Prothena Corporation plc
US ˙ NasdaqGS ˙ IE00B91XRN20

SecurityPRTA / Prothena Corporation plc
InstitutionCitigroup Inc
Latest Disclosed Ownership8,150 shares
Latest Disclosed Value $ 79,218
Citigroup Inc ownership in PRTA / Prothena Corporation plc

On May 11, 2026 - Citigroup Inc filed a 13F-HR form disclosing ownership of 8,150 shares of Prothena Corporation plc (US:PRTA) valued at $79,218 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 13, 2026 disclosing 12,318 shares of Prothena Corporation plc. This represents a change in shares of -33.84% during the quarter. The current value of the position is $72,698 USD.

Citigroup Inc has a history of taking positions in derivatives of the underlying security (PRTA) in the form of stock options. The firm currently holds call options representing 0 of underlying shares valued at $0 USD and put options representing 0 of underlying shares valued at $0 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

PRTA / Prothena Corporation plc Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-05-11 2026-03-31 13F PROTHENA CORP SHS G72800108 8,150 -4,168 -33.84 79 -32.48 0.0000
2026-02-13 2025-12-31 13F PROTHENA CORP SHS G72800108 12,318 8,726 242.93 118 234.29 0.0001
2025-11-10 2025-09-30 13F PROTHENA CORP SHS G72800108 3,592 -45,711 -92.71 35 -88.29 0.0000
2025-08-11 2025-06-30 13F PROTHENA CORP SHS G72800108 49,303 -16,523 -25.10 299 -63.27 0.0001
2025-05-12 2025-03-31 13F PROTHENA CORP SHS G72800108 65,826 -2,607 -3.81 815 -14.04 0.0004
2025-02-12 2024-12-31 13F PROTHENA CORP SHS G72800108 68,433 36,359 113.36 948 76.68 0.0006
2024-11-12 2024-09-30 13F PROTHENA CORP SHS G72800108 32,074 7,410 30.04 537 5.30 0.0003
2024-08-12 2024-06-30 13F PROTHENA CORP SHS G72800108 24,664 -235,208 -90.51 509 -92.09 0.0003
2024-05-10 2024-03-31 13F PROTHENA CORP SHS G72800108 259,872 172,291 196.72 6,437 102.29 0.0042
2024-02-09 2023-12-31 13F PROTHENA CORP SHS G72800108 87,581 19,651 28.93 3,183 -2.90 0.0022
2023-12-06 2023-09-30 13F/A-1 PROTHENA CORP SHS G72800108 67,930 20,378 42.85 3,278 0.96 0.0025
2023-11-09 2023-09-30 13F PROTHENA CORP SHS G72800108 67,930 20,378 3,278 0.0010
2023-08-10 2023-06-30 13F PROTHENA CORP SHS G72800108 47,552 -67,248 -58.58 3,247 -41.66 0.0021
2023-05-11 2023-03-31 13F PROTHENA CORP SHS G72800108 114,800 51,400 81.07 5,564 45.69 0.0039
2023-02-09 2022-12-31 13F PROTHENA CORP SHS G72800108 63,400 -34,744 -35.40 3,820 -35.83 0.0030
2022-11-10 2022-09-30 13F PROTHENA CORP SHS G72800108 98,144 12,762 14.95 5,951 156.84 0.0043
2022-08-10 2022-06-30 13F PROTHENA CORP SHS G72800108 85,382 59,797 233.72 2,317 147.28 0.0017
2022-05-12 2022-03-31 13F PROTHENA CORP SHS G72800108 25,585 -74,703 -74.49 937 -81.09 0.0006
2022-02-10 2021-12-31 13F PROTHENA CORP SHS G72800108 100,288 47,003 88.21 4,954 30.51 0.0027
2021-11-10 2021-09-30 13F PROTHENA CORP SHS G72800108 53,285 -3,067 -5.44 3,796 31.03 0.0022
2021-08-10 2021-06-30 13F PROTHENA CORP SHS G72800108 56,352 1,257 2.28 2,897 109.47 0.0017
2021-05-13 2021-03-31 13F PROTHENA CORP SHS G72800108 55,095 47,523 627.61 1,383 1,419.78 0.0009
2021-02-11 2020-12-31 13F PROTHENA CORP SHS G72800108 7,572 4,665 160.47 91 213.79 0.0001
2020-11-12 2020-09-30 13F PROTHENA CORP SHS G72800108 2,907 -19,042 -86.76 29 -87.39 0.0000
2020-08-12 2020-06-30 13F PROTHENA CORP SHS G72800108 21,949 2,197 11.12 230 9.00 0.0002
2020-05-12 2020-03-31 13F PROTHENA CORP SHS G72800108 19,752 1,194 6.43 211 -27.99 0.0002
2020-02-12 2019-12-31 13F PROTHENA CORP SHS G72800108 18,558 -19,445 -51.17 293 -1.35 0.0002
2019-11-08 2019-09-30 13F PROTHENA CORP SHS G72800108 38,003 -27,191 -41.71 297 -56.96 0.0002
2019-08-12 2019-06-30 13F PROTHENA CORP SHS G72800108 65,194 26,364 67.90 690 46.50 0.0006
2019-05-13 2019-03-31 13F PROTHENA CORP SHS G72800108 38,830 -142,416 -78.58 471 -74.76 0.0005
2019-02-12 2018-12-31 13F PROTHENA CORP SHS G72800108 181,246 104,539 136.28 1,866 85.86 0.0019
2018-11-13 2018-09-30 13F PROTHENA CORP SHS G72800108 76,707 -37,343 -32.74 1,004 -39.63 0.0009
2018-08-10 2018-06-30 13F PROTHENA CORP SHS G72800108 114,050 68,242 148.97 1,663 -1.07 0.0015
2018-05-11 2018-03-31 13F PROTHENA CORP SHS G72800108 45,808 9,517 26.22 1,681 23.51 0.0014
2018-02-12 2017-12-31 13F PROTHENA CORP SHS G72800108 36,291 18,675 106.01 1,361 19.28 0.0011
2017-11-13 2017-09-30 13F PROTHENA CORP SHS G72800108 17,616 -7,142 -28.85 1,141 -14.79 0.0009
2017-08-11 2017-06-30 13F PROTHENA CORP SHS G72800108 24,758 -3,966 -13.81 1,339 -16.47 0.0012
2017-05-12 2017-03-31 13F PROTHENA CORP SHS G72800108 28,724 -66,041 -69.69 1,603 -65.61 0.0014
2017-02-10 2016-12-31 13F PROTHENA CORP SHS G72800108 94,765 86,064 989.13 4,661 794.63 0.0042
2016-11-10 2016-09-30 13F PROTHENA CORP SHS G72800108 8,701 3,192 57.94 521 169.95 0.0005
2016-08-12 2016-06-30 13F PROTHENA CORP SHS G72800108 5,509 -21,988 -79.97 193 -82.94 0.0002
2016-05-13 2016-03-31 13F PROTHENA CORP SHS G72800108 27,497 19,715 253.34 1,131 113.80 0.0013
2016-02-12 2015-12-31 13F PROTHENA CORP SHS G72800108 7,782 -3,728 -32.39 529 1.54 0.0005
2015-11-13 2015-09-30 13F PROTHENA CORP SHS G72800108 11,510 4,022 53.71 521 31.90 0.0005
2015-08-13 2015-06-30 13F PROTHENA CORP SHS G72800108 7,488 -1,812 -19.48 395 11.27 0.0004
2015-05-14 2015-03-31 13F PROTHENA CORP SHS G72800108 9,300 -5,365 -36.58 355 16.78 0.0003
2015-02-17 2014-12-31 13F PROTHENA CORP SHS G72800108 14,665 12,834 700.93 304 660.00 0.0003
2014-11-14 2014-09-30 13F PROTHENA CORP SHS G72800108 1,831 1,190 185.65 40 185.71 0.0000
2014-08-14 2014-06-30 13F PROTHENA CORP SHS G72800108 641 -3,485 -84.46 14 -91.14 0.0000
2014-05-15 2014-03-31 13F PROTHENA CORP SHS G72800108 4,126 -3,389 -45.10 158 -20.60 0.0002
2014-02-14 2013-12-31 13F PROTHENA CORP SHS G72800108 7,515 5,099 211.05 199 306.12 0.0002
2013-11-14 2013-09-30 13F PROTHENA CORP SHS G72800108 2,416 -5,719 -70.30 49 -53.77 0.0000
2013-08-14 2013-06-30 13F PROTHENA CORP SHS G72800108 8,135 8,135 106 0.0001
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2023-12-06 2023-09-30 13F/A PROTHENA CORP SHS Call 0 -100.00 0 -100.00 n/a n/a n/a
2023-11-09 2023-09-30 13F PROTHENA CORP SHS Call 0 0 n/a n/a n/a
2023-08-10 2023-06-30 13F PROTHENA CORP SHS Call 25,000 1,707 n/a n/a n/a
2020-02-12 2019-12-31 13F PROTHENA CORP SHS Call 0 -100.00 0 -100.00 n/a n/a n/a
2019-11-08 2019-09-30 13F PROTHENA CORP SHS Call 500 -16.67 4 -33.33 n/a n/a n/a
2019-08-12 2019-06-30 13F PROTHENA CORP SHS Call 600 0.00 6 -14.29 n/a n/a n/a
2019-05-13 2019-03-31 13F PROTHENA CORP SHS Call 600 -96.13 7 -95.62 n/a n/a n/a
2019-02-12 2018-12-31 13F PROTHENA CORP SHS Call 15,500 -23.65 160 -39.85 n/a n/a n/a
2018-11-13 2018-09-30 13F PROTHENA CORP SHS Call 20,300 70.59 266 52.87 n/a n/a n/a
2018-08-10 2018-06-30 13F PROTHENA CORP SHS Call 11,900 -36.70 174 -74.78 n/a n/a n/a
2018-05-11 2018-03-31 13F PROTHENA CORP SHS Call 18,800 55.37 690 51.98 n/a n/a n/a
2018-02-12 2017-12-31 13F PROTHENA CORP SHS Call 12,100 -5.47 454 -45.24 n/a n/a n/a
2017-11-13 2017-09-30 13F PROTHENA CORP SHS Call 12,800 166.67 829 218.85 n/a n/a n/a
2017-08-11 2017-06-30 13F PROTHENA CORP SHS Call 4,800 41.18 260 36.84 n/a n/a n/a
2017-05-12 2017-03-31 13F PROTHENA CORP SHS Call 3,400 750.00 190 850.00 n/a n/a n/a
2017-02-10 2016-12-31 13F PROTHENA CORP SHS Call 400 -63.64 20 -69.70 n/a n/a n/a
2016-11-10 2016-09-30 13F PROTHENA CORP SHS Call 1,100 66 n/a n/a n/a
Disclosed Put Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share Price Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2023-12-06 2023-09-30 13F/A PROTHENA CORP SHS Put 0 -100.00 0 -100.00 n/a n/a n/a
2023-11-09 2023-09-30 13F PROTHENA CORP SHS Put 0 0 n/a n/a n/a
2023-08-10 2023-06-30 13F PROTHENA CORP SHS Put 25,000 1,707 n/a n/a n/a
2019-05-13 2019-03-31 13F PROTHENA CORP SHS Put 0 -100.00 0 -100.00 n/a n/a n/a
2019-02-12 2018-12-31 13F PROTHENA CORP SHS Put 37,400 -17.07 385 -34.75 n/a n/a n/a
2018-11-13 2018-09-30 13F PROTHENA CORP SHS Put 45,100 43.63 590 28.82 n/a n/a n/a
2018-08-10 2018-06-30 13F PROTHENA CORP SHS Put 31,400 318.67 458 66.55 n/a n/a n/a
2018-05-11 2018-03-31 13F PROTHENA CORP SHS Put 7,500 134.38 275 129.17 n/a n/a n/a
2018-02-12 2017-12-31 13F PROTHENA CORP SHS Put 3,200 -78.67 120 -87.65 n/a n/a n/a
2017-11-13 2017-09-30 13F PROTHENA CORP SHS Put 15,000 248.84 972 317.17 n/a n/a n/a
2017-08-11 2017-06-30 13F PROTHENA CORP SHS Put 4,300 -77.49 233 -78.14 n/a n/a n/a
2017-05-12 2017-03-31 13F PROTHENA CORP SHS Put 19,100 213.11 1,066 255.33 n/a n/a n/a
2017-02-10 2016-12-31 13F PROTHENA CORP SHS Put 6,100 96.77 300 61.29 n/a n/a n/a
2016-11-10 2016-09-30 13F PROTHENA CORP SHS Put 3,100 186 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.