18q213

18q21.3 is a cytogenetic band on the long arm (q) of human chromosome 18. In standard chromosomal nomenclature, it denotes a specific subregion that is identified during karyotyping and used to describe structural variants such as deletions, duplications, or translocations. The band is part of the broader 18q21 region, located in the distal portion of the chromosome’s long arm.

Genes and content in this band can vary with genome builds and individual genetic variation. The 18q21.3 region contains multiple protein-coding and noncoding genes, but there is no single gene universally assigned to this exact band. Rather, 18q21.3 serves as a locus reference for mapping rearrangements and studying their potential effects. The clinical impact of a disruption in this area depends on the size of the rearrangement and on the neighboring genomic content.

Clinical significance and research use: Structural variants involving 18q21.3 have been reported in clinical genetics, often within the context of broader distal 18q deletions or complex chromosomal rearrangements. 18q deletion syndrome generally involves loss of distal 18q material, and contributions from 18q21.3 can influence phenotypic features in combination with adjacent regions. Researchers and clinicians use this band as a reference point for reporting breakpoints and for correlating genotype with phenotype. Detection methods include karyotyping, fluorescence in situ hybridization (FISH), array comparative genomic hybridization (array CGH), and sequencing. References to this band appear in standard genome maps such as GRCh38 coordinates and chromosome browsers.