Why is this the case? Wouldn’t there be concerns that a study population might be different from the general population and thus require an internal control?
FDA acknowledges that FVIII levels can serve as a proxy for clinical outcome (reduced bleeding episodes) in hemophilia A.
Our understanding of what is "normal" in FVIII blood levels is such that a single arm, surrogate biomarker study is sufficient for approval.
That was the focus of the JAMA article.