Hereditary Sensory and Autonomic Neuropathy (HSAN)

A 35-year-old Indian man presents with progressive distal sensory loss, recurrent painless foot ulcers, and neuropathic pain in his lower limbs. Examination reveals insensitivity to pain and temperature in a stocking distribution, preserved motor strength, and normal deep tendon reflexes. His father and paternal grandfather had similar symptoms with adult-onset presentation. The inheritance pattern marked **A** in the diagram is most consistent with this clinical presentation. Which of the following genetic subtypes and inheritance patterns best explains this pedigree?