Study of ALXN1210 in Complement Inhibitor Treatment-Naïve Adult and Adolescent Participants With Atypical Hemolytic Uremic Syndrome (aHUS)

Complete TMA response during the 26-week Initial Evaluation Period is a composite outcome measure that required normalization of hematological parameters (platelet count and lactate dehydrogenase [LDH]) and improvement in kidney function (≥25% reduction in serum creatinine from baseline); for participants on dialysis, baseline was established at least 6 days after the end of dialysis. Participants had to meet these criteria for 2 separate assessments obtained at least 4 weeks (28 days) apart, and any measurement in between. To be considered a responder during the 26-week Initial Evaluation Period, the latest time point a participant could first meet the response criteria was 28 days before the Week 26 (Day 183) assessment. Formal statistical comparison analyses were not planned for this study. The percentage was based on the responders among treated participants. The 95% confidence interval (CI) was based on the asymptotic Gaussian approximation method with a continuity correction.

Participants that did not have a response were censored at the date of last visit or study discontinuation at the time when the analysis was performed. The time to complete TMA Response is reported in days. The time of the event of a confirmed complete TMA response was considered the first time point at which all the criteria for complete TMA response were met.

For participants requiring dialysis within 5 days prior to ALXN1210 treatment initiation, the number of participants no longer requiring dialysis is reported

The proportion of participants considered responders, along with a 2-sided 95% CI for the Week 52 time point, is reported. To be considered a responder during the 26-week Initial Evaluation Period, the latest time point a participant could first meet the response criteria was 28 days before the Week 26 (Day 183) assessment (components of the response maintained for at least 28 days).

Kidney function evaluated by eGFR was summarized at baseline and the Week 26 and Week 52 time points using descriptive statistics for continuous variables for the observed value, as well as the change from baseline. The baseline value was defined as the average of the values from the assessments performed prior to the first study drug infusion (these could include results from Screening and the Day 1 visit). A value of 10 milliliters (mL)/minute (min)/1.73 meters squared (m^2) for eGFR was imputed for participants requiring dialysis for acute kidney injury. The observed value and change from baseline are reported in mL/min/1.73 m^2. An increase indicated improvement in kidney function.

The CKD stage is presented as the change from baseline in the participants that Improved (excluding those with Stage 1 [normal renal function] at baseline as they cannot improve), Worsened (excluding those with Stage 5 at baseline as they cannot worsen), and Stayed the Same, compared to the CKD stage at baseline. Baseline was derived based on the last available eGFR before starting treatment. Stage 5 was considered the worst category, while Stage 1 was considered the best category. A 2-sided 95% CI for the proportion, based on exact confidence limits using the Clopper-Pearson method, was provided for each category. The CKD stage was classified based on the National Kidney Foundation Chronic Kidney Disease Stage.

The hematologic TMA parameter of platelet count was summarized at baseline and at Week 26 and Week 52 using descriptive statistics for continuous variables for the change from baseline. Results are reported in platelets*10^9/liter (L) blood.

The hematologic TMA parameter of serum LDH was summarized at baseline and at Week 26 and Week 52 using descriptive statistics for continuous variables for the change from baseline. Results are reported in units (U)/L.

The hematologic TMA parameter of hemoglobin level was summarized at baseline and at Week 26 and Week 52 using descriptive statistics for continuous variables for the change from baseline. Results are reported in grams (g)/L.

The percentage of participants with an increase from baseline in hemoglobin ≥20 g/L, observed at 2 separate assessments obtained at least 4 weeks (28 days) apart, and any measurement in between, was assessed through Week 26 and Week 52 and is presented as the percentage of responders, along with a 2-sided 95% CI. The 95% CIs are based on exact confidence limits using the Clopper-Pearson method. To be considered a responder during the 26-week and 52-week Extension Periods, the latest time point a participant could first meet the response criteria was 28 days before the respective Week 26 and Week 52 assessments (components of the response maintained for at least 28 days).

The EQ-5D-3L is a participant-answered questionnaire that scores 5 dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression (scored as a 1, 2, or 3, with 3 being the worst health state), as well as health state on a visual analogue scale (0 to 100, with 100 representing the best health state). From these scores, a summary index score is derived using the time trade-off valuation set for the United States and ranges from -1 to 1, where a score above 0.94 indicates full health. An increase in score from baseline indicates improvement in quality of life.

Quality of life was evaluated in part using FACIT Fatigue Version 4. The data were summarized at baseline and at the Week 26 and Week 52 time point using descriptive statistics for continuous variables. The FACIT Fatigue Version 4 questionnaire at baseline and the Week 52 timepoint was scored using standard scoring algorithms. The score ranges from 0-52, with a higher score indicating less Fatigue. An increase in score indicated an improvement in quality of life.