Avidity Bioscience spun off Atrium Therapeutics as an independent company. The structure of the spinoff was the distribution of Atrium Therapeutics shares as a taxable dividend. The distribution ratio for Avidity Bioscience shareholders is one share of Atrium for every 10 shares of Avidity Bioscience. The total Atrium shares received will be 0.1 x (# of Avidity Bioscience shares owned).
The Avidity Bioscience spin off of Atrium was part of a larger transaction in which Novartis purchased Avidity for $72.00 per Avidity share after the spinoff. The spinoff company changed its name to Atrium Therapeutics and took the same ticker symbol, RNA, as its original parent company, Avidity. This can cause some confusion when the parent company and spinoff daughter company have the same ticker symbol.

This action will need multiple entries in the accounting software. The information below is based on the information available from an Avidity SEC filing. That filing is available on the Avidity web site at this URL:
https://investors.aviditybiosciences.com/sec-filings?o=50
Scroll down to the DEFM14A filing dated January 30, 2026.

The Fair Market Value (FMV) of the distribution and the cost basis of the Atrium shares received possibly will not match your broker records. Tax law and IRS regulations do not specify how FMV is determined. The FMV of Atrium shares in these instructions use the average of the hi and low price of RNA (Atrium) on February 27, 2026 This price was 14.50 rounded to the nearest penny.

The Dividend Entry
Go to Accounting > Securities > Cash Distribution depending on the version of the software being used. Here is the information you need to complete the dividend entry.

• Symbol: RNA (Avidity Bioscience)
• Payout date: 2/26/2026
• Ex-Dividend date:  1/12/2026 (Record date to receive dividend.)
• Type : Dividend
• Amount: [14.50 x 0.1  x  (# of RNA shares owned) ]
  • # of Atrium  shares received = 0
  • 14.50 = average price of RNA  shares on the first regular trading day, 2/27/2026
  • For example, if you owned 100 shares of Avidity your amount would be
  • 14.50 x 0.1 x 100 = 145.00

Save the transaction and the dividend has been entered.

The Sell Entry
This sell accounts for the acquisition of Avidity by Novartis.
Accounting > Securities > Sell. Here is the information you need to complete the sell.

Step 1

• Date: 2/26/2026
• Symbol : RNA (Avidity Bioscience)

Step 2

• Shares Sold :  Sell all shares owned. (Use the Sell all link to be sure all are sold.)
• Net Proceeds: 72.00 x (# of Avidity shares owned)
  • For example, if 100 shares Avidity owned, enter 7200. (100 x 72.00)
  • You can also check your broker statement

The Buy Entry
This buy is to account for the receipt of Atrium shares
Accounting > Securities > Buy in myICLUB. Here is the information you need to complete the buy.

• Date: 2/27/2026
• Symbol :  RNA (Atrium Therapeutics)
• Shares :  0.1 x (# of Avidity shares owned). Include fractional shares, if any.
  • For example, if you owned 100 RNA shares, you were entitled to 100 x 0. 1= 10 RNA  shares.
  • If you owned 75 RNA shares, you were entitled to 75 x 0. 1= 7.5 RNA  shares.
• Total Cost: Use the same value as the Amount from the dividend entry above.
  • Be sure to use the same cash account for the Dividend entry and the Buy entry.
  • If your buy transaction included fractional RNA  shares, continue to the next step. If not, you are done with this spinoff

The Sell Entry
This sale accounts for the sale of fractional shares of Atrium received in the spinoff, if any.
Accounting > Securities > Sell. Here is the information you need to complete the sell.

Step 1

• Date: 2/27/2025
• Symbol : RNA (Atrium Therapeutics)

Step 2

• Shares Sold :  The fractional part of the shares bought in the Buy Transaction above.
  • For example, if you owned 75 shares of Avidity, you were entitled to 75 x 0.1 = 7.5 Atrium  shares. Sell 0.5 shares 
• Net Proceeds: Use the cash-in-lieu amount from your broker statement.

When saved you are finally done with all transactions related to this spinoff.

NOTE 1: Since the ticker symbol RNA was used by both the parent and spinoff companies be sure the buy of RNA for the receipt of Atrium shares, shows Atrium as the company name.

NOTE 2: The value of the shares received as a dividend is determined by the Fair Market Value (FMV) of the shares on the distribution date. IRS regulations do not have one way to determine FMV. It is therefore possible these instructions and your broker may determine FMV differently resulting in a mismatch in cost basis for the RNA (Atrium) shares held. This is not cause for concern. This is just due to the inexact nature of the tax code in this regard. Partnership tax returns have specific areas to reconcile these usually small differences. ICLUBcentral tax printer software automatically fills in these differences in the normal operation of the software using the data imported from your accounting records and that you enter from your 1099.