👤 Lonnie Zwaigenbaum

The GPHN gene codes for gephyrin, a key scaffolding protein in the neuronal postsynaptic membrane, responsible for the clustering and localization of glycine and GABA receptors at inhibitory synapses. Gephyrin has well-established functional links with several synaptic proteins that have been implicated in genetic risk for neurodevelopmental disorders such as autism spectrum disorder (ASD), schizophrenia and epilepsy including the neuroligins (NLGN2, NLGN4), the neurexins (NRXN1, NRXN2, NRXN3) and collybistin (ARHGEF9). Moreover, temporal lobe epilepsy has been linked to abnormally spliced GPHN mRNA lacking exons encoding the G-domain of the gephyrin protein, potentially arising due to cellular stress associated with epileptogenesis such as temperature and alkalosis. Here, we present clinical and genomic characterization of six unrelated subjects, with a range of neurodevelopmental diagnoses including ASD, schizophrenia or seizures, who possess rare de novo or inherited hemizygous microdeletions overlapping exons of GPHN at chromosome 14q23.3. The region of common overlap across the deletions encompasses exons 3-5, corresponding to the G-domain of the gephyrin protein. These findings, together with previous reports of homozygous GPHN mutations in connection with autosomal recessive molybdenum cofactor deficiency, will aid in clinical genetic interpretation of the GPHN mutation spectrum. Our data also add to the accumulating evidence implicating neuronal synaptic gene products as key molecular factors underlying the etiologies of a diverse range of neurodevelopmental conditions. Show less

The three members of the human neurexin gene family, neurexin 1 (NRXN1), neurexin 2 (NRXN2), and neurexin 3 (NRXN3), encode neuronal adhesion proteins that have important roles in synapse development and function. In autism spectrum disorder (ASD), as well as in other neurodevelopmental conditions, rare exonic copy-number variants and/or point mutations have been identified in the NRXN1 and NRXN2 loci. We present clinical characterization of four index cases who have been diagnosed with ASD and who possess rare inherited or de novo microdeletions at 14q24.3-31.1, a region that overlaps exons of the alpha and/or beta isoforms of NRXN3. NRXN3 deletions were found in one father with subclinical autism and in a carrier mother and father without formal ASD diagnoses, indicating issues of penetrance and expressivity at this locus. Notwithstanding these clinical complexities, this report on ASD-affected individuals who harbor NRXN3 exonic deletions advances the understanding of the genetic etiology of autism, further enabling molecular diagnoses. Show less