Stimulated saliva in X-linked hypohidrotic ectodermal dysplasia: Rheological comparison with healthy controls and resting saliva

The lubricating and moisturizing function of laryngeal mucus is increasingly recognized as a key contributor to phonation, yet its direct sampling is invasive. Saliva offers a noninvasively collectable alternative for investigating viscoelastic properties both as a surrogate for laryngeal mucus and with regard to its own role, particularly in ectodermal dysplasia (ED), where dysfunction of certain eccrine glands is associated with reduced salivary flow, characteristic voice quality, and difficulties in chewing/swallowing. A rheological characterization was performed on stimulated saliva (SS) from patients with X-linked hypohidrotic ectodermal dysplasia (XLHED) and matched healthy controls, and SS was compared with resting saliva (RS) from previous cohorts. SS was measured using a plate–plate rheometer with stress-controlled oscillatory frequency sweeps (f = 1–10 Hz; τ = 0.1 Pa) and strain sweeps (0.01–20 Pa; f = 0.5 Hz). ED saliva tended to exhibit lower storage and loss moduli at low frequencies/low strains, with convergence toward or exceedance of control values at higher frequencies/strains, indicating altered viscoelastic behavior. In healthy controls, pronounced rheological differences between resting and stimulated conditions were observed, whereas these differences were substantially attenuated in ED, most notably in adult males. Strikingly, RS from male XLHED patients closely resembled SS from healthy male controls, suggesting that “resting” saliva collection in XLHED may involve unintended functional stimulation or reflect varying degrees of impairment of the different salivary glands in XLHED. Overall, the data indicate disease- and sex-specific alterations in salivary viscoelasticity, potentially reflecting altered gland-specific secretion and/or macromolecular composition. Conclusions about the molecular basis and functional relevance require compositional, gland-specific, extensional, and tribological validation.