Galli-Galli Disease (Dowling-Degos Disease Type 3) Associated with a Novel POGLUT1 Nonsense Variant: Clinicopathologic and Immunohistochemical Correlation.

Mutations in KRT5, POFUT1, POGLUT1, and PSENEN define four genetic subtypes of Dowling-Degos disease (DDD), with varied clinical and histologic expression including those previously reported as Galli-Galli disease. We report a case of DDD3 associated with a novel early nonsense variant in POGLUT1 (c.12G>A; p.Trp4*), representing, to the best of our knowledge, the first documented case in Spain. A 55-year-old man presented with recurrent pruritic erythematous scaly papules on the trunk and hyperkeratotic brown papules on the cervical and thoracic regions. Direct microscopic examination of scales from erythematous lesions revealed yeast cells and short hyphae compatible with Malassezia sp. Initial histopathologic evaluation of a pigmented papule was interpreted as simple lentigo. Subsequent biopsy demonstrated elongated rete ridges and focal suprabasal acantholysis without dyskeratosis, raising suspicion for DDD. Whole-exome sequencing identified a heterozygous nonsense variant in POGLUT1, confirming the diagnosis of DDD3. Previous studies have shown that diffuse cytokeratin 5 (CK5) expression throughout all epidermal layers may support the diagnosis of DDD3. This case highlights diagnostic pitfalls related to subtle and focal acantholysis, emphasizes the importance of clinicopathologic correlation and serial sectioning.