Avidity Biosciences, Inc. → Atrium Therapeutics, Inc. RNA
| Parent | Avidity Biosciences, Inc. |
|---|---|
| Spinco | Atrium Therapeutics, Inc. RNA |
| Status | Completed |
| Structure | Spin-off A filing states a pro-rata distribution: holders receive shares automatically. |
| Focus | Not focus-increasing Parent and spinco remain in the same industry; the separation divides scale rather than business. |
| Ratio | 1 Atrium share for every 10 Avidity shares |
| Ratio note | Holders had to hold their Avidity shares from the record date through the distribution date to receive Atrium stock — there was no ex-distribution market to sell into early. |
| Checked against EDGAR | 2026-08-21 |
Data trap
Atrium trades under RNA, the ticker Avidity itself used before the separation. Its own standalone reporting began with the 10-Q filed 2026-05-14, but the symbol collision does not expire with that filing: vendor price and fundamental histories keyed on the ticker rather than the CIK still splice Avidity's pre-February-2026 record onto Atrium's, showing a clinical-stage company with years of history it never had. Join on CIK 2093101.
The restated filings have landed; this is kept as history.
Catalyst clock
- 2025-10-25Separation announced
- 2025-12-10Form 10 filed
- 2026-02-17Form 10 last amended
- 2026-02-26Form 10 effective
- 2026-02-12Record date
- —When-issued trading opens
- 2026-02-26Distribution
- —First standalone earnings
- —Index inclusion announced
Performance since separation
| Atrium Therapeutics, Inc. since separation | -10.51% |
|---|---|
| Avidity Biosciences, Inc. over the same window | never listed separately |
| S&P 500 (SPY) over the same window | +11.09% |
| Russell 2000 (IWM) over the same window | +12.77% |
| Excess over the S&P 500 | -21.60% |
| Excess over the Russell 2000 | -23.28% |
Measured from the first regular-way close on or after the distribution — 2026-02-27 at 14.75 — to 2026-08-21 at 13.20. Window: 6 months. That is a short window. Treat it as a fact about these few weeks, not as evidence about how the separation turns out. Two benchmarks, because one is misleading: spin-offs are usually small companies, and across this period small caps lagged the S&P by several points a year on their own. Measured against the S&P alone, roughly a third of any shortfall is company size rather than the separation. Returns are arithmetic over end-of-day closing prices. Unlike every other figure on this page, they do not come from a filing.
Filings
Every fact on this page comes from one of these.
- 10-12Bfiled 2025-12-10 · 0001193125-25-314415Initial Form 10 registration statement for the precision cardiology programs
- 10-12B/Afiled 2026-02-17 · 0001193125-26-055010Final amendment to the Form 10
- 8-Kfiled 2026-02-26 · 0001193125-26-077105Form 10 effectiveness and completion of the distribution; Ex-99.1 final information statement states the February 12 record date, the 1-for-10 ratio and that there would be no when-issued or ex-distribution trading
- 8-Kfiled 2026-02-27 · 0001193125-26-083227Separation agreements and completion detail
- 10-Qfiled 2026-05-14 · 0001193125-26-224243First standalone quarterly report
Notes
Executed as a condition of Novartis's acquisition of Avidity: the separation agreement and the merger agreement are both dated 2025-10-25, and the parent was taken private days after the spin, which is why EDGAR now reports no ticker for Avidity. The distribution was TAXABLE to Avidity holders — unusual and material for cost basis. The information statement states plainly that there would be no when-issued and no ex-distribution trading, so both fields are null by fact rather than by ignorance. The record date (February 12) preceded Form 10 effectiveness (February 26) because the timetable was set by the merger; the validator flags that ordering as unusual by design.