Cytogenetics and Cytogenomics in Clinical Diagnostics: Genome Architecture, Structural Variants, and Translational Applications.

The spatial organization of the genome within the nucleus is a fundamental regulator of gene expression, genome stability, and cell identity. This review addresses the central question of how nuclear genome architecture contributes to disease mechanisms and diagnostics, and how technological advances enable its clinical exploration. We first outline the principles of nuclear genome architecture, including chromosome territories, replication timing, and 3D domains, and their role in gene regulation and disease. We then explore the mechanisms and consequences of chromosomal rearrangements, and how replication dynamics intersect with epigenetic regulation and genome stability. Diagnostic tools are presented in chronological progression, from conventional cytogenetics to high-resolution genomic and single-cell techniques. A dedicated section focuses on cancer cytogenomics and its clinical implications. We further highlight emerging technologies for 3D genome and epigenome profiling and their integration into diagnostic workflows. Finally, we discuss current challenges, such as standardization and cost, and the transformative potential of multi-omics and artificial intelligence for future precision diagnostics. Overall, we provide a comprehensive overview of how cytogenetics and cytogenomics contribute to the understanding and clinical diagnosis of genetic and neoplastic diseases.