Genome Scan for Loci Predisposing to Anxiety Disorders Using a Novel Multivariate Approach: Strong Evidence for a Chromosome 4 Risk Locus
2006; Elsevier BV; Volume: 78; Issue: 4 Linguagem: Inglês
10.1086/501072
ISSN1537-6605
AutoresBelhassen Kâabi, Joel Gelernter, Scott W. Woods, Andrew W. Goddard, Grier P. Page, Robert C. Elston,
Tópico(s)Mental Health Research Topics
ResumoWe conducted a 10-centimorgan linkage autosomal genome scan in a set of 19 extended American pedigrees (219 subjects) ascertained through probands with panic disorder. Several anxiety disorders—including social phobia, agoraphobia, and simple phobia—in addition to panic disorder segregate in these families. In previous studies of this sample, linkage analyses were based separately on each of the individual categorical affection diagnoses. Given the substantial comorbidity between anxiety disorders and their probable shared genetic liability, it is clear that this method discards a considerable amount of information. In this article, we propose a new approach that considers panic disorder, simple phobia, social phobia, and agoraphobia as expressions of the same multivariate, putatively genetically influenced trait. We applied the most powerful multipoint Haseman-Elston method, using the grade of membership score generated from a fuzzy clustering of these phenotypes as the dependent variable in Haseman-Elston regression. One region on chromosome 4q31-q34, at marker D4S413 (with multipoint and single-point nominal P values < .00001), showed strong evidence of linkage (genomewide significance at P<.05). The same region is known to be the site of a neuropeptide Y receptor gene, NPY1R (4q31-q32), that was recently connected to anxiolytic-like effects in rats. Several other regions on four chromosomes (4q21.21-22.3, 5q14.2-14.3, 8p23.1, and 14q22.3-23.3) met criteria for suggestive linkage (multipoint nominal P values < .01). Family-by-family analysis did not show any strong evidence of heterogeneity. Our findings support the notion that the major anxiety disorders, including phobias and panic disorder, are complex traits that share at least one susceptibility locus. This method could be applied to other complex traits for which shared genetic-liability factors are thought to be important, such as substance dependencies. We conducted a 10-centimorgan linkage autosomal genome scan in a set of 19 extended American pedigrees (219 subjects) ascertained through probands with panic disorder. Several anxiety disorders—including social phobia, agoraphobia, and simple phobia—in addition to panic disorder segregate in these families. In previous studies of this sample, linkage analyses were based separately on each of the individual categorical affection diagnoses. Given the substantial comorbidity between anxiety disorders and their probable shared genetic liability, it is clear that this method discards a considerable amount of information. In this article, we propose a new approach that considers panic disorder, simple phobia, social phobia, and agoraphobia as expressions of the same multivariate, putatively genetically influenced trait. We applied the most powerful multipoint Haseman-Elston method, using the grade of membership score generated from a fuzzy clustering of these phenotypes as the dependent variable in Haseman-Elston regression. One region on chromosome 4q31-q34, at marker D4S413 (with multipoint and single-point nominal P values < .00001), showed strong evidence of linkage (genomewide significance at P<.05). The same region is known to be the site of a neuropeptide Y receptor gene, NPY1R (4q31-q32), that was recently connected to anxiolytic-like effects in rats. Several other regions on four chromosomes (4q21.21-22.3, 5q14.2-14.3, 8p23.1, and 14q22.3-23.3) met criteria for suggestive linkage (multipoint nominal P values < .01). Family-by-family analysis did not show any strong evidence of heterogeneity. Our findings support the notion that the major anxiety disorders, including phobias and panic disorder, are complex traits that share at least one susceptibility locus. This method could be applied to other complex traits for which shared genetic-liability factors are thought to be important, such as substance dependencies. Anxiety disorders are serious illnesses that cause substantial morbidity at the population level. Anxiety disorders, including simple or specific phobia (SimP [MIM %608251]), social phobia (SocP), agoraphobia (AgP), and panic disorder (PD [MIM %167870]), are common disorders, with lifetime prevalences estimated by the U.S. National Comorbidity Survey Replication study to be 4.7%, 1.4%, 12.5%, and 12.1% for PD, AgP without PD, SimP, and SocP, respectively (Kessler et al. Kessler et al., 2005Kessler RC Berglund P Demler O Jin R Merikangas KR Walters EE Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the National Comorbidity Survey Replication.Arch Gen Psychiatry. 2005; 62: 593-602Crossref PubMed Scopus (12965) Google Scholar). The DSM-IIIR (American Psychiatric Association American Psychiatric Association, 1987American Psychiatric Association Diagnostic and statistical manual of mental disorders. third edition, revised. American Psychiatric Press, Washington, DC1987Google Scholar) provides standard criteria for the diagnoses of AgP, SocP, SimP, and PD. AgP is discomfort and anxiety from being in public places or places from which escape might be difficult, such as highways or bridges. SocP, on the other hand, is fear of or great discomfort from being in situations that might involve the scrutiny of others, such as public speaking, to the extent that specific situations are avoided or endured with great distress. This condition disrupts a person’s ability to function at work or school and causes withdrawal from social activities and/or relationships. A person with SimP experiences excessive or irrational fear of a specific object or situation, such that the fear causes impairment or that exposure to the object or situation causes an immediate anxiety response. The person may have distress about having the phobia and may realize that the fear is excessive or irrational. The object or situation is endured with distress or avoided altogether. Finally, PD is characterized by sudden episodes of acute anxiety or intense fear that may occur without any apparent reason or stimulus. In general, anxiety disorders are chronic disorders, and their clinical courses are variable. Anxiety disorders are genetically influenced (Kendler et al. Kendler et al., 1999Kendler KS Karkowski LM Prescott CA Fears and phobias: reliability and heritability.Psychol Med. 1999; 29: 539-553Crossref PubMed Scopus (172) Google Scholar) and frequently co-occur (Magee et al. Magee et al., 1996Magee W Eaton WW Wittchen H-U McGonagle KA Kessler RC Agoraphobia, simple phobia, and social phobia in national comorbidity survey.Arch Gen Psychiatry. 1996; 53: 159-168Crossref PubMed Scopus (756) Google Scholar; Curtis et al. Curtis et al., 1998Curtis GC Magee WJ Eaton WW Wittchen HU Kessler RC Specific fears and phobias: epidemiology and classification.Br J Psychiatry. 1998; 173: 212-217Crossref PubMed Scopus (155) Google Scholar). There is also frequent comorbidity with other disorders, particularly psychiatric ones, including, for example, nicotine dependence (MIM #188890); elsewhere, we reported on linkage to nicotine dependence in the present study sample (Gelernter et al. Gelernter et al., 2004aGelernter J Liu X Hesselbrock V Page GP Goddard A Zhang H Results of a genomewide linkage scan: support for chromosomes 9 and 11 loci increasing risk for cigarette smoking.Am J Med Genet B Neuropsychiatr Genet. 2004; 128: 94-101Crossref Scopus (80) Google Scholar). A review of the studies that examine the genetic etiology of anxiety and PD reveals the complexity of these disorders, their multifactorial nature, and the fact that they are greatly influenced by genetic factors (van den Heuvel et al. van den Heuvel et al., 2000van den Heuvel OA van de Wetering BJ Veltman DJ Pauls DL Genetic studies of panic disorder: a review.J Clin Psychiatry. 2000; 61: 756-766Crossref PubMed Scopus (20) Google Scholar). Nevertheless, the influence of the family on anxiety is covaried by both genetic and environmental mechanisms. Hettema et al. (Hettema et al., 2001Hettema JM Neale MC Kendler KS A review and meta-analysis of the genetic epidemiology of anxiety disorders.Am J Psychiatry. 2001; 158: 1568-1578Crossref PubMed Scopus (1055) Google Scholar) showed that the role of nonshared environmental experience is significant in the etiology of anxiety. Epidemiological studies worldwide have consistently reported higher rates of anxiety disorders in women (whereas men consistently show higher rates of substance abuse and antisocial disorders), thus indicating sex as a risk factor for anxiety. However, the underlying structure of the genetic and environmental risk factors for anxiety disorders is similar for men and women (Hettema et al. Hettema et al., 2005Hettema JM Prescott CA Myers JM Neale MC Kendler KS The structure of genetic and environmental risk factors for anxiety disorders in men and women.Arch Gen Psychiatry. 2005; 62: 182-189Crossref PubMed Scopus (343) Google Scholar). Age at first onset of anxiety disorders varies from adolescence to early adulthood, with later onsets being mostly of comorbid conditions (Kessler et al. Kessler et al., 2005Kessler RC Berglund P Demler O Jin R Merikangas KR Walters EE Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the National Comorbidity Survey Replication.Arch Gen Psychiatry. 2005; 62: 593-602Crossref PubMed Scopus (12965) Google Scholar), and diagnostic variations for anxiety disorders attributed to age have been pointed out by Jeste et al. (Jeste et al., 2005Jeste DV Blazer DG First M Aging-related diagnostic variations: need for diagnostic criteria appropriate for elderly psychiatric patients.Biol Psychiatry. 2005; 58: 265-271Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar). Several studies suggest that alterations in neurotransmitter balance, in the function of neurotransmitter receptors (Sand et al. Sand et al., 2000Sand PG Godau C Riederer P Peters C Franke P Nothen MM Stober G Fritze J Maier W Propping P Lesch KP Riess O Sander T Beckmann H Deckert J Exonic variants of the GABA(B) receptor gene and panic disorder.Psychiatr Genet. 2000; 10: 191-194Crossref PubMed Scopus (16) Google Scholar) or transporters (Mazzanti et al. Mazzanti et al., 1998Mazzanti CM Lappalainen J Long JC Bengel D Naukkarinen H Eggert M Virkkunen M Linnoila M Goldman D Role of the serotonin transporter promoter polymorphism in anxiety-related traits.Arch Gen Psychiatry. 1998; 55: 936-940Crossref PubMed Scopus (207) Google Scholar; Ohara et al. Ohara et al., 1998Ohara K Nagai M Suzuki Y Ochiai M Ohara K Association between anxiety disorders and a functional polymorphism in the serotonin transporter gene.Psychiatry Res. 1998; 81: 277-279Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar; Nakamura et al. Nakamura et al., 1999Nakamura M Ueno S Sano A Tanabe H Polymorphisms of the human homologue of the Drosophila white gene are associated with mood and panic disorders.Mol Psychiatry. 1999; 4: 155-162Crossref PubMed Scopus (44) Google Scholar), or in enzymes involved in their regulation (Hamilton et al. Hamilton et al., 2002Hamilton SP Slager SL Heiman GA Deng Z Haghighi F Klein DF Hodge SE Weissman MM Fyer AJ Knowles JA Evidence for a susceptibility locus for panic disorder near the catechol-O-methyltransferase gene on chromosome 22.Biol Psychiatry. 2002; 51: 591-601Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar) may contribute to anxiety disorders. However, peripheral systems are also important for the perception and experience of anxiety, as recently demonstrated in a study by Stein et al. (Stein et al., 2004Stein MB Schork NJ Gelernter J A polymorphism of the β1-adrenergic receptor is associated with low extraversion.Biol Psychiatry. 2004; 56: 217-224Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) that showed association of a variant of the β1 adrenergic receptor gene (ADRB1 [MIM *109630]) with the social anxiety–related traits of shyness and extroversion. Several total-genome scans have been performed for anxiety phenotypes, both including and excluding PD, with variable results. Most of the previous studies focused on PD have identified only “suggestive” linkages (Knowles et al. Knowles et al., 1998Knowles JA Fyer AJ Vieland VJ Weissman MM Hodge SE Heiman GA Haghighi F de Jesus GM Rassnick H Preud’homme-Rivelli X Austin T Cunjak J Mick S Fine LD Woodley KA Das K Maier W Adams PB Freimer NB Klein DF Gilliam TC Results of a genome-wide genetic screen for panic disorder.Am J Med Genet. 1998; 81: 139-147Crossref PubMed Scopus (116) Google Scholar; Crowe et al. Crowe et al., 2001Crowe RR Goedken R Samuelson S Wilson R Nelson J Noyes Jr, R Genomewide survey of panic disorder.Am J Med Genet. 2001; 105: 105-109Crossref PubMed Scopus (85) Google Scholar; Gelernter et al. Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar), but genomewide-significant linkage results were reported by Thorgeirsson et al. (Thorgeirsson et al., 2003Thorgeirsson TE Oskarsson H Desnica N Kostic JP Stefansson JG Kolbeinsson H Lindal E Gagunashvili N Frigge ML Kong A Stefansson K Gulcher JR Anxiety with panic disorder linked to chromosome 9q in Iceland.Am J Hum Genet. 2003; 72: 1221-1230Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar) for anxiety and PD at chromosome 9q31. Significant linkages were also reported for a “panic disorder syndrome” that includes PD, bladder or kidney problems, headache, and thyroid problems (Weissman et al. Weissman et al., 2000Weissman MM Fyer AJ Haghighi F Heiman G Deng Z Hen R Hodge SE Knowles JA Potential panic disorder syndrome: clinical and genetic linkage evidence.Am J Med Genet. 2000; 96: 24-35Crossref PubMed Scopus (86) Google Scholar). Additionally, suggestive-linkage regions were reported by Gelernter et al. (Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar) for AgP, by Smoller et al. (Smoller et al., 2001Smoller JW Acierno Jr, JS Rosenbaum JF Biederman J Pollack MH Meminger S Pava JA Chadwick LH White C Bulzacchelli M Slaugenhaupt SA Targeted genome screen of panic disorder and anxiety disorder proneness using homology to murine QTL regions.Am J Med Genet. 2001; 105: 195-206Crossref PubMed Scopus (82) Google Scholar) for PD and AgP, and by Gelernter et al. (Gelernter et al., 2004bGelernter J Page GP Stein MB Woods SW Genome-wide linkage scan for loci predisposing to social phobia: evidence for a chromosome 16 risk locus.Am J Psychiatry. 2004; 161: 59-66Crossref PubMed Scopus (66) Google Scholar) for SocP, and genomewide-significant linkage to chromosome 14 markers was reported for SimP by Gelernter et al. (Gelernter et al., 2003Gelernter J Page GP Bonvicini K Woods SW Pauls DL Kruger S A chromosome 14 risk locus for simple phobia: results from a genomewide linkage scan.Mol Psychiatry. 2003; 8: 71-82Crossref PubMed Scopus (43) Google Scholar). However, despite the considerable evidence that genetic factors play a major role in the etiology of phobias and other anxiety disorders, to our knowledge no research has been completed that unequivocally (i.e., confirmed via either replication in an independent sample or identification of a variant from a linked region associated with the trait) establishes the locations of genes contributing to these disorders. Clearly, one impediment to gene mapping is the complex nature of the trait, which can translate into misspecification of the mode of inheritance, which in turn reduces the power of any genetic model–based analysis (Clerget-Darpoux et al. Clerget-Darpoux et al., 1986Clerget-Darpoux F Bonaiti-Pellie C Hochez J Effects of misspecifying genetic parameters in lod score analysis.Biometrics. 1986; 42: 393-399Crossref PubMed Scopus (360) Google Scholar; Risch and Giuffra Risch and Giuffra, 1992Risch N Giuffra L Model misspecification and multipoint linkage analysis.Hum Hered. 1992; 42: 77-92Crossref PubMed Scopus (164) Google Scholar; Dizier et al. Dizier et al., 1996Dizier MH Babron MC Clerget-Darpoux F Conclusion of LOD-score analysis for family data generated under two-locus models.Am J Hum Genet. 1996; 58: 1338-1346PubMed Google Scholar). This can be addressed through the use of genetic model–free analyses, but this approach may involve a sacrifice in power. Also, these traits are commonly analyzed univariately, one (binary) phenotype at a time, which (given that there is an underlying genetic relationship between these traits) can weaken the linkage or association signal. This highlights an additional dilemma of genetic model–based analyses that focus on a single phenotype of this multivariate trait; for example, in an analysis focused on PD, individuals with only a diagnosis of SocP would be defined as unaffected, which obviously could be inaccurate in the situation of a shared risk locus. Furthermore, these methods are related to hard clustering and assign each person to one cluster in a set of defined clusters (spectra of diagnoses or combinations of them), often assuming well-defined boundaries between the clusters and not taking into account the potential phenotype heterogeneity that characterizes most complex diseases. Also, the diagnostic criteria for anxiety disorders are constructed in such a way that they can be met with different (although usually overlapping) sets of symptoms, which is an issue that was not usually considered by previous studies. Thus, more-accurate investigations (to obtain more-powerful tests) should properly model the multivariate nature and variable expressivity of the anxiety phenotype, which is the focus of this study. An approach using fuzzy clustering may be better suited than a categorical classification approach to anxiety data. In fuzzy clustering, grade of membership (GoM) scores between 0 and 1 are assigned to every data element (individual), and this should better model the variable expression of the genetic factors. We therefore based our analysis on GoM scores, which aim to summarize the whole phenotype, reflecting the multivariate nature and heterogeneity of the set of anxiety disorders. The analysis of these GoM scores is equivalent to an analysis of all the traits together and has been shown to be a powerful form of multivariate analysis (Kaabi and Elston Kaabi and Elston, 2003Kaabi B Elston RC New multivariate test for linkage, with application to pleiotropy: fuzzy Haseman-Elston.Genet Epidemiol. 2003; 24: 253-264Crossref PubMed Scopus (11) Google Scholar). This method of linkage analysis, based on the use of GoM scores resulting from fuzzy clustering to define a new dependent variable for the various Haseman-Elston approaches, provides a means of data reduction (which implies fewer dependent variables and fewer df) and data mining (i.e., it seeks a hidden structure that may be linked to a specific marker). Thus, it addresses a common problem in genetic linkage analysis of complex traits, both by allowing for the inclusion of more diagnostic information and by accounting for the uncertainty about that information. The inclusion of all individual phenotypes and the flexibility in categorizing them results in increased power for a given sample size. Families were identified through the Anxiety Clinic at the Connecticut Mental Health Center at Yale University or through advertisements. All families were ascertained through probands with PD. Family inclusion criteria were a family history of known symptoms of panic attacks or AgP, generalized anxiety, or SocP (at least two family members, in addition to the proband, with symptoms of anxiety disorder and one member with PD). Exclusion criteria and the source of DNA are described extensively elsewhere (Gelernter et al. Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar). All subjects gave informed consent as approved by the appropriate institutional review boards. The diagnostic process was identical for all phobia variables (i.e., the anxiety disorders PD, AgP, SimP, and SocP) (Gelernter et al. Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar, Gelernter et al., 2003Gelernter J Page GP Bonvicini K Woods SW Pauls DL Kruger S A chromosome 14 risk locus for simple phobia: results from a genomewide linkage scan.Mol Psychiatry. 2003; 8: 71-82Crossref PubMed Scopus (43) Google Scholar, Gelernter et al., 2004aGelernter J Liu X Hesselbrock V Page GP Goddard A Zhang H Results of a genomewide linkage scan: support for chromosomes 9 and 11 loci increasing risk for cigarette smoking.Am J Med Genet B Neuropsychiatr Genet. 2004; 128: 94-101Crossref Scopus (80) Google ScholarGelernter et al., 2004bGelernter J Page GP Stein MB Woods SW Genome-wide linkage scan for loci predisposing to social phobia: evidence for a chromosome 16 risk locus.Am J Psychiatry. 2004; 161: 59-66Crossref PubMed Scopus (66) Google Scholar). In total, the sample includes 19 families (219 subjects), comprising 61 sibships among whom 200 subjects were given diagnoses, and 162 of these subjects were genotyped. For more-detailed descriptive statistics of the data set used in this analysis, see tables Table 1, Table 2.Table 1Summary of Descriptive Statistics of the Data SetStatisticValueNo. of pedigrees19Mean ± SD size of pedigrees (range)11.53±5.83 (3–21)No. of sibships61Mean ± SD size of sibships (range)2.28±1.33 (1–8)No. of sibships of size >142Mean ± SD size of sibships of size >1 (range)2.86±1.23 (2–8)No. of sibships with: 0 Parents with data21 1 Parent with data22 2 Parents with data18No. of sibships of size >1 with: 0 Parents with data16 1 Parent with data15 2 Parents with data11No. of male subjects99No. of female subjects120No. of pairs of type: Parent-offspring278 Sib-sib143 Sister-sister51 Brother-brother23 Brother-sister69 Open table in a new tab Table 2Frequency of Anxiety Phenotypes among SubjectsNo. (%) of SubjectsPhenotypeDefinitely AffectedProbably or Partially AffectedDefinitely UnaffectedMissing or UnknownAgP76 (38)4 (2)115 (57.5)5 (2.5)SimP74 (37)5 (2.5)116 (58)5 (2.5)SocP65 (32.5)5 (2.5)125 (62.5)5 (2.5)PD55 (27.5)7 (3.5)133 (66.5)5 (2.5) Open table in a new tab The Schedule for Affective Disorders and Schizophrenia–Lifetime (modified to permit DSM-IIIR diagnosis) or the Structured Clinical Interview for DSM-IV Axis I Disorders (First et al. First et al., 1997First MB Spitzer RL Gibbon M Williams JBW Structured clinical interview for DSM-IV axis I disorders, research version, non-patient edition (SCID-NP) version 2.0. Biometrics Research, New York State Psychiatric Institute, New York1997Google Scholar) was used for diagnostic evaluation. Assignment of the diagnoses is described elsewhere (Gelernter et al. Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar). All included individuals received direct interviews. Those not interviewed were coded as unknown or missing for the anxiety variables considered. On the basis of a review of the interview by a doctoral-level expert and the interviewer's assessment, subjects were grouped into three classifications: definitely affected, probably or partially affected, and definitely unaffected (table 2). Each of the variables was scored 2 for definitely affected, 1 for probably affected, or 0 for definitely unaffected. Genotypes from 400 autosomal markers were analyzed. These markers included 372 from ABI PRISM LD-MD10 Linkage Mapping Set version 2.0 in addition to 6 markers used as substitutes for failed markers from the ABI PRISM set. In addition, polymorphisms at several candidate loci were genotyped. Twelve markers, mostly from the ABI PRISM marker set, were added to increase marker density in regions of interest for phobias or PD on the basis of previous linkage results for these phenotypes (Gelernter et al. Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar, Gelernter et al., 2003Gelernter J Page GP Bonvicini K Woods SW Pauls DL Kruger S A chromosome 14 risk locus for simple phobia: results from a genomewide linkage scan.Mol Psychiatry. 2003; 8: 71-82Crossref PubMed Scopus (43) Google Scholar). PCR and genotyping techniques are comprehensively described elsewhere (Gelernter et al. Gelernter et al., 2001Gelernter J Bonvicini K Page G Woods SW Goddard AW Kruger S Pauls DL Goodson S Linkage genome scan for loci predisposing to panic disorder or agoraphobia.Am J Med Genet. 2001; 105: 548-557Crossref PubMed Scopus (87) Google Scholar). In construction of the genetic map, sex-averaged distances were used for markers on the Marshfield genetic map, whereas the nucleotide position was converted to centimorgans (1 Mb ≈ 1 cM) for the others (mostly candidate polymorphisms) by use of the NCBI Map Viewer (Cooperative Human Linkage Center). We checked for genotyping errors, which, if ignored, may either lead to false-positive results (i.e., increase type I error [Seaman and Holman Seaman and Holmans, 2005Seaman SR Holmans P Effect of genotyping error on type-I error rate of affected sib pair studies with genotyped parents.Hum Hered. 2005; 59: 157-164Crossref PubMed Scopus (7) Google Scholar]) or diminish evidence of linkage (i.e., yield less power [Abecasis et al. Abecasis et al., 2001Abecasis GR Cherny SS Cardon LR The impact of genotyping error on family-based analysis of quantitative traits.Eur J Hum Genet. 2001; 9: 130-134Crossref PubMed Scopus (111) Google Scholar]). When parents or additional sibs are available, genotyping errors and new mutations can often be detected as Mendelian incompatibilities or apparent double recombinants by use of common programs, such as GENEHUNTER (Kruglyak Lab Web site) and the S.A.G.E. package procedure MARKERINFO (S.A.G.E. v5.0). In cases of identified Mendelian errors, the genotypes of the child, parents, and other siblings were classified as missing for that marker. Moreover, the results of linkage studies may be compromised if a substantial number of putative sib pairs are not actually sib pairs. We used the programs SIBMED (Douglas et al. Douglas et al., 2000Douglas JA Boehnke M Lange K A multipoint method for detecting genotyping errors and mutations in sibling-pair linkage data.Am J Hum Genet. 2000; 66: 1287-1297Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, Douglas et al., 2002Douglas JA Skol AD Boehnke M Probability of detection of genotyping errors and mutations as inheritance inconsistencies in nuclear-family data.Am J Hum Genet. 2002; 70: 487-495Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar) and RELTEST (Olson Olson, 1999Olson JM Relationship estimation by Markov-process models in a sib-pair linkage study.Am J Hum Genet. 1999; 64: 1464-1472Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar) for the purpose of identifying any such misclassified individuals. By use of the anxiety variables described above, a fuzzy clustering was performed using the S-PLUS (Insightful Corporation Insightful Corporation, 2003Insightful Corporation S-PLUS software: S-PLUS® 6.2 for Windows Professional Edition. Insightful Corporation, Seattle2003Google Scholar) procedure FANNY (Kaufman and Rousseeuw Kaufman and Rousseeuw, 1990Kaufman L Rousseeuw PJ Finding groups in data: an introduction to cluster analysis. John Wiley & Sons, New York1990Crossref Google Scholar). This procedure is based on the similarity or dissimilarity of individuals with respect to the variables considered. As input for the procedure FANNY, we used the anxiety variables (SocP, SimP, AgP, and PD) coded as quantitative variables with possible values of 0, 1, or 2. We prespecified the number of clusters as two, and the rest of the FANNY parameters (including membership exponent = 2) were set to default values. The output contained the GoM scores for each cluster, the clustering vector of the nearest crisp clustering or the closest hard (i.e., crisp) clustering, and Dunn’s partition coefficient F(k) of the clustering (Dunn Dunn, 1977Dunn JC Indices of partition fuzziness and the detection of clusters in large data sets.in: Gupta M Saradis G Fuzzy automata and decision process. Elsevier, New York1977: 271-284Google Scholar), where k is the number of clusters. F(k) is the sum of all squared membership coefficients, divided by the number of observations. Its value is always between 1/k and 1. The normalized form of the coefficient is defined as (F(k)−1k1−1k)and ranges between 0 and 1. A low value of Dunn’s coefficient indicates a very fuzzy clustering, whereas a value close to 1 indicates a near-crisp clustering. We identified two groups (clusters), and every data element (individual) was assigned a GoM to these groups. By construction, the sum of these GoM scores for each person equals 1. We also performed a post hoc characterization in terms of the initial anxie
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