Casimersen, sold under the brand name Amondys 45, is an antisense oligonucleotide medication used for the treatment of Duchenne muscular dystrophy (DMD) in people who have a confirmed mutation of the dystrophin gene that is amenable to exon 45 skipping. It is an antisense oligonucleotide of phosphorodiamidate morpholino oligomer (PMO).The most common side effects include upper respiratory tract infections, cough, fever, headache, joint pain and throat pain.Casimersen was approved for medical use in the United States in February 2021, and it is the first FDA-approved targeted treatment for people who have a confirmed mutation of the DMD gene that is amenable to skipping exon 45. Medical uses
Casimersen is indicated for the treatment of Duchenne muscular dystrophy (DMD) in people who have a confirmed mutation of the DMD gene that is amenable to exon 45 skipping. History
Casimersen was evaluated in a double-blind, placebo-controlled study in which 43 participants were randomized 2:1 to receive either intravenous casimersen or placebo. All participants were male, between 7 and 20 years of age, and had a genetically confirmed mutation of the DMD gene that is amenable to exon 45 skipping.The U.S. Food and Drug Administration (FDA) granted the application for casimersen fast track, priority review, and orphan drug designations. The FDA granted the approval of Amondys 45 to Sarepta Therapeutics, Inc.

Pharmacodynamics
Duchenne Muscular Dystrophy is an X-linked recessive disorder that results in the absence of a functional dystrophin protein. Dystrophin protein is a protein that consists of an N-terminal actin-binding domain, C-terminal B-dystroglycan- binding domain, and 24 internal spectrum-like repeats.
Klippel–Feil syndrome (KFS), also known as cervical vertebral fusion syndrome, is a rare congenital condition characterized by the abnormal fusion of any two of the seven bones in the neck (cervical vertebrae). : 578  It results in a limited ability to move the neck and shortness of the neck, resulting in the appearance of a low hairline.The syndrome is difficult to diagnose, as it occurs in a group of patients affected with many different abnormalities who can only be unified by the presence of fused or segmental cervical vertebrae. KFS is not always genetic and not always known about on the date of birth. The disease was initially reported in 1884 by Maurice Klippel and André Feil from France. In 1919, in his Doctor of Philosophy thesis, André Feil suggested another classification of the syndrome, encompassing not only deformation of the cervical spine, but also deformation of the lumbar and thoracic spine. Signs and symptoms
KFS is associated with many other abnormalities of the body, hence thorough evaluation of all patients with fused cervical vertebrae at birth is required. Furthermore, it is unclear whether KFS is a unique disease, or if it is one part of a spectrum of congenital spinal deformities.KFS is usually diagnosed after birth.