William P. Scully, listed in the filing as Other at Prothena Corp Public Ltd Co (PRTA), bought $889,872 of company stock on September 28th, 2026.
The purchase covered 103,500 shares. Every share went through at $8.5978, so the whole position was built at a single price rather than scaled across a range. It arrived in one filing.
Prothena sits in the Pharmaceutical Preparations group and carries a market value of $450,738,624. That is the frame to hold the buy against: a single insider transaction of $889,872 lands differently at a company of this size than it would at a large capitalization drug maker where the same dollars would barely register.
On the other side of the ledger, the record here is thin rather than contradictory. Our tables show one filing tied to this buyer for the period, with no accompanying disposition reported alongside it. A single Form 4 is a data point, not a pattern, and it should be read that way until more filings arrive.
The role matters for how much weight to give the signal. Scully is reported as Other rather than as a named officer or a director, a classification that tells you the person has a reporting obligation without telling you what they see day to day. The filing does not state a reason for the purchase, and neither will we.
On price, the entry at $8.5978 sits below the last traded price of $8.78. That is a narrow gap, and it says only that the shares have not moved far from where the buy was executed. Nothing in the filing speaks to what the buyer expects next.
Figures in this article come from Form 4 insider transaction filings as collected and reconciled in our own tables, covering the transaction dated September 28th, 2026.
Track every Form 4 filed at PROTHENA CORP PUBLIC LTD CO (PRTA) → insiderbuying.com/companies/PRTA