Galli-Galli disease (GGD) is a rare autosomal dominant genodermatosis that falls under the broader category of reticulate pigmented disorders of the skin. GGD is thought to be an allelic variant of Dowling-Degos disease (DDD), the latter a pigmentary disorder characterized by progressive hyperpigmentation of flexural skin. The distinguishing feature of GGD is the presence of suprabasal acantholysis histologically, and as such it has also been described as "acantholytic Dowling-Degos disease" in the literature.
In 1982, Bardach et al described the first cases of disease occurring in two brothers named Galli. The brothers presented with a reticulated hyperpigmented eruption affecting the skin folds. Biopsy demonstrated proliferation of rete ridges and basal layer hyperpigmentation as seen in DDD, but also focal suprabasal acantholysis.
Initially, GGD was favored to be a distinct clinical entity from DDD due to the unique and consistent feature of acantholysis; however, subsequent research supports a common etiology for DDD and GGD, as both have been found to share the same genetic defect.
Frameshift or nonsense KRT5 gene mutations lead to haploinsufficiency of keratin 5, a protein that plays an important role in cell-cell adhesion, epidermal differentiation, and melanosome uptake. The mechanism by which specific KRT5 mutations seen in DDD and GGD cause skin disease or correlate with variable histological subtypes is not yet elucidated.
Codes
ICD10CM: L81.9 – Disorder of pigmentation, unspecified
SNOMEDCT: 370172004 – Skin pigmentation
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Differential Diagnosis & Pitfalls
Other reticulate pigmented disorders of the skin may be difficult to distinguish clinically, but the finding of suprabasal acantholysis on biopsy is exclusive to GGD.
Dowling-Degos disease – GGD is an acantholytic variant of DDD. Clinically, DDD may show comedo-like lesions and pitted perioral acneiform scars not typically seen in GGD.
Reticulate acropigmentation of Dohi (dyschromatosis symmetrica hereditaria) – Presents with acral hyper- and hypopigmented macules on the dorsal hands and feet.
Haber syndrome – Verruciform papular lesions of trunk and roseate facial erythema, often presenting in childhood.
Other considerations in the differential diagnosis include:
Darier disease – Earlier onset, seborrheic distribution, characterized by crusted yellow-brown papules rather than lentigo-like macules; nail changes and mucous membrane involvement. On biopsy, dyskeratosis seen in Darier disease and not GGD.
Grover disease – Very pruritic keratotic papules on trunk; acantholysis and dyskeratosis seen on biopsy, no elongation of rete ridges as in GGD.
Epidermolysis bullosa with mottled pigmentation – Also caused by keratin 5 mutation; has additional features of palmoplantar hyperkeratosis, bullous lesions.
Pemphigus vulgaris – Cutaneous and mucosal involvement, plus Nikolsky, plus immunofluorescence.
