LYSOGENE Annual Ordinary and Extraordinary General Meeting of 26 June 2020 Availability of the Preparatory Documents

LYSOGENE Annual Ordinary and Extraordinary General Meeting of 26 June 2020 Availability of the Preparatory Documents 150 150 Lysogene

Paris, France — 20 May 2020 at 06:00pm CEST— Lysogene (FR0013233475 – LYS), a Phase 3 gene therapy platform company targeting central nervous system (CNS) diseases, informs its shareholders that its annual ordinary and extraordinary general meeting will be held behind closed doors, without the physical attendance by shareholders, on June 26, 2020 at 09:00am (CEST), at the offices of Dechert (Paris) LLP, located at 32 rue de Monceau in Paris (75008), France.

The preliminary notice of meeting including the agenda and the text of the resolutions was published in the French bulletin of compulsory legal notices (Bulletin des Annonces Légales Obligatoires – BALO) dated May 18, 2020. A copy is available on the Company’s website https://www.lysogene.com/media-center/assemblee- generale-2020/

As an exception, the Shareholders’ Meeting being held behind closed doors, shareholders will not be able to request an admission card to physically attend the Shareholders’ Meeting. Shareholders are invited to exercise their voting rights prior to the Meeting either by (i) voting by post, (ii) granting proxy to the Chairman of the Shareholders’ Meeting or (iii) granting proxy to another person of their choice.

The Shareholders’ Meeting documents and the voting form have been made available to Shareholders under the terms and conditions specified by current French regulations.

About Lysogene

Lysogene is a gene therapy company focused on the treatment of orphan diseases of the central nervous system (CNS). The company has built a unique capability to enable a safe and effective delivery of gene therapies to the CNS to treat lysosomal diseases and other genetic disorders of the CNS. A phase 2/3 clinical trial in MPS IIIA in partnership with Sarepta Therapeutics, Inc. is ongoing and a phase 1/3 clinical trial in GM1 gangliosidosis is in preparation. In accordance with the agreements signed between Lysogene and Sarepta Therapeutics, Inc., Sarepta Therapeutics, Inc. will hold exclusive commercial rights to LYS-SAF302 in the United States and markets outside Europe; and Lysogene will maintain commercial exclusivity of LYS-SAF302 in Europe. Lysogene is also collaborating with an academic partner to define the strategy of development for the treatment of Fragile X syndrome, a genetic disease related to autism. www.lysogene.com.

Forward Looking Statement

This press release may contain certain forward-looking statements, especially on the Company’s progress of its phase 2-3 clinical trial and cash runway. Although the Company believes its expectations are based on reasonable assumptions, all statements other than statements of historical fact included in this press release about future events are subject to (i) change without notice, (ii) factors beyond the Company’s control, (iii) clinical trial results, (iv) increased manufacturing costs and (v) potential claims on its products. These statements may include, without limitation, any statements preceded by, followed by or including words such as “target,” “believe,” “expect,” “aim,” “intend,” “may,” “anticipate,” “estimate,” “plan,” “objective”, “project,” “will,” “can have,” “likely,” “should,” “would,” “could” and other words and terms of similar meaning or the negative thereof. Forward-looking statements are subject to inherent risks and uncertainties beyond the Company’s control that could cause the Company’s actual results, performance or achievements to be materially different from the expected results, performance or achievements expressed or implied by such forward-looking statements. A further list and description of these risks, uncertainties and other risks can be found in the Company’s regulatory filings with the French Autorité des Marchés Financiers, including in the 2019 registration document (Document de référence), registered with the French Markets Authorities on April 30, 2020, under number D.20-0427, and future filings and reports by the Company. Furthermore, these forward-looking statements are only as of the date of this press release. Readers are cautioned not to place undue reliance on these forward-looking statements. Except as required by law, the Company assumes no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in the forward-looking statements, even if new information becomes available in the future. If the Company updates one or more forward-looking statements, no inference should be drawn that it will or will not make additional updates with respect to those or other forward-looking statements.

This press release has been prepared in both French and English. In the event of any differences between the two texts, the French language version shall supersede.

Contacts

Stéphane Durant des Aulnois Chief Financial Officer

stephane.durant-des-aulnois@lysogene.com

+ 33 1 41 43 03 99

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