Furthermore, in all three cases of bullous pemphigoid and the 16/22 cases of epidermal acantholytic disorders—namely Hailey–Hailey disease, Darier disease, Grover disease, acantholytic acanthoma, warty dyskeratoma, cutaneous pemphigus vulgaris, as well as pemphigus foliaceus—there was moderate-to-strong membranous staining of claudin-4 in disrupted keratinocytes within acantholytic and/or bullous areas. This evidence concerns the gene CLDN4 and Darier disease.