Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder with progressive proximal weakness as the principal sign. Glucocorticoids and physical therapy are the mainstay of treatment. Exercise intolerance is the hallmark of metabolic myopathies, which require a combination of laboratory testing, electrodiagnostic testing, and muscle biopsy for diagnosis. Joint hypermobility may be an isolated finding or be associated with hypermobility Ehlers-Danlos syndrome (EDS), other variants of EDS, or marfanoid syndromes. The latter conditions are associated with aortic and cardiac valvular abnormalities. Osteogenesis imperfecta encompasses a group of disorders characterized by bone fragility presenting with a low-impact fracture as a result of minimal trauma. Management includes multidiscipline specialists. Down syndrome (DS), or trisomy 21, is the most common chromosome abnormality identified in live births. Routine evaluation of atlantoaxial instability with x-ray is no longer recommended for children with DS without symptoms of atlantoaxial instability; however, clinical evaluation of symptoms is required for sports preparticipation. Achondroplasia is the most common skeletal dysplasia. Clinical signs are macrocephaly, short limb, short stature with disproportionately shorter humerus and femur, along with characteristic findings in pelvis and lumbar spine x-rays. Caregivers should be educated on proper positioning and handling to avoid complications, including car seat–related deaths.
Case 2. KR is a 30-month-old patient who is brought to your office by his parents who are concerned about his abnormal gait, clumsiness, and frequent falls. The birth record is unremarkable, but short stature and gross motor delay have been noted at well-child visits. On examination, KR uses a hand to push into an upright position. His calf muscles appear hypertrophied, and he walks on his toes with a waddling gait. Serum creatine kinase (CK) concentration is 3,100 U/L (reference range = 50-292 U/L), corroborating your suspicion of a muscular dystrophy.
Serious musculoskeletal genetic disorders are uncommon in children who present with musculoskeletal concerns. Despite this, family physicians need to be alert to signs and symptoms of occult genetic disorders, as well as more commonly encountered genetic disorders (eg, Down syndrome [DS], Marfan syndrome [MFS], achondroplasia).
Muscular Dystrophy
Gait is a commonly assessed developmental milestone. Most children begin to develop independent gait between ages 10 and 16 months and progress to a mature gait pattern between the ages of 7 and 8 years.59 In children with Duchenne muscular dystrophy (DMD), late walking and gait disturbances may occur most often between ages 2 and 3 years.60,61 This includes slow or awkward running. Becker muscular dystrophy (BMD) presents similarly but at a later age and with less severity.
DMD and BMD are the result of a defective DMD gene located on the X chromosome. The gene is responsible for the production of dystrophin, a protein that protects and stabilizes muscle fibers.60 As X-linked recessive genetic disorders, DMD and BMD principally affect males who do not have a second X chromosome to compensate for the genetic defect. DMD is estimated to affect between 1 in 3,500 and 1 in 3,600 to 1 in 6,000 live male births, whereas BMD is much rarer at less than 8 per 100,000 live births.60,61
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