Evolutionary insights into coagulation factor IX Padua and other high-specific-activity variants.

Abstract

The high-specific-activity factor IX (FIX) variant Padua (R338L) is the most promising transgene for hemophilia B (HB) gene therapy. Although R338 is strongly conserved in mammalian evolution, amino acid substitutions at this position are underrepresented in HB databases. We therefore undertook a complete 20 amino acid scan and determined the specific activity of human (h) and canine (c) FIX variants with every amino acid substituted at position 338. Notably, we observe that hFIX-R338L is the most active variant and cFIX-R338L is sevenfold higher than wild-type (WT) cFIX. This is consistent with the previous identification of hFIX-R338L as a cause of a rare X-linked thrombophilia risk factor. Moreover, WT hFIX and cFIX are some of the least active variants. We confirmed the increased specific activity relative to FIX-WT in vivo of a new variant, cFIX-R338I, after gene therapy in an HB dog. Last, we screened 232 pediatric subjects with thromboembolic disease without identifying F9 R338 variants. Together these observations suggest a surprising evolutionary pressure to limit FIX activity with WT FIX rather than maximize FIX activity.

• Authors: Benjamin J Samelson-Jones, Jonathan D Finn, Leslie J Raffini, Elizabeth P Merricks, Rodney M Camire, Timothy C Nichols, Valder R Arruda
• Journal: Blood advances (Blood Adv) Vol. 5 Issue 5 Pg. 1324-1332 (03 09 2021) ISSN: 2473-9537 [Electronic] United States
• PMID: 33656538 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
• Copyright: © 2021 by The American Society of Hematology.

Chemical References

• Factor IX

Topics

• Animals
• Blood Coagulation
• Blood Coagulation Tests
• Child
• Dogs
• Factor IX (genetics)
• Genetic Therapy
• Hemophilia B (genetics, therapy)
• Humans