The correct answer is D. The responsible gene encodes a Ca2+ pump located in the sarcoplasmic reticulum.
This biopsy reveals diffuse suprabasilar acantholysis with a “dilapidated brick wall” appearance, which is indicative of Hailey-Hailey disease (familial benign chronic pemphigus). The responsible gene encodes a Ca2+ pump located in the Golgi apparatus (as opposed to Darier’s disease, which is due to a mutation in the ATP2A2 gene, which encodes a Ca2+ pump in the endoplasmic reticulum).
Hailey-Hailey disease is due to an autosomal dominant mutation in ATP2C1. It presents initially with flaccid vesicles on an erythematous base, with a predilection for the neck/ axillae & intertriginous areas. The vesicles rupture easily and this gives rise to macerated or crusted erosions. Nikolsky’s sign can be positive, and superinfection with herpes simplex virus (usually HSV2) can occur in the genital region.