Serum ceruloplasmin oxidase activity and immunoreactive serum ceruloplasmin in Wilson disease patients grouped according to their type of ATP7B mutation. Analysis of Wilson disease (WD) patients possessing either (1) two 'severe' mutations (SM/SM); (2) one 'severe' mutation and one missense mutation (SM/MM), or (3) two missense mutations (MM/MM). Distribution of data presented as box and whisker plots: 25th percentile, median, 75th percentile, maximum, outliers (circles), and extreme values (x). Both assays resulted in no indeterminate results or missing data. a, p-value for the comparison SM/SM with SM/MM patients; b, p-value for the comparison SM/SM with MM/MM patients. (A) Oxidase activity is significantly lower in SM/SM patients (0.0 U/L; IQR, 0.0 to 0.0) compared to SM/MM patients (3.1 U/L; IQR, 0.0 - 5.9) and MM/MM patients (17.8 U/L; IQR, 5.8 - 35.1). (B) Immunoreactive serum ceruloplasmin is significantly lower in SM/SM patients (0.02 g/L; IQR, 0.01 - 0.02) compared to SM/MM patients (0.07, g/L; IQR 0.06 - 0.10) and MM/MM patients (0.11 g/L; IQR, 0.10 - 0.17).