Open-Label Extension Study of Trofinetide for Rett Syndrome: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Open-Label Extension Study of Trofinetide for Rett Syndrome (NCT04776746), a na phase 3 study. The primary outcome is Percentage of Patients With Treatment-emergent Adverse Events (TEAEs), With Serious Adverse Events (SAEs), and With Withdrawals Due to AEs.

2. Clinical Question

This question is descriptive rather than comparative. It concerns the frequency of recorded safety events during continued trofinetide exposure in this study, not whether trofinetide caused an event or whether its risk differs from another option. In a single-group, open-label study, reports can help characterize the events observed during treatment, but they cannot by themselves separate treatment effects from the underlying condition, other circumstances, or the way events were identified and recorded.

3. Trial Design

The registry describes NCT04776746 as a Phase 3 open-label extension study of continued treatment with trofinetide for Rett syndrome. The study model is single group, allocation is listed as not applicable, and masking is absent. Participants received trofinetide oral solution; the record does not describe a concurrent control arm. Enrollment was 77. The stated study purpose was to investigate the safety and tolerability of continued long-term oral trofinetide treatment in girls and women with Rett syndrome.

The registry lists a mean study drug exposure of 426 days, corresponding to 1.2 years, for the primary outcome timeframe. That is a group-level exposure summary. It should not be read as the duration experienced by every participant. The primary outcome population is described as all patients enrolled and treated. Withdrawals due to adverse events include study drug discontinuation as well as study termination, so the outcome’s wording encompasses more than discontinuation of study medication alone.

The registry records a start date of 2020-11-08 and a primary completion date of 2023-06-30. The current recorded status is terminated. The reason for termination is not reported in the registry record, so the status alone does not explain why the study ended or whether the planned follow-up was completed as intended.

Because this is an open-label, single-group extension, its design is suited to describing experiences recorded among people receiving continued treatment. It does not provide a randomized like-for-like comparison. The registry record does not report a protocol rationale for the design, the number of sites, eligibility details beyond the stated population, or a planned control group. These details should not be inferred from the study title or phase designation.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All patients enrolled and treated

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: All patients enrolled and treated with trofinetide

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Patients With Treatment-emergent Adverse Events (TEAEs), With Serious Adverse Events (SAEs), and With Withdrawals Due to AEs, measured over Mean study drug exposure was 426 days, corresponding to 1.2 years.

The primary outcome is titled as the percentage of patients with treatment-emergent adverse events, serious adverse events, and withdrawals due to adverse events. The measurement unit is participants, and the registry describes its parameter as a count of participants. In practical terms, the outcome concerns how many participants experienced the listed safety events during the stated study period, with the title expressing the intended measure as a percentage. The outcome population is all patients enrolled and treated.

Safety and tolerability outcomes are used in extension studies to describe events recorded during continued exposure, including events serious enough to meet the study’s serious-adverse-event classification and events leading to withdrawal. Capturing withdrawals matters because stopping treatment or ending study participation due to an adverse event is itself relevant to tolerability. The registry specifically includes both study drug discontinuation and study termination within withdrawals due to adverse events.

The registry record reports the endpoint title and timeframe, but does not provide a separate result for each component of that title in the registry record for this analysis. The posted adverse-event summary gives group counts for serious events and other adverse events, along with deaths, but a count for withdrawals due to adverse events is not reported in the registry record. The endpoint should therefore be understood as a safety-focused measure, not as a measure of symptom improvement or comparative treatment benefit.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a binary outcome type and describes the primary parameter as a count of participants. For safety outcomes, a participant-level count records whether people experienced an event or category of events during the specified observation period. This is different from counting every episode: a participant with repeated episodes may still contribute once to a participant count, depending on the outcome definition. The registry record does not explain in detail how repeat events were handled for each reported category.

What does a participant count tell the reader?

A count is an absolute description of the number of participants recorded with an outcome. When a denominator is also reported, the reader can understand the count in relation to the group at risk. The posted summary gives 23 with serious adverse events among 77 at risk, and 57 with other adverse events among 77 at risk. These values are reported as counts and denominators, not as a comparison between treatment groups. The record does not supply uncertainty intervals for these counts in the registry record for this analysis.

Counts can be straightforward to interpret, but their meaning depends on how the event is defined, how long participants are observed, and how completely events are captured. The mean exposure of 426 days, corresponding to 1.2 years, gives an overall description of treatment exposure. It does not reveal the follow-up duration for each participant. If observation time varies, raw counts do not account for that variation in the way an exposure-adjusted rate or time-to-event analysis might. Such analyses are not reported in the registry record.

Why does the single-group design matter?

In a randomized comparison, a concurrent control group can help distinguish outcomes occurring during treatment from outcomes that might also occur under another assigned condition. Here, there is no control group: the study is recorded as single group, with allocation not applicable and no masking. The event counts therefore describe the experience of the trofinetide group but do not estimate a treatment-versus-control contrast. General statistical reasoning: a before-and-after or single-group description cannot, on its own, remove confounding from the natural course of illness, background care, participant selection, or other factors.

The open-label design means the record does not describe masked treatment assignment. General statistical reasoning: awareness of treatment may influence reporting, clinical attention, or decisions about stopping treatment. The direction and size of any such influence cannot be established from the registry information. This does not make the recorded counts unusable; it defines the limits on how they should be interpreted.

How should the event percentages be read?

The serious-event terms are reported with percentages: seizure at 6.5%; vomiting, pneumonia, urinary tract infection, and acute respiratory failure each at 2.6%; and cardiac arrest at 1.3%. These are registry-reported values, not newly calculated estimates. They describe the listed terms in this study group. A term’s percentage does not convey severity beyond its classification, duration, recurrence, timing, or causal relationship to treatment. The record does not provide those details in the registry record.

Serious adverse events are not the same as all adverse events. The registry distinguishes serious events from other adverse events in its summary. Also, a list of selected serious-event terms should not be assumed to enumerate every event category or every event experienced. The record does not explain how the terms were selected for display, so the listed terms should be treated as the reported examples rather than a complete clinical narrative.

What can planning calculations establish?

The registry information describes sample-size illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that the study was designed or conducted as a two-arm randomized comparison. The actual trial is single group, and the registry record does not report a rationale for its enrollment or an original sample-size justification. The planning assumptions do not turn the observed single-group safety counts into randomized evidence.

For general context, a confidence interval expresses the range of estimates compatible with data under a statistical model and quantifies precision; it is not a guarantee that the true value lies within the interval. No confidence interval for the adverse-event findings is reported in the registry record. Over-dispersion is a general issue when outcome variability exceeds what a simple statistical model expects; it can make model-based uncertainty too narrow if ignored. The registry entries do not report an over-dispersion assessment or a model-based analysis of these safety counts.

What analysis details are absent?

The registry reports 0 analyses for the recorded outcomes in the registry record for this analysis. That means no statistical analysis result is included in this record summary; it does not establish what analyses may have been performed outside the registry. A detailed statistical analysis plan, handling of repeated events, confidence intervals, adjusted estimates, and rules for missing outcome data are not reported in the registry record. Those omissions limit assessment of precision and analytical choices, but should not be filled by assumption.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome title covers treatment-emergent adverse events, serious adverse events, and withdrawals due to adverse events. The registry also lists 5 outcome measures, while the registry entries available for this analysis report 0 analyses. A multiplicity strategy for interpreting multiple outcomes or multiple event categories is not reported in the registry record. In general, examining many outcomes can increase the chance of finding an unusual result, so prespecified outcome priorities and adjustment methods can matter. No such methods should be inferred.

The record does not report a detailed statistical analysis plan, including whether any outcomes were designated for formal hypothesis testing, how any testing hierarchy was set, or whether estimates were adjusted for multiple comparisons. Because there is no reported control-group contrast and no analyses are listed, the posted counts are best read descriptively rather than as evidence from a set of confirmatory significance tests.

The stated primary population is all patients enrolled and treated. How participants with incomplete follow-up, missing event information, or withdrawal for reasons other than adverse events were handled is not reported in the registry record. The registry notes that withdrawals due to adverse events include both study drug discontinuation and study termination, but this definition does not specify how missing outcomes after withdrawal were treated.

Missing-data methods can affect interpretation because participants who leave early may have less opportunity for events to be observed, while the reasons for leaving may be related to safety. General statistical reasoning: complete-case summaries and methods that make assumptions about unobserved outcomes can lead to different interpretations. The record does not state whether follow-up continued after treatment discontinuation, whether events were sought after withdrawal, or how censoring and incomplete observation were addressed. These details are not reported in the registry record and cannot be assumed.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: seizure (6.5%), vomiting (2.6%), pneumonia (2.6%), urinary tract infection (2.6%), acute respiratory failure (2.6%).

The registry reports 23 participants with serious adverse events among 77 at risk in the trofinetide group. It separately reports 57 participants with other adverse events among 77 at risk, and 4 deaths. These figures are counts within the study group. They are not a treatment-versus-control comparison, and they do not establish that treatment caused an event. The record does not provide event-by-event timing, recurrence, clinical context, or a causal assessment in the registry record for this analysis.

The serious-event terms listed include seizure at 6.5%; vomiting, pneumonia, urinary tract infection, and acute respiratory failure each at 2.6%; and cardiac arrest at 1.3%. These are the percentages reported for those terms in the registry record. They should not be read as percentages of events that were caused by trofinetide. The record does not explain the method used to select these terms for listing or whether the list is exhaustive.

The counts should also be read in light of the average exposure: 426 days, corresponding to 1.2 years. This is a mean, not an individual follow-up duration. No exposure-adjusted event rates are reported in the registry record. The count of deaths is reported, but cause, timing, and relationship to treatment are not reported in the registry record. These limitations make the figures useful as descriptive safety information, not as a standalone estimate of comparative risk.

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

The registry record documents a safety experience during continued trofinetide treatment in a single-group, open-label study of girls and women with Rett syndrome. It reports 23 participants with serious adverse events among 77 at risk, 57 with other adverse events among 77 at risk, and 4 deaths. It also lists selected serious-event terms with registry-reported percentages. These observations are relevant to describing what was recorded during the study, alongside the mean exposure of 426 days, corresponding to 1.2 years.

The findings do not show how often the same outcomes would have occurred without trofinetide or with a different treatment. There was no concurrent comparator group and no masking. The counts therefore cannot establish a causal effect or a relative safety difference. Nor do the reported term percentages show whether events were treatment-related; that relationship is not reported in the registry record for this analysis.

The record also does not provide a complete breakdown of the primary endpoint’s components. Although the endpoint title includes treatment-emergent adverse events, serious adverse events, and withdrawals due to adverse events, a withdrawal count is not reported in the registry record. The listed count of other adverse events should not be treated as a complete primary-endpoint result without a specific definition linking the measures.

The termination status is a registry designation, not an explanation of why the study ended. The reason for termination is not reported in the registry record. The record does not establish whether all planned observations were completed or whether termination was related to safety. These questions require information not present in the listed details.

In short, the record supports a descriptive account of adverse events and exposure in the enrolled and treated group. It does not establish treatment efficacy, prove or exclude causation for an individual event, or provide a randomized estimate of risk. Interpretation should remain within those boundaries.

13. Why This Trial Matters Statistically

Extension studies address a different statistical question from trials designed primarily to compare assigned treatments. Their safety summaries can describe events observed during continued treatment, which is important when the intended research question concerns longer-term exposure and tolerability. In this record, the stated purpose was to investigate safety and tolerability of continued long-term oral trofinetide treatment in girls and women with Rett syndrome.

The design details are essential for understanding what the numbers mean. This study is open-label and single group, with allocation not applicable and no masking. Those features mean the counts describe outcomes in the treated group rather than a contrast protected by randomized assignment. Stating that distinction prevents descriptive safety observations from being mistaken for comparative evidence.

The record also illustrates why denominators and exposure context matter. It reports counts among 77 at risk and gives a mean exposure of 426 days, corresponding to 1.2 years. The mean helps characterize the observation period at group level, but does not replace participant-level follow-up information or an exposure-adjusted analysis. Without those details, counts should not be interpreted as rates over a uniform duration.

Finally, transparent gaps matter statistically. The registry includes a primary endpoint that combines several safety components, but a withdrawal count and a detailed analysis plan are not reported in the registry record. The study is marked terminated, with no reason stated. Recognizing what is present and what is absent allows readers to use the posted safety information without assigning it a causal or comparative meaning that the design and record do not support.

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 design limitation is the absence of a concurrent control group. A single-group, open-label record can describe events during trofinetide treatment but cannot establish how those events compare with outcomes under another treatment or without treatment. The study’s lack of masking also means the record does not describe blinded event assessment. Any effect of awareness on reporting or clinical decisions cannot be evaluated from the registry entries.

The registry summary gives counts for serious and other adverse events, but does not report detailed event-level information such as timing, duration, recurrence, clinical context, or causal attribution. It lists selected serious-event terms, but does not state whether that list is exhaustive or how terms were selected. The reported death count is not accompanied by cause, timing, or a relationship to treatment in the registry record for this analysis.

The primary endpoint includes treatment-emergent adverse events, serious adverse events, and withdrawals due to adverse events. A separate withdrawal result is not reported in the registry record. The mean exposure of 426 days, corresponding to 1.2 years, does not describe each participant’s follow-up, and no exposure-adjusted rates are reported in the registry record. Missing-data procedures and follow-up after withdrawal are not reported.

The registry reports 0 analyses, so inferential estimates, confidence intervals, and a detailed statistical analysis plan are not available in this record summary. The reason for the terminated status is also not reported in the registry record. These gaps limit assessment of precision, completeness, and the circumstances under which the study ended. They should be treated as unknown rather than filled with assumptions.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Open-Label Extension Study of Trofinetide for Rett Syndrome — NCT04776746.
• Registry record last updated 2024-09-27; status last verified 2024-09.
• Results first posted 2024-09-27.
• 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

NCT04776746 is a Phase 3, open-label extension study of continued trofinetide treatment for Rett syndrome. The registry describes a single-group design, no masking, and allocation as not applicable. Trofinetide was given as an oral solution, and enrollment was 77. The stated purpose was to investigate safety and tolerability in girls and women with Rett syndrome.

The primary outcome concerns treatment-emergent adverse events, serious adverse events, and withdrawals due to adverse events among all patients enrolled and treated. Mean study drug exposure was 426 days, corresponding to 1.2 years. The adverse-event summary reports 23 participants with serious adverse events among 77 at risk, 57 with other adverse events among 77 at risk, and 4 deaths. Selected serious-event terms and their reported percentages are listed in the registry.

The record gives a start date of 2020-11-08, a primary completion date of 2023-06-30, and a status of terminated. The reason for termination, a separate withdrawal count, and detailed statistical analysis methods are not reported in the registry record. As a single-group open-label study, the results describe recorded safety outcomes but do not provide a randomized comparison or establish causation.