Interstitial deletions of the long arm of chromosome 6 are rare. Clinically, 
these deletions are considered to be part of a unique microdeletion syndrome 
associated with intellectual disability and speech impairment, typical 
dysmorphic features, structural anomalies of the brain, microcephaly, and 
non-specific multiple organ anomalies. The critical region for the interstitial 
6q microdeletion phenotype was mapped to 6q24-6q25, particularly the 6q25.3 
region containing the genes ARID1B and ZDHHC14. It has been hypothesized that 
haploinsufficiency of these genes impairs normal development of the brain and is 
responsible for the phenotype. This case report describes a girl presenting with 
typical features of 6q microdeletion syndrome, including global developmental 
delay, speech impairment, distinct dysmorphic features, dysgenesis of the corpus 
callosum, common limb anomalies, and hearing loss. Chromosome analysis by 
array-CGH revealed a small interstitial 6q deletion spanning approximately 1.1 
Mb of DNA and containing only one coding gene, ARID1B. We suggest that ARID1B is 
the key gene behind 6q microdeletion syndrome, and we discuss its possible role 
in the phenotypic manifestations.