See Molecular Genetics for details of the deletion.

Genomic coordinates represent the minimum deletion size associated with the 1q21.1 recurrent deletion as designated by ClinGen. Deletion coordinates may vary slightly based on array design used by the testing laboratory. Note that the size of the deletion as calculated from these genomic positions may differ from the expected deletion size due to the presence of segmental duplications near breakpoints. Previous reports have used various size ranges for this recurrent deletion, with the most common sizes used being 1.2 Mb and 1.35 Mb. However, these estimates likely include some of the flanking segmental duplication regions and are not specific to the unique DNA sequence [Mefford et al 2008, Brunetti-Pierri et al 2008, Bernier et al 2016, Bourgois et al 2023]. Therefore, these various size estimates (0.8 Mb, 1.2 Mb, and 1.35 Mb) should be considered the same from a clinical standpoint. The phenotype of significantly larger or smaller deletions within this region may be clinically distinct from the 1q21.1 recurrent deletion (see Genetically Related Disorders).

See Molecular Genetics for genes of interest included in this region.

Chromosome microarray analysis (CMA) using oligonucleotide arrays or SNP genotyping arrays. CMA designs in current clinical use target the 1q21.1 region. Note: The 1q21.1 recurrent deletion may not have been detectable by older oligonucleotide or BAC platforms.

Targeted deletion analysis methods can include FISH, quantitative PCR (qPCR), and multiplex ligation-dependent probe amplification (MLPA) as well as other targeted quantitative methods. Targeted deletion analysis is not appropriate for an individual in whom the 1q21.1 recurrent deletion was not detected by CMA designed to target this region.