LYSOGENE : Terms of availability of a registration document or its updates

PRESS RELEASE

Lysogene Announces Filing of 2021 Universal Registration

Document

Paris, France - 20 April 2022 at 08:00 am - Lysogene (FR0013233475 - LYS), a phase 3 gene therapy platform Company targeting central nervous system (CNS) diseases, today announced the filing of its 2021 Universal Registration Document (URD) with the French market authority "Autorité des Marchés Financiers" (AMF) on 19 April 2022.

This 2021 Registration Document includes in particular:

• • The annual financial report ;

• • The management report ;

• • The report on corporate governance.

This document can be accessed on the Investors section of the Company's website atwww.lysogene.com.In addition, the Universal Registration Document is available on the AMF's website atwww.amf-france.org.

Printed copies of both documents are available, free of charge, at the Company's headquarters and registered office located at 18-20 rue Jacques Dulud, 92 200 Neuilly-sur-Seine, France.

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 delivery of gene therapies to the CNS to treat lysosomal diseases and other disorders of the CNS. A phase 2/3 clinical trial in MPS IIIA is ongoing. An adaptive clinical trial in GM1 gangliosidosis is also ongoing. Lysogene is also developing an innovative AAV gene therapy approach 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 clinical trials 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, (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 2020 universal registration document, registered with the French Markets Authorities on April 12, 2021, under number D.21-0296, 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

[e-mail] + 33 1 41 43 03 99