The molecular genetics of schizophrenia

NURR1 promoter polymorphisms: Parkinson's disease, schizophrenia, and personality traits

We have previously identified mutations in exon three in NURR1 (NR4A2) in two patients with schizophrenia (SZ) and one patient with bipolar disease with psychotic symptoms. In the present study we analyzed the promoter region of NURR1 and identified five polymorphic sites: three were found to be in strong linkage disequilibrium with a previously identified polymorphic site in the sixth intron. One polymorphism of this haplotype and the two other independent polymorphisms were investigated for their possible association with SZ and Parkinson's disease (PD) by comparing their frequencies in a Swedish material consisting of 134 subjects with SZ and 207 matched controls and 108 subjects with PD and 125 matched controls. Exon 1 was also investigated in our Parkinson and control material but no variances were found. The distributions of the two most informative polymorphisms in the promoter were investigated in an American material as well consisting of 141 subjects with SZ and 139 matched controls. Furthermore, the identified markers were screened for association with putative endophenotypes of SZ in the Swedish material. The distribution of sequence variants among the Swedish controls matched for SZ was investigated with regard to personality. No significant genotype or allelic association of the three sequence variants with SZ or PD was found. Several comparisons regarding endophenotypes or personality indicated association at the 5% confidence level, although correction for multiple testing rendered none of these findings significant. We conclude that the identified polymorphic sites in the human NURR1 are unlikely to be involved in conferring susceptibility for SZ or PD in our patient material.

Characterization of trinucleotide- and tandem repeat-containing transcripts obtained from human spinal cord cDNA library by high-density filter hybridization

In order to identify trinucleotide- and tandem repeat-containing transcripts in human spinal cord, hybridization of a high-density spinal cord cDNA library filter was carried out using a radioactively labeled degenerate oligonucleotide designed to detect different trinucleotide repeats including those known to occur in disease-associated expansions, in a single step. The sequence analysis of the trinucleotide repeat-containing transcripts (TNRTs) revealed 23 known mammalian genes with trinucleotide repeat-containing regions (TNRs), some of which were not previously reported to contain TNRs, and 18 cDNA clones with no or insignificant sequence homology to known genes. Amongst the known genes detected was the fragile X gene (FMR-1) containing (CGG)30. Other genes containing extended TNRs of 9 to 21 repeats were calcium-dependent protease, ATBF1-A, ferritin H chain, and the G protein Gsalpha2. Ten sequences containing perfect TNRs and two sequences containing perfect tandem repeats (derived from 11 TNRTs) were further analyzed for allelic variation using primers flanking the TNR, and five were shown to exhibit two to five alleles per TNR. These transcripts were further investigated for their chromosomal localization where unknown or only partially characterized. The transcripts that were polymorphic in the TNR region were ATBF1-A (a homeodomain protein), clone 390013 on chromosome Xp11, a member of the family of the 14.3.3 protein kinase C regulators, a human translation initiation factor (an isolog of the yeast Suilisol gene 1), and a novel sequence (TR21). Only the first two transcripts showed the presence of rare expanded alleles. Characterization of polymorphic TNRs in novel and even known genes expressed in human spinal cord is likely to help in the identification of new candidates for genes involved in neurodegenerative disorders.

Schizophrenia

Schizophrenia is among the most severe and debilitating of psychiatric disorders. Diagnosis is currently by criterion-based systems, including positive (eg, hallucinations and delusions) and negative (eg, avolition and alogia) symptoms. The importance of negative symptoms in the course and outcome of the illness is increasingly being studied. Current research seeks to detect causal mechanisms in schizophrenia through studies of neural connectivity and function, as well as models of genetic transmission, such as polygenic models of inheritance in genetic research. Potential genes have been identified that may confer vulnerability to the illness, perhaps in conjunction with environmental factors. Neuroimaging research with magnetic resonance imaging and positron emission tomography has investigated differences in volumes and functional dysregulation in specific neural subregions. Areas studied include the frontal and temporal cortex, the hippocampus, the thalamus, and the cerebellum. Despite these advances, treatment of symptoms and psychosocial and cognitive impairments remains only partially successful for many patients.

A piece in the puzzle: an ion channel candidate gene for schizophrenia

Mutations in ion channels have been found to cause a variety of mendelian genetic diseases, and polyglutamine repeat expansion is a newly recognized pathogenic mechanism that causes several rare, genetic, late-onset neurological syndromes. Polymorphic polyglutamine tracts are present in a recently described human, calcium-activated potassium channel, KCNN3 (also known as hKCa3), and alleles of this gene that contain longer repeats have been associated with schizophrenia. The physiological function of the channel is consistent with an etiological role in this disease; drugs designed to target this channel might therefore provide novel psychotherapeutics.