Mercier et al. (2013) reviewed the features of 26 female carriers of pathogenic mutations in the DMD gene who were referred for symptoms related to the disorder before 17 years of age. Five had a Duchenne-like phenotype with loss of ambulation before age 15 years, 13 had a Becker-like phenotype with muscle weakness but persistence of ambulation after age 15 years, and 8 had exercise intolerance. Initial symptoms included significant muscle weakness (88%), mostly affecting the lower limbs, or exercise intolerance (27%). Cardiac dysfunction was present in 19%, and cognitive impairment in 27%. Cognitive impairment was associated with mutations in the distal part of the gene. Muscle biopsy showed dystrophic changes in 83% and mosaic immunostaining for dystrophin in 81%. The X-chromosome inactivation pattern was biased in 62% of cases. Mercier et al. (2013) concluded that carrier females may have significant symptoms of the disorder.
Duchenne was convinced that the "truth" of his pathognomic experiments could only be effectively rendered by photography, the subject's expressions being too fleeting to be drawn or painted. "Only photography," he writes, "as truthful as a mirror, could attain such desirable perfection."  He worked with a talented, young photographer, Adrien Tournachon , (the brother of Felix Nadar ), and also taught himself the art in order to document his experiments.  From an art-historical point of view, the Mechanism of Human Physiognomy was the first publication on the expression of human emotions to be illustrated with actual photographs. Photography had only recently been invented, and there was a widespread belief that this was a medium that could capture the "truth" of any situation in a way that other mediums were unable to do.