New Insights into Chromosomal Regions 15p11.2-15q11.2 by Studying Submicroscopic Variations Using Molecular...

Area of Science:

• Genetics
• Molecular Cytogenetics
• Genomic Variation

Background:

• The 15p11.2-15q11.2 chromosomal region comprises both heterochromatic and euchromatic DNA.
• Previous reports identified heteromorphisms in 15p11.2-15q11.1 and a euchromatic variant (EV) region in 15q11.2.

Purpose of the Study:

• To investigate genomic variations within the 15p11.2-15q11.2 region using advanced molecular cytogenetics.
• To characterize the formation mechanisms of small supernumerary marker chromosomes 15 (sSMC(15)) and submicroscopic variations.

Main Methods:

• Utilized five-color fluorescence in situ hybridization (FISH) probe sets to analyze genomic regions at the single-cell level.
• Examined 44 cases with normal chromosomes 15, including 38 cases with sSMC(15).

Main Results:

• Determined frequencies of heteromorphisms for D15Z1 (16%), D15Z3 (7.4%), and D15Z4 (13.5%).
• Observed copy number gains or losses in the 15q11.2 EV region in 41% of examined chromosomes 15.
• Identified distinct breakpoint clusters for sSMC(15) formation compared to Prader-Willi/Angelman syndrome microdeletions; 25% of sSMC(15) cases resulted from interchromosomal U-type exchange.

Conclusions:

• Detailed molecular cytogenetic analysis of 15p11.2-15q11.2 provides novel insights into sSMC(15) formation.
• Highlights the importance of characterizing breakpoints in sSMC(15) and identifies novel asymmetric sSMCs.