Background: Pathogenic mutations in the X-linked Neuroligin 4 gene (NLGN4X) in autism spectrum disorders (ASDs) and/or mental retardation (MR) are rare. However, nothing is known regarding a possible altered expression level of NLGN4X that would be caused by mutations in regulatory sequences. We investigated this issue by analyzing these regions in patients with ASDs and no mutation in the NLGN4X coding sequence.
Methods: We studied 96 patients who met all DSM-IV criteria for autism. The entire coding sequence and the regulatory sequences of the NLGN4X gene were analyzed by polymerase chain reaction and direct sequencing.
Results: We identified a de novo 1 base pair (-335G>A) substitution located in the promoter region in a patient with autism and nonsyndromic profound MR. Interestingly, this variation is associated with an increased level of the NLGN4X transcript in the patient compared with male control subjects as well as his father. Further in vitro luciferase reporter and electrophoretic mobility shift assays confirmed, respectively, that this mutation increases gene expression and is probably caused by altered binding of transcription factors in the mutated promoter sequence.
Conclusions: This result brings further insight about the phenotypic spectrum of NLGN4X mutations and suggests that the analysis of the expression level of NLGN4X might detect new cases.