KRT9 and hereditary palmoplantar keratoderma: In this cohort study, 142 patients with palmoplantar keratoderma from 76 families underwent deep phenotyping as well as genotyping, which yielded a diagnosis in 83% and identified 27 disease-causing variants across 13 genes: AAGAB, DSG1, KRT1, DSP, KRT9, AQP5, LORICRIN, KRT16, SERPINA12, COL7A1, ABCA12, CARD14, and DST. AAGAB variants correlated with punctate palmoplantar keratoderma, whereas other subtypes showed more complex genotype-phenotype patterns.