Understand the source comparison
Follistatin Isoform Comparison
Understanding the three isoforms clarifies why FS-344 is the preferred injectable form. FS-344 344 Precursor (injected) Strong Cleaved to FS-315 in vivo FS-315 315 Circulation Main muscle-targeting form FS-288 288 Tissue-bound (gonads) Moderate Concentrates in
No winner is assigned.
This page preserves a source comparison for education. It does not add a rating, recommendation or clinical judgment.
- Understanding the three isoforms clarifies why FS-344 is the preferred injectable form.
- FS-344
- 344
- Precursor (injected)
- Strong
- Cleaved to FS-315 in vivo
- FS-315
- 315
- Circulation
- Main muscle-targeting form
- FS-288
- 288
- Tissue-bound (gonads)
- Moderate
- Concentrates in reproductive tissue
- FS-344 is preferred for injection because it is more stable as a recombinant protein and converts to FS-315 systemically. Injecting FS-315 directly is possible but offers no clear advantage and is less commonly available.
- A key 2009 study demonstrated that AAV-delivered follistatin 344 produced the greatest effects on muscle size and function in nonhuman primates, with increases in muscle fiber size of 15-36% in treated quadriceps (Kota et al. 2009, PubMed 19208403). The study also confirmed tolerability with no adverse effects on cardiac pathology or reproductive function in either sex.