A 29-year-old Middle Eastern man is evaluated for difficulty breathing and nonproductive cough for the past month. He reports difficulty walking and frequent falls over the last year but has not seen a physician. The patient has no other medical problems. He is married and has a 3-year-old son.
His blood pressure is 96/60 mm Hg and pulse is 100/min. Jugular venous pressure is estimated at 12 mm H₂O. Lung examination shows bibasilar crackles. The point of maximal impulse is displaced to the left and a third heart sound is present. The proximal extremity muscles are atrophied, but both calves are prominently enlarged.
Chest x-ray shows cardiomegaly.
The son's risk of developing his father's condition is closest to which of the following?

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11ec193a_972e_159e_853d_9945762284ed_MD0002_00 This patient's difficulty with ambulation, symptoms of heart failure, proximal muscle atrophy, and calf muscle pseudohypertrophy are suggestive of a dystrophinopathy. Patients with Becker muscular dystrophy (BMD) are affected later in life (early adulthood) than those with Duchenne muscular dystrophy (DMD) (around age 2-3). Weakness is the presenting symptom in both disorders and affects proximal lower extremities prior to distal and upper extremities. Both disorders are inherited in an X-linked recessive manner, meaning that sons can only inherit the mutation from their mother. Because the mother's risk of being a carrier is extremely small, the risk of the son inheriting his father's disorder is nearly 0%. Diagnosis of both muscular dystrophies is made based on clinical features, elevated creatine kinase, abnormal electromyograph, and genetic analysis/muscle biopsy (decreased or absent dystrophin). Treatment for both disorders is supportive. Patients with DMD usually survive until their mid-30s, and those with BMD survive beyond their 40s. Respiratory and cardiac insufficiencies are the most common causes of death. Educational objective: Becker muscular dystrophy (BMD) and Duchenne muscular dystrophy (DMD) are inherited X-linked recessive disorders. Patients with BMD are affected later in life than those with DMD. Diagnosis is made with genetic analysis or muscle biopsy (gold standard), which shows reduced (BMD) or absent (DMD) dystrophin. Respiratory failure and heart failure are the most common causes of death in both disorders. __________ References: Cardiac assessment in Duchenne and Becker muscular dystrophies. (http://www.ncbi.nlm.nih.gov/pubmed/20857240) Effects of angiotensin-converting enzyme inhibitors and/or beta blockers on the cardiomyopathy in Duchenne muscular dystrophy. (http://www.ncbi.nlm.nih.gov/pubmed/22463839)

A 29-Year-Old Middle Eastern Man Is Evaluated for Difficulty Breathing