Genome-wide association study of Tourette's syndrome.

Tourette's syndrome (TS) is a developmental disorder that has one of the highest familial recurrence rates among neuropsychiatric diseases with complex inheritance. However, the identification of definitive TS susceptibility genes remains elusive. Here, we report the first genome-wide association study (GWAS) of TS in 1285 cases and 4964 ancestry-matched controls of European ancestry, including two European-derived population isolates, Ashkenazi Jews from North America and Israel and French Canadians from Quebec, Canada. In a primary meta-analysis of GWAS data from these European ancestry samples, no markers achieved a genome-wide threshold of significance (P<5 × 10(-8)); the top signal was found in rs7868992 on chromosome 9q32 within COL27A1 (P=1.85 × 10(-6)). A secondary analysis including an additional 211 cases and 285 controls from two closely related Latin American population isolates from the Central Valley of Costa Rica and Antioquia, Colombia also identified rs7868992 as the top signal (P=3.6 × 10(-7) for the combined sample of 1496 cases and 5249 controls following imputation with 1000 Genomes data). This study lays the groundwork for the eventual identification of common TS susceptibility variants in larger cohorts and helps to provide a more complete understanding of the full genetic architecture of this disorder.

A family-based association analysis and meta-analysis of the reading disabilities candidate gene DYX1C1.

Reading disabilities (RD) have a significant genetic basis and have shown linkage to multiple regions including chromosome 15q. Dyslexia susceptibility 1 candidate gene 1 (DYX1C1) on chromosome 15q21 was originally proposed as a candidate gene with two potentially functional polymorphisms at the -3G/A and 1249G/T positions showing association with RD. However, subsequent studies have yielded mixed results. We performed a literature review and meta-analysis of the -3G/A and 1249G/T polymorphisms, including new unpublished data from two family-based samples. Ten markers in DYX1C1 were genotyped in the two independently ascertained samples. Single marker and -3G/A:1249G/T haplotype analyses were performed for RD in both samples, and quantitative trait analyses using standardized reading-related measures was performed in one of the samples. For the meta-analysis, we used a random-effects model to summarize studies that tested for association between -3G/A or 1249G/T and RD. No significant association was found between the DYX1C1 SNPs and RD or any of the reading-related measures tested after correction for the number of tests performed. The previously reported risk haplotype (-3A:1249T) was not biased in transmission. A total of 9 and 10 study samples were included in the meta-analysis of the -3G/A and 1249G/T polymorphisms, respectively. Neither polymorphism reached statistical significance, but the heterogeneity for the 1249G/T polymorphism was high. The results of this study do not provide evidence for association between the putatively functional SNPs -3G/A and 1249G/T and RD.

Mutation screen and association analysis of the glucocorticoid receptor gene (NR3C1) in childhood-onset mood disorders (COMD).

Depressive disorders are highly heterogeneous psychiatric disorders involving deficits to cognitive, psychomotor, and emotional processing. Considerable evidence links disruption to the hypothalamic-pituitary-adrenal (HPA) axis to the etiology of depression, with specific deficits reported in glucocorticoid receptor (GR)-mediated negative feedback. Given the role of GR-mediated negative feedback in mediating response to stress, and the clear link between stress and depression, it is plausible that polymorphisms in the GR gene (NR3C1) act to increase susceptibility. Maternal behavior in rats epigenetically alters a NGF1-A transcription factor binding-site in the promoter region of the GR gene, providing a mechanism by which environmental cues can regulate GR expression and thus response to stress. The analogous region of the human GR gene (NR3C1) has not been studied, but it is possible that polymorphisms in this region may alter the binding of transcription factors known to regulate GR expression. In this study, we have performed bioinformatic analyses on the promoter region of NR3C1 to identify conserved promoter sequences and predicted transcription factor binding sites. These regions were screened with denaturing high-performance liquid chromatography (DHPLC) and direct re-sequencing, and several novel polymorphic variants were identified. We genotyped nine polymorphisms across NR3C1 in a large sample of Hungarian nuclear families ascertained through affected probands with a diagnosis of childhood-onset mood disorders (COMD). Single-marker analysis provided little evidence for an association of this gene with COMD, but multi-marker analysis across a region of high linkage disequilibrium revealed modest evidence for the biased transmission of several haplotypes.

Cytokine Genes TNF, IL1A, IL1B, IL6, IL1RN and IL10, and childhood-onset mood disorders.

BACKGROUND/AIMS: Inflammatory cytokines induce a behavioral syndrome, known as sickness behavior, that strongly resembles symptoms typically seen in depression. This resemblance has led to the theory that an imbalance of inflammatory cytokine activity may be a contributing factor in depressive disorders. Support for this is found in multiple lines of evidence, such as the effects of cytokines on the activities of the hypothalamic-pituitary-adrenal axis, serotonin and brain-derived neurotrophic factor, and hippocampal function, all of which are implicated in the etiology of depression. In addition, associations between inflammatory activity and depressive symptomology have been documented in a number of studies, and the depressogenic effects of cytokine therapy are well known. Accordingly, given that depression has a substantial genetic basis, genes involved in the regulation of inflammatory cytokine activity are strong candidates for involvement in genetic susceptibility to depressive disorders. Here, we have tested 6 key genes of this type, TNF, IL1A, IL1B, IL6, IL1RN and IL10, as candidates for involvement in childhood-onset mood disorders. METHODS: In this study of 384 families, each ascertained through a child with depression diagnosed before the age of 15 years, 11 polymorphisms of known or likely functional significance (coding and regulatory variants) were analyzed. RESULTS: Testing for biased transmission of alleles from parents to their affected offspring, we found no evidence for an association between childhood-onset mood disorders and any of the polymorphisms, either individually or as haplotypes. CONCLUSION: The present study does not support the involvement of the TNF, IL1A, IL1B, IL6, IL1RN and IL10 variants as major genetic risk factors contributing to early-onset mood disorders.

Association study between Gilles de la Tourette Syndrome and two genes in the Robo-Slit pathway located in the chromosome 11q24 linked/associated region.

Gilles de la Tourette Syndrome (GTS) is an inherited neuropsychiatric disorder characterized by the presence of motor and phonic tics. Previous genetic studies have identified linkage and association between GTS and the 11q24 chromosomal region. We selected for study, within this region, two possible susceptibility genes for GTS, the ROBO3 and ROBO4 genes. These two genes were selected because of the recent identification of SLITRK1 as a potential susceptibility gene for GTS based on a translocation breakpoint and the further finding of two mutations in the SLITRK1 gene in three patients with GTS. While thus far, the SLITRK1 gene appears to account for only a few cases of GTS, these findings, if confirmed, point to other genes in these pathways that may contribute to GTS. Based on this, we examined two genes in the Slit-Robo pathway involved in cell migration, axonal pathfinding, and/or neuronal differentiation because of their location in 11q24, a region previously identified as linked and associated with GTS. We selected six haplotype tagging single nucleotide polymorphisms (SNPs) for ROBO3 and four for ROBO4 and genotyped them in our sample of trios and sibpair families diagnosed with GTS. Based on 155 nuclear families with 255 affected children, we did not find evidence for association between GTS and either the ROBO3 or ROBO4 genes. Thus, these two genes are unlikely to be the susceptibility genes contributing to GTS on 11q24.

The contribution of alternative splicing to genetic risk for psychiatric disorders.

A genetic contribution to psychiatric disorders has clearly been established and genome-wide association studies now provide the location of risk genes and genetic variants associated with risk. However, the mechanism by which these genes and variants contribute to psychiatric disorders is mostly undetermined. This is in part because non-synonymous protein coding changes cannot explain the majority of variants associated with complex genetic traits. Based on this, it is predicted that these variants are causing gene expression changes, including changes to alternative splicing. Genetic changes influencing alternative splicing have been identified as risk factors in Mendelian disorders; however, currently there is a paucity of research on the role of alternative splicing in complex traits. This stems partly from the difficulty of predicting the role of genetic variation in splicing. Alterations to canonical splice site sequences, nucleotides adjacent to splice junctions, and exonic and intronic splicing regulatory sequences can influence splice site choice. Recent studies have identified global changes in alternatively spliced transcripts in brain tissues, some of which correlate with altered levels of splicing trans factors. Disease-associated variants have also been found to affect cis-acting splicing regulatory sequences and alter the ratio of alternatively spliced transcripts. These findings are reviewed here, as well as the current datasets and resources available to study alternative splicing in psychiatric disorders. Identifying and understanding risk variants that cause alternative splicing is critical to understanding the mechanisms of risk as well as to pave the way for new therapeutic options.

Association of the glutamate receptor subunit gene GRIN2B with attention-deficit/hyperactivity disorder.

The glutamatergic signaling pathway represents an ideal candidate susceptibility system for attention-deficit/hyperactivity disorder (ADHD). Disruption of specific N-methyl-D-aspartate-type glutamate receptor subunit genes (GRIN1, 2A-D) in mice leads to significant alterations in cognitive and/or locomotor behavior including impairments in latent learning, spatial memory tasks and hyperactivity. Here, we tested for association of GRIN2B variants with ADHD, by genotyping nine single nucleotide polymorphisms (SNPs) in 205 nuclear families identified through probands with ADHD. Transmission of alleles from heterozygous parents to affected offspring was examined using the transmission/disequilibrium test. Quantitative trait analyses for the ADHD symptom dimensions [inattentive (IA) and hyperactive/impulsive (HI)] and cognitive measures of verbal working memory and verbal short-term memory were performed using the fbat program. Three SNPs showed significantly biased transmission (P < 0.05), with the strongest evidence of association found for rs2,284,411 (chi(2)= 7.903, 1 degree of freedom, P= 0.005). Quantitative trait analyses showed associations of these markers with both the IA and the HI symptom dimensions of ADHD but not with the cognitive measures of verbal short-term memory or verbal working memory. Our data suggest an association between variations in the GRIN2B subunit gene and ADHD as measured categorically or as a quantitatively distributed trait.

Sticky traps for monitoring Pseudacteon parasitoids of Solenopsis fire ants.

A newly developed method for passively trapping adult Pseudacteon phorid flies, which parasitize workers of Solenopsis saevissima complex fire ants, is described. Adult flies responding to deployed Solenopsis invicta midden were captured when they landed on a Tanglefoot-coated perch, which is part of the trap. This sampling method provided a uniform, repeatable, and verifiable sample that allowed continuous and simultaneous sampling among locations, which can only be accomplished with other techniques by substantially increasing the number of observers. A field test showed the superior operational efficiency and effectiveness of this method relative to other techniques. These traps have been shown effective in various phorid habitats in Texas and Florida. We expect this trap to also be effective in detecting/monitoring phorid flies in other locations.

Decoding the non-coding genome: elucidating genetic risk outside the coding genome.

Current evidence emerging from genome-wide association studies indicates that the genetic underpinnings of complex traits are likely attributable to genetic variation that changes gene expression, rather than (or in combination with) variation that changes protein-coding sequences. This is particularly compelling with respect to psychiatric disorders, as genetic changes in regulatory regions may result in differential transcriptional responses to developmental cues and environmental/psychosocial stressors. Until recently, however, the link between transcriptional regulation and psychiatric genetic risk has been understudied. Multiple obstacles have contributed to the paucity of research in this area, including challenges in identifying the positions of remote (distal from the promoter) regulatory elements (e.g. enhancers) and their target genes and the underrepresentation of neural cell types and brain tissues in epigenome projects - the availability of high-quality brain tissues for epigenetic and transcriptome profiling, particularly for the adolescent and developing brain, has been limited. Further challenges have arisen in the prediction and testing of the functional impact of DNA variation with respect to multiple aspects of transcriptional control, including regulatory-element interaction (e.g. between enhancers and promoters), transcription factor binding and DNA methylation. Further, the brain has uncommon DNA-methylation marks with unique genomic distributions not found in other tissues - current evidence suggests the involvement of non-CG methylation and 5-hydroxymethylation in neurodevelopmental processes but much remains unknown. We review here knowledge gaps as well as both technological and resource obstacles that will need to be overcome in order to elucidate the involvement of brain-relevant gene-regulatory variants in genetic risk for psychiatric disorders.

Genetic study of the myelin oligodendrocyte glycoprotein (MOG) gene in schizophrenia.

Schizophrenia (SCZ) is a neuropsychiatric disorder that affects approximately 1% of the general population. The human leukocyte antigen (HLA) system has been implicated in several genetic studies of SCZ. The myelin oligodendrocyte glycoprotein (MOG) gene, which is located close to the HLA region, is considered a candidate for SCZ due to its association with white matter abnormalities and its importance in mediating the complement cascade. Four polymorphisms in the MOG gene (CA)n (TAAA)n, and two intronic polymorphisms, C1334T and C10991T, were investigated for the possibility of association with SCZ using 111 SCZ proband and their families. We examined the transmission of the alleles of each of these polymorphisms with the transmission disequilibrium test. We did not observe significant evidence for biased transmission of alleles at the (CA)n (chi2=2.430, 6 df, P=0.876) (TAAA)n (chi2=3.550, 5 df, P=0.616), C1334T (chi2=0.040, 1 df, P=0.841) and C10991T (chi2=0.154, 1 df, P=0.695) polymorphisms. Overall haplotype analysis using the TRANSMIT program was also not significant (chi2=7.954, 9 df, P=0.539). Furthermore, our results comparing mean age at onset in the genotype groups using the Kruskal-Wallis Test were not significant. Our case-control analyses (182 cases age-, sex- and ethnicity-matched with healthy controls) and combined z-score [(CA)n: z-score=-1.126, P=0.130; (TAAA)n: z-score=-0.233, P=0.408; C1334T: z-score=0.703, P=0.241; C10991T: z-score=0.551, P=0.291] were also not significant. Although our data are negative, the intriguing hypothesis for MOG in SCZ may warrant further investigation of this gene.

Population frequencies of the A1 allele at the dopamine D2 receptor locus.

The reported association of a polymorphic allele at the dopamine D2 receptor locus (DRD2) and alcoholism has recently been the focus of considerable interest and controversy. Evidence both for and against an association of the A1 allele of the TaqI A system have been reported. One of the inconsistencies in these studies is the frequency of the A1 allele in the controls. We undertook this study to determine the frequencies of the DRD2 A1 allele in different populations. The frequency of the DRD2 A1 allele was studied in 381 unrelated people from 16 different populations. On a global scale the frequency of the A1 allele was found to be dramatically different among the populations studied, from as low as 0.09 to as high as 0.75. Because of these significant differences an association study with this polymorphism must carefully control for ethnic origin of subjects and the results must be evaluated with caution.

Haplotype study of three polymorphisms at the dopamine transporter locus confirm linkage to attention-deficit/hyperactivity disorder.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) is often treated using methylphenidate, a psychostimulant that inhibits the dopamine transporter. This led E.H. Cook and colleagues to consider the dopamine transporter locus (DAT1) as a primary candidate gene for ADHD. That group reported a significant association between ADHD and the 480-base pair (bp) allele of the variable number of tandem repeats (VNTR) polymorphism located in the 3' untranslated region of the DAT1 gene. This association was later replicated in additional studies. METHODS: The DAT1 gene has additional common polymorphisms in intron 9 and exon 9. We investigated the possibility of linkage of DAT1 and ADHD using the VNTR polymorphism and two additional common polymorphisms in 102 nuclear families with an ADHD proband. Using the transmission disequilibrium test, we examined the transmission of the alleles of each of these polymorphisms, as well as the haplotypes of the polymorphisms. RESULTS: We did not observe significant evidence for the biased transmission of the alleles of either the VNTR or the additional two polymorphisms when examined individually, although there was a trend for the biased transmission of the 480-bp allele of the VNTR. When we examined the haplotypes of the three polymorphisms we found significant evidence for biased transmission of one of the haplotypes containing the 480-bp VNTR allele. We also genotyped six additional DNA sequence variants of the DAT1 gene. However, these variants were not sufficiently polymorphic in our sample to be informative. Two of the DNA variants that result in an amino acid change, Ala559Val and Glu602Gly, were not observed in our sample. CONCLUSIONS: Our results support previous findings of an association between the DAT1 gene and ADHD.

BDNF and COMT polymorphisms: relation to memory phenotypes in young adults with childhood-onset mood disorder.

Recent investigations in several species have suggested a role for brain-derived neurotrophic factor (BDNF) in memory, which may be mediated by the influence of BDNF on neuronal plasticity in the hippocampus. BDNF polymorphisms have also been associated with mood disorders. Catechol-O-methyltransferase (COMT) metabolizes dopamine and has been implicated in prefrontal function, another area of the brain relevant for memory. In a sample of 63 young adults with a history of childhood-onset mood disorder, we typed three BDNF polymorphisms, including the BDNF Val66Met single nucleotide polymorphism (SNP), and the COMT Val108/158Met SNP. Multivariate analysis of variance was used to test the association between BDNF and COMT markers and measures of declarative memory. Variants at the three BDNF markers and one COMT marker were not associated with declarative memory function p-values ranged from 0.25 to 0.98. Higher IQ (F = 6.18, df = 4, 58, p = 0.0003) and female gender (F = 4.41, df = 4, 58, p = 0.0035) were associated with more optimal performance on the memory tasks. This study did not provide evidence supporting an association between BDNF and COMT genes and declarative memory phenotypes.

Linkage study in families with posterior helical ear pits and Wiedemann-Beckwith syndrome.

The Wiedemann-Beckwith syndrome (WBS) is defined by a group of anomalies, including macrosomia, macroglossia, omphalocele, and ear creases. Several minor anomalies have also been reported in the syndrome, including posterior helical ear pits (PHEP). Two independent linkage studies of pedigrees with autosomal dominant inheritance have shown linkage of WBS to 11p15.5 markers. Further confirming the location of WBS to this location is the finding of 11p15.5 duplications and translocations, as well as uniparental disomy for a small area of 11p15.5. In this study, members of previously described families exhibiting autosomal dominant inheritance of the PHEP phenotype were genotyped for three markers in the 11p15.5 region. These three markers were in the insulin-like growth factor (IGF2), insulin (INS), and tyrosine hydroxylase (TH) region. The data were examined by linkage analysis using the same genetic model used previously to demonstrate linkage of WBS to markers on chromosome 11p15.5: an autosomal dominant model with a penetrance of 0.90 and a gene frequency of 0.001. In one large pedigree, linkage analysis of the 11p15.5 markers excluded the PHEP phenotype from the IGF2, INS, and TH region. In the four other pedigrees examined, the marker loci were not sufficiently informative or the pedigrees did not provide sufficient power to exclude linkage from this region. The strongest evidence against linkage of the PHEP phenotype to 11p15.5 was evident by inspection of the segregation of the haplotypes of the markers in the pedigrees. In two informative pedigrees, relatives with the PHEP phenotype did not share the same haplotype of markers identical by descent. Our results show that the PHEP phenotype is not linked to chromosome 11p15.5 in the informative families tested. In the families examined, there are not enough individuals with WBS to determine if WBS was linked to 11p15.5 in these families. Although locus heterogeneity has not been demonstrated in WBS, it is possible that a second WBS locus exists and that the PHEP phenotype in these families is linked to a second WBS locus. Alternatively, the PHEP phenotype may occur independently of WBS so that the association of WBS and PHEP in our pedigrees may, in fact, represent causal heterogeneity.

Linkage study of the alpha2A adrenergic receptor in attention-deficit hyperactivity disorder families.

Attention-deficit hyperactivity disorder (ADHD) is a common childhood psychiatric disorder, characterized by marked and pervasive inattention, hyperactivity, and impulsiveness. An alteration in the expression or function of the adrenergic system has been suggested to be involved in ADHD based on animal models, pharmacological interventions, and the neural circuitry of attentional processes. The efficacy of clonidine in reducing disruptive behaviors in some children with ADHD argues for a causal role of the adrenergic system and more specifically for the alpha2A receptors as clonidine is an alpha2A agonist that inhibits release of noradrenaline into the synapse. In animal studies, alpha2A receptor agonists have also been shown to improve performance on working memory tasks under distracting conditions, indicating that these receptors function in the regulation of attention. We examined the possibility that the gene for the alpha2A adrenergic receptor (ADRA2A) is linked to ADHD by testing a polymorphism located in the promoter region of the ADRA2A gene in a sample of 94 nuclear families with an ADHD proband. We found no evidence for linkage of the ADRA2A gene with ADHD, using the transmission disequilibrium test in this set of families.

No evidence for a major gene effect of the dopamine D4 receptor gene in the susceptibility to Gilles de la Tourette syndrome in five Canadian families.

Gilles de la Tourette Syndrome (TS) is neuropsychiatric disorder characterized by both motor and vocal tics affecting approximately 1/10,000 females and 1/2000 males. Because of the success of neuroleptics and other agents interacting with the dopaminergic system in the suppression of tics, a defect in the dopamine system has been hypothesized in the etiology of TS. In this paper we test the hypothesis that the dopamine D4 receptor (DRD4) is linked to the genetic susceptibility to TS in five families. We tested three polymorphisms in the DRD4 gene and a polymorphism in the closely linked locus, tyrosine hydroxylase (TH). We found no evidence for linkage of DRD4 or TH to TS using an autosomal dominant model with reduced penetrance or using non-parametric methods. The presence of a mutation that results in a truncated non-functional D4 receptor protein was also tested for, but was not observed in these families.

Linkage study of the dopamine D5 receptor gene and Gilles de la Tourette syndrome.

A defect in the dopamine system has been hypothesized as the etiological defect in Gilles de la Tourette syndrome (TS). In this report, we test the hypothesis that the dopamine D5 receptor locus (DRD5) is linked to the genetic susceptibility to TS in five families studied in Canada. We tested for linkage to the dopamine D5 receptor gene using a microsatellite polymorphism located in the same cosmid clone. Using an autosomal dominant model with reduced penetrance, we were able to exclude linkage in four of the five families for the TS and chronic multiple tics (CMT) phenotype. Also, no evidence for linkage was found using nonparametric methods in all five families.

Linkage study of catechol-O-methyltransferase and attention-deficit hyperactivity disorder.

Attention-deficit hyperactivity disorder is the most common child psychiatric disorder with a prevalence rate in an Ontario study of 9% in boys and 3% in girls [Szatmari et al., 1989]. This disorder is characterized by problems in the areas of attention, overactivity, impulse control, and distractibility. Strong evidence for a genetic component has been provided from twin, family, and adoption studies [for review see Levy et al., 1998] and molecular genetic studies are in progress by several groups worldwide. The Catechol-O-Methyltransferase (COMT) gene is an interesting candidate for ADHD as it is involved in the breakdown of dopamine and norepinephrine, neurotransmitters strongly implicated in the etiology of ADHD. In addition, children with velo-cardio-facial syndrome, a deletion syndrome of the chromosomal region 22q11 where the COMT gene has been localized, often have symptoms of ADHD suggesting this gene may have an etiological role in ADHD. In this study, we have tested for linkage in ADHD families using the functional polymorphism at codon 158 that determines COMT activity [Lachman et al., 1996] and analyzed the data with the transmission disequilibrium test (TDT). A total of 77 nuclear families collected from Toronto were genotyped. We find no evidence for linkage of this polymorphism and ADHD in our sample. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:710-713, 1999.

Intergenerational CAG repeat expansion at ERDA1 in a family with childhood-onset depression, schizoaffective disorder, and recurrent major depression.

Reported evidence of anticipation for schizophrenia and bipolar disorder has recently precipitated a search for unstable trinucleotide repeats for these diseases. Several initial studies suggested an increase in the frequency of large CAG/CTG repeats in the genomes of schizophrenic and bipolar individuals. Published reports do not demonstrate expansion per se, and may be suggestive of allelic association with the disease rather than actual dynamic DNA mutations. This report documents evidence of a significant expansion of CAG/CTG repeats from one generation to the next in a family demonstrating evidence of anticipation for psychiatric disorders. Using the repeat expansion detection (RED) technique, we observed that a proband with multiple psychiatric diagnoses, including childhood-onset depression, inherited a larger CAG/CTG repeat than either parent. Analysis of the ERDA1 locus on 17q21.3 revealed that the proband inherited a very large allele from the father which increased in repeat number through transmission. The mother was diagnosed with schizoaffective disorder and the father with depression. While this DNA mutation may be a stochastic event unconnected with the disease, it could represent DNA instability as an etiologic factor in psychiatric diseases.

Alleles at the dopamine D4 receptor locus do not contribute to the genetic susceptibility to schizophrenia in a large Swedish kindred.

The discovery of a functional polymorphism within the dopamine D4 receptor gene (DRD4) has not only strengthened the hypotheses implicating DRD4 in the etiology of neuropyschiatric disorders, but also provided a genetic marker for testing these hypotheses. The possibility of the dopamine D4 receptor as a candidate gene for schizophrenia was investigated in a large Swedish kindred segregating for schizophrenia. Linkage to schizophrenia was tested by linkage analyses of 6 polymorphic markers (at 4 loci) in chromosome 11p15.5 including the dopamine D4 receptor (DRD4) and the tyrosine hydroxylase (TH) loci. Schizophrenia was excluded from close linkage to the DRD4 locus using two of the polymorphisms located within the dopamine D4 receptor gene. The first DRD4 polymorphism consists of variation in the number of a 48 bp imperfect direct repeat in the third exon; the second consists of a variable number of repeated G nucleotides in the first intron. In addition, some of the individuals homozygous for four or seven copies of 48 bp repeat alleles were tested for previously reported sequence variation among repeats. No single haplotype of the DRD4 alleles or haplotype of other markers in chromosome 11p15.5 was found to be common to the schizophrenic individuals in this family. Therefore, we find no evidence for linkage of the D4 receptor, or this region of 11p15.5, with genetic susceptibility to schizophrenia in this kindred.