A Study to Evaluate GBT021601-012 Single Dose and Multiple Dose in Participants With Sickle Cell Disease (SCD): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate GBT021601-012 Single Dose and Multiple Dose in Participants With Sickle Cell Disease (SCD) (NCT04983264), a non-randomized phase 1 study. The primary outcome is Number of Participants With Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs).

2. Clinical Question

The clinical question is therefore primarily one of early-stage safety and drug exposure, rather than a comparison of clinical benefit against another treatment. The posted adverse-event counts are separated by treatment period and by whether events were SCD-related or non-SCD-related. Because participants could be followed across periods, those period-specific counts should not be treated as separate, independent groups or added to estimate the number of distinct participants affected. The registry record does not report a randomized efficacy comparison or a clinical endpoint that would establish whether GBT021601 changes the course of SCD.

3. Trial Design

This was a Phase 1, non-randomized, unmasked, single-group study. The registry records 6 participants and describes the study as an intrapatient single-dose and multiple ascending-dose evaluation of GBT021601. The study status is completed. The recorded start date is 2021-05-21, and the primary completion date is 2022-12-06.

The study description separates treatment into Part A, a single-dose period; Part B, a multiple ascending-dose period; and Part C, an extended treatment period. The posted safety counts are reported within these periods. The number at risk was 6 in Parts A and B and 4 in Part C. Those period-specific figures do not establish that each period represents a new group of participants. In an intrapatient design, a participant may contribute information across multiple periods, so comparisons between periods do not have the same interpretation as comparisons between randomized groups.

There was no masking and no randomized allocation. The registry record does not report the detailed dose levels, the dose-escalation rules, the criteria for moving between periods, or the reasons that the number at risk differs in Part C. It also does not report the protocol’s sample-size justification, interim-analysis plan, or prespecified statistical analysis plan. Those details should not be inferred from the study title or the fact that dose escalation was part of the design.

The registry lists GBT021601 as the intervention and identifies pharmacokinetic outcomes across plasma, whole blood, and red blood cells, alongside safety outcomes. The study is not a like-for-like controlled comparison: without a randomized comparator, the posted results describe events observed during treatment and do not establish what would have occurred in a separate untreated or differently treated group.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Part A: Single Dose Period

Part B: Multiple Dose Period

Reasons for not completing this period:

Part C: Extended Treatment Period

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Safety population was defined as all participants who received any amount of study drug (GBT021601).

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: Safety population was defined as all participants who received any amount of study drug (GBT021601).

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Events (SAEs), measured over From first dose of study drug (Day 1) to at least 56 days after last dose of study drug (up to a maximum of 316 days).

The primary outcome is the number of participants with treatment-emergent adverse events (TEAEs) and serious adverse events (SAEs). A TEAE is an adverse event that begins or worsens during the on-treatment period. The registry defines that period as starting with the first dose and continuing through at least 56 days after the last dose, with the stated maximum follow-up of 316 days. The endpoint’s timeframe is from the first dose on Day 1 to at least 56 days after the last dose.

An adverse event is an untoward medical occurrence after a participant receives a product or device; it does not have to be caused by the treatment. An SAE is an event meeting the registry’s seriousness criteria, including death, a life-threatening experience, inpatient hospitalization or its prolongation, persistent or significant disability, a congenital anomaly or birth defect, or an important medical event.

Counting participants with events is useful in an early-phase safety study because it gives a direct description of how many people experienced events during the defined follow-up. The outcome includes SCD-related and non-SCD-related events, so the counts should not be read as evidence that the study drug caused them. The registry defines the safety population as all participants who received any amount of GBT021601. The registry record does not report a causal attribution rule or a separate comparative estimate against a control group.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

For a safety outcome expressed as a count of participants, the basic descriptive result is the number of participants meeting the event definition in the relevant group. The accompanying number at risk identifies the participants represented in that group. Such counts are useful for showing what was observed, but they do not, by themselves, quantify uncertainty as fully as an estimate with a confidence interval or support a causal comparison.

What does a confidence interval add?

In general, a confidence interval describes the statistical uncertainty around an estimated quantity. It gives a range of values compatible with the data under the assumptions of the analysis. With a small number of participants, estimates of event frequency can be imprecise: a small change in the observed count may substantially alter the estimate. A confidence interval would help communicate that uncertainty, but confidence intervals for the primary outcome are not reported in the registry record.

For a single-group study, a proportion of participants with an event is descriptive of the observed study population and follow-up. It is not a treatment-effect estimate relative to a control. A between-group effect requires a comparator and an analysis that accounts for how participants were assigned or matched. Here, allocation was non-randomized, masking was absent, and the model was single-group. No randomized comparator is reported, so conventional comparative treatment-effect interpretation is not available from these data.

How should repeated treatment periods be understood?

The study is described as intrapatient and reports separate counts for Parts A, B, and C. In general, repeated periods within participants create dependence: one person’s outcomes in different periods are not independent observations. A simple comparison of period counts would not account for that dependence, differences in time at risk, or changes in who remained under observation. The registry record does not report an analysis that models repeated measures, adjusts for exposure time, or compares event rates across periods. The different numbers at risk in Part C also mean that its descriptive count has a different participant denominator from Parts A and B.

Event counts and event counts per participant are not interchangeable. A participant can experience more than one event, and an event may be recorded under more than one related classification. The primary outcome is framed as participants with TEAEs and SAEs, whereas the adverse-event information is split by period and SCD relation. Without participant-level data or a report of overlap between categories, it is not possible to reconstruct a unique total of participants with any event from the posted group counts.

What is the role of pharmacokinetic outcomes?

Pharmacokinetics concerns drug concentration over time and is commonly described with measures such as maximum concentration, minimum concentration, time to maximum concentration, and area under a concentration-time curve. These measures characterize exposure in the specified biological samples. The registry lists several such outcomes for plasma, whole blood, and red blood cells, including outcomes assigned to Parts A, B, and C. Listing an outcome does not establish what its measured value was or how it varied across participants. Numerical results and associated uncertainty for those measures are not reported in the registry record.

Pharmacodynamic outcomes concern biological responses associated with exposure. The study purpose includes pharmacodynamics, but the registry material summarized for this analysis does not provide numerical pharmacodynamic results. No conclusions about the size or consistency of a biological response can therefore be drawn from the outcome names alone.

What is not described about the statistical plan?

The registry record does not report the planned statistical methods for the primary endpoint, a sample-size justification, or an interim-analysis plan. It does not report how missing observations were handled, whether any participants were excluded from particular analyses, or how event categories were adjudicated. The record lists 27 outcome measures and no analyses. These omissions mean the posted counts can be described, but it is not possible to verify whether they reflect a prespecified analysis or to assess the analysis choices against a complete protocol.

In general, multiple outcomes can raise a multiplicity issue: examining many endpoints can increase the chance of observing an apparently unusual result by chance if formal significance tests are used. Whether any adjustment is appropriate depends on the study’s goals and analysis plan. Since inferential analyses and multiplicity procedures are not reported in the registry record, no adjusted significance claims should be inferred. The posted information is best read as descriptive early-phase evidence, with the limitations of a small, non-randomized, single-group study kept explicit.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 27 outcome measures, including the primary adverse-event outcome and multiple pharmacokinetic outcomes across study parts and biological samples. It reports no analyses. The registry record does not describe a prespecified strategy for prioritizing secondary outcomes, controlling multiplicity, or interpreting any formal hypothesis tests. In general, multiplicity matters when several outcomes are tested because the chance of at least one apparently notable result can increase as the number of tests grows. No claim about statistical significance or multiplicity adjustment can be established from the posted information.

The registry record also does not report how missing outcome data were handled, whether participants discontinued or had incomplete follow-up, or how missing pharmacokinetic measurements were treated. The reason the number at risk is 4 in Part C, compared with 6 in Parts A and B, is not reported in the registry record. It should not be assumed that the difference reflects a particular reason or that missingness was unrelated to outcomes.

The safety population is defined as all participants who received any amount of study drug. The record does not give a detailed analysis-population flow or clarify whether every listed outcome used that same population. It does not report participant-level overlap between event categories, missing-event procedures, or a statistical analysis plan. These gaps limit assessment of whether the reported counts fully represent all follow-up and how robust any derived estimate would be to incomplete data.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: sickle cell anaemia with crisis (33.3%).

The serious adverse-event counts are reported separately for SCD-related and non-SCD-related events within each treatment period. SCD-related serious events were recorded for 0 of 6 participants in Part A, 2 of 6 in Part B, and 0 of 4 in Part C. Non-SCD-related serious events were recorded for 0 of 6 in Part A, 0 of 6 in Part B, and 0 of 4 in Part C. The recorded death count was 0 in every period.

These figures describe participants with reported events in the relevant categories; they do not demonstrate that the study drug caused or prevented an event. The study had no randomized control group, and its periods are not independent treatment arms. Nor should the counts for Parts A, B, and C be summed to estimate the number of distinct participants with a serious event, because the registry does not report whether the same participant contributed events in more than one period.

The registry lists “Sickle cell anaemia with crisis” as a top serious-event term with 33.3%, but the denominator and calculation method are not reported in the registry record. That percentage should therefore be read as a posted event-term statistic, not automatically as a participant-level risk across the study. The available figures are descriptive and do not replace a fuller account of event timing, recurrence, severity details, or attribution.

12. What the Result Does, and Does Not, Mean

The results describe safety events recorded during a Phase 1 study of GBT021601 in participants with SCD. They show that SCD-related serious adverse events were reported in Part B, while no non-SCD-related serious adverse events or deaths were reported in the listed period-specific groups. Other adverse events were also recorded, with counts shown separately by period and SCD relation. These observations are relevant to describing what occurred among the participants followed in this study.

They do not establish that GBT021601 caused the events, because an adverse event need not be causally related to treatment and the record does not report a comparative control group. They also do not establish that the treatment reduces, increases, or has no effect on clinical outcomes. A single-group dose study is not designed, on the information reported, to provide a randomized estimate of comparative clinical benefit. Its small enrollment and absence of an independent comparator limit the precision and generalizability of any safety interpretation.

The treatment periods should not be read as if they were separate randomized arms. Part A, Part B, and Part C differ in purpose and number at risk, and participants may contribute information across periods. Differences in observed counts could reflect the participants included, observation time, chance, or other factors; the record does not provide analyses that separate these possibilities.

The registry lists pharmacokinetic and pharmacodynamic outcomes as study objectives or measures, but numerical pharmacokinetic and pharmacodynamic results are not reported in the registry record. The outcome listings alone cannot show the level of drug exposure or the magnitude of a biological response. Overall, the posted data are descriptive and useful for understanding the recorded safety observations, but they are not a conclusive causal or comparative assessment.

13. Why This Trial Matters Statistically

Early-phase studies address questions that can precede a larger comparative evaluation: whether a drug has been studied at different dosing stages, what safety events were observed, and what pharmacokinetic measurements were planned. This study’s intrapatient single-dose and multiple ascending-dose structure makes the distinction between descriptive observation and comparative inference especially important. The posted adverse-event counts offer a view of events by period, while the absence of a randomized control group sets a clear boundary on what those counts can establish.

Statistically, the small enrolled population makes transparent reporting particularly valuable. Counts should be read alongside the number at risk, the event definitions, and the follow-up window. The record defines TEAEs and SAEs and specifies a safety population, which helps explain the intended scope of the primary outcome. At the same time, details such as participant-level overlap, missing-data handling, analysis methods, and uncertainty estimates are not reported in the registry record. Those omissions constrain reproducibility and make it harder to distinguish the precision of an estimate from the simple fact that an event was observed.

The study also illustrates why pharmacokinetic outcomes and clinical outcomes should not be conflated. The listed concentration measures are relevant to characterizing exposure, but their numerical results are not reported in the registry record. Even when exposure measures are available, they do not by themselves establish a clinical treatment effect. Likewise, the adverse-event counts describe safety observations but do not prove attribution.

For clinical researchers and biostatisticians, the central lesson is interpretive discipline: preserve the study’s single-group, repeated-period structure; report denominators with counts; avoid treating participants across periods as independent; and distinguish event description from causal inference. The registry record supplies a limited but meaningful account of observed safety data, while leaving important analysis details unavailable.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitations are tied to the design and the detail available in the registry record. This was a non-randomized, unmasked, single-group Phase 1 study with an enrollment of 6. No independent control group is reported, so the adverse-event counts cannot estimate a comparative treatment effect or distinguish treatment-related events from events that might have occurred without the study drug.

The reported counts are divided among three periods, and the number at risk is 6 in Parts A and B and 4 in Part C. The registry record does not explain the change in the number at risk. It also does not report whether the same participants contributed to multiple periods, the duration of each period, individual exposure time, or participant-level event histories. These missing details prevent calculation or interpretation of an overall count of unique participants with events from the period-specific results.

Although the primary outcome covers TEAEs and SAEs, the posted group information separates serious and other adverse events by SCD relation. The record does not report overlap between those categories, detailed event timing, or a complete explanation of the “other” event classification. It lists a serious-event term with a percentage but does not report its denominator or calculation details.

The registry record does not report numerical pharmacokinetic or pharmacodynamic results, confidence intervals for the safety counts, a statistical analysis plan, missing-data methods, a sample-size justification, or interim-analysis procedures. It lists 27 outcome measures and no analyses. These limits mean the results can be described but cannot be independently checked against a complete prespecified analysis or used to make precise comparative claims.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study to Evaluate GBT021601-012 Single Dose and Multiple Dose in Participants With Sickle Cell Disease (SCD) — NCT04983264.
• Registry record last updated 2024-06-10; status last verified 2023-12.
• Results first posted 2024-06-10.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT04983264 is a completed Phase 1 study of GBT021601 in participants with sickle cell disease. The registry describes an intrapatient single-dose and multiple ascending-dose study intended to evaluate pharmacokinetics, safety, tolerability, and pharmacodynamics. The design is recorded as non-randomized, unmasked, and single-group, with an enrollment of 6.

The primary outcome concerns participants with treatment-emergent adverse events and serious adverse events. The posted safety counts are divided across Parts A, B, and C and distinguish SCD-related from non-SCD-related events. No deaths are reported in the period-specific groups. These counts are descriptive and are not a randomized comparison.

The registry lists 27 outcome measures and no analyses. Numerical pharmacokinetic and pharmacodynamic results, the statistical analysis plan, missing-data procedures, and the sample-size justification are not reported in the registry record. Interpretation should therefore remain limited to the observed safety counts and the stated design.