CRISPR/Cas9 and reproductive failure: applications, ethical challenges, and future perspectives in human germline genome editing.

Reproductive failure affects millions of couples worldwide and frequently arises from genetic defects that impair gametogenesis, fertilization, or early embryonic development. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) genome-editing technology has emerged as a powerful experimental platform for dissecting infertility-associated genes and, in principle, correcting pathogenic variants in germline cells or preimplantation embryos. This review critically examines current applications of CRISPR/Cas9 in reproductive biology, including disease modeling in animal systems, editing of spermatogonial stem cells (SSCs), manipulation of oocytes and zygotes, and proof-of-concept studies in human embryos. Particular emphasis is placed on the major technical barriers that currently preclude clinical translation, including off-target mutagenesis, embryo mosaicism, and the low efficiency of homology-directed repair relative to non-homologous end joining. Limitations related to delivery strategies, DNA damage responses, chromosomal rearrangements, and the genetic heterogeneity of infertility are also evaluated. Comparative discussion highlights how germline editing differs fundamentally from somatic CRISPR therapies that have already reached clinical application in hematologic disorders. The review further analyzes ethical and regulatory challenges associated with heritable genome modification, including long-term safety, consent across generations, international governance disparities, and the continued reliance on assisted reproductive technologies combined with preimplantation genetic testing as safer clinical alternatives. Collectively, current evidence indicates that CRISPR/Cas9 remains primarily a research tool for elucidating reproductive biology rather than an imminent therapeutic option for human infertility. Continued technological refinement, rigorous preclinical validation, and globally harmonized oversight will be essential before germline applications can be ethically or clinically justified.