Prothena Corp Public Ltd Co (PRTA) shareholders
PRTANasdaqPharmaceutical PreparationsFiscal year ends December 31
Financials through Q3 FY2026, quarter ended Sep 30, 2026Last filing: 10-Q on Nov 5, 2026Score 12/3017% below fair value
$8.16−0.07 (-0.85%)
Close on Nov 13, 2026Market cap $418.91MP/E –Yield –
Ownership
Institutional holdings as of Jun 30, 2026, from 13F filings
Held by institutions
92.2%
47M of 51M shares
Institutional holders
188
29 new, 23 sold out
Net institutional buying
0M
In Q2 2026
Insider trades, 12 months
20 buys · 2 sales
Net bought $13.13M
Shares held by institutions
Holders of more than 5%
Latest Schedule 13D (active) or 13G (passive) filed by each holder
| Holder | Shares | % of class | Filing | As of |
|---|---|---|---|---|
| EcoR1 Capital, LLC Joint filing with Oleg Nodelman (21.50%), EcoR1 Capital Fund Qualified, L.P. (20.20%) | 11,584,280 | 21.50% | 13D (active) amendment | Dec 31, 2024 |
| Abigail P. Johnson Joint filing with FMR LLC (13.80%) | 7,199,218 | 13.80% | 13G (passive) amendment | Jun 30, 2026 |
| Scully William P | 5,378,846 | 10.30% | 13G (passive) amendment | May 7, 2026 |
| Fennell Todd W. | 5,248,846 | 10.20% | 13G (passive) amendment | Aug 18, 2026 |
| Rubric Capital Management LP Joint filing with David Rosen (9.29%) | 5,000,000 | 9.29% | 13G (passive) amendment | Mar 31, 2026 |
| BlackRock, Inc. | 3,587,480 | 6.90% | 13G (passive) amendment | Jun 30, 2026 |
| Logos Global Management GP LLC Joint filing with Logos Global Management LP (5.50%), Logos Global Master Fund LP (5.50%) and 2 more | 2,950,000 | 5.50% | 13G (passive) | May 29, 2025 |
Top institutional holders
13F holdings as of Jun 30, 2026
| Holder | Shares | % of PRTA | Value | Change | % of portfolio |
|---|---|---|---|---|---|
| FMR LLC | 7,199,218 | 14.02% | $70.48M | −352,000 | 0.00% |
| Rubric Capital Management LP | 5,000,000 | 9.74% | $48.95M | – | 0.45% |
| BlackRock, Inc. | 4,867,955 | 9.48% | $47.66M | +223,795 | 0.00% |
| State Street Corp | 2,393,424 | 4.66% | $23.43M | +454,926 | 0.00% |
| Acadian Asset Management LLC | 2,010,645 | 3.92% | $19.68M | +463,052 | 0.02% |
| Vanguard Portfolio Management LLC | 1,651,293 | 3.22% | $16.17M | +205,314 | 0.00% |
| D. E. Shaw & Co., Inc. | 1,611,457 | 3.14% | $15.78M | −151,890 | 0.01% |
| ADAR1 Capital Management, LLC | 1,554,535 | 3.03% | $15.22M | −26,908 | 0.70% |
| Two Sigma Investments, LP | 1,264,987 | 2.46% | $12.38M | +59,009 | 0.01% |
| Palo Alto Investors LP | 1,143,155 | 2.23% | $11.19M | −65,413 | 1.55% |
| Geode Capital Management, LLC | 1,125,877 | 2.19% | $11.02M | +27,711 | 0.00% |
| Federated Hermes, Inc. | 1,084,401 | 2.11% | $10.62M | +24,552 | 0.02% |
| Morgan Stanley | 995,348 | 1.94% | $9.74M | −235,100 | 0.00% |
| Goldman Sachs Group Inc | 979,730 | 1.91% | $9.59M | +160,845 | 0.00% |
| Jacobs Levy Equity Management, Inc | 965,988 | 1.88% | $9.46M | −6,029 | 0.03% |
| Dimensional Fund Advisors LP | 905,651 | 1.76% | $8.87M | +123,048 | 0.00% |
| Qube Research & Technologies Ltd | 791,169 | 1.54% | $7.75M | +176,566 | 0.01% |
| Renaissance Technologies LLC | 697,615 | 1.36% | $6.83M | +90,100 | 0.01% |
| Man Group plc | 678,116 | 1.32% | $6.64M | +296,542 | 0.01% |
| Mariner, LLC | 625,095 | 1.22% | $6.12M | +62,013 | 0.01% |
Institutional buying and selling by quarter
Positions opened, added to, reduced and closed by 13F filers
| Quarter | Holders | Shares held | % of shares | New / added | Reduced / closed | Shares bought | Shares sold |
|---|---|---|---|---|---|---|---|
| Q2 2026 | 188 | 47M | 92.2% | 29 / 56 | 57 / 23 | 4M | 4M |
| Q1 2026 | 185 | 47M | 91.5% | 29 / 68 | 51 / 23 | 7M | 5M |
| Q4 2025 | 182 | 47M | 92.2% | 25 / 64 | 56 / 25 | 9M | 5M |
| Q3 2025 | 187 | 43M | 84.4% | 32 / 57 | 61 / 33 | 11M | 9M |
| Q2 2025 | 188 | 42M | 81.6% | 51 / 53 | 41 / 23 | 15M | 26M |
| Q1 2025 | 161 | 52M | 100.0% | 17 / 42 | 58 / 24 | 1M | 3M |
| Q4 2024 | 170 | 54M | 100.0% | 34 / 62 | 40 / 28 | 5M | 3M |
| Q3 2024 | 164 | 51M | 100.0% | 24 / 49 | 46 / 19 | 8M | 4M |
| Q2 2024 | 160 | 51M | 100.0% | 27 / 57 | 43 / 34 | 2M | 6M |
| Q1 2024 | 169 | 55M | 100.0% | 25 / 57 | 62 / 41 | 6M | 5M |
| Q4 2023 | 187 | 55M | 100.0% | 41 / 69 | 45 / 38 | 6M | 5M |
| Q3 2023 | 186 | 53M | 100.0% | 25 / 73 | 51 / 32 | 3M | 2M |
Officers, directors and major owners
People who filed Forms 3, 4 or 5 in the last two years
| Name | Role | Shares owned | % of shares | Latest filing |
|---|---|---|---|---|
| Gene G. Kinney | President and CEO, Director | 68,793 | 0.13% | Jul 30, 2026 |
| Karin L. Walker | Chief Accounting Officer | 25,000 | 0.05% | Jul 30, 2026 |
| Brandon S. Smith | Chief Operating Officer | 52,000 | 0.10% | Jul 30, 2026 |
| Michael John Isaacs | General Counsel & Company Sec. | 35,745 | 0.07% | Jul 30, 2026 |
| Chad J. Swanson | Chief Development Officer | 44,200 | 0.09% | Jul 30, 2026 |
| Anne Evans Kingston | Chief Strategy Officer | 55,782 | 0.11% | Jul 30, 2026 |
| Tran Nguyen | Chief Strategy Officer and CFO | 40,205 | 0.08% | Jul 30, 2026 |
| Wagner M. Zago | Chief Scientific Officer | 85,000 | 0.17% | Jul 30, 2026 |
| Michael J. Malecek | Chief Legal Officer | 80,000 | 0.16% | Mar 5, 2026 |
| David A. Ford | Chief People Officer | – | – | Mar 7, 2025 |
| Carol D. Karp | Chief Regulatory Officer | 5,000 | 0.01% | Mar 7, 2025 |
| Shane Cooke | Director | 5,000 | 0.01% | May 15, 2026 |
| Lars Ekman | Director | 3,148 | 0.01% | May 15, 2026 |
| Richard T. Collier | Director | 6,219 | 0.01% | May 15, 2026 |
| Dennis J. Selkoe | Director | 4,208 | 0.01% | May 15, 2026 |
| Daniel G. Welch | Director | – | – | May 15, 2026 |
| William H. Dunn Jr. | Director | – | – | May 15, 2026 |
| Paula K. Cobb | Director | – | – | May 16, 2025 |
| Helen Susan Kim | Director | – | – | May 16, 2025 |
| Todd W. Fennell | 10% owner | – | – | Nov 13, 2026 |
| William P. Scully | 10% owner | 1,693,000 | 3.30% | Nov 10, 2026 |
| EcoR1 Capital, LLC | 10% owner | 5,304,596 | 10.33% | May 6, 2025 |
Insider trades
Common stock transactions reported on Form 4, newest first
| Insider | Date | Transaction | Shares | Price | Value | Shares after |
|---|---|---|---|---|---|---|
| William P. Scully 10% owner | Nov 9, 2026 | Buy | +140,000 | $8.53 | $1.19M | 977,000 |
| William P. Scully 10% owner | Nov 6, 2026 | Gift | −916,444 | – | – | 837,000 |
| William P. Scully 10% owner | Oct 27, 2026 | Gift | +566,444 | – | – | 1,753,444 |
| William P. Scully 10% owner | Oct 23, 2026 | Buy | +50,000 | $8.07 | $403.52K | 1,187,000 |
| William P. Scully 10% owner | Oct 22, 2026 | Buy | +100,000 | $8.19 | $818.52K | 1,137,000 |
| William P. Scully 10% owner | Oct 14, 2026 | Buy | +10,000 | $8.46 | $84.57K | 1,037,000 |
| William P. Scully 10% owner | Oct 13, 2026 | Buy | +100,000 | $8.35 | $835.48K | 1,027,000 |
| William P. Scully 10% owner | Oct 8, 2026 | Buy | +90,000 | $8.57 | $770.90K | 529,000 |
| William P. Scully 10% owner | Oct 7, 2026 | Buy | +125,000 | $8.40 | $1.05M | 439,000 |
| William P. Scully 10% owner | Oct 2, 2026 | Buy | +100,000 | $8.57 | $857.24K | 314,000 |
| William P. Scully 10% owner | Sep 29, 2026 | Buy | +162,000 | $8.68 | $1.41M | 214,000 |
| William P. Scully 10% owner | Sep 28, 2026 | Buy | +103,500 | $8.60 | $890.10K | 187,000 |
| William P. Scully 10% owner | Sep 18, 2026 | Buy | +100,000 | $8.43 | $843.00K | 927,000 |
| William P. Scully 10% owner | Sep 2, 2026 | Buy | +27,000 | $9.47 | $255.69K | 827,000 |
| William P. Scully 10% owner | Aug 20, 2026 | Buy | +50,000 | $8.79 | $439.50K | 800,000 |
| William P. Scully 10% owner | Aug 18, 2026 | Gift | −627,553 | – | – | 750,000 |
| William P. Scully 10% owner | Aug 17, 2026 | Gift | +336,000 | – | – | 1,377,553 |
| William P. Scully 10% owner | Aug 10, 2026 | Gift | +251,553 | – | – | 1,041,553 |
| William P. Scully 10% owner | Aug 7, 2026 | Buy | +34,000 | $8.62 | $293.08K | 790,000 |
| William P. Scully 10% owner | Aug 7, 2026 | Buy | +3,500 | $8.62 | $30.17K | 83,500 |
| Anne Evans Kingston Chief Strategy Officer | Jul 29, 2026 | Sale(10b5-1 plan) | −7,662 | $8.47 | $64.90K | 55,782 |
| Michael John Isaacs General Counsel & Company Sec. | Jul 29, 2026 | Sale(10b5-1 plan) | −8,386 | $8.47 | $71.03K | 35,745 |
| Wagner M. Zago Chief Scientific Officer | Jul 28, 2026 | Option exercise | +51,000 | – | – | 85,000 |
| Wagner M. Zago Chief Scientific Officer | Jul 28, 2026 | Returned to company | −51,000 | $8.56 | $436.56K | 34,000 |
| Gene G. Kinney President and CEO, Director | Jul 28, 2026 | Returned to company | −84,000 | $8.56 | $719.04K | 68,793 |
| Gene G. Kinney President and CEO, Director | Jul 28, 2026 | Option exercise | +84,000 | – | – | 152,793 |
| Anne Evans Kingston Chief Strategy Officer | Jul 28, 2026 | Tax withholding | −3,498 | $8.56 | $29.94K | 63,444 |
| Chad J. Swanson Chief Development Officer | Jul 28, 2026 | Returned to company | −40,800 | $8.56 | $349.25K | 44,200 |
| Chad J. Swanson Chief Development Officer | Jul 28, 2026 | Tax withholding | −3,467 | $8.56 | $29.68K | 40,733 |
| Chad J. Swanson Chief Development Officer | Jul 28, 2026 | Option exercise | +51,000 | – | – | 85,000 |
| Michael John Isaacs General Counsel & Company Sec. | Jul 28, 2026 | Tax withholding | −4,694 | $8.56 | $40.18K | 44,131 |
| Brandon S. Smith Chief Operating Officer | Jul 28, 2026 | Returned to company | −78,000 | $8.56 | $667.68K | 52,000 |
| Brandon S. Smith Chief Operating Officer | Jul 28, 2026 | Option exercise | +78,000 | – | – | 130,000 |
| Karin L. Walker Chief Accounting Officer | Jul 28, 2026 | Option exercise | +15,000 | – | – | 25,000 |
| Karin L. Walker Chief Accounting Officer | Jul 28, 2026 | Returned to company | −15,000 | $8.56 | $128.40K | 10,000 |
| Tran Nguyen Chief Strategy Officer and CFO | Jul 28, 2026 | Returned to company | −57,000 | $8.56 | $487.92K | 40,205 |
| Tran Nguyen Chief Strategy Officer and CFO | Jul 28, 2026 | Option exercise | +57,000 | – | – | 97,205 |
| William P. Scully 10% owner | Jun 16, 2026 | Buy | +20,000 | $7.90 | $158.00K | 756,000 |
| William P. Scully 10% owner | Jun 15, 2026 | Gift | −325,000 | – | – | 736,000 |
| William P. Scully 10% owner | Jun 11, 2026 | Buy | +125,000 | $8.17 | $1.02M | 1,061,000 |
| William P. Scully 10% owner | Jun 4, 2026 | Buy | +50,000 | $9.31 | $465.50K | 936,000 |
| William P. Scully 10% owner | Jun 2, 2026 | Buy | +50,000 | $9.43 | $471.50K | 886,000 |
| William P. Scully 10% owner | May 22, 2026 | Buy | +100,000 | $9.81 | $981.00K | 836,000 |
| Brandon S. Smith Chief Operating Officer | Jul 28, 2025 | Award | +130,000 | – | – | 130,000 |
| Karin L. Walker Chief Accounting Officer | Jul 28, 2025 | Award | +25,000 | – | – | 25,000 |
| Gene G. Kinney President and CEO, Director | Jul 28, 2025 | Award | +140,000 | – | – | 152,793 |
| Wagner M. Zago Chief Scientific Officer | Jul 28, 2025 | Award | +85,000 | – | – | 85,000 |
| Tran Nguyen Chief Strategy Officer and CFO | Jul 28, 2025 | Award | +95,000 | – | – | 97,205 |
| Michael J. Malecek Chief Legal Officer | Jul 28, 2025 | Award | +80,000 | – | – | 80,000 |
| Chad J. Swanson Chief Development Officer | Jul 28, 2025 | Award | +85,000 | – | – | 85,000 |
| EcoR1 Capital, LLC 10% owner | May 6, 2025 | Sale | −1,984,053 | $7.64 | $15.16M | 5,304,596 |
| EcoR1 Capital, LLC 10% owner | May 5, 2025 | Sale | −977,693 | $8.11 | $7.93M | 7,288,649 |
| EcoR1 Capital, LLC 10% owner | May 2, 2025 | Sale | −3,317,938 | $8.36 | $27.74M | 8,266,342 |
| William P. Scully 10% owner | Jan 15, 2025 | Gift | −12,000 | – | – | 47,000 |
| William P. Scully 10% owner | Jan 14, 2025 | Buy | +100,000 | $12.79 | $1.28M | 735,993 |
| William P. Scully 10% owner | Jan 3, 2025 | Gift | −1,000 | – | – | 635,993 |
| William P. Scully 10% owner | Jan 2, 2025 | Gift | −13,200 | – | – | 636,993 |
| William P. Scully 10% owner | Dec 31, 2024 | Buy | +1,200 | $13.37 | $16.04K | 619,393 |
| William P. Scully 10% owner | Dec 31, 2024 | Buy | +800 | $13.39 | $10.71K | 620,193 |
| William P. Scully 10% owner | Dec 31, 2024 | Buy | +30,000 | $12.99 | $389.70K | 650,193 |
Awards, option exercises, tax withholding and gifts are shown alongside open-market buys and sales. Each name links to the filing on SEC EDGAR.
Short interest
Shares sold short and not yet bought back, as of Oct 30, 2026 (FINRA, reported twice a month)
Short % of float
22.67%
8M shares short
Days to cover
15.7
At 1M shares a day
Change since last report
-0.4%
From 8M shares
Short volume, 20 days
65.0%
Of volume reported to FINRA
Shares sold short, last 12 months
Short sale volume counts trades marked short on any given day, including market-maker hedging, so it runs far higher than the share of Prothena Corp Public's stock actually held short. Settlement fails (shares not delivered on time) peaked at 6,503 shares on Aug 31, 2026 over the last 90 days.
Planned insider sales
Notices of proposed sale filed on Form 144 before shares are sold
| Seller | Filed | Shares | Market value | Planned sale | Acquired through |
|---|---|---|---|---|---|
| Michael John Isaacs Officer | Jul 29, 2026 | 8,386 | $71.06K | Jul 29, 2026 | Restricted Stock |
| Anne Evans Kingston Officer | Jul 29, 2026 | 7,662 | $64.92K | Jul 29, 2026 | Restricted Stock |
| Michael J. Malecek Previous Officer | Jun 9, 2026 | 80,000 | $740.00K | Jun 9, 2026 | EMPLOYEE RESTRICTED SHARE UNIT AWARD |
| Karin L. Walker Officer | Jan 24, 2024 | 5,000 | $170.00K | Jan 24, 2024 | Exercise of stock options |
| Karin L. Walker Officer | Dec 20, 2023 | 5,000 | $186.45K | Dec 20, 2023 | Exercise of Stock Options |
| Karin L. Walker Officer | Nov 30, 2023 | 5,000 | $170.00K | Nov 30, 2023 | Exercise of stock options |
| Karin L. Walker Officer | Oct 25, 2023 | 5,000 | $206.35K | Oct 25, 2023 | Exercise of Stock Options |
| Brandon S. Smith Officer | Oct 11, 2023 | 4,000 | $189.16K | Oct 11, 2023 | Exercise of Stock Options |
| Carol D. Karp Officer | Oct 4, 2023 | 5,000 | $237.00K | Oct 4, 2023 | Exercise of Stock Options |
| Michael J. Malecek Officer | Sep 27, 2023 | 5,000 | $241.05K | Sep 27, 2023 | Exercise of Stock Option |
| Patel Sanjiv Director | Sep 25, 2023 | 35,000 | $1.75M | Sep 25, 2023 | STOCK OPTION EXERCISE |
| Karin L. Walker Officer | Sep 19, 2023 | 5,000 | $261.81K | Sep 19, 2023 | Stock Option Exercise |
| Brandon S. Smith Officer | Sep 13, 2023 | 4,000 | $221.56K | Sep 13, 2023 | Exercise of stock options |
| Hideki Garren Officer | Sep 13, 2023 | 2,000 | $110.78K | Sep 13, 2023 | Exercise of Stock Options |
| Carol D. Karp Officer | Sep 6, 2023 | 5,000 | $273.05K | Sep 6, 2023 | Exercise of stock options |
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