[Show abstract][Hide abstract] ABSTRACT: Prior evidence has supported the existence of multiple susceptibility genes for schizophrenia. Multipoint linkage analysis of the 270 Irish high-density pedigrees that we have studied, as well as results from several other samples, suggest that at least one such gene is located in region 6p24-21. In the present study, family-based association analysis of 36 simple sequence-length-polymorphism markers and of 17 SNP markers implicated two regions, separated by approximately 7 Mb. The first region, and the focus of this report, is 6p22.3. In this region, single-nucleotide polymorphisms within the 140-kb gene DTNBP1 (dystrobrevin-binding protein 1, or dysbindin) are strongly associated with schizophrenia. Uncorrected, empirical P values produced by the program TRANSMIT were significant (P<.01) for a number of individual SNP markers, and most remained significant when the data were restricted to include only one affected offspring per nuclear family per extended pedigree; multiple three-marker haplotypes were highly significant (P=.008-.0001) under the restricted conditions. The pattern of linkage disequilibrium is consistent with the presence of more than one susceptibility allele, but this important issue is unresolved. The number of markers tested in the adjacent genes, all of which are negative, is not sufficient to rule out the possibility that the dysbindin gene is not the actual susceptibility gene, but this possibility appears to be very unlikely. We conclude that further investigation of dysbindin is warranted.
The American Journal of Human Genetics 08/2002; 71(2):337-48. · 10.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: From our linkage study of Irish families with a high density of schizophrenia, we have previously reported evidence for susceptibility genes in regions 5q21-31, 6p24-21, 8p22-21, and 10p15-p11. In this report, we describe the cumulative results from independent genome scans of three a priori random subsets of 90 families each, and from multipoint analysis of all 270 families in ten regions. Of these ten regions, three (13q32, 18p11-q11, and 18q22-23) did not generate scores above the empirical baseline pairwise scan results, and one (6q13-26) generated a weak signal. Six other regions produced more positive pairwise and multipoint results. They showed the following maximum multipoint H-LOD (heterogeneity LOD) and NPL scores: 2p14-13: 0.89 (P = 0.06) and 2.08 (P = 0.02), 4q24-32: 1.84 (P = 0.007) and 1.67 (P = 0.03), 5q21-31: 2.88 (P= 0.0007), and 2.65 (P = 0.002), 6p25-24: 2.13 (P = 0.005) and 3.59 (P = 0.0005), 6p23: 2.42 (P = 0.001) and 3.07 (P = 0.001), 8p22-21: 1.57 (P = 0.01) and 2.56 (P = 0.005), 10p15-11: 2.04 (P = 0.005) and 1.78 (P = 0.03). The degree of 'internal replication' across subsets differed, with 5q, 6p, and 8p being most consistent and 2p and 10p being least consistent. On 6p, the data suggested the presence of two susceptibility genes, in 6p25-24 and 6p23-22. Very few families were positive on more than one region, and little correlation between regions was evident, suggesting substantial locus heterogeneity. The levels of statistical significance were modest, as expected from loci contributing to complex traits. However, our internal replications, when considered along with the positive results obtained in multiple other samples, suggests that most of these six regions are likely to contain genes that influence liability to schizophrenia.
[Show abstract][Hide abstract] ABSTRACT: A large body of genetic epidemiological data strongly implicate genetic factors in the etiology of smoking behavior. Polymorphisms of genes in the dopaminergic system are plausible functional candidate genes and a linkage and an association study suggested that the type 5 dopamine receptor gene (DRD5) may be etiologically involved. We investigated the association of four DRD5 polymorphisms with smoking initiation and progression to nicotine dependence in a population-based sample of over 900 subjects. For smoking initiation, there was no significant association with the four DRD5 markers we studied; however, maximum likelihood analyses suggested the presence of a haplotype protective against smoking initiation. For progression to nicotine dependence, there were no strongly significant associations with the four DRD5 markers or for the estimated haplotypes. These data are not consistent with a strong etiological role for DRD5 in the etiology of these complex smoking behaviors.
American Journal of Medical Genetics 05/2001; 105(3):259-65. · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Several types of evidence, including experiments with mice that lack the nicotinic acetylcholine receptor beta2-subunit gene (CHRNB2), have suggested that a beta2-containing nicotinic receptor is necessary for at least some of the reinforcing properties of nicotine. However, sequence variations in CHRNB2 have not been reported, and its role in influencing human smoking behavior and nicotine dependence is not known. We screened most of the introns and exons and found five novel single nucleotide polymorphisms (SNPs). We tested four of these SNPs in three large, carefully selected samples: nonsmokers (n = 317) and regular smokers low levels of nicotine dependence (ND, n = 238), or smokers with high-ND (n = 317). None of the four polymorphisms we tested, nor their estimated haplotypes, were associated with smoking initiation or progression to nicotine dependence.
American Journal of Medical Genetics 11/2000; 96(5):646-53. · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cigarette smoking is associated with considerable morbidity, mortality, and public health costs. Genetic factors influence both smoking initiation and nicotine dependence, but none of the genes involved have been identified. A genome scan using 451 markers was conducted to identify chromosomal regions linked to nicotine dependence in a collection of 130 families containing 343 genotyped individuals (308 nicotine-dependent) from Christchurch, New Zealand. By pairwise analysis, the best result was with marker D2S1326 which gave a lod score under heterogeneity (H-LOD) of 2.63 (P=0.0012) and a nonparametric linkage (NPL, Zall) score of 2.65 (P=0.0011). To identify regions that warranted further study, rather than comparing the pairwise scores from the scan to theoretical thresholds, we compared them to an empirical baseline, found here to be H-LOD scores of 0.5 and Zall scores of 1.0. We also found a number of large (31-88 cM) regions where many (8-16) consecutive markers yielded small but positive Zall scores. Selected regions of chromosomes 2, 4, 10, 16, 17 and 18 were investigated further by additional genotyping of the Christchurch sample and an independent sample from Richmond, Virginia (91 families with 264 genotyped individuals, 211 nicotine-dependent). Multipoint nonparametric analysis showed the following maximums for the Christchurch sample: Chr. 2 (Zlr=2.61, P=0.005), Chr. 4 (Zlr=1.36, P=0.09), Chr. 10 (Zlr=2.43, P=0.008), Chr. 16 (Zlr=0.85, P=0.19), Chr. 17 (Zlr=1.64, P=0.05), Chr. 18 (Zlr=1.54, P=0.06). Analysis of the Richmond sample showed the following maximums: Chr. 2 (Zlr=1.00, P=0.15), Chr. 4 (Zlr=0.39, P=0.34), Chr. 10 (Zlr=1.21, P=0.11), Chr. 16 (Zlr=1.11, P=0.13), Chr. 17 (Zlr=1.60, P=0.05), Chr. 18 (Zlr=1.33, P=0.09). It is probable that the small samples used here provided only limited power to detect linkage. It may have been difficult therefore to detect genes of small effect, or those that are influencing risk in only a small proportion of the families. When simply judged against the usual standards of linkage significance, none of the individual regions yielded strong evidence in either sample. Some or all of the most positive results in the genome scan of the Christchurch sample, therefore, could be due to chance. However, the presence in the Christchurch scan of multiple large regions containing many consecutive positive markers, coupled with the relatively positive results in these same regions in the Richmond sample, suggests that some of these regions may contain genes influencing nicotine dependence and therefore deserve further study.
[Show abstract][Hide abstract] ABSTRACT: In our genomic scan of 265 Irish families with schizophrenia, we have thus far generated modest evidence for the presence of vulnerability genes in three chromosomal regions, i.e., 5q21-q31, 6p24-p22, and 8p22-p21. Outside of those regions, of all markers tested to date, D10S674 produced one of the highest pairwise heterogeneity lod (H-LOD) scores, 3.2 (P = 0.0004), when initially tested on a subset of 88 families. We then tested a total of 12 markers across a region of 32 centimorgans in region 10p15-p11 of all 265 families. The strongest evidence for linkage occurred assuming an intermediate phenotypic definition, and a recessive genetic model. The largest pairwise H-LOD score was found with marker D10S2443 (maximum 1.95, P = 0.005). Using multipoint H-LODs, we found a broad peak (maximum 1.91, P = 0.006) extending over the 11 centimorgans from marker D10S674 to marker D10S1426. Multipoint nonparametric linkage analysis produced a much broader peak, but with the maximum in the same location near D10S2443 (maximum z = 1.88, P = 0.03). Based on estimates from the multipoint analysis, this putative vulnerability locus appears to be segregating in 5-15% of the families studied, but this estimate should be viewed with caution. When evaluated in the context of our genome scan results, the evidence suggests the possibility of a fourth vulnerability locus for schizophrenia in these Irish families, in region 10p15-p11.
American Journal of Medical Genetics 08/1998; 81(4):296-301. · 3.23 Impact Factor