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.