Affected sibling pair linkage analysis of qualitative and quantitative traits for schizophrenia on chromosome 22 in a Chinese population

Association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and age of onset in schizophrenia

Different lines of evidence indicate that methylenetetrahydrofolate reductase (MTHFR) functional gene polymorphisms, causative in aberrant folate-homocysteine metabolism, are associated with increased vulnerability to several heritable developmental disorders. Opposing views are expressed considering the possible association between MTHFR and susceptibility for schizophrenia. In order to evaluate if age of onset could explain some of this discrepancy we investigated the relationship between two functional MTHFR gene polymorphisms and age at onset in this disorder. Scandinavian patients (n = 820) diagnosed with schizophrenia, schizoaffective disorder, and schizophreniform disorder were investigated. Two functional MTHFR single nucleotide polymorphisms (SNPs; rs1801131 and rs1801133) were genotyped and the effect of MTHFR polymorphisms on the age of onset was examined with survival analysis. In an attempt to replicate the findings from the Scandinavian sample, the association between rs1801133 and age at onset was also analyzed in Chinese high-risk families, with two or more affected siblings (n = 243). Among the Scandinavian patients the functional MTHFR SNP rs1801133 (C677T) significantly affected age at onset of schizophrenia in a dose-dependent manner (P = 0.0015), with lower age of onset with increasing numbers of the mutant T-allele. There was no evidence of rs1801131 (A1298C) affecting age of onset in schizophrenia. Within the Chinese high-risk families carriers of the MTHFR 677T allele showed earlier age at onset than siblings being homozygous for the wild-type allele (P = 0.008). The MTHFR C677T polymorphism may play a role as a modifying factor for age of onset in schizophrenia.

Heritability of age of onset of psychosis in schizophrenia

Schizophrenia is a genetically complex illness with heterogeneous clinical presentation, including variable age of onset. In this study, the heritability, or proportion of variation in age of onset of psychotic symptoms due to genetic factors, was estimated using a maximum likelihood method. The subjects were 717 members of families with more than one member affected with schizophrenia from Mexican and Central American populations. Age of onset of psychosis was determined by best-estimate consensus diagnosis based on the Diagnostic Interview for Genetic Studies, Family Interview for Genetic Studies, and each subject's medical records. Mean age of onset was 21.44 years (SD 8.07); 20.55 years for males (SD 6.90), and 22.67 for females (SD 9.34). Variance components were estimated using a polygenic model in the SOLAR software package. The sex of the participant was a significant covariate (P = 0.010) accounting for 0.02 of the total variance in age of onset. The heritability of age of onset of psychosis was 0.33 (SE = 0.09; P = 0.00004). These findings suggest that genetic factors significantly contribute to the age of onset of psychotic symptoms in individuals with schizophrenia and that sex influences this trait as well.

Identifying potential risk haplotypes for schizophrenia at the DTNBP1 locus in Han Chinese and Scottish populations

The dystrobrevin-binding protein 1 (DTNBP1) gene on chromosome 6p has emerged as a potential susceptibility gene for schizophrenia. Although a number of attempts to replicate the original association finding have been successful, they have not identified any obvious pathogenic variants or a single at risk haplotype common to all populations studied. In the present study we attempted further replication in an independent sample of 638 nuclear families from the Han Chinese population of Sichuan Province, SW China. We also examined 580 Scottish schizophrenic cases and 620 controls. We genotyped 10 single-nucleotide polymorphisms (SNPs) in DTNBP1 that were used in the original report of association, plus rs2619538 (SNP 'A') in the putative promoter region, which has also been associated with schizophrenia. In the Chinese trios we found that two SNPs (P1635 and P1765) were significantly overtransmitted, but with alleles opposite to those reported in the original studies. SNPs P1757 and P1765 formed a common haplotype, which also showed significant overtransmission. In the Scottish cases and controls, no individual markers were significantly associated with schizophrenia. A single haplotype, which included rs2619538 and P1583, and one rare haplotype, composed of P1320 and P1757, were significantly associated with schizophrenia, but no previously reported haplotypes were associated. Based on the data from the Chinese population, our results provide statistical support for DTNBP1 as a susceptibility gene for schizophrenia, albeit with haplotypes different from those of the original study. However, our lack of replication in the Scottish samples also indicates that caution is warranted when evaluating the robustness of the evidence for DTNBP1 as genetic risk factor for schizophrenia.

Italian validation of MOAS and NOSIE: a useful package for psychiatric assessment and monitoring of aggressive behaviours

A validation of two rating scales is presented. We first translated the Modified Overt Aggression Scale (MOAS) and the Nurses' Observation Scale for In-patient Evaluation (NOSIE), which cover different aspects of psychopathology, into Italian. We then tested their validity and reliability in terms of inter-rater and internal consistency. For validity, both cases and controls were included: for the MOAS we compared patients who were aggressive (cases) to those who were presumably non-aggressive (controls). For the NOSIE, cases were acute inpatients and controls were subjects with expected stable behaviour. The Brief Psychiatric Rating Scale (BPRS) was also administered to cases in order to test convergent validity. Either the NOSIE and/or MOAS scales were administered to 358 psychiatric inpatients. A subset of these patients (131 for the MOAS and 226 for the NOSIE) was also used to test the inter-rater reliability. Both scales showed good psychometric properties. The correlation coefficients between raters were much higher than 0.75 (for the NOSIE) or 0.90 (for the MOAS), while the discriminant power between cases and controls was confirmed for both scales and good concordance with BPRS was observed. The NOSIE showed good internal consistency for all domains except neatness. In general the MOAS showed better results than the NOSIE for all psychometric properties, although both scales are suitable for monitoring the behaviour and aggression of acute ward inpatients.

Evidence for association between novel polymorphisms in the PRODH gene and schizophrenia in a Chinese population

Haploinsufficiency for or mutation in at least one gene from the velocardiofacial syndrome (VCFS) region at chromosome 22q11 is implicated in psychosis. Linkage disequilibrium mapping of the region in patients identified a segment containing two genes, proline dehydrogenase (PRODH) and DGCR6, as candidates [Liu et al., 2002a] and by analysis of additional polymorphisms the PRODH gene was associated with schizophrenia in adult and early onset patients. In the present study we provide additional evidence in support of genetic association between PRODH and schizophrenia in a Chinese population. We analyzed the PRODH gene in a samples of schizophrenic patients and their families from Sichuan, SW China consisting of 528 family trios and sibling pairs. We genotyped six SNPs, PRODH*1195C-->T, PRODH*1482C-->T, PRODH*1483A-->G, PRODH*1766A-->G, PRODH*1852G-->A PRODH*1945T-->C, two of which (PRODH*1483A-->G and PRODH*1852G-->A) have not been previously reported. We found association with schizophrenia for two haplotypes consisting of PRODH*1945T-->C and PRODH*1852G-->A (Global P = 0.006), and PRODH*1852G-->A and PRODH*1766A-->G (Global P = 0.01) which include one of the newly identified markers. After six-fold Bonferroni correction for multiple testing the PRODH*1945T-C/PRODH*1852G-A haplotypes remained significant. This is a sub-haplotype of the PRODH haplotype previously associated with schizophrenia and it also maps to the 3' region of the gene, indicating that this is the region most likely to contain the underlying risk alleles. Overall this finding supports a role for the PRODH locus in schizophrenia.

Ten-year review of rating scales. VI: scales assessing externalizing behaviors

OBJECTIVE

This is the sixth article in a series of 10-year reviews of rating scales. The current article reviews scales that assess externalizing behaviors such as disruptive behavior disorders and aggression.

METHOD

Relevant scales were found by searching popular electronic databases. The search was then broadened by a review of the references in selected articles. Due to the paucity of well-established scales, any such scales with potential utility for elucidating the functioning of youths with externalizing behaviors were selected.

RESULTS

None of these scales is diagnosis-based, although some correlate with DSM-IV-defined disruptive behavior disorders. Most scales assessing disruptive behavior disorders have a solid normative base, good psychometric functioning, and high clinical utility. Scales assessing aggression comprise a bimodal group. Several have been adapted from the adult literature and are widely used in clinical practice, while others address theoretical aspects of aggression and are used predominantly in research. Empirical support for all of the scales assessing aggression varies widely, although several show potential for routine clinical practice.

CONCLUSIONS

Overall, these scales measure a variety of constructs with considerable utility for assessing youths' externalizing behaviors, predicting outcome, and evaluating treatment effects. Many need further validation with youth.

Recent advances in human quantitative-trait-locus mapping: comparison of methods for discordant sibling pairs

Extreme discordant sibling pairs (EDSPs) are theoretically powerful for the mapping of quantitative-trait loci (QTLs) in humans. EDSPs have not been used much in practice, however, because of the need to screen very large populations to find enough pairs that are extreme and discordant. Given appropriate statistical methods, another alternative is to use moderately discordant sibling pairs (MDSPs)--pairs that are discordant but not at the far extremes of the distribution. Such pairs can be powerful yet far easier to collect than extreme discordant pairs. Recent work on statistical methods for QTL mapping in humans has included a number of methods that, though not developed specifically for discordant pairs, may well be powerful for MDSPs and possibly even EDSPs. In the present article, we survey the new statistics and discuss their applicability to discordant pairs. We then use simulation to study the type I error and the power of various statistics for EDSPs and for MDSPs. We conclude that the best statistic(s) for discordant pairs (moderate or extreme) is (are) to be found among the new statistics. We suggest that the new statistics are appropriate for many other designs as well-and that, in fact, they open the way for the exploration of entirely novel designs.

Search for common haplotypes on chromosome 22q in patients with schizophrenia or bipolar disorder from the Faroe Islands

Chromosome 22q may harbor risk genes for schizophrenia and bipolar affective disorder. This is evidenced through genetic mapping studies, investigations of cytogenetic abnormalities, and direct examination of candidate genes. Patients with schizophrenia and bipolar affective disorder from the Faroe Islands were typed for 35 evenly distributed polymorphic markers on 22q in a search for shared risk genes in the two disorders. No single marker was strongly associated with either disease, but five two-marker segments that cluster within two regions on the chromosome have haplotypes occurring with different frequencies in patients compared to controls. Two segments were of most interest when the results of the association tests were combined with the probabilities of identity by descent of single haplotypes. For bipolar patients, the strongest evidence for a candidate region harboring a risk gene was found at a segment of at least 1.1 cM including markers D22S1161 and D22S922 (P=0.0081 in the test for association). Our results also support the a priori evidence of a susceptibility gene to schizophrenia at a segment of at least 0.45 cM including markers D22S279 and D22S276 (P=0.0075). Patients were tested for the presence of a missense mutation in the WKL1 gene encoding a putative cation channel close to segment D22S1161--D22S922, which has been associated with schizophrenia. We did not find this mutation in schizophrenic or bipolar patients or the controls from the Faroe Islands.