Studies with better data are still needed to fully understand the epidemiology of Duchenne muscular dystrophy (DMD), according to a recently published review.
An updated systematic literature review sought to update what is known about the prevalence of Duchenne muscular dystrophy (DMD) as well as examine the quality of the studies of this rare disease.
The researchers noted that as with other rare diseases, having high-quality epidemiological evidence available is key for policy makers who must make decisions in allocating scarce resources.
DMD is caused by gene mutations on X-chromosomes and predominately affects male children (females are typically carriers). The mutation leads to the absence of dytrophin or structural defects of that protein, which is essential for the growth of muscle tissue. The disease is characterized by a progressive degeneration of skeletal muscles, cardiac complications, and respiratory disorders. Some patients can experience behavioral and cognitive impairment. Direct and indirect costs of DMD are high due to multidisciplinary treatments, which increase as the disease progresses.
Writing in the Orphanet Journal of Rare Diseases, investigators noted that the most recently published reviews included studies up until 2015 and that additional prevalence information was needed. In particular, they wanted to update the previous systematic review and meta-analysis and to assess the quality of the available epidemiological studies.
“Generating epidemiological evidence on DMD is fundamental to support public health decision-making in allocating resources considering the high disease’s costs related to the need of multidisciplinary care, the elevated direct and indirect burden of patients and caregivers and the recently available expensive therapies,” investigators said.
Using Medline and Embase, the authors searched for original research articles on the epidemiology of DMD from inception until October 1, 2019. To determine quality, the authors used a STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) checklist adapted for observational studies on rare diseases. A meta-analysis was performed using random-effects logistic models for overall and birth prevalence and within 2 different underlying populations in order to derive the pooled epidemiological prevalence estimates.
A total of 44 studies were used in the systematic review and 40 were used in the meta-analysis.
The pooled global prevalence of patients with DMD was 7.1 cases (95% CI, 5.0-10.1) per 100,000 men and lower in the general population of males and females: 2.8 cases (95% CI, 1.6-4.6) per 100,000.
The pooled global birth prevalence for patients with DMD was 19.8 cases (95% CI, 16.6-23.6) per 100,000 live male births, with a large amount of heterogeneity seen among these studies.
Birth prevalence is much higher than prevalence, the authors noted, because children with DMD may not live past childhood in developing countries.
Quality of the studies
Of the 44 studies, 81.8% (36) were considered to be of medium quality, with the other 18.2% (8) were classified as low quality. No included studies were found to be of high quality.
Most of the studies (84.1%) had design and setting adequately reported but participants were adequately characterized only in 9.1% of the studies. The description of DMD identification was appropriate in 84.1% of the studies and unclear in 11.4%.
There are several reasons why the quality of available data could be low, such as that some studies lacked recent data due to privacy issues or DMD underreporting.
The authors noted that of the 29 studies reporting DMD birth prevalence, 37.9% (11) studies were based on primary data collection, using questionnaires, blood samples analysis, muscle biopsy, and genetic screening. The remaining 62.1% (18) relied on secondary data.
Secondary data most included clinical charts, administrative databases and patient or disease registries; 1 study used a community survey. Even with primary data, genetic screening results may be outdated as reports prior to technological advancements may yield outdated results.
Study design, case definitions, inclusion criteria, sample sizes and DMD diagnostic methods are other reasons that prevalence estimations could be extremely variable, investigators noted.
The analysis did have some limitations. Investigators were unable to stratify results based on ethnicity and it was not possible to compare epidemiology across countries, as the number of available studies in general is low and there is a large heterogeneity among them. Disease coding through the International Classification of Diseases is also not available as DMD is classified under muscular dystrophy, an umbrella term for multiple disorders.
But the authors said the report highlights “the need for high quality studies in this field. High quality studies with more transparent reporting are required to better understand the epidemiology of DMD.”
“To our knowledge, this is the first comprehensive systematic review which evaluated the pooled global epidemiology of DMD,” investigators said.
Crisafulli S, Sultana J, Fontana A, Messina S, Trifirò G. Global epidemiology of Duchenne muscular dystrophy: an updated systematic review and meta-analysis. Orphanet J. Rare Dis. 2020; 15(141): 1-20. doi:10.1186/s13023-020-01430-8