• array CGH;
  • array comparative genomic hybridization;
  • chromosome 6q;
  • genotype-phenotype correlation;
  • interstitial deletion;
  • Prader-Willi syndrome;
  • SIM1 gene

Interstitial deletions of the long arm of chromosome 6 are relatively rare, with fewer than 100 cases reported. Phenotypic variation is in large part due to differences in size and location of the segmental aneuploidy. We report three new patients with interstitial deletions of chromosome 6q defined at the molecular level by array comparative genomic hybridization (array CGH). In two of three cases, the molecular breakpoints differed from those indicated by conventional karyotyping, demonstrating the enhanced resolution of array CGH. Two patients had minimal deletions of 6 and 8.8 Mb involving 6q16.2[RIGHTWARDS ARROW]q21, and the third patient had a deletion of 11.3 Mb spanning 6q15[RIGHTWARDS ARROW]q21. All three had developmental delay, craniofacial dysmorphology, and functional eye disorders, suggesting that genes affecting brain and craniofacial development are located in 6q16.2[RIGHTWARDS ARROW]q21, the deleted region common to all three patients. Furthermore, gene(s) for discordant phenotypic features, such as central diabetes insipidus, may reside at 6q15, the monosomic region unique to patient 3. All three cases described here showed loss of paternal alleles within the deleted segment, providing further evidence of the predominantly paternal origin for 6q deletions and rearrangements.