and psychosocial services.

Diagnostic Accuracy of Phenotype Classification in Duchenne and Becker Muscular Dystrophy Using Medical Record Data1

Dystrophinopathies are caused by mutations in DMD resulting in progressive muscle weakness. They are historically divided into the more severe Duchenne (DMD) and milder Becker (BMD) muscular dystrophy phenotypes. Classification is important for research and clinical care. The purpose of this study was to describe a multi-variable approach to classifying cases from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) and to assess the accuracy of the diagnostic classification scheme. We used age at loss of mobility, molecular testing results, and age at symptom onset to classify cases as having DMD or BMD and to assess sensitivity and specificity. Mobility status showed low sensitivity and high specificity for predicting DMD (65.5% and 99.3%, respectively) and BMD (62.8% and 97.7%, respectively) phenotypes. Molecular testing showed 90.9% sensitivity and 66.4% specificity for DMD; 76.3% sensitivity and 90.0% specificity for BMD. Age of onset predicted DMD with sensitivity of 73.9% and specificity of 69.0%; BMD had 99.7% specificity and 36.7% sensitivity. Mobility status, molecular test results, and age at symptom onset are important but inconsistent measures for accurately classifying individuals into DMD or BMD phenotypes. These results have implications for prognosis in newly diagnosed individuals and for classifying phenotype in clinical trials.

Risk factors for falls among boys under 18 years with muscular dystrophy

PURPOSE

Studies have shown that children with muscular dystrophy are at increased risk for falls, however there is insufficient information about what predicts the first and subsequent events. The purpose of this study was to describe the experience of injury with emphasis on identifying risk factors for fall-related injuries.

METHODS

We studied 269 boys with muscular dystrophy describing their injury experience and identifying risk and protective factors associated with 281 non-simultaneous injuries and 127 falls that resulted in Emergency Department visits and/or inpatient hospitalization during the period 1998-2014. We used a Cox model to estimate the predictors of an initial fall and a zero-inflated Poisson model to identify the predictors for the number of falls.

RESULTS

Falls accounted for the greatest number of injury occurrences; The most frequent injury type was contusion. The factors that were protective for falls were steroid use, wheelchair use, or having a heart condition. Baseline age was negatively associated with the risk of having any fall, but not significantly related to subsequent falls.

CONCLUSION

Wheelchair use and heart conditions associated with reduced risk of falls likely reflects decreased mobility. Clinicians should help families identify factors associated with falls among those who remain ambulatory.

The effect of steroid treatment on weight in nonambulatory males with Duchenne muscular dystrophy

To describe the long-term effect of steroid treatment on weight in nonambulatory males with Duchenne Muscular Dystrophy (DMD), we identified 392 males age 7-29 years with 4,512 weights collected after ambulation loss (176 steroid-naïve and 216 treated with steroids ≥6 months) from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet). Comparisons were made between the weight growth curves for steroid-naïve males with DMD, steroid-treated males with DMD, and the US pediatric male population. Using linear mixed-effects models adjusted for race/ethnicity and birth year, we evaluated the association between weight-for-age and steroid treatment characteristics (age at initiation, dosing interval, cumulative duration, cumulative dose, type). The weight growth curves for steroid-naïve and steroid-treated nonambulatory males with DMD were wider than the US pediatric male growth curves. Mean weight-for-age z scores were lower in both steroid-naïve (mean = -1.3) and steroid-treated (mean = -0.02) nonambulatory males with DMD, compared to the US pediatric male population. Longer treatment duration and greater cumulative dose were significantly associated with lower mean weight-for-age z scores. Providers should consider the effect of steroid treatment on weight when making postambulation treatment decisions for males with DMD.

Health Care Transition Experiences of Males with Childhood-onset Duchenne and Becker Muscular Dystrophy: Findings from the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet) Health Care Transitions and Other Life Experiences Survey

Introduction:

As the proportion of males with Duchenne muscular dystrophy (DMD) surviving into adulthood increases, more information is needed regarding their health care transition planning, an essential process for adolescents and young adults with DMD. The objective of this study was to describe the health care transition experiences of a population of males living with Duchenne or Becker muscular dystrophy (DBMD).

Methods:

The eligible participants, identified through the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet) surveillance project, were 16–31 years old and lived in Arizona, Colorado, Georgia, Iowa, or western New York (n=258). The MD STARnet Health Care Transitions and Other Life Experiences Survey was conducted in 2013 and administered online or in a telephone interview. Sixty-five males (25%) completed the survey. Among non-ambulatory males, response differences were compared by age group. Statistical comparisons were conducted using Fisher’s exact test, or when appropriate, the Chisquare test.

Results:

Twenty-one percent of non-ambulatory males aged 16–18 years, 28% of non-ambulatory males aged 19–23 years, 25% of non-ambulatory males aged 24–30 years, and 18 ambulatory males had a written transition plan. Nineteen percent of non-ambulatory males aged 24–30 years had delayed or gone without needed health care in the past 12 months. Among non-ambulatory males aged 24–30 years, 75% had cardiology providers and 69% had pulmonology providers involved in their care in the past 12 months. Twentyeight percent of non-ambulatory males aged 19–23 years and 25% of non-ambulatory males aged 24–30 years reported that they did not receive health care or other services at least once because they were unable to leave their home. Non-ambulatory males aged 16–18 years (29%) were less likely to have ever discussed how to obtain or keep health insurance as they get older compared to non-ambulatory males aged 24-30 years (69%) (p <0.01).

Discussion:

This study identified potential barriers to the successful health care transition of males with DBMD. The results of this study may indicate a lack of targeted informational resources and education focused on supporting the transition of young men with DBMD as they age from adolescence into adulthood within the healthcare system. Future studies could determine the reasons for the potential barriers to health care and identify the optimal transition programs for males with DBMD. There are a few online resources on transition available to adolescents and young adults with special health care needs.

Muscular Dystrophy Surveillance, Tracking, and Research Network pilot: Population-based surveillance of major muscular dystrophies at four U.S. sites, 2007-2011

BACKGROUND

For 10 years, the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) conducted surveillance for Duchenne and Becker muscular dystrophy (DBMD). We piloted expanding surveillance to other MDs that vary in severity, onset, and sources of care.

METHODS

Our retrospective surveillance included individuals diagnosed with one of nine eligible MDs before or during the study period (January 2007-December 2011), one or more health encounters, and residence in one of four U.S. sites (Arizona, Colorado, Iowa, or western New York) at any time within the study period. We developed case definitions, surveillance protocols, and software applications for medical record abstraction, clinical review, and data pooling. Potential cases were identified by International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 359.0, 359.1, and 359.21 and International Classification of Diseases, Tenth Revision (ICD-10) codes G71.0 and G71.1. Descriptive statistics were compared by MD type. Percentage of MD cases identified by each ICD-9-CM code was calculated.

RESULTS

Of 2,862 cases, 32.9% were myotonic, dystrophy 25.8% DBMD, 9.7% facioscapulohumeral MD, and 9.1% limb-girdle MD. Most cases were male (63.6%), non-Hispanic (59.8%), and White (80.2%). About, half of cases were genetically diagnosed in self (39.1%) or family (6.2%). About, half had a family history of MD (48.9%). The hereditary progressive MD code (359.1) was the most common code for identifying eligible cases. The myotonic code (359.21) identified 83.4% of eligible myotonic dystrophy cases (786/943).

CONCLUSIONS

MD STARnet is the only multisite, population-based active surveillance system available for MD in the United States. Continuing our expanded surveillance will contribute important epidemiologic and health outcome information about several MDs.

DMD genotype correlations from the Duchenne Registry: Endogenous exon skipping is a factor in prolonged ambulation for individuals with a defined mutation subtype

Antisense oligonucleotide (AON)‐mediated exon skipping is an emerging therapeutic for individuals with Duchenne muscular dystrophy (DMD). Skipping of exons adjacent to common exon deletions in DMD using AONs can produce in‐frame transcripts and functional protein. Targeted skipping of DMD exons 8, 44, 45, 50, 51, 52, 53, and 55 is predicted to benefit 47% of affected individuals. We observed a correlation between mutation subgroups and age at loss of ambulation in the Duchenne Registry, a large database of phenotypic and genetic data for DMD (N = 765). Males amenable to exon 44 (N = 74) and exon 8 skipping (N = 18) showed prolonged ambulation compared to other exon skip groups and nonsense mutations (P = 0.035 and P < 0.01, respectively). In particular, exon 45 deletions were associated with prolonged age at loss of ambulation relative to the rest of the exon 44 skip amenable cohort and other DMD mutations. Exon 3–7 deletions also showed prolonged ambulation relative to all other exon 8 skippable mutations. Cultured myotubes from DMD patients with deletions of exons 3–7 or exon 45 showed higher endogenous skipping than other mutations, providing a potential biological rationale for our observations. These results highlight the utility of aggregating phenotypic and genotypic data for rare pediatric diseases to reveal progression differences, identify potentially confounding factors, and probe molecular mechanisms that may affect disease severity.

Is There a Delay in Diagnosis of Duchenne Muscular Dystrophy Among Preterm-Born Males?

The objective of this study was to investigate whether males who were born preterm took longer to receive a Duchenne muscular dystrophy diagnosis than term males. Data for males with Duchenne muscular dystrophy identified through a population-based surveillance system were analyzed using a Kaplan-Meier estimator. The first signs and symptoms were noted at a median age of 2 years in both groups. Median age when first signs and symptoms prompted medical evaluation was 2.59 years among preterm and 4.01 years among term males. Median age at definitive diagnosis was 4.25 years and 4.92 years for preterm and term males, respectively. Neither difference was statistically significant. Preterm males tended to be seen for their initial medical evaluation earlier than term males, though they were not diagnosed significantly earlier. It may take clinicians longer after the initial evaluation of preterm males to arrive at a Duchenne muscular dystrophy diagnosis.

A Pilot Survey Study of Adherence to Care Considerations for Duchenne Muscular Dystrophy

Introduction Care Considerations supported by the Centers for Disease Control and Prevention for the management of Duchenne muscular dystrophy were published in 2010, but there has been limited study of implementation in the United States. Methods A questionnaire collecting information about standard care practices and perceived barriers was piloted by 9 clinic directors of facilities within the Muscular Dystrophy Surveillance, Tracking and Research network. Results Six clinic directors completed the questionnaire; 1 adult-only clinic was excluded. Over 80% adherence was found for 30 of 55 recommendations examined. Greatest variability was for initiation of corticosteroids, bone health monitoring, type of pulmonary function testing, and psychosocial management. Barriers included unclear guidelines, inadequate time and funding, family-specific barriers and lack of empirical support for some recommendations. Discussion This pilot study showed implementation of the 2010 Care Considerations, except for recommendations based largely on expert consensus. Complete adherence requires more studies and active promotion.

Health profile of a cohort of adults with Duchenne muscular dystrophy

INTRODUCTION

As the Duchenne muscular dystrophy (DMD) population ages, it is essential that we understand the late-stage health profile and provide the appropriate care for this emerging population.

METHODS

We undertook a descriptive study to document the health profile of a cohort of adults with DMD using data from the Muscular Dystrophy Surveillance Tracking and Research network (MD STARnet). Data included information collected from Arizona, Colorado, Iowa, Georgia, and 12 counties in western New York on individuals born since January 1982 and followed through December 2012.

RESULTS

In 208 adults with DMD, the number of individuals (N) and median ages (years) at which certain critical milestones were crossed and interventions initiated were as follows: development of cardiomyopathy, N = 145 (16.7); initiation of non-invasive ventilation, N = 99 (18.0); gastrostomy, N = 47 (19.0); and death, N = 59 (21.8).

DISCUSSION

These population-based data provide critical information about late-stage health profiles among adults with DMD for developing appropriate models of care. Muscle Nerve 58: 219-223, 2018.

Prevalence and Genetic Profile of Duchene and Becker Muscular Dystrophy in Puerto Rico

BACKGROUND

Duchenne and Becker Muscular Dystrophy (DMD and BMD, respectively), are common forms of inherited muscle disease. Information regarding the epidemiology of these conditions, including genotype, is still sparse.

OBJECTIVE

To establish the prevalence and genetic profile of DMD and BMD in Puerto Rico.

METHODS

We collected data from medical records in all Muscular Dystrophy Association (MDA) clinics in Puerto Rico in order to estimate the prevalence of DMD and BMD and to describe the genotypic profile of these patients. Patients selected for data analysis matched "definite", "probable" and "possible" case definitions as established by MD STARnet.

RESULTS

A total of 141 patients matched the inclusion criteria, with 64.5% and 35.5% being categorized into DMD and BMD, respectively. DMD and BMD prevalence in Puerto Rico was estimated at 5.18 and 2.84 per 100,000 males, respectively. Deletion was the most common form of mutation (66.7%) in the dystrophin gene, with exons in segment 45 to 47 being the most frequently affected.

CONCLUSIONS

This is the first report of the prevalence and genetic profile characteristics of DMD and BMD in Puerto Rico. Prevalence of DMD was similar to that reported worldwide, while prevalence of BMD was higher. Genetic profile was consistent with that reported in the literature.

Bone Health and Endocrine Care of Boys with Duchenne Muscular Dystrophy: Data from the MD STARnet

BACKGROUND

Patients with Duchenne muscular dystrophy (DMD) are at high risk of endocrine and bone health complications resulting from the high glucocorticoid (GC) doses used to treat this condition. There are limited data characterizing the clinical management of these complications.

OBJECTIVE

To determine the frequency of bone health screening, endocrinologist evaluation, and use of endocrine and bone health pharmacotherapy in the clinical care of males with DMD.

METHODS

A population based cohort study using data from the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) was conducted. Clinical data was abstracted from the medical records of 683 males with DMD at five surveillance sites across the US.

RESULTS

A DXA scan had been documented in 24% of cases; the percentage of cases with DXA varied across surveillance sites from 13% to 43%, p < 0.001. History of fracture and greater disease duration were associated with greater odds of having a DXA. Only 4.7% of cases had documentation of an endocrinologist evaluation. The frequency of documented endocrine and bone health pharmacotherapy use included calcium (42.8%), vitamin D (36.6%), bisphosphonates (13.3%), growth hormone (1.9%), testosterone (1.7%), insulin (1.2%), and metformin (0.3%)Conclusions:A low percentage of DMD males had record of DXA scan, endocrinologist evaluation, or treatment with endocrine or bone health pharmacotherapy. Endocrine and bone health care may represent an unmet need in the DMD population.

Delayed onset of ambulation in boys with Duchenne muscular dystrophy: Potential use as an endpoint in clinical trials

Individuals with Duchenne muscular dystrophy (DMD) often exhibit delayed motor and cognitive development, including delayed onset of ambulation. Data on age when loss of independent ambulation occurs are well established for DMD; however, age at onset of walking has not been well described. We hypothesize that an effective medication given in early infancy would advance the age when walking is achieved so that it is closer to age-matched norms, and that this discrete event could serve as the primary outcome measure in a clinical trial. This study examined three data sets, Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet); Dutch Natural History Survey (DNHS); and Parent Project Muscular Dystrophy (PPMD). The distribution of onset of ambulation in DMD (mean ± SD) and median age, in months, at the onset of ambulation was 17.3 (±5.5) and 16.0 in MD STARnet, 21.8 (±7.1) and 20.0 in DNHS, and 16.1 (±4.4) and 15 in PPMD. Age of ambulation in these data sets were all significantly later (P <0.001) than the corresponding age for typically developing boys, 12.1 (±1.8). A hypothetical clinical trial study design and power analyses are presented based on these data.

Associations between timing of corticosteroid treatment initiation and clinical outcomes in Duchenne muscular dystrophy

The long-term efficacy of corticosteroid treatment and timing of treatment initiation among Duchenne muscular dystrophy (DMD) patients is not well-understood. We used data from a longitudinal, population-based DMD surveillance program to examine associations between timing of treatment initiation (early childhood [before or at age 5 years], late childhood [after age 5 years], and naïve [not treated]) and five clinical outcomes (age at loss of ambulation; ages at onset of cardiomyopathy, scoliosis, and first fracture; and pulmonary function). Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using survival analysis. DMD patients who initiated corticosteroid treatment in early childhood had a higher risk of earlier onset cardiomyopathy compared to cases who initiated treatment in late childhood (HR = 2.0, 95% CI = [1.2, 3.4]) or treatment naïve patients (HR = 1.9, 95% CI = [1.1, 3.2]), and higher risk of suffering a fracture (HR = 2.3, 95% CI = [1.4, 3.7] and HR = 2.6, 95% CI = [1.6, 4.2], respectively). Patients with early childhood treatment had slightly decreased respiratory function compared with those with late childhood treatment. Ages at loss of ambulation or scoliosis diagnosis did not differ statistically among treatment groups. We caution that the results from our study are subject to several limitations, as they were based on data abstracted from medical records. Further investigations using improved reporting of disease onset and outcomes are warranted to obtain a more definitive assessment of the association between the timing of corticosteroid treatment and disease severity.

A Roadmap to Newborn Screening for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy, with an estimated frequency of 1:5000 live births. The impact of the disease presents as early as infancy with significant developmental delays, and ultimately loss of ambulation and respiratory insufficiency. Glucocorticoids are the only pharmacological agents known to alter the natural progression of the disease by prolonging ambulation, reducing scoliosis, and assisted ventilation. Introduction of therapy at an early age may halt the muscle pathology in DMD. In anticipation of the potentially disease-modifying products that are reaching regulatory review, Parent Project Muscular Dystrophy (PPMD) formally initiated a national Duchenne Newborn Screening (DNBS) effort in December 2014 to build public health infrastructure for newborn screening (NBS) for Duchenne in the United States. The effort includes a formalized national Duchenne Newborn Screening Steering Committee, six related Working Groups, a Duchenne Screening Test Development Project led by PerkinElmer, a program with the American College of Medical Genetic and Genomics' Newborn Screening Translation Research Network (NBSTRN), and collaborations with other Duchenne partners and federal agencies involved in NBS. We herein review the organization and effort of the U.S. DNBS program to develop the evidence supporting the implementation of NBS for DMD.

Secondary Conditions Among Males With Duchenne or Becker Muscular Dystrophy

Duchenne and Becker muscular dystrophy are X-linked neuromuscular disorders characterized by progressive muscle degeneration. Despite the involvement of multiple systems, secondary conditions among affected males have not been comprehensively described. Two hundred nine caregivers of affected males (aged 3-31 years) identified by the Muscular Dystrophy Surveillance, Tracking, and Research Network completed a mailed survey that included questions about secondary conditions impacting multiple body functions. The 5 most commonly reported conditions in males with Duchenne were cognitive deficits (38.4%), constipation (31.7%), anxiety (29.3%), depression (27.4%), and obesity (19.5%). Higher frequencies of anxiety, depression, and kidney stones were found among nonambulatory males compared to ambulatory males. Attention-deficit hyperactivity disorder (ADHD) was more common in ambulatory than nonambulatory males. These data support clinical care recommendations for monitoring of patients with Duchenne or Becker muscular dystrophy by a multidisciplinary team to prevent and treat conditions that may be secondary to the diagnosis.

Application of the International Classification of Functioning, Disability and Health system to symptoms of the Duchenne and Becker muscular dystrophies

PURPOSE

Duchenne and Becker muscular dystrophies, collectively referred to as dystrophinopathies, are X-linked recessive diseases that affect dystrophin production resulting in compromised muscle function across multiple systems. The International Classification of Functioning, Disability and Health provides a systematic classification scheme from which body functions affected by a dystrophinopathy can be identified and used to examine functional health.

MATERIALS AND METHODS

The infrastructure of the Muscular Dystrophy Surveillance, Tracking, and Research Network was used to identify commonly affected body functions and link selected functions to clinical surveillance data collected through medical record abstraction.

RESULTS

Seventy-one (24 second-, 41 third- and 7 fourth-level) body function categories were selected via clinician review and consensus. Of these, 15 of 24 retained second-level categories were linked to data elements from the Muscular Dystrophy Surveillance, Tracking, and Research Network surveillance database.

CONCLUSIONS

Our findings support continued development of a core set of body functions from the International Classification of Functioning, Disability and Health system that are representative of disease progression in dystrophinopathies and the incorporation of these functions in standardized evaluations of functional health and implementation of individualized rehabilitation care plans. Implications for Rehabilitation Duchenne and Becker muscular dystrophies, collectively referred to as dystrophinopathies, are X-linked recessive disorders that affect the production of dystrophin resulting in compromised muscle function across multiple systems. The severity and progressive nature of dystrophinopathies can have considerable impact on a patient's participation in activities across multiple life domains. Our findings support continued development of an International Classification of Functioning, Disability and Health core set for childhood-onset dystrophinopathies. A standardized dystrophinopathy International Classification of Functioning, Disability and Health documentation form can be used as a screening tool by rehabilitation professionals and for patient goal setting when developing rehabilitation plans. Patient reports of perceived functional health should be incorporated into the rehabilitation plan and therapeutic progress monitored by a standardized form.

Perceived quality of life among caregivers of children with a childhood-onset dystrophinopathy: a double ABCX model of caregiver stressors and perceived resources

Background

Duchenne and Becker muscular dystrophies, collectively referred to as dystrophinopathies, are recessive X-linked disorders characterized by progressive muscle weakness and ultimately cardiac and respiratory failure. Immediate family members are often primary caregivers of individuals with a dystrophinopathy.

Methods

We explored the impact of this role by inviting primary caregivers (n = 209) of males diagnosed with childhood-onset dystrophinopathy who were identified by the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) to complete a mailed questionnaire measuring perceived social support and stress, spirituality, and family quality of life (FQoL). Bivariate and multivariate analyses examined associations between study variables using the Double ABCX model as an analytic framework.

Results

Higher stressor pile-up was associated with lower perceived social support (r = -0.29, p < .001), availability of supportive family (r = -0.30, p < .001) or non-family (r = -0.19, p < .01) relationships, and higher perceived stress (r = 0.33, p < .001); but not with spirituality (r = -0.14, p > 0.05). FQoL was positively associated with all support measures (correlations ranged from: 0.25 to 0.58, p-values 0.01–0.001) and negatively associated with perceived stress and control (r = -0.49, p < .001). The association between stressor pile-up and FQoL was completely mediated through global perceived social support, supportive family relationships, and perceived stress and control; supportive non-family relationships did not remain statistically significant after controlling for other mediators.

Conclusions

Findings suggest caregiver adaptation to a dystrophinopathy diagnosis can be optimized by increased perceived control, supporting family resources, and creation of a healthy family identity. Our findings will help identify areas for family intervention and guide clinicians in identifying resources that minimize stress and maximize family adaptation.

Fast detection of deletion breakpoints using quantitative PCR

The routine detection of large and medium copy number variants (CNVs) is well established. Hemizygotic deletions or duplications in the large Duchenne muscular dystrophy DMD gene responsible for Duchenne and Becker muscular dystrophies are routinely identified using multiple ligation probe amplification and array-based comparative genomic hybridization. These methods only map deleted or duplicated exons, without providing the exact location of breakpoints. Commonly used methods for the detection of CNV breakpoints include long-range PCR and primer walking, their success being limited by the deletion size, GC content and presence of DNA repeats. Here, we present a strategy for detecting the breakpoints of medium and large CNVs regardless of their size. The hemizygous deletion of exons 45-50 in the DMD gene and the large autosomal heterozygous PARK2 deletion were used to demonstrate the workflow that relies on real-time quantitative PCR to narrow down the deletion region and Sanger sequencing for breakpoint confirmation. The strategy is fast, reliable and cost-efficient, making it amenable to widespread use in genetic laboratories.

Serum Levels of MicroRNA-206 and Novel Mini-STR Assays for Carrier Detection in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is an X-linked neuromuscular disorder in which the detection of female carriers is of the utmost importance for genetic counseling. Haplotyping with polymorphic markers and quantitation of creatine kinase levels (CK) allow tracking of the at-risk haplotype and evidence muscle damage, respectively. Such approaches are useful for carrier detection in cases of unknown mutations. The lack of informative markers and the inaccuracy of CK affect carrier detection. Therefore, herein we designed novel mini-STR (Short Tandem Repeats) assays to amplify 10 loci within the DMD gene and estimated allele frequencies and the polymorphism information content among other parameters in 337 unrelated individuals from three Mexican populations. In addition, we tested the utility of the assays for carrier detection in three families. Moreover, given that serum levels of miR-206 discern between DMD patients and controls with a high area under the curve (AUC), the potential applicability for carrier detection was assessed. The serum levels of miR-206 of non-carriers (n = 24) and carriers (n = 23) were compared by relative quantitation using real-time PCR (p < 0.05), which resulted in an AUC = 0.80 in the Receiver Operating Characteristic curve analysis. In conclusion, miR-206 has potential as a "liquid biopsy" for carrier detection and genetic counseling in DMD.

Corticosteroid Treatment and Growth Patterns in Ambulatory Males with Duchenne Muscular Dystrophy

OBJECTIVES

To evaluate growth patterns of ambulatory males with Duchenne muscular dystrophy (DMD) treated with corticosteroids compared with ambulatory, steroid-naïve males with DMD and age-matched unaffected general-population males and to test associations between growth and steroid treatment patterns among treated males.

STUDY DESIGN

Using data from the Muscular Dystrophy Surveillance, Tracking, and Research Network, we identified a total of 1768 height, 2246 weight, and 1755 body mass index (BMI) measurements between age 2 and 12 years for 324 ambulatory males who were treated with corticosteroids for at least 6 months. Growth curve comparisons and linear mixed-effects modeling, adjusted for race/ethnicity and birth year, were used to evaluate growth and steroid treatment patterns (age at initiation, dosing interval, duration, cumulative dose).

RESULTS

Growth curves for ambulatory males treated with corticosteroids showed significantly shorter stature, heavier weight, and greater BMI compared with ambulatory, steroid-naïve males with DMD and general-population US males. Adjusted linear mixed-effects models for ambulatory males treated with corticosteroids showed that earlier initiation, daily dosing, longer duration, and greater dosages predicted shorter stature with prednisone. Longer duration and greater dosages predicted shorter stature for deflazacort. Daily prednisone dosing predicted lighter weight, but longer duration, and greater dosages predicted heavier weight. Early initiation, less than daily dosing, longer duration, and greater doses predicted greater BMIs. Deflazacort predicted shorter stature, but lighter weight, compared with prednisone.

CONCLUSION

Prolonged steroid use is significantly associated with short stature and heavier weight. Growth alterations associated with steroid treatment should be considered when making treatment decisions for males with DMD.

Age at onset of first signs or symptoms predicts age at loss of ambulation in Duchenne and Becker Muscular Dystrophy: Data from the MD STARnet

PURPOSE

We investigated the prognostic utility of onset age at first signs and symptoms (SS) to predict onset age at loss of ambulation (LOA) for childhood-onset Duchenne and Becker Muscular Dystrophies (DBMD).

METHODS

Our cohort comprised male cases with DBMD ascertained by the population-based Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet). Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models for associations between onset ages of first SS and LOA. Covariates controlled for were corticosteroid use, family history of DBMD, birth year, race/ethnicity, and MD STARnet site. Onset age at first SS was considered as a continuous and as a categorical variable.

RESULTS

A one-year increase in onset age at first SS was significantly associated with a 10% reduction in annual risk of LOA (HR = 0.90, CI = 0.87-0.94). Treating onset age at first SS as a categorical variable yielded a similar association (≥ 5 years: referent; ≥ 3 to < 5 years: HR = 1.36, CI = 1.02-1.81; 18 months to < 3 years: HR = 1.72, CI = 1.31-2.26; < 18 months: HR = 1.52, CI = 1.14-2.02).

CONCLUSIONS

Earlier onset age at first SS is associated with earlier onset age at LOA and may have clinical utility in differentiating childhood-onset Duchenne and Becker muscular dystrophies.

Rehabilitative technology use among individuals with Duchenne/Becker muscular dystrophy

PURPOSE

To document use of rehabilitative technology among individuals with Duchenne/Becker muscular dystrophy (DBMD) among sites of the Muscular Dystrophy Surveillance, Tracking, and Research network (MD STARnet).

METHODS

Data from 362 caregivers who participated in the MD STARnet caregiver interview between April 2006 and March 2012 (54.7% response rate) were analyzed to assess the type, frequency and duration of use of assistive technology.

RESULTS

Caregiver reports of technology use by individuals with DBMD across five MD STARnet sites in the US demonstrated significant regional differences in the proportion of individuals who had ever used night splints (36.9%-73.0%), standers (3.1%-22.2%) and scooters (10.7%-54.5%). Among individuals who used night splints 59.7% stopped using them at a mean age of 10.3 years after a mean duration of 2.9 years in spite of the current recommendation to continue using them through the non-ambulatory phase.

DISCUSSION

Results of this comprehensive survey document the frequency of assistive device use by individuals with DBMD in the USA and also provides data on differences across the sites. Further research is needed to understand the reasons for and the impact of these differences on clinical outcomes and health related quality of life of individuals with DBMD.

Health services received by individuals with duchenne/becker muscular dystrophy

INTRODUCTION

Anecdotal reports from families and care providers suggest a wide variation in services received by individuals with Duchenne/Becker muscular dystrophy (DBMD).

METHODS

We documented the type and frequency of health services received by individuals with DBMD using the Muscular Dystrophy Surveillance Tracking and Research Network (MD STARnet) interview data released in June 2012. Interviews with eligible caregivers from 5 sites (Arizona, Colorado, Georgia, Iowa, and western New York) were conducted from April 2007 to March 2012.

RESULTS

Two hundred ninety-six caregivers (66% of those contactable) participated in the interview. There were significant differences among sites in the specialists seen and services received. Concurrence with cardiac recommendations was higher than that with respiratory recommendations.

CONCLUSIONS

The results of this survey support and quantify the anecdotal reports from families and care providers regarding the disparities in services received by individuals with DBMD. It remains to be determined whether these differences affect outcomes.

Risk Factors for First Fractures Among Males With Duchenne or Becker Muscular Dystrophy

BACKGROUND

Fractures are a significant concern for individuals with Duchenne/Becker muscular dystrophy with 21% to 44% of males experiencing a fracture. Factors that increase or decrease the risk for fracture have been suggested in past research, although statistical risk has not been determined.

METHODS

In this retrospective cohort study, we used the Muscular Dystrophy Surveillance, Tracking and Research Network cohort, a large, population-based sample to identify risk factors associated with first fractures in patients with Duchenne or Becker muscular dystrophy. Our study cohort included males with Duchenne or Becker muscular dystrophy born between 1982 and 2006 who resided in Arizona, Colorado, Georgia, Iowa, and Western New York, retrospectively identified and followed through 2010. We utilized a multivariate Cox proportional hazard model to determine hazard ratios for relevant factors associated with first fracture risk including race/ethnicity, surveillance site, ambulation status, calcium/vitamin D use and duration, bisphosphonate use and duration, and corticosteroid use and duration.

RESULTS

Of 747 cases, 249 had at least 1 fracture (33.3%). Full-time wheelchair use increased the risk of first fracture by 75% for every 3 months of use (hazard ratio=1.75, 95% confidence interval, 1.14, 2.68), but corticosteroid use, bisphosphonate use, and calcium/vitamin D use did not significantly affect risk in the final adjusted model.

CONCLUSIONS

In this cohort, first fractures were common and full-time wheelchair use, but not corticosteroid use, was identified as a risk factor. The impact of prevention measures should be more thoroughly assessed.

CLINICAL RELEVANCE

Fractures are a significant concern for individuals with dystrophinopathies, but the contribution of various risk factors has not been consistently demonstrated.

Corticosteroid Treatments in Males With Duchenne Muscular Dystrophy: Treatment Duration and Time to Loss of Ambulation

This population-based study examines the association between corticosteroid treatment and time to loss of ambulation, stratifying by treatment duration (short: 0.25-3 years, long: >3 years), among 477 Duchenne muscular dystrophy cases identified by the Muscular Dystrophy Surveillance Tracking and Research Network (MDSTARnet). Those cases who received short-term corticosteroid treatment had a time to loss of ambulation that was 0.8 years shorter (t test) and an annual risk of losing ambulation 77% higher than the untreated (Cox regression). Conversely, cases who received long-term corticosteroid treatment had a time to loss of ambulation that was 2 years longer and an annual risk of losing ambulation 82% lower than the untreated, up to age 11 years; after which the risks were not statistically different. The relationship of corticosteroids and time to loss of ambulation is more complex than depicted by previous studies limited to treatment responders or subjects who lost ambulation during study follow-up.

Non-Invasive Biomarkers for Duchenne Muscular Dystrophy and Carrier Detection

Non-invasive biological indicators of the absence/presence or progress of the disease that could be used to support diagnosis and to evaluate the effectiveness of treatment are of utmost importance in Duchenne Muscular Dystrophy (DMD). This neuromuscular disorder affects male children, causing weakness and disability, whereas female relatives are at risk of being carriers of the disease. A biomarker with both high sensitivity and specificity for accurate prediction is preferred. Until now creatine kinase (CK) levels have been used for DMD diagnosis but these fail to assess disease progression. Herein we examined the potential applicability of serum levels of matrix metalloproteinase 9 (MMP-9) and matrix metalloproteinase 2 (MMP-2), tissue inhibitor of metalloproteinases 1 (TIMP-1), myostatin (GDF-8) and follistatin (FSTN) as non-invasive biomarkers to distinguish between DMD steroid naïve patients and healthy controls of similar age and also for carrier detection. Our data suggest that serum levels of MMP-9, GDF-8 and FSTN are useful to discriminate DMD from controls (p < 0.05), to correlate with some neuromuscular assessments for DMD, and also to differentiate between Becker muscular dystrophy (BMD) and Limb-girdle muscular dystrophy (LGMD) patients. In DMD individuals under steroid treatment, GDF-8 levels increased as FSTN levels decreased, resembling the proportions of these proteins in healthy controls and also the baseline ratio of patients without steroids. GDF-8 and FSTN serum levels were also useful for carrier detection (p < 0.05). Longitudinal studies with larger cohorts are necessary to confirm that these molecules correlate with disease progression. The biomarkers presented herein could potentially outperform CK levels for carrier detection and also harbor potential for monitoring disease progression.

Genitourinary health in a population-based cohort of males with Duchenne and Becker Muscular dystrophies

INTRODUCTION

Genitourinary (GU) health among patients with Duchenne and Becker muscular dystrophies (DBMD) has not been explored using population-based data.

METHODS

Medical records of 918 males ascertained by the Muscular Dystrophy Surveillance, Tracking, and Research Network were reviewed for documentation of GU-related hospitalizations and prescribed medications. Percentages of males who received these medical interventions were calculated, and hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated for associations with sociodemographics (study site, race/ethnicity), symptoms (early- vs. late-onset, ambulation status, scoliosis), and treatments (respiratory support, steroids).

RESULTS

Among the 918 males, 81 (9%) had a GU condition, with voiding dysfunction (n = 40), GU tract infection (n = 19), and kidney/ureter calculus (n = 9) most frequently seen. The Kaplan-Meier curve produced a cumulative probability of 27%. Cox regression showed GU conditions were more common when males were non-ambulatory (HR 2.7, 95% CI 1.3-5.6).

CONCLUSIONS

Our findings highlight the need for increased awareness of GU health and multidisciplinary care of DBMD patients.

Prevalence of Duchenne and Becker muscular dystrophies in the United States

OBJECTIVE

To estimate prevalence of childhood-onset Duchenne and Becker muscular dystrophies (DBMD) in 6 sites in the United States by race/ethnicity and phenotype (Duchenne muscular dystrophy [DMD] or Becker muscular dystrophy [BMD]).

METHODS

In 2002, the Centers for Disease Control and Prevention established the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) to conduct longitudinal, population-based surveillance and research of DBMD in the United States. Six sites conducted active, multiple-source case finding and record abstraction to identify MD STARnet cases born January 1982 to December 2011. We used cross-sectional analyses to estimate prevalence of DBMD per 10 000 boys, ages 5 to 9 years, for 4 quinquennia (1991-1995, 1996-2000, 2001-2005, and 2006-2010) and prevalence per 10 000 male individuals, ages 5 to 24 years, in 2010. Prevalence was also estimated by race/ethnicity and phenotype.

RESULTS

Overall, 649 cases resided in an MD STARnet site during ≥1 quinquennia. Prevalence estimates per 10 000 boys, ages 5 to 9 years, were 1.93, 2.05, 2.04, and 1.51, respectively, for 1991-1995, 1996-2000, 2001-2005, and 2006-2010. Prevalence tended to be higher for Hispanic individuals than non-Hispanic white or black individuals, and higher for DMD than BMD. In 2010, prevalence of DBMD was 1.38 per 10 000 male individuals, ages 5 to 24 years.

CONCLUSIONS

We present population-based prevalence estimates for DBMD in 6 US sites. Prevalence differed by race/ethnicity, suggesting potential cultural and socioeconomic influences in the diagnosis of DBMD. Prevalence also was higher for DMD than BMD. Continued longitudinal surveillance will permit us to examine racial/ethnic and socioeconomic differences in treatment and outcomes for MD STARnet cases.

Neurobehavioral Concerns Among Males with Dystrophinopathy Using Population-Based Surveillance Data from the Muscular Dystrophy Surveillance, Tracking, and Research Network

OBJECTIVE

To describe the occurrence of selected neurobehavioral concerns among males with a dystrophinopathy and to explore the associations with corticosteroid or supportive device use.

METHODS

Medical record abstraction of neurobehavioral concerns was conducted for 857 affected males from 765 families, born since 1982 and followed through 2011, and enrolled in the population-based Muscular Dystrophy Surveillance, Tracking, and Research Network. Cumulative probabilities for attention-deficit hyperactivity disorder (ADHD), behavior problems, and depressed mood were calculated from Kaplan-Meier estimates for the subsample of oldest affected males (n = 765). Hazard ratios (HRs) and 95% confidence intervals (95% CIs) for corticosteroid and supportive device use were estimated from Cox regression models with time-dependent covariates.

RESULTS

Of the 857 affected males, 375 (44%) had at least 1 of the 3 selected neurobehavioral concerns; a similar percentage (45%) was found among the 765 oldest affected males. The estimated cumulative probabilities among these oldest affected males were 23% for ADHD, 43% for behavior problems, and 51% for depressed mood. Corticosteroid (HR = 2.35, 95% CI = 1.75-3.16) and mobility device (HR = 1.53, 95% CI = 1.06-2.21) use were associated with behavior problems. Use of a mobility device (HR = 3.53, 95% CI = 2.13-5.85), but not corticosteroids, was associated with depressed mood. ADHD was not significantly associated with corticosteroid or mobility device use. Respiratory assist device use was not examined due to low numbers of users before onset of neurobehavioral concerns.

CONCLUSION

Selected neurobehavioral concerns were common among males with a dystrophinopathy. Reported associations highlight the importance of increased monitoring of neurobehavioral concerns as interventions are implemented and disease progresses.

Online self-report data for duchenne muscular dystrophy confirms natural history and can be used to assess for therapeutic benefits

To assess the utility of online patient self-report outcomes in a rare disease, we attempted to observe the effects of corticosteroids in delaying age at fulltime wheelchair use in Duchenne muscular dystrophy (DMD) using data from 1,057 males from DuchenneConnect, an online registry. Data collected were compared to prior natural history data in regard to age at diagnosis, mutation spectrum, and age at loss of ambulation. Because registrants reported differences in steroid and other medication usage, as well as age and ambulation status, we could explore these data for correlations with age at loss of ambulation. Using multivariate analysis, current steroid usage was the most significant and largest independent predictor of improved wheelchair-free survival. Thus, these online self-report data were sufficient to retrospectively observe that current steroid use by patients with DMD is associated with a delay in loss of ambulation. Comparing commonly used steroid drugs, deflazacort prolonged ambulation longer than prednisone (median 14 years and 13 years, respectively). Further, use of Vitamin D and Coenzyme Q10, insurance status, and age at diagnosis after 4 years were also significant, but smaller, independent predictors of longer wheelchair-free survival. Nine other common supplements were also individually tested but had lower study power. This study demonstrates the utility of DuchenneConnect data to observe therapeutic differences, and highlights needs for improvement in quality and quantity of patient-report data, which may allow exploration of drug/therapeutic practice combinations impractical to study in clinical trial settings. Further, with the low barrier to participation, we anticipate substantial growth in the dataset in the coming years.

Complementary and alternative medicine for Duchenne and Becker muscular dystrophies: characteristics of users and caregivers

BACKGROUND

Complementary and alternative medicine is frequently used in the management of chronic pediatric diseases, but little is known about its use by those with Duchenne or Becker muscular dystrophy.

METHODS

Complementary and alternative medicine use by male patients with Duchenne or Becker muscular dystrophy and associations with characteristics of male patients and their caregivers were examined through interviews with 362 primary caregivers identified from the Muscular Dystrophy Surveillance, Tracking, and Research Network.

RESULTS

Overall, 272 of the 362 (75.1%) primary caregivers reported that they had used any complementary and alternative medicine for the oldest Muscular Dystrophy Surveillance, Tracking, and Research Network male in their family. The most commonly reported therapies were from the mind-body medicine domain (61.0%) followed by those from the biologically based practice (39.2%), manipulative and body-based practice (29.3%), and whole medical system (6.9%) domains. Aquatherapy, prayer and/or blessing, special diet, and massage were the most frequently used therapies. Compared with nonusers, male patients who used any therapy were more likely to have an early onset of symptoms and use a wheel chair; their caregivers were more likely to be non-Hispanic white. Among domains, associations were observed with caregiver education and family income (mind-body medicines [excluding prayer and/or blessing only] and whole medical systems) and Muscular Dystrophy Surveillance, Tracking, and Research Network site (biologically based practices and mind-body medicines [excluding prayer and/or blessing only]).

CONCLUSIONS

Complementary and alternative medicine use was common in the management of Duchenne and Becker muscular dystrophies among Muscular Dystrophy Surveillance, Tracking, and Research Network males. This widespread use suggests further study to evaluate the efficacy of integrating complementary and alternative medicine into treatment regimens for Duchenne and Becker muscular dystrophies.