A Gene Therapy Study for Homozygous Familial Hypercholesterolemia (HoFH): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Gene Therapy Study for Homozygous Familial Hypercholesterolemia (HoFH) (NCT02651675), a non-randomized phase 1, phase 2 study. The primary outcome is Number of Participants With IP (Investigational Product) Related Adverse Events.

2. Clinical Question

3. Trial Design

This was a Phase 1 and Phase 2 study of AAV8-mediated LDLR gene replacement for HoFH. The registry describes it as a first-in-human investigation intended to examine safety and preliminary effectiveness in adults. It lists a start date of 2016-03, primary completion on 2020-11-27, and a terminated status. Enrollment was 9.

The design was sequential and non-randomized, with no masking. The registry lists three cohorts: Cohort 1 at 2.5E12 genome copies/kg, Cohort 2 at 7.5E12 GC/kg, and Cohort 2 Expansion at 7.5E12 GC/kg. Each adverse-event group lists 3 participants at risk. The record says a Data Safety Monitoring Board approved expansion of Dose 2, and that 3 additional subjects enrolled and received prophylactic corticosteroids. It does not report the protocol rationale for the cohort sequence, the basis for the expansion decision, or how comparisons between cohorts were intended to be interpreted.

Because assignment was not randomized and there is no concurrent control group listed, the cohorts should not be read as equivalent arms in a controlled treatment comparison. They describe successive groups in a study rather than treatment groups balanced by random allocation. The record does not report a statistical analysis plan explaining whether dose comparisons were planned, how confounding was to be addressed, or whether any analyses were adjusted. The study status is terminated; the reason for termination is 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

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 Number of Participants With IP (Investigational Product) Related Adverse Events, measured over Up to 24 weeks.

The primary endpoint is the number of participants with investigational-product-related adverse events, with a timeframe of up to 24 weeks. The registry describes safety assessment through physical examinations, clinical laboratory parameters, and adverse-event reporting. As a participant count, the endpoint is a binary outcome at the individual level: a participant is counted according to whether an event meeting the endpoint definition occurred. The endpoint does not measure how often events occurred within a participant or how severe every event was.

Safety endpoints are used in early clinical studies to characterize adverse events observed after an intervention and to guide continued evaluation. Counts can show how many participants were affected, but the meaning depends on the endpoint definition, the observation period, and the completeness of event reporting. Attribution to the investigational product is also important: an event occurring during a study is not automatically an investigational-product-related event.

The registry lists this endpoint but does not report its result. The posted serious and other adverse-event counts do not by themselves establish which events were considered investigational-product-related. They should therefore not be substituted for the primary endpoint. The registry record also does not report event-level details, severity grading, or the assessment process used to determine relatedness.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count represent?

A count endpoint records the number of participants who meet a specified event definition. For an event outcome, the count is informative only when read alongside the number of participants observed and the definition and timeframe used. Here, the primary endpoint is the number of participants with investigational-product-related adverse events up to 24 weeks. The registry names physical examinations, clinical laboratory parameters, and adverse-event reporting as assessment approaches, but it does not report the primary endpoint result.

Counts are descriptive. They do not, on their own, estimate how likely an event would be in a broader population, nor do they distinguish treatment-related events from events that occurred during follow-up but were judged unrelated. A participant count also differs from an event count: one participant may experience more than one event. The registry’s posted adverse-event categories do not provide enough detail to reconstruct participant-level event histories.

Why does the cohort structure matter?

Randomization is a general method for making treatment groups comparable in expectation, so that observed differences can more credibly be attributed to treatment assignment. This study was non-randomized and sequential. Its groups therefore cannot be interpreted as randomized arms. Cohort membership may be associated with calendar sequence, dose, or other differences in study conduct. The record also notes prophylactic corticosteroids in Cohort 2 Expansion. Without a control group or a reported adjustment strategy, a difference in observed counts would not isolate the effect of dose or any other single factor.

Sequential dose cohorts can be useful for describing observations as a study progresses, but interpretation requires care. The record does not report the rules governing movement from one cohort to another, the full decision process for expansion, or an analysis plan for comparing cohorts. A Data Safety Monitoring Board approval of expansion is recorded, but the board’s criteria and supporting review are not reported. No inference about the board’s reasoning should be made beyond the stated approval.

What can uncertainty measures add?

In general, a confidence interval expresses uncertainty around an estimate under a specified statistical model and procedure. Wider intervals indicate less precision, while narrower intervals indicate greater precision, subject to the assumptions used. For a participant count or event proportion, an interval can help show how much uncertainty remains when only a small group is observed. An interval does not correct for non-randomized allocation, incomplete follow-up, outcome misclassification, or unmeasured differences between cohorts.

The registry record does not report confidence intervals or other uncertainty estimates for these adverse-event counts. With 3 participants at risk in each cohort, the group-level counts are necessarily limited descriptions of the participants observed; they do not establish precise population risks. No additional numerical estimate should be inferred from those counts without a specified method and complete supporting information.

What do hypothesis tests and adjusted analyses require?

In general, a hypothesis test evaluates data under a defined null hypothesis and statistical model. A p-value, when reported, describes how compatible the observed data are with that model under the null; it is not the probability that the null hypothesis is true and does not measure clinical importance. Adjusted analyses can account for measured covariates, but they depend on the model, available data, and assumptions. Neither approach resolves the central limitation of a non-randomized cohort comparison by itself.

The registry record reports no analysis entries. It does not report p-values, model-based estimates, covariate adjustments, or a statistical analysis plan. It is therefore not possible to describe a sponsor analysis or to infer which inferential method, if any, was used. The posted counts should be presented descriptively rather than assigned a significance interpretation.

How should planning calculations be read?

In general, a sample-size planning illustration asks how many participants might be needed under specified assumptions to detect an effect of a chosen size with a chosen error rate and power. Such an illustration is not an observed result and does not show that a completed study had adequate power. It depends on the assumed effect, allocation, outcome variability, and statistical method. The registry does not report its own sample-size justification, so a planning illustration should not be mistaken for the original design rationale or for evidence that the study was planned around the observed cohort outcomes.

For this study, the record specifies that planning illustrations use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect set as a stated fraction of the observed effect. Those assumptions describe an illustrative calculation, not the actual sequential, non-randomized design. A two-arm equal-allocation illustration does not make the study’s cohorts randomized or comparable. The record does not report an analysis plan or analysis entries that would support interpreting the illustrations as observed power.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Cohort 1", "Cohort 2", "Cohort 2 Expansion")
n      <- c(3, 3, 3)
events <- c(1, 3, 2)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Cohort 1  3  1  33.3  0.8  90.6  6.1  79.2  6.8  80.6
ARM  Cohort 2  3  3  100.0  29.2  100.0  43.9  100.0  39.8  99.4
ARM  Cohort 2 Expansion  3  2  66.7  9.4  99.2  20.8  93.9  19.4  93.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 6 outcome measures, including the primary safety endpoint and secondary outcomes concerning percent change in LDL-C, percent change in lipid parameters, participants with investigational-product-related adverse events, and vector shedding in urine and plasma. The record does not report a multiplicity strategy explaining how inference across these outcomes was controlled or prioritized. Without such a plan, results across multiple outcomes, if reported, would need cautious interpretation, particularly if selective emphasis were possible. No inferential outcome analyses are reported in the registry record.

The registry does not report how missing outcome data were handled, whether all enrolled participants completed the relevant follow-up, or whether any imputation or sensitivity analysis was performed. It also does not report the analysis population used for the primary endpoint. The primary timeframe is up to 24 weeks, but the record does not describe participant-level follow-up or the completeness of assessments within that timeframe. These omissions prevent evaluation of how missingness might affect the endpoint count.

The record’s termination status does not explain why the study ended or whether termination affected follow-up or reporting. Those details are not reported in the registry record. Consequently, the posted figures should be read as the registry’s available descriptive counts, not as a complete account of analysis populations, missingness, or inferential control across outcomes.

12. 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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: device failure (33.3%), cardiac arrest (33.3%), pnuemonia (33.3%), acute respiratory failure (33.3%), acute coronary syndrome (33.3%).

The serious adverse-event groups list 3 participants at risk in each cohort. The affected counts are 2 in Cohort 1, 1 in Cohort 2, and 1 in Cohort 2 Expansion. The corresponding counts for other adverse events are 2, 3, and 2. These are counts of affected participants as classified in the posted record; they are not a count of every event experienced.

The record lists one death in Cohort 2 Expansion. It does not report the cause, timing, or relationship to the investigational product, so those details cannot be inferred. Serious terms listed are device failure, cardiac arrest, pnuemonia, acute respiratory failure, acute coronary syndrome, and dyspnoea, each reported as 33.3%. The record does not explain whether terms occurred in the same participants or whether they were judged related to treatment.

Serious events are not automatically investigational-product-related events. The primary endpoint specifically concerns events related to the investigational product, while the posted group counts do not establish that relationship. With small, sequential, non-randomized cohorts and no reported statistical analysis, these figures are descriptive safety observations rather than a controlled comparison.

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

The registry record describes an early investigation of liver-directed gene replacement for adults with HoFH and identifies safety as the primary question. It records three sequential cohorts, each with 3 participants at risk in the adverse-event information. The posted counts indicate that serious and other adverse events were recorded in these cohorts, and the record lists one death in Cohort 2 Expansion. These observations are relevant to describing what was reported during the study.

They do not establish the frequency of investigational-product-related adverse events, because the primary endpoint result is not reported and the posted categories do not identify relatedness. The record also does not provide enough information to determine the cause or treatment relationship of the death, participant-level overlap among serious-event terms, or completeness of follow-up. The listed serious terms and their reported percentages should not be read as a complete event history or as evidence of causation.

The cohort counts do not demonstrate that one dose is safer or less safe than another. Allocation was non-randomized, the design was sequential, and the expansion cohort is described as receiving prophylactic corticosteroids. There is no concurrent control group listed, and no analysis entries or uncertainty estimates are reported. Consequently, differences among the counts cannot be separated from cohort sequence or other differences in study conduct.

The record lists secondary outcomes related to LDL-C, other lipid measures, and vector shedding, but it does not report results for those outcomes in the information summarized. The stated study purpose of evaluating preliminary effectiveness is not itself evidence of an effectiveness result. Overall, the posted information supports a limited descriptive account of cohort structure and adverse-event reporting; it does not support a causal or comparative conclusion about treatment effects.

14. Why This Trial Matters Statistically

This study raises statistical issues common to early clinical research: small sequential cohorts, no randomized allocation, and a safety endpoint that depends on event classification and follow-up. Those features shape what can be learned from the observed counts. A count can document events among enrolled participants, but it cannot alone establish a treatment effect or precisely characterize risk in a broader population.

The distinction between any event recorded during a study and an event judged related to the investigational product is especially important. The primary endpoint focuses on related events, while the posted safety counts are organized into serious and other adverse events. Treating these as interchangeable would change the question being answered. The registry does not report the primary endpoint result or the attribution details needed to connect the posted counts to it.

The sequential design also makes dose comparisons vulnerable to differences between cohorts beyond dose. Non-randomized assignment does not balance such differences by design, and the expansion cohort includes a note about prophylactic corticosteroids. Any comparison must therefore remain descriptive unless a suitable analysis and supporting data are reported. The record contains no analysis entries, estimates of uncertainty, or reported comparison strategy.

Finally, a planning illustration is not evidence that a study had adequate power, and it does not substitute for a reported design justification or analysis plan. The registry does not report its own sample-size justification. For readers assessing evidence, distinguishing design intent, observed counts, outcome definitions, and inferential analyses is essential. Here, the registry allows a careful description of the study but leaves important questions about analysis, missing data, event relatedness, and precision unanswered.

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.

Several limitations are specific to the information recorded for this trial. The study enrolled 9 participants across sequential cohorts, with 3 at risk in each adverse-event group. Such small groups provide limited descriptive information and cannot support stable comparisons between cohorts. The record does not report confidence intervals or other uncertainty estimates for the posted counts.

The absence of randomization and a concurrent control group limits causal interpretation. Cohorts differ by sequence and listed dose, while Cohort 2 Expansion also has a note about prophylactic corticosteroids. The registry does not report how these factors were addressed analytically. It also does not report the reason for termination or whether the status affected planned follow-up or outcome reporting.

The primary endpoint result is not reported. The serious and other event counts cannot be assumed to represent investigational-product-related events. The record does not provide detailed event-level information, relatedness assessments, or enough context to determine overlap among listed serious terms. Although one death is recorded in the expansion cohort, its cause, timing, and relationship to the intervention are not reported.

Further limitations include the lack of reported analysis entries, an analysis population, missing-data handling, and a multiplicity strategy. The registry lists secondary outcome topics but does not report their results in the information described. These gaps restrict interpretation to the design features and descriptive safety counts that are explicitly recorded.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Gene Therapy Study for Homozygous Familial Hypercholesterolemia (HoFH) — NCT02651675.
• Registry record last updated 2023-07-13; status last verified 2023-06.
• Results first posted 2023-07-13.
• 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

NCT02651675 is a Phase 1 and Phase 2, non-randomized, unmasked, sequential study of AAV8-mediated LDLR gene replacement in adults with HoFH. The registry lists 9 participants enrolled, a start date of 2016-03, primary completion on 2020-11-27, and terminated status. It describes three cohorts, with Cohort 1 receiving 2.5E12 genome copies/kg and Cohort 2 and Cohort 2 Expansion receiving 7.5E12 GC/kg.

The primary endpoint is the number of participants with investigational-product-related adverse events up to 24 weeks. Its result is not reported in the registry record. Posted serious and other adverse-event counts are descriptive and do not establish event relatedness or a causal comparison. The record includes one death in Cohort 2 Expansion but does not report its cause or relationship to treatment. No analysis entries, uncertainty estimates, missing-data methods, or sample-size justification are reported.