18q2133

18q21.33 is a cytogenetic location on the long arm (q) of chromosome 18. In human genetics, chromosomal positions are described using a banding pattern, and 18q21.33 refers to a sub-band within the q21 region. The precise base-pair coordinates of this band depend on the reference genome assembly being used (for example GRCh38), but in general it denotes a specific, relatively small segment of the chromosome that researchers and clinicians reference when describing rearrangements or testing results.

The region contains multiple genes and regulatory elements, with gene content that can vary somewhat between genome annotations. Because 18q21.33 is a band designation rather than a single gene, there is no single “18q21.33 gene”; rather, several genes may be located in or near this band depending on the annotation version.

Clinical significance associated with alterations in the 18q21.33 area is primarily described in the context of copy-number changes, such as deletions or duplications. Such alterations have been reported in individuals with developmental or neurodevelopmental concerns, congenital anomalies, and other phenotypes, but the observed effects are highly dependent on the size of the rearrangement and the specific genes affected. Consequently, interpretations require integration of genetic testing results with clinical features.

Detection methods commonly used to evaluate this region include karyotyping with G-banding, fluorescence in situ hybridization (FISH) using probes for 18q21.33, chromosomal microarray analysis (CMA) to identify copy-number changes, and sequencing-based approaches for breakpoint characterization when needed. In clinical genetics, 18q21.33 serves as a reference point for describing chromosomal rearrangements on chromosome 18.