“there were serious methodological concerns identified by FDA,” according to the documents.
To measure the drug’s effect on muscle function, the company performed a six-minute walk test on the trial’s participants. The FDA reports there was “no nominally significant difference” between patients taking either the higher dose of eteplirsen, the lower dose or the placebo. The agency also griped about the fact that the company chose to compare the performance of the patients on the six-minute walk test against “historical controls,” or DMD patients who were in different trials in the past. - Forbes
You can read all about the "serious methodological concerns" here.
The simple description of Sereptas plan to demonstrate the efficacy of their product:
1) expression of an altered messenger RNA in muscle (pharmacodynamic)
2) production of dystrophin protein in muscle (pharmacodynamic)
3) improvement or preservation of muscle function (clinical).
Throughout the approval process, critics have expressed concerns with the small population — 12 patients — involved in clinical trials for the rare disease, along with flaws in how the clinical study was designed. These factors make “judgment on science difficult,” Califf (the FDA commissioner) said.
No it doesn't. More data points lead to better understanding of the accuracy of what is being measured. It is simple precision and accuracy. You may leave college with a poor grasp of the math behind statistics but you get the concept. The more data points the clearer the picture gets. Poor precision leads to greater doubts about accuracy. You aren't making a "judgment on science" that is "difficult". You are doing math.
Here is an example of data on the production of dystrophin protein in muscle.
Western blots and immunofluorescence were used to quantitate dystrophin.
Table 2: Applicant’s Quantification of Dystrophin by Western Blot and Immunofluorescence Analyses
Patient Western Blot % of normal Immunofluorescence % positive fibers
A 2.05 18.5
B 1.15 19.1
C 0.38 33.5
D 1.62 24.0
E 0.52 21.5
F 0.98 12.8
G 0 7.1
H 2.47 20.7
I 0.96 28.2
J 0 1.4
L 0.14 4.5
A quick glance at Figure 1: Correlation between Two Methods Used to Quantify Dystrophin in Skeletal Muscle: Patients from Study 201/202 tells you all you need to know. As the FDA put it, "Of note, the correlation between the two independent methods used to quantify dystrophin in muscle samples was weak." They also stated, "As discussed above, we believe that immunofluorescence analysis (percent positive fibers) is not a reliable method to quantify dystrophin content." What other criticisms of Sereptas methodology did the FDA panel mention?
Regarding the first pharmacodynamic goal, to demonstrate expression of an altered mRNA in muscle the FDA states;
Because even a minimal PCR signal is interpreted as “positive,” this biomarker provides little support of efficacy for eteplirsen; it does provide evidence that eteplirsen causes at least some degree of exon 51 skipping, as intended.
Regarding the second pharmacodynamic goal, the demonstrate production of dystrophin protein in muscle the FDA states;
FDA conducted an inspection of the facility where the data reported in the publication were generated. Significant methodological concerns were identified, which cast serious doubt on the reliability of assessments from the first three biopsies.and
Thus, the review team does not consider “percent dystrophin‐positive fibers” to be a meaningful way to estimate dystrophin content, and we believe the results reported by the applicant on this measure do not establish that a significant increase in dystrophin occurred in response to eteplirsen treatmentand
In any case, the level of dystrophin was 0.9% of normal after 3.5 years, such that, in absolute terms, the increase from baseline would be, at most, 0.9%, assuming a “worst case” for untreated patients, i.e., zero dystrophin.
Regarding the clinical goal, improvement or preservation of muscle function, the FDA stated;
Two patients in the 30 mg/kg group became unable to ambulate soon after the study start. The applicant then pooled the six remaining eteplirsen patients and compared them to the four placebo patients, an unplanned post hoc analysis. No nominally significant difference between eteplirsen and placebo was identified in that post hoc analysis.and
The applicant conducted a number of additional post hoc analyses, comparing the 6 patients who received eteplirsen in the 24‐week double‐blind phase of Study 201 and could still ambulate at the end of Study 201 (and continued on open‐label eteplirsen in Study 202) to those originally treated with placebo in the double‐blind phase of Study 201, and later switched to open‐label eteplirsen.
The applicant conducted a post hoc comparison of the patients in Study 201/202 to data from the “Italian DMD Registry” and the “Leuven Neuromuscular Reference Center” registry.
The problems of externally‐controlled studies are well recognized.
Dr. Ronald Farkas, who led the FDAs clinical team in the neurology products division, suddenly departed the agency just before the approval of Exondys 51. The arguments for the governments approval of Exondys 51 not come in a highly detailed document such as the one Dr. Farkas and his team presented.
Both FDA camps had “exercised reasonable scientific judgment,” Califf found, adding that it’s “exceedingly rare” to overrule a decision by the director of the Center for Drug Evaluation and Research. Without any additional technical expertise of his own, Califf said, he deferred to CDER Director Dr. Janet Woodcock.An appeal to the authority of someone elses knowledge!
The jury is still out. Serepta still has to put up or shut up. The FDA has just bought them some time and money. How much money? $300,000 per year. Good grief. With BS artists like these, who needs scientists anymore?