Is late diagnosis of Duchenne muscular dystrophy still a reality?

Duchenne muscular dystrophy (DMD) is a progressive X-linked recessive neuromuscular disorder caused by pathogenic variants in the DMD gene manifesting in early childhood with progressive muscle weakness. First symptoms of muscle weakness usually appear around age of three, however, other signs of the disease like muscle hypertrophy, poor motor skills and social, language and motor delay can be detected earlier. Significant delays in the diagnostic process for DMD have been reported in many countries, with the diagnosis generally being made around five years. A collaborative historical cohort study was conducted to identify the age at diagnosis of DMD in five neuromuscular centers in Brazil, covering cases diagnosed between January 2019 and March 2024. In addition to data from the centers, data on age at diagnosis were obtained from The Brazilian National Network for Rare Diseases (RARAS). The final analytic cohort included 173 DMD individuals. The mean age at which patients were diagnosed with probable DMD based on clinical suspicion was 5.7 (±2.7) years, with diagnostic confirmation by genetic testing/muscle biopsy at 6.9 (±4.0) years, with medians of 6.0 and 6.8 years, respectively. The mean age at which parents noticed symptoms was 3.4 (±1.9) years with a median of 3.0 years. The most frequently observed initial symptoms by parents included frequent falls (35.5 %), gait abnormalities (31.4 %), difficulties in stair climbing (17.2 %), developmental delay (13.6 %), and difficulties in rising from the floor (8.9 %). The presence of co-occurring neurocognitive conditions was associated with a delay of 1.12 years (p = 0.008) in the median age at suspected diagnosis and 1.0 years in the median age at diagnosis confirmation (p = 0,022). These results suggest that while there have been improvements in the age of diagnosis of DMD in Brazil in recent decades, diagnosis still occurs later than ideal and then what has been achieved in high-income countries.