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Joint Analysis of the DRD5 Marker Concludes Association with Attention-Deficit/Hyperactivity Disorder Confined to the Predominantly Inattentive and Combined Subtypes

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable, heterogeneous disorder of early onset, consisting of a triad of symptoms: inattention, hyperactivity, and impulsivity. The disorder has a significant genetic component, and theories of etiology include abnormalities in the dopaminergic system, with DRD4, DAT1, SNAP25, and DRD5 being implicated as major susceptibility genes. An initial report of association between ADHD and the common 148-bp allele of a microsatellite marker located 18.5 kb from the DRD5 gene has been followed by several studies showing nonsignificant trends toward association with the same allele. To establish the postulated association of the (CA)(n) repeat with ADHD, we collected genotypic information from 14 independent samples of probands and their parents, analyzed them individually and, in the absence of heterogeneity, analyzed them as a joint sample. The joint analysis showed association with the DRD5 locus (P=.00005; odds ratio 1.24; 95% confidence interval 1.12-1.38). This association appears to be confined to the predominantly inattentive and combined clinical subtypes.

The Wellcome trust UK-Irish bipolar affective disorder sibling-pair genome screen: first stage report.

We have completed the first stage of a two-stage genome wide screen designed to identify chromosomal regions that may harbour susceptibility genes for bipolar affective disorder. The first stage screening sample included 509 subjects from 151 nuclear families recruited within the United Kingdom and Republic of Ireland. This sample contained 154 narrowly defined affected sibling pairs (DSM-IV BPI) and 258 broadly defined affected sibling pairs (DSM-IV BPI, SABP, BPII, BPNOS or MDD(R)), approximately two thirds of all families contained at least one other additional typed individual. All individuals were genotyped using 398 highly polymorphic microsatellite markers from Applied Biosystemss Linkage Mapping Set Version 2. The average inter-marker distance was 9.6 cM and the mean heterozygosity was 0.78. Analysis of these data using non-parametric linkage methods (MAPMAKER/SIBS) found no evidence for loci of major effect and no regions reached genome-wide significance for either suggestive or significant linkage. We identified 19 points across the genome where the MLS exceeded a value set for follow up in our second stage screen (MLS≥0.74 (equivalent to a nominal pointwise significance of 5%) under the narrowest diagnostic model). These points were on chromosomes 2, 3, 4, 6, 7, 9, 10, 12, 17, 18 & X. Some of these points overlapped with previous linkage reports both within bipolar affective disorder and other psychiatric illnesses. Under the narrowest diagnostic model, the single most significant multipoint linkage was on chromosome 18 at marker D18S452 (MLS=1.54). Overall the highest MLS was 1.70 on chromosome 2 at marker D2S125, under the broadest diagnostic model.

Nicotinic acetylcholine receptor alpha4 subunit gene polymorphism and attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a highly heritable, common psychiatric disorder that presents in childhood and that probably involves several genes. There are several lines of evidence suggesting that the nicotinic system may be functionally significant in ADHD: (a) nicotine promotes the release of dopamine and has been shown to improve attention in adults with ADHD, smokers and non-smokers; (b) ADHD is a significant risk factor for early initiation of cigarette smoking in children; (c) maternal cigarette smoking appears to be a risk factor for ADHD; (d) animal studies in rats and monkeys also suggest that nicotine may be involved in attentional systems and locomotor activity; and (e) a central nicotinic agonist, ABT-418, improves attention in both monkeys and ADHD adults. The current study examined the alpha 4 receptor, one of the sites of action of ABT-418. A known Cfol polymorphism within the nicotinic acetylcholine alpha 4 receptor gene, CHRNA4, was studied in 70 ADHD parent-proband trios from an ongoing sample collection of children aged 6-12 with ADHD, according to DSM-IV criteria. Children with known major medical or psychiatric conditions or mental retardation (IQ < 70) were excluded from the study. The Transmission Disequilibrium Test demonstrated no evidence that variation at the nicotinic acetylcholine alpha 4 receptor Cfol polymorphism influences susceptibility to ADHD (P > 0.35). The continuing sample collection will enable further study of other potential nicotinic system polymorphisms in ADHD in more powerful samples.

Stage 2 of the Wellcome Trust UK-Irish bipolar affective disorder sibling-pair genome screen: evidence for linkage on chromosomes 6q16-q21, 4q12-q21, 9p21, 10p14-p12 and 18q22

Bipolar affective disorder (BPAD) is a common psychiatric disorder with complex genetic aetiology. We have undertaken a genome-wide scan in one of the largest samples of bipolar affected sibling pairs (ASPs) using a two-stage approach combining sample splitting and marker grid tightening. In this second stage analysis, we have examined 17 regions that achieved a nominally significant maximum likelihood LOD score (MLS) threshold of 0.74 (or 1.18 for the X-chromosome) in stage one. The second stage has added 135 ASP families to bring the total stage 2 sample to 395 ASPs. In total, 494 microsatellite markers have been used to screen the human genome at a density of 10 cM in the first stage sample (260 ASPs) and 5 cM in the second stage. Under the broad diagnostic model, two markers gave LOD scores exceeding 3 with two-point analysis: D4S392 (LOD=3.30) and D10S197 (LOD=3.18). Multipoint analysis demonstrated suggestive evidence of linkage between BPAD and chromosomal regions 6q16–q21 (MLS=2.61) and 4q12–q21 (MLS=2.38). 6q16–q21 is of particular interest because our data, together with those from two recent genome scans, make this the best supported linkage region in BPAD. Further, our data show evidence of a gender effect at this locus with increased sharing predominantly within the male–male pairs. Our scan also provides support for linkage (MLS≥1.5) at several other regions that have been implicated in meta-analyses of bipolar disorder and/or schizophrenia including 9p21, 10p14–p12 and 18q22.

Molecular genetic studies of bipolar disorder and puerperal psychosis at two polymorphisms in the estrogen receptor alpha gene (ESR 1)

A number of lines of evidence point to the possible involvement of estrogen pathways in the pathophysiology of bipolar disorder in general and puerperal psychosis in particular. There is strong evidence from clinical, follow-up, and genetic studies to support the hypothesis that most cases of puerperal psychosis are manifestations of an affective disorder diathesis with a puerperal trigger and that genes influence susceptibility to both diathesis and trigger. The nature of the trigger is unknown but in view of the abrupt onset at a time of major physiological change it is widely believed that biological, probably hormonal, mechanisms are of paramount importance, with estrogen receiving the most attention to date. We have undertaken a case control association study of bipolar disorder and puerperal psychosis at two known polymorphisms within the estrogen receptor alpha gene (ESR 1) in a sample of 219 unrelated bipolar probands and 219 controls. We could exclude these polymorphisms from an important contribution to susceptibility to bipolar disorder with a high level of confidence. We found no support for the hypothesis that they contribute specific susceptibility to the puerperal trigger, but due to the small numbers of puerperal probands (n = 26) no firm conclusions can be drawn regarding their involvement in puerperal psychosis. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:850-853, 2000.

Bipolar disorder and variation at a common polymorphism (A1832G) within exon 8 of the Wolfram gene

A number of linkage studies provide evidence consistent with the existence of a bipolar susceptibility gene on chromosome 4p16. The gene for Wolfram syndrome, a rare recessive neurodegenerative disorder, lies in this region and has recently been cloned. Psychiatric disturbances including psychosis, mood disorder, and suicide have been reported at increased frequency in Wolfram patients and in heterozygous carriers of a Wolfram mutation. In the current investigation we have undertaken a case-control association study using a single nucleotide polymorphism (causing an amino acid change) in exon 8 of the Wolfram gene in a UK Caucasian sample of 312 Diagnostic and Statistical Manual of Mental Disorders (fourth edition; DSM IV) bipolar I probands and 301 comparison individuals. We found no evidence that variation at this polymorphism influences susceptibility to bipolar disorder. It remains possible that variation at other sites within or near the Wolfram gene plays important roles in determining susceptibility to affective illness. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:154-157, 2000.

Tumour necrosis factor alpha and bipolar affective puerperal psychosis.

The macrophage theory of depression proposes that an excessive secretion of monocyte/macrophage cytokines causes symptoms of depression. It has been suggested that changes in immune function that accompany pregnancy and childbirth could contribute to the affective symptoms suffered by many puerperal women. Tumour necrosis factor alpha (TNFalpha) is a pro-inflammatory cytokine that has been implicated in inflammatory infections and immune diseases. Production of TNFalpha has been shown to be regulated by oestrogen, which suggests it as a potential candidate for susceptibility to post-partum mood disorders. Several polymorphisms have been identified in the TNFalpha gene. The -308 promoter polymorphism has been associated with elevated production of TNFalpha and has been found to influence the neurological outcome of various infections. In a case-control association study, we have examined the frequency of this polymorphism in groups of parous DSM-IV Bipolar females with (N = 116) and without (N = 56) puerperal psychosis, and a female non-psychiatric comparison group (N = 72). We provided no support for the hypothesis that this polymorphism influences susceptibility to bipolar disorder, or acts as a trigger for puerperal psychosis. However, variation at other polymorphisms within TNFalpha or in other oestrogen-regulated genes involved in immune function remain interesting candidates for study in post-partum mood disorders.

No association between two polymorphisms at the 5HT2A gene and bipolar affective puerperal psychosis

Objective: To examine whether variation at two common polymorphisms, T102C and −1438AG, of the serotonin 2A gene (5HT2A) are involved in the puerperal triggering mechanism of bipolar affective puerperal psychosis.

Variation in the coding sequence and flanking splice junctions of the estrogen receptor alpha (ERα) gene does not play an important role in genetic susceptibility to bipolar disorder or bipolar affective puerperal psychosis

Genes involved in estrogen pathways have been proposed as possible candidates influencing susceptibility to bipolar disorder and the affective symptoms suffered by many women during the puerperal period. The estrogen receptor alpha (ERα) gene in particular has been a subject of interest and has recently been intensively screened for variations of potential relevance to psychiatric disorders, resulting in the identification of four mutations in individuals with bipolar disorder or puerperal psychosis. We have examined the frequency of these four ERα variations in a case control study using a group of mixed gender bipolar individuals (N = 231), further classified into subsets of parous bipolar females with (N = 112) and without (N = 50) puerperal psychosis, and a non‐psychiatric comparison group (N = 110). We have also investigated the families in which the variations were initially detected, for evidence of co‐segregation of the variants with mood disorder. We found no evidence in our case control sample to support the involvement of any of the ERα variations in either the aetiology of bipolar disorder or puerperal triggering of bipolar episodes. Nor did we find co‐segregation of ERα variants and disease in any of the four families examined. We conclude that variation in the coding sequence and flanking splice junctions of the ERα gene does not play an important pathogenic role in the majority of cases of Bipolar Disorder or Bipolar Affective Puerperal Psychosis.

Association analysis of the proneurotensin gene and bipolar disorder

Neurotensin (NT) localizes within dopaminergic neurones in the mesocortical, mesolimbic and nigrostriatal systems, and it is now clear that NT can selectively modulate dopaminergic neurotransmission. It has therefore been proposed that altered NT function might contribute to the pathogenesis of neuropsychiatric disorders in which disordered dopaminergic neurotransmission is suspected. We have previously screened the gene encoding NT in a sample of schizophrenic and bipolar subjects, and identified three sequence variants. These have now been tested for association with bipolar disorder using a case-control sample of unrelated bipolar subjects and matched controls. No evidence for association was found, and our data therefore suggest that sequence variation in this gene does not make an important contribution to susceptibility to bipolar disorder.