Two rare deletions upstream of the NRXN1 gene (2p16.3) affecting the non-coding mRNA AK127244 segregate with diverse psychopathological phenotypes in a family.

CNVs spanning the 2p16.3 (NRXN1) and the 15q11.2 gene rich region have been associated with severe neuropsychiatric disorders including schizophrenia. Recently, studies have also revealed that CNVs in non-coding regions play an essential role in genomic variability in addition to disease susceptibility. In this study, we describe a family affected by a wide range of psychiatric disorders including early onset schizophrenia, schizophreniform disorder, and affective disorders. Microarray analysis identified two rare deletions immediately upstream of the NRXN1 gene affecting the non-coding mRNA AK127244 in addition to the pathogenic 15q11.2 deletion in distinct family members. The two deletions upstream of the NRXN1 gene were found to segregate with psychiatric disorders in the family and further similar deletions have been observed in patients diagnosed with autism spectrum disorder. Thus, we suggest that non-coding regions upstream of the NRXN1 gene affecting AK127244 might (as NRXN1) contain susceptibility regions for a wide spectrum of neuropsychiatric disorders.

A Novel Locus Harbouring a Functional CD164 Nonsense Mutation Identified in a Large Danish Family with Nonsyndromic Hearing Impairment.

Nonsyndromic hearing impairment (NSHI) is a highly heterogeneous condition with more than eighty known causative genes. However, in the clinical setting, a large number of NSHI families have unexplained etiology, suggesting that there are many more genes to be identified. In this study we used SNP-based linkage analysis and follow up microsatellite markers to identify a novel locus (DFNA66) on chromosome 6q15-21 (LOD 5.1) in a large Danish family with dominantly inherited NSHI. By locus specific capture and next-generation sequencing, we identified a c.574C>T heterozygous nonsense mutation (p.R192*) in CD164. This gene encodes a 197 amino acid transmembrane sialomucin (known as endolyn, MUC-24 or CD164), which is widely expressed and involved in cell adhesion and migration. The mutation segregated with the phenotype and was absent in 1200 Danish control individuals and in databases with whole-genome and exome sequence data. The predicted effect of the mutation was a truncation of the last six C-terminal residues of the cytoplasmic tail of CD164, including a highly conserved canonical sorting motif (YXXФ). In whole blood from an affected individual, we found by RT-PCR both the wild-type and the mutated transcript suggesting that the mutant transcript escapes nonsense mediated decay. Functional studies in HEK cells demonstrated that the truncated protein was almost completely retained on the plasma cell membrane in contrast to the wild-type protein, which targeted primarily to the endo-lysosomal compartments, implicating failed endocytosis as a possible disease mechanism. In the mouse ear, we found CD164 expressed in the inner and outer hair cells of the organ of Corti, as well as in other locations in the cochlear duct. In conclusion, we have identified a new DFNA locus located on chromosome 6q15-21 and implicated CD164 as a novel gene for hearing impairment.