Safety and Therapeutic Effects of Sapropterin Dihydrochloride on Neuropsychiatric Symptoms in Phenylketonuria (PKU) Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Therapeutic Effects of Sapropterin Dihydrochloride on Neuropsychiatric Symptoms in Phenylketonuria (PKU) Patients (NCT01114737), a randomized phase 3 study. The primary outcome is Change in Attention-Deficit Hyperactivity Disorder Rating Scale-IV (ADHD-RS) / Adult ADHD Self-Report Scale (ASRS) Total Score From Baseline to Week 13.

2. Clinical Question

3. Trial Design

This was a phase 3, randomized, quadruple-masked, parallel-group study, with placebo as the comparator. The registry describes the study as double-blind and placebo-controlled in its title and summary. It lists an enrollment of 206 and a completed status. The start is recorded as 2010-08 and primary completion as 2013-03.

The primary outcome is change in ADHD-RS / ASRS total score from baseline to Week 13. Its description specifies participants with ADHD symptoms at screening who had a blood Phe level reduction after treatment with 6R-BH4. The posted arm results likewise refer to responders with ADHD symptoms, with 19 participants in each arm. These subgroup counts are not the total enrollment, and the record does not describe the full analysis population in the primary result.

The randomized treatment period safety groups list 108 participants at risk in the placebo group and 98 in the 6R-BH4 group. The record also includes open-label treatment period groups and a 6R-BH4 treatment period group. These additional periods have their own safety counts; they are not interchangeable with the randomized comparison for the primary endpoint.

The study includes 19 outcome measures and 19 analyses in the registry record. It lists secondary outcomes involving anxiety, depression, clinical global severity, executive function, ADHD symptoms, and changes over later study intervals. The record does not report the details of random-sequence generation, allocation concealment, a full schedule of study visits, or the operational procedures used to maintain masking. It also does not report a protocol-level account of the analysis population or all analysis procedures.

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.

Randomized Treatment Period

Reasons for not completing this period:

Open-Label Treatment Period

Reasons for not completing this period:

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 Change in Attention-Deficit Hyperactivity Disorder Rating Scale-IV (ADHD-RS) / Adult ADHD Self-Report Scale (ASRS) Total Score From Baseline to Week 13, measured over Baseline to Week 13.

The primary endpoint is change from baseline to Week 13 in the combined ADHD-RS / ASRS total score. These rating measures assess ADHD symptoms; the registry states that the total score ranges from 0 to 54 and that higher values correspond to worse symptom severity. The endpoint therefore expresses change on a symptom-rating scale rather than a clinical event count or a direct measure of function.

The registry describes the endpoint as an assessment of ADHD symptoms among PKU subjects who had symptoms at screening and had a blood Phe level reduction after treatment with 6R-BH4. The posted primary results are correspondingly limited to participants labelled responders with ADHD symptoms. The least-squares mean change is -4.9 in the placebo arm and -9.1 in the 6R-BH4 arm. A negative change indicates a lower follow-up score than baseline; given the scale direction, that represents a decrease in measured symptom severity within that arm. It does not by itself establish a between-arm treatment effect.

Using a standardized rating scale gives a defined outcome for comparing changes across randomized groups. The registry record does not report a threshold for a clinically important change, nor does it describe how the combined ADHD-RS / ASRS score was constructed or which version was used for each participant. The endpoint is therefore interpretable as score change, while the clinical importance of a particular difference is not established by the posted description alone.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous: each participant has a score, and the analysis concerns average score change. A least-squares mean is a model-based group mean. Unlike a simple arithmetic mean, it can account for covariates included in the fitted model. The registry reports least-squares means for the two arms and identifies ANCOVA as the method for the between-arm analysis. The covariates and full model specification are not reported in the registry record, so the adjustment cannot be reconstructed from the description.

What does the confidence interval describe?

A confidence interval expresses uncertainty around an estimated effect. Here, the sponsor-reported mean difference is -4.2, with a 95% confidence interval from -8.9 to 0.6. The interval includes zero, which is the value corresponding to no difference on the scale of the reported contrast. The interval therefore does not rule out no between-arm difference under the model. It also includes values on either side of zero, so the direction is not estimated with high precision. A confidence interval does not assign a probability to the specific effect being inside that particular interval, and it does not capture every possible source of bias or uncertainty.

How should the p-value be read?

The reported p-value is 0.085. In general, a p-value describes how unusual data at least as incompatible with a null hypothesis as the observed data would be if that null hypothesis and the model assumptions held. It is not the probability that the null hypothesis is true, and it is not a measure of clinical importance. The trial's posted planning assumptions refer to a two-sided significance level of 0.05; compared with that reference, the reported p-value does not meet the stated threshold. The confidence interval and p-value are consistent in not establishing a between-arm difference at that level.

Why distinguish arm changes from the contrast?

The arm-level least-squares means are -4.9 for placebo and -9.1 for 6R-BH4. Those values describe change within each arm. The ANCOVA result is a mean difference in final values. Because it is a model-based between-group comparison and the registry does not give the model details, it should not be reconstructed by subtracting the arm-level estimates. The adjusted comparison is the relevant reported inferential result.

What does the subgroup definition change?

The primary result concerns responders with ADHD symptoms, not an undifferentiated group of all enrolled participants. Each arm has 19 participants in this result. Restricting a result to a defined subgroup can be appropriate when it matches the research question, but it limits the population to which the estimate directly applies. The registry record does not describe how responder status was determined beyond the endpoint description's reference to blood Phe level reduction after treatment, nor does it provide the complete analysis-population rules.

What does a planning illustration mean?

Sample-size illustrations based on an observed effect are planning exercises: they describe participant counts under stated assumptions for a future design. The record's planning assumptions specify a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects defined as fractions of the observed effect. Such illustrations are not observed power and do not explain the trial's original design. The protocol's sample-size justification is not reported in the registry record. No planning count should be treated as an achieved property of the trial or as evidence that the primary analysis had a particular probability of detecting an effect.

Finally, an ANCOVA estimate depends on the analysis model and the data included. General statistical reasoning recognizes that missing outcome data, influential observations, model assumptions, and choices about adjustment can affect precision or interpretation. The registry record does not report enough detail to assess those issues fully for this endpoint. The posted interval and p-value should therefore be read as results of the sponsor-reported analysis, not as a complete account of every possible analysis.

10. Analyses Reported by the Sponsor

The registry reports the sponsor's primary comparison as an ANCOVA estimate: a mean difference in final values of -4.2, with a 95% confidence interval from -8.9 to 0.6 and p = 0.085. The corresponding arm-level least-squares mean changes are -4.9 for placebo and -9.1 for 6R-BH4. The arm-level values are not a substitute for the adjusted between-arm analysis, which is the sponsor's reported inferential result.

No separate recalculated contrast is reported in the registry record. The registry does not provide the participant-level data or enough model detail to reproduce the ANCOVA estimate independently. Accordingly, there is no recalculated result to set against the sponsor's estimate. The sponsor's own analysis is the result to interpret: its confidence interval includes zero, and its p-value is 0.085. This does not establish a between-arm difference at the 0.05 level referenced in the planning assumptions.

The sample-size illustrations associated with observed effects are planning exercises, not observed power and not evidence about the trial's original design. The registry record does not report the original sample-size justification or provide further analysis specifications that would support an independent reconstruction.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 19 outcome measures and 19 analyses, with 17 secondary outcomes posted. The primary outcome is change in ADHD-RS / ASRS total score from baseline to Week 13. Listed secondary outcomes include anxiety, depression, clinical global severity, executive function, and later-period rating-scale changes. Considering multiple outcomes can increase the chance of observing an apparently notable result by chance if no adjustment is made. Whether and how multiplicity was controlled for is not reported in the registry record. The record also does not state a hierarchy of endpoints or identify which secondary comparisons were confirmatory.

The record does not explain why 17 secondary outcomes are posted when 19 outcome measures and analyses are listed. It does not report whether unposted outcomes were not collected, not analyzed, or omitted for another reason. No assumptions about those possibilities can be made from the registry entry alone.

Missing-data handling is not reported in the registry record for the primary endpoint. The record does not specify how participants without a Week 13 score were handled, whether imputation was used, or whether sensitivity analyses were conducted. The posted primary outcome group contains 19 participants per arm, but the registry does not describe how those participants relate to all randomized participants or provide the full flow into the endpoint analysis. It is therefore not possible to assess from this information alone whether missing outcomes could have influenced the estimate.

The analysis population and its formal definition are also not reported in the registry record. The endpoint description identifies subjects with ADHD symptoms at screening who had a blood Phe level reduction after treatment; the result groups are labelled responders with ADHD symptoms. Details such as the operational responder threshold, handling of deviations from assigned treatment, and whether the analysis followed randomized assignment are not specified. The record identifies ANCOVA but does not report covariates or a complete statistical analysis plan. These omissions limit assessment of multiplicity, missingness, and the exact population represented by the estimate.

12. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: animal bite (1.0%), petit mal epilepsy (1.0%), necrotising fasciitis (0.9%), concussion (0.9%), amino acid level increased (0.9%).

During the randomized treatment period, the registry records 3 participants with serious adverse events among 108 at risk in the placebo group, and 0 among 98 at risk in the 6R-BH4 group. The figures are counts of participants affected as recorded in the safety results. The registry also lists other adverse events affecting 80 participants in the placebo group and 79 in the 6R-BH4 group, with the same respective at-risk counts of 108 and 98.

These counts describe the posted safety groups and period; they are not the primary ADHD endpoint results. The registry also reports safety results for open-label and 6R-BH4 treatment periods. Those groups have different labels and participant counts, so they should not be merged with the randomized-period comparison without further study details. The record does not provide an explanation of overlap between treatment-period groups.

The listed serious-event terms include Animal bite and Petit mal epilepsy at 1.0% each, and Necrotising fasciitis, Concussion, and Amino acid level increased at 0.9% each. The record's serious-event listing does not provide further context for these terms. Death counts are not reported in the registry record. Small event counts and the absence of additional detail limit what can be concluded from these descriptive figures; they do not by themselves establish comparative safety.

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

The posted primary result describes score changes in participants with ADHD symptoms who met the endpoint's responder description. The 6R-BH4 group had a least-squares mean change of -9.1 and the placebo group -4.9. The sponsor-reported adjusted comparison was -4.2, with a 95% confidence interval from -8.9 to 0.6 and p = 0.085. Since the scale runs from 0 to 54 and higher scores indicate worse severity, negative within-arm changes indicate lower measured scores. The adjusted comparison remains uncertain because its interval includes zero.

The result does not establish that the treatment caused a reduction in ADHD symptoms relative to placebo. It also does not show that the groups had identical outcomes or that a clinically important effect is impossible. No threshold for clinically important score change is reported in the registry record, and the confidence interval covers a range of possible differences. The p-value is not a measure of the probability that the treatment works, nor does it quantify the size or importance of an effect.

The primary results apply directly to the responder subgroup represented by 19 participants per arm, not automatically to all 206 enrolled participants. The endpoint description conditions on symptoms at screening and blood Phe level reduction after treatment. Without a complete account of the subgroup definition and analysis population, the generalizability of the estimate is limited.

The safety figures are descriptive counts by treatment period. They do not provide a complete comparative safety assessment, and the different randomized and open-label groups should be kept distinct. Neither the efficacy estimate nor the safety counts, read in isolation, answer every question about the intervention. They describe specific posted outcomes in this study, with uncertainty and reporting limitations that matter to interpretation.

14. Why This Trial Matters Statistically

This trial is statistically informative because its primary outcome is a defined continuous symptom score and the registry reports both arm-level changes and an adjusted between-arm comparison. That distinction illustrates why a difference in observed changes within each arm is not necessarily the same quantity as a model-based treatment contrast. The ANCOVA estimate, its confidence interval, and its p-value provide the relevant summary for the reported comparison.

The result also illustrates the value of reading precision alongside a point estimate. The estimate of -4.2 suggests a direction, while the 95% confidence interval from -8.9 to 0.6 includes zero. The evidence therefore does not resolve whether the groups differed at the 0.05 level used in the trial's planning assumptions. This is different from demonstrating equivalence or showing that an effect is absent.

Subgroup definition is another important statistical issue. The reported population consists of responders with ADHD symptoms, with 19 participants in each arm. The estimate is consequently narrower in scope than a result for all randomized participants. Readers need to distinguish the trial's overall enrollment from the population included in a particular endpoint result.

Finally, the registry includes multiple outcomes and analyses but does not report a multiplicity plan, missing-data procedures, or a full analysis specification. These are not minor technicalities: they affect how confidently readers can interpret an isolated endpoint and judge the robustness of a result. The record offers useful estimates, but its limits on population, precision, and analysis detail are essential parts of their statistical meaning.

15. 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 primary result is reported for a restricted subgroup: responders with ADHD symptoms. The endpoint description identifies subjects with ADHD symptoms at screening and a blood Phe level reduction after treatment, but the registry record does not state the operational responder threshold or provide a complete definition of the analysis population. The posted count of 19 participants per arm is much narrower than the overall enrollment of 206, and the record does not provide a participant flow explaining how that subgroup was formed.

The primary estimate is imprecise in the sense that its 95% confidence interval extends from -8.9 to 0.6 and includes zero. The registry does not report a clinically important difference threshold, so the practical importance of values across that interval cannot be determined from the score results alone. The model details are also incomplete: ANCOVA is named, but the covariates, missing-data approach, and full analysis plan are not reported in the registry record.

There are 19 outcome measures and analyses listed, while 17 secondary outcomes are posted. The reason for this difference is not reported. A multiplicity strategy and any endpoint hierarchy are also not reported, so the role of secondary analyses in confirmatory inference is unclear. Missing-data handling and sensitivity analyses are not described for the primary endpoint.

Safety results cover multiple treatment periods, including randomized and open-label periods. The record does not explain how participants overlap across these groups, and deaths are not reported in the registry record. Consequently, the safety counts should be interpreted only within their labelled periods and not treated as a complete comparative safety account. The registry does not report the original sample-size justification, interim analyses, or other protocol details needed to assess the trial's design and analysis more fully.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Safety and Therapeutic Effects of Sapropterin Dihydrochloride on Neuropsychiatric Symptoms in Phenylketonuria (PKU) Patients — NCT01114737.
• Registry record last updated 2016-02-01; status last verified 2015-12.
• Results first posted 2016-02-01.
• 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.

19. Record Summary

NCT01114737 is a completed phase 3, randomized, quadruple-masked, parallel-group study of sapropterin dihydrochloride and placebo in phenylketonuria. The registry lists enrollment of 206, a start of 2010-08, and primary completion in 2013-03. Its primary outcome is change in ADHD-RS / ASRS total score from baseline to Week 13 among subjects described as having ADHD symptoms and a blood Phe level reduction after treatment.

Among the posted responder subgroup, the least-squares mean changes were -4.9 for placebo and -9.1 for 6R-BH4. The reported ANCOVA mean difference was -4.2, with a 95% confidence interval from -8.9 to 0.6 and p = 0.085. The interval includes zero, leaving uncertainty about the between-arm difference. The registry does not report the full analysis specification, missing-data procedures, multiplicity plan, or original sample-size justification.