SION insider ownership: who sold, why, and what they still hold

What stands out

Outside holders and shareholders represented on the board, not part of management, sold heavily: ORBIMED ADVISORS LLC ($55.7M), Peter Thompson ($55.7M) and RA CAPITAL MANAGEMENT, L.P. ($43.3M).ORBIMED ADVISORS LLC: largest sale, Apr 15, 2026 · Peter Thompson: largest sale, Apr 15, 2026 · RA CAPITAL MANAGEMENT, L.P.: largest sale, Sep 17, 2026

A share of stake is shown for 0 of the 2 officers and directors who sold. 13 are left out

Left out: Michael Cloonan, Elena Ridloff, Charlotte McKee, Bruce Booth, Paul Clancy, Harold Fleming, Joshua Resnick, Joanne Viney, Peter Thompson, Marcella Ruddy, Laurie Stelzer, Jennifer Fitzpatrick and Caroline Beer (share of stake is being verified).

Disclosed company stock is not an insider's whole wealth.

Who sold, and how much of their stake

Officers and directors, past 12 months. Their share of stake is being verified and is not shown yet; amounts and trading plans are below.

Michael Cloonan

President & CEO, Director

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$4.4MDisclosed plan

Jennifer Fitzpatrick

CLO and Head of Program Mgmt.

Not confirmed

Share of stake not shown: share of stake is being verified. Why

$1.2MDisclosed plan

Amounts, filings and trading plans for each seller

Selling by month

Officers and directors, Oct 2025 to Oct 2026. Each sale is counted once: under a disclosed plan, else to cover taxes, else no plan disclosed.

Disclosed planOne dollar scale for every month; the tallest bar is labeled

Recent activity

Past 30 days, Sep 14, 2026 to Oct 13, 2026

No officer or director trades were reported for the past 30 days. The most recent before that:

Jul 6, 2026Jennifer Fitzpatrick sold 10K shares ($447K) under a disclosed trading plan. 10K shares came in from vesting or option exercises the same day, so the holding rose by 0 net.

Who	Shares	Price	% of total stake	Total stake after	Trade date	Filed
Jennifer Fitzpatrick CLO and Head of Program Mgmt.	10,250	$43.60	n/a	n/a	Jul 6, 2026	Jul 7, 2026

Outside holders, reported separately

RA CAPITAL MANAGEMENT, L.P. sold $43.3M, TPG GP A, LLC sold $10.0M and ORBIMED ADVISORS LLC sold $55.7M, plus 2 more in the past 12 months. Large shareholders and the funds or companies that board members represent are not part of management, so they are left out of the figures above.

Details

Common questions

Is the Sionna Therapeutics, Inc. CEO selling stock?

Yes. Michael Cloonan sold 125K shares ($4.4M) in the past 12 months, all of it under a trading plan disclosed in the filings.

Why are Sionna Therapeutics, Inc. insiders selling?

Filings rarely give a reason, and we don't guess at one. What they show is how the sales were made: 100% of sales by value ran under 10b5-1 trading plans disclosed in the filings. A trading plan schedules sales in advance.

Are any Sionna Therapeutics, Inc. insiders buying?

No. Officers and directors reported no purchases in the past 12 months.

The evidence

Who sold2 officers and directors: amount, % of holdings, trading plan

Who sold	Amount	% of holdings	Trading plan
Michael Cloonan President & CEO, Director	$4.4M 125K shares	Not confirmed share of stake is being verified. Why	Disclosed plan
Jennifer Fitzpatrick CLO and Head of Program Mgmt.	$1.2M 31K shares	Not confirmed share of stake is being verified. Why	Disclosed plan

Board members representing outside shareholders, reported separately: Peter Thompson (the shareholder sold $55.7M), Bruce Booth (the shareholder sold $15.9M). Details

Outside holder, reported separately: RA CAPITAL MANAGEMENT, L.P. (a 10% owner, not part of management). Sold $43.3M (3.99M shares) from Oct 24, 2025 to Sep 17, 2026. Latest filing

Outside holder, reported separately: TPG GP A, LLC (a 10% owner, not part of management). Sold $10.0M (250K shares) from Jan 22, 2026 to Jan 22, 2026. Latest filing

Outside holder, reported separately: ORBIMED ADVISORS LLC (an outside shareholder, not part of management). Sold $55.7M (1.24M shares) from Nov 24, 2025 to Jul 7, 2026. Latest filing

The full ownership picture0 of 13 officers and directors confirmed

Vested shares across all share classes, held directly and through trusts, LLCs and family members, as reported on SEC Forms 3, 4 and 5. Unvested awards and options are never counted as owned shares.

Insider

Held Oct 13, 2025

Sold

Held Oct 13, 2026

Still held

Michael Cloonan

Holdings and share of stake are being verified. Share-of-stake figures and holdings for this company are held back while they are verified. Sales and other transactions for Michael Cloonan are complete.

President & CEO, Director

n/a

−125K

n/a

Vesting, gifts, unvested awards and holding lines for Michael Cloonan

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Michael Cloonan are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
332,459	$6.11	Mar 1, 2032	$449K
656,984	$6.11	Mar 12, 2034	$887K
450,252	$18.00	Feb 5, 2035	$0
53,142	$6.11	Mar 1, 2032	$72K
436,100	$7.18	Jan 1, 2036	$122K

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Elena Ridloff

CFO and CBO

n/a

Vesting, gifts, unvested awards and holding lines for Elena Ridloff

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Elena Ridloff are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
32,509	$0.78	Sep 16, 2031	$217K
109,605	$6.11	Mar 1, 2032	$148K
145,751	$6.11	Mar 12, 2034	$197K
157,820	$18.00	Feb 5, 2035	$0
165,440	$7.18	Jan 1, 2036	$46K

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Charlotte McKee

CMO and Head of R&D

n/a

Vesting, gifts, unvested awards and holding lines for Charlotte McKee

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Charlotte McKee are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
107,020	$6.11	Mar 1, 2032	$144K
141,865	$6.11	Mar 12, 2034	$192K
148,536	$18.00	Feb 5, 2035	$0
155,700	$7.18	Jan 1, 2036	$44K

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Bruce Booth

Director

n/a

Vesting, gifts, unvested awards and holding lines for Bruce Booth

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Bruce Booth are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Paul Clancy

Director

n/a

Vesting, gifts, unvested awards and holding lines for Paul Clancy

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Paul Clancy are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
119,772	$6.11	May 25, 2032	$162K
65,713	$6.11	Mar 12, 2034	$89K
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Harold Fleming

Director

n/a

Vesting, gifts, unvested awards and holding lines for Harold Fleming

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Harold Fleming are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Joshua Resnick

Director

n/a

Vesting, gifts, unvested awards and holding lines for Joshua Resnick

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Joshua Resnick are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Joanne Viney

Director

n/a

Vesting, gifts, unvested awards and holding lines for Joanne Viney

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Joanne Viney are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
39,919	$18.00	Feb 5, 2035	$0
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Peter Thompson

Director

n/a

Vesting, gifts, unvested awards and holding lines for Peter Thompson

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Peter Thompson are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Marcella Ruddy

Director

n/a

Vesting, gifts, unvested awards and holding lines for Marcella Ruddy

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Marcella Ruddy are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
39,919	$18.00	Feb 5, 2035	$0
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Laurie Stelzer

Director

n/a

Vesting, gifts, unvested awards and holding lines for Laurie Stelzer

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Laurie Stelzer are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
44,480	$10.33	Nov 13, 2034	$0
19,959	$16.99	Jun 11, 2035	$0
17,340	$36.73	Jun 16, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Jennifer Fitzpatrick

CLO and Head of Program Mgmt.

n/a

−31K

n/a

Vesting, gifts, unvested awards and holding lines for Jennifer Fitzpatrick

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Jennifer Fitzpatrick are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
147,149	$6.11	Jul 14, 2034	$199K
120,686	$18.00	Feb 5, 2035	$0
40,685	$6.11	Jul 14, 2034	$55K
103,140	$7.18	Jan 1, 2036	$29K

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Caroline Beer

Chief Business Officer

n/a

Vesting, gifts, unvested awards and holding lines for Caroline Beer

Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Caroline Beer are complete; balances and unit counts will be added when the check is finished.

0gifted (net of own trusts)

Stock options (not counted as shares):

Options held	Strike price	Expires	Intrinsic value (estimate)
255,000	$28.47	Sep 30, 2035	$0
139,340	$39.21	Jan 1, 2036	$0

Estimate: options held × ($7.46 − strike price), using the most recent insider trade price on Form 4 (Sep 17, 2026), not a market close.

Holdings and share of stake for Sionna Therapeutics, Inc. are being verified, so no balances, unit counts or percentages are shown. Sales, proceeds, plan and tax status, titles and dates come straight from individual filings.

What explains the selling$5.6M of sales by plan status, purpose, seller and month

Officer and director open-market sales: $5.6M across 155,750 shares. Plan status and stated purpose are separate questions, and a sale can have both.

By plan status

Disclosed plan · $5.6M · 100%

Seller	Shares sold	Proceeds	Under a disclosed plan	Share of total	Sales dates
Michael Cloonan President & CEO, Director	125K	$4.4M	100%	78%	Oct 15, 2025 to Oct 21, 2025
Jennifer Fitzpatrick CLO and Head of Program Mgmt.	31K	$1.2M	100%	22%	Dec 5, 2025 to Jul 6, 2026

Sales by month

Month	Sale proceeds	Disclosed plan	To cover taxes	No plan disclosed
Oct 2025	$4.4M	$4.4M	$0	$0
Nov 2025	$0	$0	$0	$0
Dec 2025	$415K	$415K	$0	$0
Jan 2026	$0	$0	$0	$0
Feb 2026	$0	$0	$0	$0
Mar 2026	$347K	$347K	$0	$0
Apr 2026	$0	$0	$0	$0
May 2026	$0	$0	$0	$0
Jun 2026	$0	$0	$0	$0
Jul 2026	$447K	$447K	$0	$0
Aug 2026	$0	$0	$0	$0
Sep 2026	$0	$0	$0	$0
Oct 2026	$0	$0	$0	$0

Board members representing outside shareholders (2)Listed and sourced; not part of the management totals or the answer line

Directors whose reported holdings sit mostly in an investment fund or a corporate shareholder they represent, not in their own name, with beneficial ownership disclaimed except for their own financial interest. Listed and sourced here; not part of the management totals or the answer line. Shares a fund hands to its own investors are distributions, not sales.

Board member	Held Oct 13, 2025	Sold	Held Oct 13, 2026	Still held
Peter Thompson ! Holdings and share of stake are being verified. Share-of-stake figures and holdings for this company are held back while they are verified. Sales and other transactions for Peter Thompson are complete. Director	n/a	−1.24M	n/a	n/a
Vesting, gifts, unvested awards and holding lines for Peter Thompson Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Peter Thompson are complete; balances and unit counts will be added when the check is finished. 0gifted (net of own trusts) Some sales match sales reported by ORBIMED ADVISORS LLC exactly (date, shares and price). Possibly the same shares reported by both; the filings don't confirm it.
Bruce Booth ! Holdings and share of stake are being verified. Share-of-stake figures and holdings for this company are held back while they are verified. Sales and other transactions for Bruce Booth are complete. Director	n/a	−492K	n/a	n/a
Vesting, gifts, unvested awards and holding lines for Bruce Booth Holdings and share of stake are being verified. Sales, proceeds, plan and tax status and dates for Bruce Booth are complete; balances and unit counts will be added when the check is finished. 0gifted (net of own trusts)

Known gaps and uncertainty13 officers and directors not confirmed

Holdings and share of stake are being verified. Balances, unit counts and every share-of-stake figure for Sionna Therapeutics, Inc. are held back until that check is finished. Sales, proceeds, plan and tax status, titles and dates come straight from individual filings and are complete.

External context: we only cite outside events when a documented connection exists. None is shown for this period.

Sources and methodology100 filings on record, 51 filed in the 12-month period, and how we read them

All 100 Forms 3, 4 and 5 on record for Sionna Therapeutics, Inc. (SEC CIK 2036042), filed from Feb 6, 2025 to Sep 21, 2026; 51 of them were filed in the 12 months this page covers, retrieved from SEC EDGAR on Oct 13, 2026. Prices are the ones reported in each filing, often weighted averages.

Holdings. Each holding line (a share class plus an owner, such as a trust or LLC) carries its last reported balance forward. Entities first reported during the period start at zero, so transfers between an insider's own trusts don't count as selling. Lines not reported for three years or more are listed separately and left out of totals.

Sales. A sale counts as under a 10b5-1 plan if its footnote cites one or the filing's Rule 10b5-1 box is checked, and as tax-related if its footnote cites tax obligations or sell-to-cover. Shares withheld by the company for taxes are listed separately. Sales with neither attribute are labeled "no plan disclosed".

Full methodology

Former or inactive filers (2)No filing in 18 months; last reported balances, not in any total

Name	Last filed	Last reported balance
Atlas Venture Fund XI, L.P.	Feb 10, 2025	3,694,020 shares, last reported balance as of Feb 10, 2025
Lucian Iancovici		No balance on record

Spotted something wrong on this page? Report an error. We check every report against the SEC filing and list what we fix in the corrections log.

Sionna Therapeutics, Inc. insiders sold $5.6M in the past 12 months. How much of their stake is that?

What stands out

Who sold, and how much of their stake

Selling by month

Recent activity

Outside holders, reported separately

Common questions

Is the Sionna Therapeutics, Inc. CEO selling stock?

Why are Sionna Therapeutics, Inc. insiders selling?

Are any Sionna Therapeutics, Inc. insiders buying?

The evidence

Sales by month