Long-term Outcome of N-Carbamylglutamate Treatment in Propionic Acidemia and Methylmalonic Acidemia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Long-term Outcome of N-Carbamylglutamate Treatment in Propionic Acidemia and Methylmalonic Acidemia (NCT01597440), a randomized phase 2 study. The primary outcome is Neurodevelopment.

2. Clinical Question

The study addressed a question about long-term outcomes in two metabolic disorders associated with hyperammonemia. Its stated aim also included whether treatment could restore urine ammonia levels to normal levels. However, urine ammonia is not identified in the posted primary outcome description, and a result for it is not reported in the registry record. The record therefore documents the question and intended measures, not an answer to the treatment question.

3. Trial Design

The registry classifies this as a phase 2, randomized, quadruple-masked, parallel-arm study. It lists N-carbamylglutamate and standard of care as the active intervention and placebo with standard-of-care therapy as the comparator. A parallel design assigns participants to a regimen intended to be followed as a group-specific treatment, rather than having each participant cross between regimens. Random allocation is intended to reduce systematic differences between treatment groups, while masking is intended to limit the influence of treatment knowledge on care or assessment.

The record does not specify which groups of people were masked, how masking was maintained, or how allocation was generated. It also does not report treatment dose, treatment duration, eligibility criteria, recruitment locations, or the reason for termination. These details should not be inferred from the design labels. The study is marked terminated, and the record states that it closed prematurely.

Enrollment was 1. The record does not report the number assigned to each arm, and it identifies no analysis population. This makes the planned randomized comparison distinct from what can be learned from the posted results: a randomized design describes the intended method of assigning treatment, but it cannot yield a meaningful group comparison when there are no reported analyzed groups and outcome results.

The registry lists a start date of 2012-09 and a primary completion date of 2015-02. The planned primary outcome timeframe was 30 months. These record dates and the intended timeframe do not establish how long any participant was followed; actual follow-up duration is not reported in the registry record. A sample-size justification and detailed statistical analysis plan are also not reported in the registry record.

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

Analysis population for the primary outcome, as defined in the registry: The study was closed prematurely. There is no analysis population.

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: One participant, infant under 1 month old, with organic acidemia.

6. Primary Endpoint

The registry lists the primary outcome as Neurodevelopment, measured over 30 months.

The primary outcome is named Neurodevelopment. Its description combines scores from the Bayley III Cognitive Composite and Motor Composite with the Functional Status Scale. It also includes safety assessment through adverse events and laboratory blood tests. The planned assessment timeframe is 30 months.

These measures address different aspects of the study question. Cognitive and motor composite scores are intended to assess developmental functioning, while a functional status measure provides another way to characterize a participant’s level of function. Adverse-event reports and laboratory tests address safety rather than developmental performance. Considering the measures together can provide a broader description of outcomes than a single score, but they should not be treated as interchangeable measures of one underlying result.

For a treatment comparison, the registry would need to report how each measure was summarized, the number of participants contributing data, and results by treatment group. The record does not provide endpoint values, a summary statistic, an estimate of the difference between groups, or an uncertainty interval. It also does not specify how the listed developmental measures would be combined or interpreted as a single primary endpoint. The registry record states that the study closed prematurely and that there is no analysis population. Consequently, the endpoint description indicates what the study intended to assess; it does not report an observed neurodevelopmental result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

In general, randomization assigns participants to treatment groups using a chance-based process. When implemented as intended in a sufficiently informative study, it can reduce systematic differences between groups at the start of treatment. This supports interpreting an observed difference as an effect of the assigned regimens, subject to adherence, missing outcomes, and other design and analysis considerations. Randomization does not ensure that groups will be balanced in every characteristic, especially when enrollment is very small. In this record, the trial is classified as randomized, but the allocation method and the number assigned to each arm are not reported in the registry record. There are no analyzed groups to compare.

What does masking mean?

Quadruple masking indicates that the registry categorized the study as masked, but the record does not identify which roles were masked or describe the masking procedures. In general, masking can reduce the risk that knowledge of treatment assignment influences participant reporting, clinical care, outcome assessment, or data handling. It cannot prevent every source of bias, and the label alone does not demonstrate that masking was maintained. Because no outcomes were analyzed, there is no result whose susceptibility to unmasking can be evaluated.

What can an endpoint description establish?

An endpoint defines what a study intends to measure and when. The primary endpoint is neurodevelopment, described through Bayley III cognitive and motor composite measures and the Functional Status Scale, together with safety assessment through adverse events and laboratory blood tests. Its stated timeframe is 30 months. In general, a clear endpoint definition supports consistent measurement and interpretation. The registry description does not state how these separate measures were to be summarized, whether one was designated as the main component, or how results across them would be handled. It reports no participant-level or group-level endpoint values.

Why do estimates and uncertainty matter?

A treatment comparison is usually expressed through an estimate of the difference between groups, accompanied by a measure of uncertainty such as a confidence interval. The estimate describes the observed contrast under the chosen analysis; the interval communicates how imprecisely it is estimated. A p-value, when used, assesses compatibility of data with a specified null hypothesis under a statistical model. These quantities answer different questions and require observed data, a defined comparison, and an analysis population. None is reported for the primary outcome in this registry record. It would be inappropriate to invent an estimate or infer one from the study design or the adverse-event counts.

With sparse data, any estimate that could be calculated would generally be highly uncertain, and standard methods may rely on assumptions that are difficult to assess. The record’s enrollment of 1 and lack of an analysis population make that concern especially important. Here, the issue is not merely a wide reported interval: no comparative outcome estimate or interval is posted. This is a lack of a result, not an imprecise estimate that can be interpreted on its own.

What is over-dispersion, in general?

For count outcomes, some statistical models assume that variation follows a particular distribution. Over-dispersion means that observed variability exceeds what the model assumes. If it is ignored, standard errors can be too small and intervals or tests can appear more conclusive than the data warrant. This is a general statistical issue; the registry record does not report a count-outcome model, an over-dispersion assessment, or any fitted analysis for this study. It is not possible to say whether such a method was considered.

How should planning illustrations be read?

The registry describes planning assumptions using a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect defined as a stated fraction of an observed effect. These are assumptions for a planning illustration, not a report of the trial’s actual design rationale. The record does not report a sample-size justification for the trial or the observed effect used for the illustration. Any participant counts displayed as planning values would be hypothetical requirements under those assumptions, not actual enrollment, an observed treatment result, or observed power. Planning values cannot substitute for an outcome analysis.

A sample-size justification ordinarily links a target effect, variability assumptions, a type I error rate, desired power, and the planned analysis to a recruitment target. Because the trial’s own justification is not reported in the registry record, its intended detectable effect and rationale for the planned enrollment cannot be evaluated. The planning assumptions described in the record do not establish that the trial was designed with a particular clinical threshold or that it achieved a stated power.

What does the registry say about analyses?

The registry reports zero analyses and says there is no analysis population because the study closed prematurely. It does not report a statistical model, adjustment variables, handling of repeated measurements, missing-data method, or analysis set. These are not details that can be reconstructed from the randomized, masked design. In general, a prespecified analysis plan helps guard against selecting analyses after results are known, but the presence or content of such a plan is not reported in the registry record. Statistical interpretation must therefore remain limited to the recorded design, endpoint definitions, and sparse adverse-event counts.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome description includes several components: the Bayley III Cognitive Composite, the Bayley III Motor Composite, the Functional Status Scale, adverse events, and laboratory blood tests. The record does not report how these measures were prioritized for statistical testing, whether one measure was intended to carry the main inference, or how multiple outcomes or time points would be handled. This matters because testing multiple outcomes can increase the chance of finding an apparently notable result by chance. In general, a prespecified approach to multiplicity can control that risk, but no such approach is reported in the registry record.

The registry also lists adverse events as a secondary outcome. It does not report a detailed analysis plan for this outcome, including whether event counts, participant counts, or event rates were intended as the main summary. The figures posted are sparse and do not provide a treatment comparison with a usable placebo denominator. No correction for multiple comparisons or hierarchy among outcomes is reported.

Missing-data handling cannot be assessed. The record states that the study closed prematurely and that there is no analysis population, but it does not give a participant flow, reasons for missing outcome measurements, or the extent of missingness for any measure. It does not specify whether an intention-to-treat, per-protocol, or other analysis set was planned or used. These concepts describe possible analytic approaches in general; none can be attributed to this study from the registry record.

Because there is no analysis population and no outcome analysis, it is not possible to evaluate the consequences of missing data, multiplicity, or analysis-set choices. These are unresolved reporting gaps, not evidence that a particular method was or was not used outside what the registry record states.

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 5% reporting threshold.

Most frequent non-serious adverse event terms

The posted serious adverse-event figures list 1 participant at risk in the Carbaglu group and 0 affected. The placebo group lists 0 participants at risk and 0 affected. The other-adverse-event figures list 1 at risk and 1 affected in the Carbaglu group, and 0 at risk and 0 affected in the placebo group. These counts should be read as the registry’s reported group entries, not as a reliable comparison of safety between regimens.

A group with zero participants listed as at risk has no denominator from which to estimate an event frequency. The apparent zero in the placebo group therefore does not establish an absence of events among an informative group of participants. Likewise, the Carbaglu counts are too limited to characterize the range or frequency of events. The registry lists no serious adverse event terms, and death counts are not reported as numeric values. A blank or unreported death count should not be interpreted as zero deaths.

In general, safety interpretation depends on the number of people observed, the observation period, consistent event definitions, and the severity and timing of events. Those details are not reported sufficiently to support a comparative safety assessment. The counts are descriptive registry entries, not evidence that either regimen is safer or less safe.

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

The record documents a randomized, quadruple-masked phase 2 study intended to compare N-carbamylglutamate plus standard of care with placebo plus standard of care in propionic acidemia and methylmalonic acidemia. It identifies neurodevelopment and safety outcomes and gives a planned primary outcome timeframe of 30 months. It also records that the study was terminated, closed prematurely, and enrolled 1 participant.

What it does not provide is a comparative outcome result. There is no analysis population, no primary outcome summary, no estimate of a difference between groups, and no uncertainty interval or test. Consequently, the posted information cannot show whether outcomes favored one regimen, were similar, or varied substantially. These possibilities are not distinguishable without outcome analyses.

The absence of an analysis is not a finding of no effect. Nor does the planned randomized design establish that treatment had a beneficial or harmful effect. Design features describe how a study was intended to reduce bias; they do not replace the outcome data needed to estimate effects. The sparse adverse-event counts also cannot establish comparative safety, particularly because no placebo participants are listed as at risk.

General clinical and statistical interpretation requires attention to the measured outcomes, the number of participants contributing data, and the uncertainty around any treatment contrast. Those elements are not available for the primary outcome in the registry record. The result should therefore be understood as an incomplete record of an intended clinical investigation, not as evidence for or against either treatment strategy.

13. Why This Trial Matters Statistically

This trial matters statistically because it illustrates the distinction between a planned randomized comparison and an analyzable treatment comparison. Randomization and masking are important design features, but they can support causal interpretation only when the study generates and reports adequate outcome data. Here, the record reports enrollment of 1, premature closure, and no analysis population. The intended design cannot compensate for those limitations.

The case also demonstrates why a trial’s endpoint must be considered alongside its reported results. The registry describes several developmental and safety measures, but gives no analyzed outcome values. A detailed endpoint description can clarify what investigators intended to learn, yet it cannot establish what happened to participants or how outcomes differed between groups.

Safety counts likewise require denominators and context. A zero count in a group with zero participants at risk is not an informative estimate of risk. Small descriptive counts should not be converted into comparative claims, especially without follow-up details or a defined analysis.

Finally, planning illustrations and trial results answer different questions. Planning assumptions describe what a hypothetical study might require under stated conditions. They do not show that those conditions were met, establish a trial’s own sample-size rationale, or create evidence when no outcome analysis is reported. Keeping these distinctions clear prevents design labels, sparse counts, or hypothetical planning values from being mistaken for an observed treatment effect.

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 most consequential limitation is the lack of an analysis population and outcome analyses after premature study closure. Enrollment was 1, and the record does not report allocation counts or outcome results by arm. The randomized comparison therefore cannot be evaluated. The reason for termination is not reported in the registry record, so the circumstances of early closure cannot be characterized.

Important design details are also missing. The record does not describe the allocation sequence, which roles were masked, the specific treatment regimen, adherence, eligibility criteria, or actual follow-up. Although the planned timeframe is 30 months, the duration of observation actually achieved is not reported. A statistical analysis plan, multiplicity strategy, and missing-data approach are not reported in the registry record.

The primary outcome encompasses several distinct measures, but the record does not explain how they were to be summarized or how their results would support a primary conclusion. No laboratory results or urine ammonia results are reported, despite the stated aims and safety description. The reason these outcomes are absent cannot be inferred.

Safety information is limited to very sparse counts. The placebo group has no participants listed as at risk for either serious or other adverse events, and the death entries are not numeric. The posted counts cannot support a comparative safety assessment or a conclusion about uncommon events. Taken together, these limitations mean that the registry record describes an intended study and some adverse-event entries, but not an estimable treatment effect.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Long-term Outcome of N-Carbamylglutamate Treatment in Propionic Acidemia and Methylmalonic Acidemia — NCT01597440.
• Registry record last updated 2017-04-26; status last verified 2017-03.
• Results first posted 2017-04-26.
• 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

NCT01597440 is a phase 2 randomized, quadruple-masked, parallel study of N-carbamylglutamate plus standard of care versus placebo plus standard-of-care therapy for propionic acidemia and methylmalonic acidemia. Its primary outcome is neurodevelopment, measured using Bayley III cognitive and motor composites and the Functional Status Scale, alongside safety assessments. The planned timeframe was 30 months.

The record lists enrollment of 1, a start date of 2012-09, and a primary completion date of 2015-02. The study is marked terminated and is described as having closed prematurely. The record reports no analysis population and zero analyses. It contains sparse adverse-event counts but no comparative outcome estimate. The reason for termination and the trial’s own sample-size justification are not reported in the registry record.