De novo Xq11.11 microdeletion including ARHGEF9 in a boy with mental retardation, epilepsy, macrosomia, and dysmorphic features.

We report on a novel Xq11.11 microdeletion in a patient presenting with severe mental retardation (MR), focal epilepsy, tall stature, macrocephaly, and dysmorphism. This 1.3 Mb deletion, identified using array CGH, includes a single gene with known function-ARHGEF9-plus 1 gene with unknown function and three putative genes. ARHGEF9 encodes collybistin (Cb) that plays an important role in the localization of gephyrin which is the key protein of the scaffolding system of inhibitory synapses and is essential for postsynaptic clustering of both GABA(A) and glycine receptors. Cb-deficient male mice show reduced exploratory behavior, impaired spatial learning, increased anxiety scores, and reduction of gephyrin-dependent GABA receptor clusters in amygdala and hippocampus. Mutations or disruption of ARHGEF9 due to chromosomal rearrangements have been found in three patients with various clinical presentations: nevertheless, all 3 presented with MR and 2 with epilepsy. The case we report on provides further evidence for the role of ARHGEF9 in cognitive development. The other phenotypic features in our patient, including macrosomia and dysmorphism, may also be related to the loss of this gene. Alternatively, they may be consequences of the loss of one or more of the other genes located within the deletion or of the disruption of sequences regulating neighboring genes. Additional case reports with identical or overlapping deletions would help in defining the phenotype associated with ARHGEF9 haploinsufficiency.