The purpose of this guidance is to provide recommendations regarding the chemistry, manufacturing, and controls (CMC) information that should be provided in an investigational new drug application (IND) submitted by a sponsor-investigator (hereafter referred to as sponsor) developing an individualized antisense oligonucleotide (ASO) drug product for a severely debilitating or life-threatening (SDLT) disease caused by a unique genetic variant where only a small number of individuals are prospectively identified (typically one or two). These individualized ASO drug products should be from a well-characterized chemical class for which there is substantial clinical and nonclinical experience that is either publicly available or to which the sponsor has a right to reference.