X-Linked Charcot-Marie-Tooth (CMTX1, GJB1)

A 35-year-old man presents with progressive distal weakness and atrophy of intrinsic foot muscles, pes cavus, and hammer toes over the past 10 years. Nerve conduction studies show motor velocities of 32 m/s with secondary axonal loss. His 28-year-old sister reports mild, intermittent distal paresthesias that began only recently. Their father is unaffected. The pedigree pattern shown in the diagram is marked **A**. Which of the following statements best characterizes the inheritance pattern and expected genetic counselling for this family?