Nineteen biopsies from five patients (three families) with Darier's disease were studied by electron microscopy. Vacuolated basal and prickle cells containing normal or slightly increased amounts of tonofilament aggregates appear to become corps ronds precursors in the lacunae, and by further vacuolization become mature corps ronds in the stratum granulosum. On the other hand, vacuolated cells of the lower malpighian layer may develop premature aggregation of tonofilaments that compress the preexisting vacuoles into slits and give rise to intralacunar grains. While there are parakeratotic-like cells in the stratum corneum, their relationship to grains is unclear.
It appears that abnormal cytoplasmic vacuolization is an early event triggered by the mutant gene. Whether corps ronds or grains are formed seems to depend on the progression of this abnormal vacuolization and the rate of subsequent keratinization.
Gottlieb SK, Lutzner MA. Darier's DiseaseAn Electron Microscopic Study. Arch Dermatol. 1973;107(2):225-230. doi:10.1001/archderm.1973.01620170037011