Clinical Efficacy Trial of Mexiletine for Myotonic Dystrophy Type 1: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Efficacy Trial of Mexiletine for Myotonic Dystrophy Type 1 (NCT01406873), a randomized phase 2 study. The primary outcome is Mean Change From Baseline in Ambulation Using the 6 Minute Walk Distance.

2. Clinical Question

The registry also describes the trial as examining ambulation, myotonia, muscle function and strength, pain, gastrointestinal functioning, cardiac conduction, and quality of life. The primary endpoint addresses walking performance specifically; it does not by itself represent all of those domains. The posted numerical comparison is an estimate from the primary endpoint data, not a complete account of every outcome or the trial’s safety findings.

3. Trial Design

The registry identifies this as a randomized, phase 2, placebo-controlled trial with a parallel-group model and quadruple masking. The sponsor was the University of Rochester. The record lists the study as completed, with a start date of 2011-06 and primary completion date of 2017-02. Enrollment is listed as 42. The arm descriptions state that 20 subjects would be randomized to mexiletine and 20 to placebo; these descriptions are not the same as the analyzed sample sizes for every outcome.

The study description sets out a six-month treatment period and a broad set of clinical aims. It identifies walking, myotonia, muscle function and strength, pain, gastrointestinal functioning, cardiac conduction, and quality of life as areas of interest. Mexiletine was compared with placebo, described as a sugar pill. The record says the placebo control was intended to establish antimyotonic efficacy and safety.

For the primary endpoint, the posted analysis includes 19 participants in the mexiletine group and 20 in the placebo group. The record defines the intent-to-treat efficacy population as randomized participants who received at least one dose and had a post-baseline efficacy assessment. It also notes that follow-up data were not collected for one participant in the mexiletine arm because of a broken foot. The precise reasons that the primary endpoint analysis includes its reported group sizes, beyond that note, are not reported in the registry record.

The study’s original sample-size justification, intended allocation procedure details, and prespecified statistical analysis plan are not reported in the registry record. The posted analysis and planning illustrations should therefore be read separately from any assumptions that may have informed the original trial design.

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:

Analysis population for the primary outcome, as defined in the registry: Intent to Treat (ITT) population was defined as all participants who were randomized to the study, received at least one dose of study medication and have post-baseline efficacy assessment. Follow-up data was not collected on one participant in the mexiletine arm due to a broken foot.

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 Mean Change From Baseline in Ambulation Using the 6 Minute Walk Distance, measured over Baseline to 6 months.

The primary endpoint was mean change from baseline to 6 months in distance walked during a 6-minute walk assessment, measured in meters. Participants were asked to walk as far as they could back and forth along a fixed 20 meter route for 6 minutes, and the total distance was recorded. The registry defines change as the difference between the average distance at baseline and the average distance at 6 months.

This measure turns a timed walking task into a continuous outcome: each participant’s result is expressed as a distance, and the group result is summarized as a mean change. A continuous measure can show both the direction and the scale of observed change, while also allowing assessment of how variable individual results were. The registry reports standard deviations for the group changes, which describe that variability.

Walking distance was selected as the primary measure of ambulation, one of the study’s stated areas of interest. It is a specific performance measure, rather than a direct measure of every aspect of DM1 or of the other outcomes listed in the study description. Interpretation should therefore remain tied to this walking task and its measurement conditions. The endpoint results do not, on their own, establish what happened to pain, gastrointestinal functioning, cardiac conduction, quality of life, or all other aspects of muscle function.

7. Results Posted in the Registry

• Mexiletine: mean 17.44 versus 7.25 on control; difference 10.19 (95% CI -14.55 to 34.93), standardized effect d = 0.26; z-test p = 0.419.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Mean Change From Baseline in Quantitative Measure of Hand Grip Myotonia

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Mexiletine: mean -1.01 versus 0.43 on control; difference -1.44 (95% CI -2.51 to -0.37), standardized effect d = -0.86; z-test p = 0.008.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Mexiletine than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Mean Change From Baseline in Manual Muscle Testing (MMT) Score

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Mexiletine: mean 0.05 versus -0.06 on control; difference 0.11 (95% CI -0.00 to 0.22), standardized effect d = 0.60; z-test p = 0.058.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Mexiletine and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes span different aspects of the trial: hand-grip myotonia, manual muscle testing, cardiac conduction and heart-rate measures, disease burden and quality of life, and treatment dose reduction or interruption. The posted results include numerical comparisons for hand-grip myotonia and manual muscle testing. Those findings address distinct outcomes from the primary walking endpoint and should be interpreted as complementary rather than as direct confirmation or contradiction of the walking result.

Across the posted continuous secondary results, the observed pattern is not uniform. The hand-grip myotonia comparison has a negative mean difference, an unadjusted p-value of 0.008, and a registry-reported ANCOVA superiority analysis with p < 0.01. The manual muscle testing comparison is positive, but its unadjusted p-value is 0.058 and its interval includes zero. These results are not repeated as a full endpoint-by-endpoint interpretation; the important point is that outcomes differ in their direction, scale, and statistical uncertainty.

The registry lists five secondary outcomes in the study description, while the posted results include a subset of secondary measures. The record does not provide a complete reported numerical result for every listed secondary outcome. No conclusions about unposted numerical results can be drawn from their inclusion in the study description alone.

Secondary results generally carry less weight when many outcomes are assessed without a reported plan for controlling the chance of false-positive findings across them. The registry does not report a multiplicity adjustment or a prespecified hierarchy for interpreting secondary outcomes. An isolated small p-value among several outcomes may be less persuasive than a result from an analysis that accounted for the full set of planned comparisons. These results can inform the overall pattern and identify outcomes for further study, but they do not override the uncertainty in the primary endpoint or establish a broad effect across all measured domains.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Percentage of Participants That Had a Dose Reduction or a Study Drug Withdrawal or Suspension Over 6 Months
• Mean Change From Baseline in Quantitative Measure of Hand Grip Myotonia
• Mean Change From Baseline in Manual Muscle Testing (MMT) Score
• Mean Change From Baseline in PR, QRS, and QTc Intervals, and Average Minimum Heart Rate (HR) Via Electrocardiogram (ECG) Monitoring
• Mean Change From Baseline in Patient-Reported Disease Burden and Quality of Life

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous, so the registry reports a mean change for each group and a standard deviation describing the spread of individual changes around that group mean. The mean gives a compact description of the group’s average observed change. The standard deviation adds information about how much participants’ changes varied; it is not the uncertainty interval for the group mean or for the difference between groups.

What does the mean difference represent?

The recalculated mean difference compares the mexiletine group’s mean change with the placebo group’s mean change. For the primary endpoint, this difference is 10.19 meters. It is an unadjusted comparison derived from the posted arm summaries. It does not account for baseline covariates or other possible features of the analysis that are not contained in those summaries. A positive value means the recorded mean change was numerically greater in the mexiletine group; it does not, by itself, establish that the difference is reliable or clinically important.

Unadjusted recalculations are useful for a transparent comparison of the posted descriptive results. They are not necessarily identical to a trial’s planned primary analysis. For example, a model can adjust for baseline values or other prespecified variables, and such an analysis may yield a different estimate or uncertainty. The primary statistical model and any adjusted primary result are not reported in the registry record. The recalculation should therefore be read for what it is: a summary-statistic comparison, rather than an assertion about an unreported sponsor analysis.

How should the uncertainty be read?

A confidence interval expresses uncertainty around an estimated effect under the assumptions of the statistical method used. It gives a range of effect values that are compatible with the data and method; it does not guarantee that the true effect lies in that range, and it does not show the distribution of individual participant outcomes. The primary interval extends from -14.55 to 34.93 meters. Because it crosses zero, it includes both a possible negative difference and a possible positive difference, as well as no difference. Its breadth also indicates that the posted estimate is imprecise.

The unadjusted p-value for the primary comparison is 0.419. A p-value describes how unusual data at least as discordant with a specified null hypothesis would be under the assumptions of the test. It is not the probability that the null hypothesis is true, nor is it a measure of the size or clinical importance of an effect. The p-value must be read alongside the estimated difference and its interval, rather than as a stand-alone verdict.

What does the ANCOVA result add?

For hand-grip myotonia, the registry reports an ANCOVA superiority analysis with p < 0.01. ANCOVA is a general statistical method that compares outcome values across groups while adjusting for one or more covariates, often including a baseline measure. Adjustment can improve the comparison when the selected covariates are relevant and the model is appropriate. The registry does not report the covariates, model details, adjusted effect estimate, or interval for this analysis. Consequently, the reported p-value cannot be used to reconstruct the size or precision of an adjusted effect. The manual muscle testing result has no reported ANCOVA analysis in the record.

Why does variability matter?

Standard deviations are large relative to the primary mean difference. When participant-level outcomes vary widely, a group average may be estimated less precisely unless there is adequate information to distinguish the average difference from that variability. The reported primary interval reflects this uncertainty. General statistical interpretation should also distinguish the standard deviation, which describes observed dispersion, from the standard error, which describes uncertainty in an estimated mean. The posted summaries include standard errors in the recalculation details, but the practical interpretation is most clearly conveyed by the estimated difference and its interval.

These methods describe the posted endpoint summaries; they do not establish the original analysis choices. The prespecified primary model, assumptions about missing outcomes, planned handling of multiple endpoints, and any interim analyses are not reported in the registry record. Those omissions limit how closely the posted summaries can be connected to the trial’s original statistical plan.

11. Confidence Intervals and Precision

The primary mean difference is 10.19 meters, with an interval from -14.55 to 34.93 meters. The interval includes zero, so the posted data do not precisely distinguish a positive between-group difference from no difference or a difference in the other direction. The range also includes values that differ meaningfully in scale from the point estimate. This is an important qualification: the point estimate alone does not convey how uncertain the comparison is.

In general, a confidence interval communicates the uncertainty of an estimated group contrast under the method’s assumptions. A narrower interval indicates greater precision; a wider interval leaves more possible values compatible with the data. An interval is not a prediction range for individual participants, and it does not assign equal probability to every value within its bounds. The registry does not specify the confidence level or primary analysis method for this interval, so interpretation should not assume an unreported level or model.

The primary group standard deviations are 39.84 meters and 38.93 meters, while the analyzed group sizes are 19 and 20. These summaries help explain why an estimate can remain uncertain even when its point estimate is positive. Variation among participants is substantial in relation to the estimated group difference, and the reported interval reflects that uncertainty. The unadjusted p-value, 0.419, is consistent with the interval’s inclusion of zero, but it should not be treated as a measure of precision by itself.

Precision is distinct from clinical importance. The registry does not report a threshold for a clinically important difference in walking distance. The interval can therefore be described statistically, but the record alone does not establish how its values map to clinical importance.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations based on the observed effect, not the original trial’s design assumptions. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set at the stated fraction of the observed effect. The original trial’s own sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm for a planned study to have an 80% chance of detecting the specified effect under the stated assumptions, if that effect is the true one and the model assumptions hold. The 90% power column uses the same interpretation with a higher target chance of detection. These are design-planning quantities, not statements about the chance that this completed trial detected an effect or about the probability that a result is true.

The rows reduce the effect being targeted from the full observed effect to 75% of the observed effect and then to 50% of the observed effect. The corresponding planning requirements increase as the target effect becomes smaller. This is a general feature of statistical planning: smaller differences are harder to distinguish from background variability, so more participants are typically needed to achieve the same target power.

For the primary endpoint, the planning figures for 100% of the observed effect are 235 participants per arm for 80% power and 314 participants per arm for 90% power. For 75% of the observed effect, the figures are 417 and 558 participants per arm; for 50%, they are 938 and 1,256 participants per arm. These calculations use the observed effect as their starting point, which is uncertain and may not represent the effect a future study should expect. This is not observed power.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 10.190; pooled standard deviation σ = 39.375.
2. n = 2 × (1.96 + 0.842)² × 39.375² / 10.190² = 234.4, rounded up to 235 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 10.19                      # observed difference in means
sigma <- 39.3753297369291                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1406873)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 235 (80% power), 314 (90% power)
 75% of observed effect: n per arm = 417 (80% power), 558 (90% power)
 50% of observed effect: n per arm = 938 (80% power), 1,256 (90% power)
power.t.test: 235.4 
Simulated power at n = 235 per arm: 0.798 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The trial assessed a primary walking endpoint alongside several secondary outcomes. When statistical tests are conducted across multiple outcomes, the chance of observing at least one apparently notable result can rise, even if there is no real effect on any of them. Statistical approaches to multiplicity can control or otherwise address that issue, for example by adjusting significance thresholds or specifying a hierarchy in which outcomes are tested. The registry record does not report a multiplicity strategy, a confirmatory hierarchy, or how secondary p-values should be interpreted as a family.

The hand-grip myotonia analysis includes a registry-reported ANCOVA superiority result with p < 0.01, while the manual muscle testing comparison has a recalculated unadjusted p-value of 0.058. Without a stated multiplicity plan, these findings should be considered exploratory or supportive rather than treated as a collection of independent confirmations. The record does not report enough information to determine whether other analyses were conducted but not posted.

Missing outcome data also matter. The primary population definition requires randomization, at least one dose of study medication, and a post-baseline efficacy assessment. The record notes that follow-up data were not collected for one participant in the mexiletine arm because of a broken foot. It does not report a detailed missing-data model, imputation method, sensitivity analysis, or the assumptions used to handle missing outcomes. Those methods can affect how robust a result is to missingness, particularly if the chance of missing data is related to participants’ outcomes.

The record lists different analyzed group sizes across the primary and secondary outcomes. The reason for each endpoint-specific analysis size, apart from the noted missing primary follow-up, is not reported in the registry record. The primary analysis population is therefore narrower than a description that simply says all randomized participants, because it also requires a dose and a post-baseline assessment. The record does not report a separate intention-to-treat analysis including all randomized participants regardless of post-baseline assessment.

The primary statistical model, covariate adjustment, interim analyses, and full prespecified statistical plan are not reported in the registry record. These gaps do not erase the descriptive results, but they limit assessment of whether the posted analyses follow the original plan and how sensitive conclusions are to analytic choices.

15. 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 4% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: stroke (4.8%), fracture (4.8%).

The registry lists one participant with a serious adverse event in each group, with 21 participants at risk in each group. It lists no deaths in either group. The record also reports other adverse events affecting 21 participants in the mexiletine group and 20 in the placebo group. These are posted counts; they do not by themselves describe the seriousness, duration, relatedness, or clinical course of every event.

The top serious-event terms listed are Stroke and Fracture, each reported as 4.8%. The registry summary does not identify which treatment group those terms belong to, nor does it provide enough detail in this record to establish whether each term represents an affected participant, an event count, or a particular clinical course. The percentages should therefore be read as registry-listed event-term figures, not as comparative treatment risks.

Safety comparisons require context, including definitions, exposure, event timing, and assessment of possible relationship to study medication. The posted counts are useful for describing what the registry lists, but the small trial and limited summary detail do not support broad conclusions about safety differences.

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

The primary endpoint results show a numerically greater mean increase in six-minute walking distance in the mexiletine group than in the placebo group: 17.44 meters versus 7.25 meters. The recalculated unadjusted difference is 10.19 meters. Its interval, from -14.55 to 34.93 meters, includes zero, and the unadjusted p-value is 0.419. In statistical terms, these data do not provide a precise estimate of the between-group difference in walking change.

That finding does not establish that the groups had identical outcomes. The interval is compatible with a range that includes differences in either direction as well as no difference. Nor does the positive point estimate establish a reliable benefit. The estimate and its uncertainty must be considered together, and the registry does not report a clinically important threshold for interpreting the scale of the difference.

The trial assessed more than walking. The secondary results include a hand-grip myotonia comparison with a reported ANCOVA p-value of p < 0.01, and a manual muscle testing comparison whose unadjusted p-value is 0.058. Other study domains are named in the registry, but numerical results for all of them are not included in the posted secondary results. Findings from one measure should not be generalized automatically to other aspects of DM1.

The study was a phase 2 randomized placebo-controlled trial, and the primary endpoint analysis included the group sizes and population specified in the registry. Its results contribute a limited set of observations under the trial’s measurement and follow-up conditions. The record does not supply the detail needed to evaluate all analysis choices, missing-data assumptions, multiplicity handling, or clinical importance thresholds.

These statistics are not medical advice and do not determine an individual treatment choice. They describe the recorded group outcomes and the uncertainty around a summary comparison; they do not establish a broad conclusion about treatment effectiveness or safety beyond the specific posted results.

17. Why This Trial Matters Statistically

This trial illustrates why a group mean and a p-value are not enough to interpret a clinical comparison. The primary point estimate is positive, but its interval ranges across zero and the unadjusted p-value is 0.419. Looking at the estimate together with its precision prevents the numerical direction of the mean difference from being mistaken for decisive evidence.

The endpoint also makes the distinction between a measured domain and a broad clinical claim visible. A six-minute walking assessment records distance under a specified task. It does not directly measure every outcome named in the study description, such as cardiac conduction, gastrointestinal functioning, or quality of life. A trial can therefore have different patterns across its primary and secondary measures without those measures being interchangeable.

Secondary findings highlight the need to consider multiplicity and analysis reporting. The registry reports an ANCOVA superiority result for hand-grip myotonia but does not report a multiplicity strategy or full model details. Without those details, readers cannot determine how that result was positioned within the complete set of planned tests. Statistical significance on an individual secondary measure is not, on its own, evidence that all related outcomes move in the same direction.

The record also shows why enrollment, arm descriptions, and endpoint analysis populations should be distinguished. The enrollment figure and planned arm descriptions do not replace the outcome-specific analyzed group sizes, and the primary population definition includes receipt of medication and a post-baseline assessment. Missing-data and analysis-population details are central to evaluating how directly results represent all randomized participants.

Finally, the planning illustrations demonstrate the sensitivity of sample-size requirements to the effect size being targeted. They are based on the observed effect, rather than the original trial’s documented design justification. Separating such planning calculations from observed results helps prevent mistaken claims about the power of a completed study.

18. 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 endpoint summary gives an unadjusted recalculation rather than a reported primary model result. The registry does not report whether the primary analysis adjusted for baseline walking distance or other covariates, or whether the posted interval and p-value correspond to the original prespecified analysis. This limits comparison between the descriptive result and the study’s intended statistical approach.

The primary efficacy population excludes randomized participants who did not receive at least one dose or lacked a post-baseline efficacy assessment, according to the registry’s definition. One participant in the mexiletine arm had no follow-up data because of a broken foot. The record does not report detailed missing-data procedures or sensitivity analyses, so the impact of missing outcomes cannot be assessed fully.

Multiplicity handling is not reported despite the presence of a primary endpoint and several secondary outcomes. The registry also lacks full model details for the reported ANCOVA result, including the covariates used and an adjusted effect estimate with an interval. The numerical secondary results do not cover every domain named in the study description.

The primary interval is broad and includes zero. The record does not report a clinically important difference threshold for the walking measure, making it difficult to connect the range of statistically compatible values with clinical importance. The safety summary is also limited: it provides counts and selected event terms but not detailed event narratives, timing, relatedness, or group attribution for the listed terms.

The registry’s original sample-size justification, interim-analysis plan, and complete statistical analysis plan are not reported. The planning illustrations use the observed effect and stated generic assumptions; they should not be read as evidence of what guided the original enrollment target.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Clinical Efficacy Trial of Mexiletine for Myotonic Dystrophy Type 1 — NCT01406873.
• Registry record last updated 2018-06-19; status last verified 2018-05.
• Results first posted 2018-03-29.
• 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.

22. Record Summary

The registry describes a completed randomized, quadruple-masked, parallel-group, phase 2 trial comparing mexiletine with placebo in myotonic dystrophy type 1. The study assessed outcomes over 6 months, with change in six-minute walking distance as the primary endpoint. The primary group means were 17.44 meters for mexiletine and 7.25 meters for placebo; the recalculated unadjusted mean difference was 10.19 meters, with an interval from -14.55 to 34.93 meters and p = 0.419.

The posted secondary results include a hand-grip myotonia comparison and a manual muscle testing comparison, with differing statistical patterns. One serious adverse event was reported in each group, and no deaths were listed. The registry record does not report the full primary analysis plan, multiplicity strategy, detailed missing-data methods, or original sample-size justification.