A Study to Assess Efficacy and Safety of Two Different Dose Regimens of Risankizumab Administered Subcutaneously in Japanese Subjects With Generalized Pustular Psoriasis or Erythrodermic Psoriasis

For GPP * Have a diagnosis of GPP for at least 60 days prior to informed consent based on the diagnostic criteria of the Japanese Dermatological Association (JDA). Subjects not fulfilling one of the diagnostic criteria i.e., "accompanying systemic symptoms including fever or malaise" at the time of screening can be entered. * Subjects with an erythema area with pustules accounting for ≥ 10% of the body surface area (BSA), and with a severity assessment criteria score (JDA total score) specified by the JDA of less than 14. * Must be candidates for systemic therapy or phototherapy for GPP, as assessed by the investigator. For EP * Have a diagnosis of EP prior to informed consent. * Subjects with an inflammatory erythema area accounting for ≥ 80% of the BSA at screening and at the time of the first administration of the study drug. * Must be candidates for systemic therapy or phototherapy for EP, as assessed by the investigator.

* Previous exposure to risankizumab. * Currently enrolled in another investigational study or less than 30 days (from screening) since completing another investigational study (participation in observational studies is permitted). For GPP * Subjects with active ongoing inflammatory diseases other than GPP that might confound trial evaluations according to investigator's judgment. For EP * Subjects with active ongoing inflammatory diseases other than EP that might confound trial evaluations according to investigator's judgment. * Subject diagnosed with medication-induced or medication-exacerbated EP.