Pectus excavatum

A 16-year-old boy comes to his outpatient provider for evaluation of exercise intolerance. His symptoms have been ongoing for many years but have recently become more bothersome after he started playing soccer for his high school team. He fatigues more easily than his friends and cannot keep up with them during matches. The patient also experiences frequent bruising after minor falls. Family history is noncontributory. In the office, his temperature is 37.1°C (98.8°F), blood pressure is 108/73 mmHg, pulse is 65/min, and respiratory rate is 15/min. Physical examination reveals hyperelastic skin, hypermobile joints and multiple bruises over the bilateral lower extremities. Examination of the chest reveals the following finding:  


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Which of the following is the most likely underlying etiology of this patient’s symptoms?