Diagnostic tests for children with suspected DMD If there is a high clinical suspicion of DMD, such as onset in preschool boys, significant hypertrophy of the gastrocnemius muscle on physical examination, significant elevation of creatine phosphokinase, electromyography showing myogenic damage, screening for missing or duplicated DMD gene fragments, and if the gene test is negative, then muscle biopsy dystrophin immunohistochemical staining will be performed to aid in the diagnosis. Does a negative DMD gene test rule out Duchenne muscular dystrophy? No. The DMD gene is large, with 79 exons, and many testing centers in China currently apply different testing methods and detect different exon sites and numbers, with some units only detecting certain hotspot mutations. Even if the MLPA technology is applied to detect 79 exons, it can only detect the deletion or duplication of large segments of the gene, but not the subtle point mutations, so the positive rate of the genetic test is not 100%, and a negative test result cannot exclude the possibility of Duchenne muscular dystrophy.