Phenylketonuria, Oxidative Stress, and BH4: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Phenylketonuria, Oxidative Stress, and BH4 (NCT01395394), a non-randomized phase 2 study. The primary outcome is Lipid Peroxidation.

2. Clinical Question

The study was designed to examine measures of oxidative stress and endothelial function in PKU. Its official title focuses on the ability of Kuvan to prevent meal-induced lipid peroxidation and endothelial dysfunction. The primary outcome is a continuous measure summarized as a mean with standard deviation, in umole/L. Measurements were scheduled every other hour during a six-hour study visit. The registry describes a single visit for responders and healthy controls, and baseline and post-therapy visits for non-responders.

The registry record says recruitment difficulties led to termination and that analysis was limited to preliminary data on 11 patients. TBARS results were available for only 3 BH4 responders. Numerical group results and an estimated treatment effect are not reported in the registry record, so the primary question cannot be answered from the posted results.

3. Trial Design

This was a Phase 2, non-randomized, unmasked, parallel study sponsored by Emory University. The registry lists an enrollment of 12 and identifies PKU as the condition under study. The study started in 2011-06, had a primary completion date of 2013-06, and is listed as terminated. The stated reason for termination was difficulty recruiting patients.

The design combined groups with different treatment histories and different visit schedules. BH4 responders were assessed at a single visit while taking their already prescribed BH4 with the meal. Healthy controls, matched to an enrolled PKU participant by age, gender, and body mass index class, attended one visit and did not receive BH4. BH4 non-responders completed a meal challenge without BH4 at their first visit, then took BH4 for two weeks before a second meal challenge with their final dose.

This structure does not create a randomized treatment comparison. Responder status, health status, and treatment exposure distinguish the groups, and the registry does not describe random assignment or masking. The non-responder group also has a repeated-measure structure, whereas responders and healthy controls have a single visit. These differences matter when interpreting group contrasts: they cannot be attributed solely to BH4 exposure on the basis of this design.

The registry describes assessment of markers every other hour during each six-hour visit and gives an estimated participation time of one month. It states that values would be assessed groupwise and that intrapersonal change would be assessed in non-responders. The actual statistical plan, including the approach to repeated measurements, is not reported in the registry record. Because the study ended after recruitment difficulties and the listed outcome data are preliminary, the design description should not be mistaken for evidence that the intended comparisons were completed or yielded conclusive results.

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.

Baseline Study Visit

Reasons for not completing this period:

Study Visit 2 (Non-responders Only)

Analysis population for the primary outcome, as defined in the registry: Study was terminated due to difficulty recruiting patients, thus analysis was limited to preliminary data on 11 patients only. TBARS was measured in 3 BH4 responders only - data were unavailable for 8 other participants (2 responders, 3 non-responders, and 3 controls) due to inadequate sample volume.

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.

6. Primary Endpoint

The registry lists the primary outcome as Lipid Peroxidation, measured over Lipid peroxidation will be measured every other hour for six hours at baseline (study visit 1) for all study groups.

The listed primary endpoint is lipid peroxidation, a continuous measure reported in umole/L and described using a mean and standard deviation. The registry says markers were measured every other hour during each six-hour study visit. Its stated timeframe identifies baseline measurement for all study groups, while the outcome description separately explains that responders and healthy controls had one visit and non-responders had a baseline visit and a visit after two weeks of Kuvan therapy.

Lipid peroxidation is used as a marker of oxidative stress. In general, a biochemical marker can help researchers quantify a biological process that is otherwise not directly represented by a clinical event. Measuring it around a meal challenge allows the study to examine whether the marker changes over the visit and whether patterns differ among the described groups. The registry’s official title frames the question around meal-induced lipid peroxidation and endothelial dysfunction, but the named primary outcome is lipid peroxidation.

The registry identifies TBARS as the measure for which data were available in only 3 BH4 responders. It says data were unavailable for 8 other participants because of inadequate sample volume, with the unavailable data spanning responders, non-responders, and controls. Numerical lipid-peroxidation values, variability estimates, and a treatment-effect estimate are not reported in the registry record. Thus the endpoint and its intended measurement schedule are described, but the posted record does not provide the numerical evidence needed to assess the size or precision of any observed change.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary outcome summarized by a mean and standard deviation. It also says the study would assess values groupwise and examine intrapersonal change in BH4 non-responders. These descriptions identify the intended summaries and comparisons, but the actual statistical analysis plan is not reported in the registry record. No analysis results are listed in the record.

What does a mean and standard deviation describe?

As a general statistical explanation, the mean gives a central summary of measured values, while the standard deviation describes how spread out individual values are around that mean. These summaries can help describe a continuous biomarker, but they do not by themselves show whether a difference between groups is compatible with random variation or how precisely the difference is estimated. That assessment generally requires an effect estimate with an uncertainty interval or an inferential test. Such estimates and tests are not reported for the primary endpoint in the registry record.

Why does the repeated-measure structure matter?

The registry describes repeated visits for BH4 non-responders: a baseline meal challenge without BH4 and a second challenge after two weeks of BH4 therapy. It also describes a single visit for responders and healthy controls. In general, repeated measurements from the same participant are related rather than independent. An analysis should account for that within-person relationship when estimating change or uncertainty. The statistical method used for this structure is not reported in the registry record, so it is not possible to determine how repeated observations were handled.

Measurements were scheduled every other hour during a six-hour visit. In general, measurements taken over time can be analyzed as separate time-specific summaries, as an overall trajectory, or using a model that accounts for correlation across time. These choices answer different questions and can produce different estimates. The registry does not report which approach was used, whether a particular time point was designated for comparison, or how multiple measurements within a visit were incorporated into an inferential analysis.

Why is non-random allocation important?

In general, random allocation helps balance measured and unmeasured participant characteristics across treatment groups, on average. This study was non-randomized, and its groups were defined by BH4 responder status or healthy-control status. Responders took already prescribed BH4, non-responders had a before-and-after sequence, and healthy controls did not receive BH4. Consequently, a group contrast would not isolate a treatment effect in the way a randomized comparison is intended to do. The registry record does not report an adjustment strategy that could address differences between these groups.

How should planning calculations be read?

Any sample-size illustration associated with the posted material is a planning exercise based on an observed effect, not a result from the study’s own design process. The stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. Such calculations estimate how many participants per arm might be needed under those assumptions. They are not observed power and do not demonstrate that the study had adequate power. The protocol’s sample-size justification is not reported in the registry record, and planning illustrations should not be treated as a substitute for the missing outcome estimates.

What does over-dispersion mean in general?

For a continuous outcome, variation may be greater than a chosen model expects. More generally, over-dispersion refers to observed variability exceeding the variability assumed by a statistical model. If a model understates variability, its uncertainty estimates can be too narrow. Appropriate modeling depends on the outcome distribution and design. The registry does not report a model for the primary outcome, so there is no basis to say whether over-dispersion was assessed or relevant to the sponsor’s analysis.

The registry lists no analyses. It does not report a statistical test, confidence interval, covariate-adjustment method, interim-analysis plan, or multiplicity procedure. Without these details and without numerical primary outcome results, independent reassessment of the efficacy analysis is not possible from the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry describes measurements at repeated time points during each six-hour meal-challenge visit, multiple study groups, and a before-and-after assessment for BH4 non-responders. It also identifies lipid peroxidation as the primary outcome and mentions endothelial function in the study purpose. When many outcomes, groups, or time points are examined, the chance of finding an apparently notable result by chance can increase. In general, a prespecified analysis plan can clarify which comparisons are primary and how multiplicity is handled.

A multiplicity procedure and a detailed hierarchy of outcomes or time-point comparisons are not reported in the registry record. The record lists zero analyses, and numerical inferential results for the primary endpoint are not reported. It is therefore not possible to determine whether any adjustment was planned or performed, or how many comparisons informed any result.

Missing outcome data are a central limitation. The registry says TBARS was measured in 3 BH4 responders only; data were unavailable for 8 other participants because of inadequate sample volume. It identifies those unavailable records as including 2 responders, 3 non-responders, and 3 controls. The registry does not report a missing-data method, an imputation approach, or a sensitivity analysis. It also does not describe whether missingness was assessed as related to participant characteristics or measured outcomes.

The record states that preliminary analysis was limited to 11 patients, but it does not describe a full analysis population, exclusions from specific analyses, or how participants with incomplete measurements were handled. The analysis populations and the statistical plan for missing observations are not reported in the registry record. These omissions mean that the available TBARS measurements should be interpreted as a partial dataset rather than as a complete account of the planned study assessments.

11. Safety Results

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

Other (non-serious) adverse events

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

The registry’s adverse-event figures list BH4 non-responders, healthy controls, and BH4 responders as the safety groups. The reported numbers at risk are 4, 3, and 5, respectively. Each group has 0 participants with a serious adverse event and 0 with another adverse event in the posted figures. These are reported event counts, not estimates of comparative risk.

The zero counts should not be interpreted as proof that adverse events cannot occur. The study was terminated because of difficulty recruiting patients, and the outcome data are described as preliminary. A small safety experience can fail to capture uncommon events or provide a precise estimate of event frequency. The registry does not report a comparison or uncertainty interval for the safety figures.

Death counts are not reported in the registry record. The adverse-event information should therefore be read as a narrow account of the counts recorded for the listed groups, not as a comprehensive safety assessment or a basis for comparing treatments. The non-randomized design and different group characteristics also limit direct comparisons across the groups.

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

This record documents a Phase 2 study intended to examine oxidative-stress and endothelial-function measures in people with PKU during meal challenges, with attention to BH4 exposure and response status. It specifies lipid peroxidation as the primary outcome and describes measurement during study visits. It also documents that recruitment difficulties led to termination and that only preliminary data on 11 patients were analyzed.

What the record does not provide is equally important. Numerical primary-outcome summaries, effect estimates, confidence intervals, and outcome p-values are not reported in the registry record. The available text therefore cannot show whether lipid peroxidation changed after BH4, whether responder and non-responder groups differed, or how uncertain any apparent pattern might be. The limitation to TBARS data from 3 responders, with data unavailable for 8 other participants, further constrains interpretation.

The design cannot establish a causal treatment effect from a direct randomized comparison. BH4 responders, non-responders, and healthy controls differ in status and exposure, and non-responders had repeated visits while the other groups had one visit. Even if descriptive group values were available, a contrast could reflect differences in group composition, treatment exposure, visit schedule, or other factors. The registry does not report an adjusted analysis that would resolve these concerns.

The record also does not establish that BH4 prevents meal-induced lipid peroxidation or endothelial dysfunction. The study title states the research question, not a result. The endpoint measurement and safety counts should be understood as components of a terminated, preliminary investigation. The available registry information supports conclusions about the study’s design and limitations, but not a conclusion that the intervention does or does not change the measured biological outcomes.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of how design and data availability shape what can be learned from a clinical investigation. Its question concerns biological measurements around a meal challenge, with different schedules for responders, non-responders, and healthy controls. Because allocation was non-randomized, those groups do not provide a clean randomized comparison of BH4 exposure. Recognizing that distinction prevents descriptive contrasts from being mistaken for causal effects.

The repeated assessment of non-responders also highlights the value of matching an analysis to the structure of the data. Measurements from the same person are generally related, and time-specific measurements within a visit may also be related. A suitable analysis would need to account for those dependencies. The registry describes the intended repeated assessments but does not report the statistical method used.

Missing biomarker data matter because the available TBARS measurements came from only 3 BH4 responders, while data for 8 other participants were unavailable because of inadequate sample volume. In general, missingness can reduce precision and can also affect how representative the observed measurements are. Without information about missing-data handling or sensitivity analyses, the direction and size of any resulting bias cannot be assessed.

Finally, the record distinguishes a planned research question from an established result. It reports termination due to recruitment difficulty and preliminary analysis, while providing no numerical primary-outcome estimates or inferential analysis. This makes the record a useful reminder that endpoint definitions and study aims alone do not answer an efficacy question. Transparent reporting of estimates, uncertainty, analysis populations, and missing-data methods is essential for readers to evaluate what a study’s results can 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.

Recruitment difficulty led to termination, and the registry says the analysis was limited to preliminary data on 11 patients. The registry lists enrollment of 12, but does not explain the relationship between the enrollment figure and the preliminary analysis population. The reason for that difference is not reported in the registry record.

TBARS data were available for only 3 BH4 responders. Data were unavailable for 8 other participants because of inadequate sample volume, including 2 responders, 3 non-responders, and 3 controls. This limits the completeness of the primary outcome information across the study groups. The registry does not report imputation, sensitivity analyses, or another method for addressing the unavailable measurements.

The study was non-randomized and unmasked. Responders and non-responders were classified by BH4 response, while healthy controls formed a separate group. Treatment exposure and visit schedules also differed: non-responders had a baseline and post-therapy visit, whereas responders and controls attended one visit. These features complicate group comparisons and prevent a straightforward causal interpretation.

The registry describes repeated measurements during six-hour visits but does not report how within-person or within-visit dependence was handled. The analysis plan, multiplicity approach, and detailed analysis populations are not reported in the registry record. It also provides no numerical primary endpoint estimates or confidence intervals, leaving the effect size and precision unknown. Death counts are not reported, and the listed zero adverse-event counts do not replace a complete safety assessment.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Phenylketonuria, Oxidative Stress, and BH4 — NCT01395394.
• Registry record last updated 2014-08-28; status last verified 2014-08.
• Results first posted 2014-08-28.
• 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

NCT01395394 is a Phase 2, non-randomized, unmasked, parallel study sponsored by Emory University, listed as terminated after recruitment difficulties. It examined meal-challenge measures related to oxidative stress and endothelial function in PKU, with BH4 responders, BH4 non-responders, and healthy controls. The primary outcome was lipid peroxidation, measured in umole/L and described as a mean with standard deviation.

The registry describes a baseline and post-therapy meal challenge for non-responders and single visits for responders and healthy controls. Preliminary analysis was limited to 11 patients. TBARS data were available for 3 responders; data for 8 other participants were unavailable because of inadequate sample volume. Numerical primary outcome results and statistical analyses are not reported in the registry record. The posted safety figures list zero serious and zero other adverse events in each group; death counts are not reported.