Neuregulin 1: genetic support for schizophrenia subtypes
SIR—The deficit syndrome is a form of chronic schizophrenia characterized by enduring, idiopathic negative symptoms. Patients with this clinically distinct disease subtype have been suggested to differ in several biological aspects from patients with a more benign course with exacerbations and remissions. We hypothesized that part of the heterogeneity of disease course in schizophrenia is related to different contributing genetic factors. The neuregulin 1 gene (NRG1), assumed to be involved in glutamate neurotransmission and neurodevelopment, was recently reported to be associated with schizophrenia in several, but not all populations. We have investigated the association of NRG1 with schizophrenia in patients with and without the deficit syndrome. In order to enrich the sample for patients with the deficit syndrome, 282 schizophrenia patients were mainly recruited from psychiatric hospitals. Patients had at least three Dutch-born Caucasian grandparents. DSM-IV diagnosis of schizophrenia, excluding schizoaffective disorder, was made using the Comprehensive Assessment of Symptoms and History and information from medical records. The Schedule for the Deficit Syndrome (SDS) was completed for 260 patients (92.2%), 130 of whom met deficit criteria. In 29 patients with severe negative symptoms, it could not be ruled out that these symptoms were secondary to factors such as substance abuse. Following the SDS, they were classified as nondeficit schizophrenia. The Medical Ethical Committee of the UMC Utrecht approved the study and all patients gave written informed consent. The control panel (n1⁄4585) consisted of 472 DNA samples from random Dutch individuals, obtained from the Immunogenetics and Transplantation Immunology Section of the Department of Immunohematology and Blood Transfusion, LUMC, Leiden and 113 healthy controls from our department. Under optimal conditions, these samples have approximately 90% power to detect a locus with a relative risk of 1.5, and still 75% to detect a locus with an RR of 1.25. All five single-nucleotide polymorphisms (SNPs) from the previously reported at-risk haplotype were first screened in DNA pools from an unselected subset of patients (n1⁄4208) and independent controls (n1⁄4 179), using the SNaPshot technique (Applied Biosystems, Foster City, CA, USA). SNP8NRG221533 was genotyped individually on a 7900HT TaqMan system (Applied Biosystems). Microsatellites 478B14642 and 478B14-848) were analyzed on an ABI 3700 sequencer (Applied Biosystems) and genotyped by two independent raters. Genepop software was used to verify Hardy–Weinberg equilibrium (HWE). Haplotypes, linkage disequilibrium (LD) and likelihood ratios were calculated using UNPHASED software. Alleles and haplotypes with frequencies o1% were combined. Global P-values were calculated using n 1 degrees of freedom (n1⁄4number of alleles or haplotypes). No correction of P-values for testing several markers and haplotypes was applied, because the markers were in LD and tests are therefore not independent. SNP8NRG221533, which was the most strongly associated single marker in previous studies, showed a significantly higher frequency of the T allele in the schizophrenia pool than in controls (Po0.01). This marker was then genotyped individually in the extended sample, as was microsatellite 478B14-848, which is part of the reported at-risk haplotype. Before testing for association, we calculated LD between the markers, and found it to be low (D0 1⁄40.20), which is in agreement with a recent study. Therefore, we genotyped microsatellite 478B14-642, instead of the even more distant third microsatellite from the reported atrisk haplotype. This marker is located much closer to the SNP, and was recently found to be in a different LD block than 478B14-848. Indeed, in our sample, 478B14-642 was in considerable LD with SNP8NR G221533 (D0 1⁄40.60), but not with 478B14-848. All three markers were in HWE. Interestingly, SNP8NRG221533 was associated with nondeficit schizophrenia (P1⁄4 0.004), but not with deficit schizophrenia (P1⁄4 0.542). Likewise, haplotypes of SNP8NRG221533 and 478B14-642 were Scientific Correspondence