A Retrospective Study of the Natural History of Patients With Severe Perinatal and Infantile Hypophosphatasia (HPP): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Retrospective Study of the Natural History of Patients With Severe Perinatal and Infantile Hypophosphatasia (HPP) (NCT01419028), a registered phase not stated study. The primary outcome is Survival.

2. Clinical Question

The study question is descriptive rather than a test of whether one treatment is better than another. Its stated aim is to characterize the natural history of patients with severe perinatal or infantile onset HPP. The primary outcome is overall survival, defined as the time from birth to death. A secondary outcome is invasive ventilator-free survival time.

Because the registry describes a retrospective observational study, the record does not establish a treatment contrast or a causal effect. It also does not describe a control group suitable for comparing outcomes between otherwise similar groups. The clinical question is therefore about the course of the condition in the patients represented in the record, not about comparative efficacy. The registry record does not report detailed eligibility criteria, participant characteristics, or the clinical setting in which the records were abstracted.

3. Trial Design

This is a retrospective, non-interventional epidemiologic study of patients with severe perinatal and infantile hypophosphatasia. Its purpose is to characterize natural history, not to assign treatment or compare randomized groups. The registry lists one retrospective observational group: patients with a confirmed diagnosis of perinatal or infantile onset HPP. Enrollment is listed as 48.

The study began in 2012-08, and primary completion is listed as 2013-06. Its status is completed. The primary outcome is survival, expressed as a median time in days with a 95% confidence interval. The outcome timeframe is retrospective data collected on or before the date of abstraction. Overall survival is defined as time from birth to death. Invasive ventilator-free survival time is listed as a secondary outcome, but its detailed definition and results are not reported in the registry record.

The record does not describe a randomized allocation process, a prospective treatment assignment, or a comparator group. It explicitly identifies the study as not a randomized comparison and notes that allocation is not stated. Consequently, the listed group should be understood as an observational cohort, not as one side of a treatment contrast.

The registry record does not report how patients were identified, the abstraction procedures, the exact dates covered by the retrospective records, or the criteria used to define severe disease. It also does not report a protocol or a sample-size justification for the study itself. Planning illustrations based on an observed effect are not the same as a prospective design justification, and they do not establish the study's original design or analysis plan.

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

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: Thirteen participants were alive at the time of data abstraction and were censored in the analysis

6. Primary Endpoint

The registry lists the primary outcome as Survival, measured over Retrospective data collected on or before the data of abstraction..

The primary endpoint is overall survival, defined as the time from birth to death. It is reported using a median time in days and a 95% confidence interval. This endpoint describes how long patients in the study cohort survived from the specified starting point. Survival outcomes are useful for natural-history research because they retain information about the timing of an event, rather than reducing the outcome to whether an event occurred by a single chosen time.

The median is the point in the estimated survival distribution at which half of the cohort is expected to have experienced the event and half to remain event-free, subject to the study's follow-up and estimation methods. A confidence interval communicates uncertainty around that estimate: a wider interval generally indicates less precision, while a narrower interval generally indicates greater precision. These are general statistical interpretations; the registry record does not report the median estimate, the interval limits, the number of deaths, or the estimation method used.

For a retrospective study, the time origin and event definition matter. The stated time origin is birth, and the event is death. The record describes the timeframe as retrospective data collected on or before the date of abstraction, but does not report the abstraction date or the completeness of follow-up. Those omissions limit what can be inferred about how much observation contributed to the survival estimate.

Invasive ventilator-free survival time is listed as a secondary outcome. The registry record does not report its definition, estimate, or uncertainty interval.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Time-to-event analysis concerns the time until a specified event, while allowing some participants' event times to be unknown because observation ends before the event occurs. Those participants contribute information up to their last known observation. This is called censoring in general statistical practice. The registry's primary outcome is time from birth to death, but it does not describe censoring, follow-up completeness, or the method used to handle participants whose deaths were not observed in the available records.

What does the median survival time describe?

The median survival time is a summary of the estimated time-to-event distribution. It marks the point at which the estimated proportion surviving reaches one half. Unlike a mean, the median does not require adding all event times and dividing by the number of participants. It is often interpretable when survival times are skewed or when some observations are censored. However, the estimate depends on the observed event and follow-up information. If the available data do not extend far enough for the estimated survival curve to reach one half, a median may not be estimable. The registry record does not state whether this occurred or report the median value.

How should a confidence interval be read?

A confidence interval expresses uncertainty around an estimate under the statistical procedure used. In general, a 95% confidence interval is generated by a method that would cover the target quantity in 95% of repeated samples under its assumptions. It is not a range containing 95% of individual survival times. Its width reflects precision as well as the amount and pattern of information in the data. The registry specifies a 95% confidence interval for the median, but does not report the interval limits or the method used to calculate it. Accordingly, its precision cannot be judged from the record.

What does a hazard ratio mean?

A hazard ratio compares event rates at a given time between groups, under the assumptions of the model used to estimate it. It is not the same as a ratio of median survival times, nor does it directly state the difference in the probability of an event over the full follow-up period. Hazard ratios are most commonly interpreted in a comparative analysis. This study is described as a retrospective observational natural-history study and not a randomized comparison. The registry record does not report a hazard ratio or a group contrast, so no such comparison can be interpreted for this study.

What is over-dispersion?

In general, over-dispersion occurs when the variability in data is greater than a statistical model assumes. If a model ignores it, standard errors may be too small and confidence intervals or tests may appear more certain than warranted. This concept is relevant to some count-data models, but the registry record does not identify a count model or report an analysis of over-dispersion. It should not be assumed to have been relevant to the primary survival analysis.

How do planning illustrations differ from results?

Sample-size calculations are planning tools that estimate how much information may be needed to detect a specified effect under stated assumptions. The registry's planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect set as a stated fraction of an observed effect. For time-to-event illustrations, the calculation concerns the total number of events. These assumptions describe an illustration, not necessarily the study's own design. The record does not report a protocol-based sample-size justification, and the study itself is not described as a randomized comparison. Such calculations are not observed power and do not replace the missing outcome estimates.

The record lists no analyses and does not describe the estimator, model, software, covariate adjustment, or sensitivity analyses. It also does not report the number of events or the pattern of follow-up. Those omissions prevent an independent assessment of model assumptions or reproducibility. General explanations of medians, confidence intervals, censoring, hazard ratios, and over-dispersion do not establish which methods were actually used in this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures: survival as the primary outcome and invasive ventilator-free survival time as a secondary outcome. It does not report a multiplicity strategy, such as a hierarchy of tests or an adjustment for testing more than one outcome. Because no analyses are listed, the record also does not show whether either outcome was tested statistically or whether any multiplicity procedure was applied. It would be inappropriate to assume that a particular strategy was used.

The registry record does not report how missing data were handled. For a retrospective time-to-event outcome, relevant details would include how the last known observation was established, how incomplete follow-up was treated, and whether the available records were considered sufficient to classify event status. The record does not give these details, the amount of missing information, or the number of participants with incomplete outcome data.

The record identifies a cohort of patients with confirmed perinatal or infantile onset HPP, but does not report further analysis-population definitions. It does not say whether all enrolled patients contributed to each outcome, whether any participants were excluded from an analysis, or how eligibility and outcome availability were reconciled. The listed enrollment of 48 should therefore not be treated as evidence that every participant contributed complete information to every analysis.

These reporting gaps matter because multiplicity, missingness, and the analysis population can affect how outcome estimates are interpreted. The registry record does not report enough detail to assess those aspects. No assumptions about imputation, exclusions, or outcome ascertainment should be substituted for the absent information.

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

The record describes a retrospective study intended to characterize the natural history of severe perinatal or infantile onset HPP. It specifies a cohort of patients with a confirmed diagnosis, an enrollment of 48, and overall survival from birth to death as the primary outcome. It also identifies invasive ventilator-free survival time as a secondary outcome. These details establish the broad descriptive question and the outcome framework.

The record does not report a numerical median survival estimate, its 95% confidence interval, or numerical results for the secondary outcome. It therefore does not show how long participants survived on average or at the median, how precise the estimate was, or how ventilator-free survival was distributed. The absence of these results is not evidence that an outcome was favorable or unfavorable; it means the relevant estimates are not reported in the registry record.

This study is not a randomized comparison, and the record does not describe a like-for-like control group. Its design does not support attributing differences in outcomes to a treatment. The natural-history aim is distinct from a test of intervention efficacy. No conclusion about a treatment's benefit, lack of benefit, or safety follows from the available registry information.

The enrollment count is not a substitute for information about event counts, follow-up duration, or completeness of records. Nor do the adverse-event fields provide a substitute for the primary survival result: the registry's adverse-event entry records zero in its listed categories, while the death count for that entry is not reported. The meaning of those fields for overall study follow-up is not explained.

In short, the registry record reports the study's broad purpose and design but leaves the central numerical results and important analysis details unreported. Interpretation should not go beyond those recorded details.

12. Why This Trial Matters Statistically

Natural-history studies can provide a descriptive account of disease outcomes when their cohort and outcome definitions are clearly specified. This record identifies severe perinatal or infantile onset HPP, a retrospective observational design, an enrollment of 48, and survival from birth to death as the primary endpoint. Those elements make the intended statistical question understandable even though the numerical result is not reported.

The record also illustrates why an endpoint definition is not the same as an endpoint result. A median survival time with a 95% confidence interval would convey both a central estimate and its uncertainty. Without the estimate and interval limits, readers cannot assess the duration represented by the cohort or how precisely it was measured. Event counts and follow-up information would further help assess the information supporting a time-to-event estimate, but these are not reported in the registry record.

The non-interventional design is important statistically. A natural-history cohort can describe outcomes in its participants, but it does not by itself establish what would have happened under a different intervention. The registry explicitly notes that this is not a randomized comparison and does not identify a like-for-like control group. That distinction helps prevent a descriptive study from being read as a treatment-effect analysis.

Finally, the record separates the stated study aim from the details needed to evaluate its analysis. It lists two outcome measures but no analyses, and it does not report how missing observations or analysis populations were handled. Recognizing those limits is part of interpreting registry evidence responsibly: the study question is visible, while the numerical findings and several methodological details are not.

13. 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 principal limitation for interpreting this study from the registry record is that the primary numerical result is absent. Although the endpoint is defined as survival from birth to death and is specified as a median in days with a 95% confidence interval, neither the estimate nor its interval limits are reported. The record also does not give the number of deaths, follow-up duration, censoring information, or the method used to calculate the estimate.

The retrospective design depends on existing records, but the registry does not describe how those records were identified, abstracted, or checked for completeness. It does not report the abstraction date, the dates covered by the records, or the handling of incomplete or missing information. These omissions prevent assessment of how consistently survival and ventilator-free survival were ascertained.

The record gives limited information about the participants beyond confirmed perinatal or infantile onset HPP and the listed enrollment of 48. More detailed eligibility criteria and characteristics are not reported. The definition of severe disease is not described. The secondary outcome is named, but its operational definition and result are not reported.

The study is not a randomized comparison, and no suitable comparator is described. The registry does not report an analysis plan, a study-specific sample-size justification, adjustment methods, or sensitivity analyses. It lists no analyses. These limitations make it impossible to assess the robustness of the numerical findings, which are themselves not reported.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: A Retrospective Study of the Natural History of Patients With Severe Perinatal and Infantile Hypophosphatasia (HPP) — NCT01419028.
• Registry record last updated 2019-04-01; status last verified 2019-03.
• Results first posted 2014-07-21.
• 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.

17. Record Summary

NCT01419028 is a completed retrospective, non-interventional epidemiologic study of the natural history of severe perinatal and infantile hypophosphatasia. The registry lists Alexion Pharmaceuticals, Inc. as sponsor and an enrollment of 48. The study began in 2012-08, with primary completion in 2013-06.

The listed group consists of patients with a confirmed diagnosis of perinatal or infantile onset HPP. Overall survival, defined as time from birth to death, is the primary outcome and is specified as a median time in days with a 95% confidence interval. Invasive ventilator-free survival time is a secondary outcome. The registry record does not report numerical outcome estimates, the confidence-interval limits, or analyses.

The study is not a randomized comparison, and allocation is not stated. The record does not report detailed methods for follow-up, missing data, or analysis populations. The registry lists zero in its serious and other adverse-event count fields for the retrospective observational group; the death count in that entry is not reported.