Objective: To determine the sex and age distribution of aquaporin-4 (AQP4) autoimmunity using data derived from clinical service laboratory testing of 56,464 patient samples.
Design: Observational analysis.
Setting: Mayo Clinic Neuroimmunology Laboratory.
Patients: Between October 1, 2005, and January 4, 2011, 56,464 patients were tested for AQP4-IgG; 2960 (5.2%) patients were seropositive.
Main outcome measure: Seropositivity for AQP4-IgG.
Results: Patients seropositive for AQP4-IgG were older than seronegative patients (mean [SD] age, 46  vs 42  years, respectively; P < .001). More females than males were tested (37,662 vs 16,810, respectively; P < .001). Among 2743 seropositive patients, 146 (5.3%) were pediatric (aged ≤18 years) and 333 (12.1%) were elderly (aged ≥65 years). The sex distribution of seropositive patients was 2465 females and 306 males (absolute female:male ratio, 8.1:1; P < .001). After adjusting for the number of females tested, an excess of females persisted (adjusted female:male ratio, 3.6:1). Female predominance for AQP4-IgG was more striking in adults (absolute female:male ratio, 8.4:1; adjusted female:male ratio, 3.5:1) than in pediatric patients (absolute female:male ratio, 4.3:1; adjusted female:male ratio, 2.9:1) (P < .001). Elderly women were more likely to be seropositive than individuals in other age categories (13.1% vs 6.0%, respectively; P < .001). The proportion of AQP4-IgG-seropositive individuals (detection rate), defined by decade of age, increased exponentially in women after age 50 years.
Conclusions: Seropositivity for AQP4-IgG occurs predominantly in females, particularly in individuals older than 18 years. Among seropositive patients, 1 in 6 is in the extremes of age. The detection rate of AQP4-IgG increased in women after age 50 years.