C18orf2, a novel, highly conserved intronless gene within intron 5 of the GNAL gene on chromosome 18p11

We have characterized a novel intronless human gene (C18orf2) which is embedded in intron 5 of the G-protein gene (GNAL) on chromosome 18p11. This gene codes for a 199 amino acid polypeptide with a predicted molecular weight of 22.1 kDa. It is highly homologous to a number of predicted developmental proteins in organisms ranging from yeasts to Drosophila. C18orf2 mRNA was found to be expressed in various tissues.

Quantitative genetic study of maximal electroshock seizure threshold in mice: evidence for a major seizure susceptibility locus on distal chromosome 1

We conducted a quantitative trait locus (QTL) mapping study to dissect the multifactorial nature of maximal electroshock seizure threshold (MEST) in C57BL/6 (B6) and DBA/2 (D2) mice. MEST determination involved a standard paradigm in which 8- to 12-week-old mice received one shock per day with a daily incremental increase in electrical current until a maximal seizure (tonic hindlimb extension) was induced. Mean MEST values in parental strains were separated by over five standard deviation units, with D2 mice showing lower values than B6 mice. The distribution of MEST values in B6xD2 F2 intercrossed mice spanned the entire phenotypic range defined by parental strains. Statistical mapping yielded significant evidence for QTLs on chromosomes 1, 2, 5, and 15, which together explained over 60% of the phenotypic variance in the model. The chromosome 1 QTL represents a locus of major effect, accounting for about one-third of the genetic variance. Experiments involving a congenic strain (B6.D2-Mtv7(a)/Ty) enabled more precise mapping of the chromosome 1 QTL and indicate that it lies in the genetic interval between markers D1Mit145 and D1Mit17. These results support the hypothesis that the distal portion of chromosome 1 harbors a gene(s) that has a fundamental role in regulating seizure susceptibility.

Lack of association between an interleukin 1 beta (IL-1beta) gene variation and refractory temporal lobe epilepsy

PURPOSE

We attempted to confirm recent findings of Kanemoto et al. that demonstrated a positive association (p < 0.017) between a polymorphism in the promoter region of the interleukin 1-beta (IL-1beta) gene and the clinical phenotype of temporal lobe epilepsy with hippocampal sclerosis (TLE+HS).

METHODS

We determined the frequency of this polymorphism in a group of 61 TLE+HS patients of European ancestry and compared it with that found in 119 ethnically matched control subjects.

RESULTS

Analysis of genotype and allele frequencies showed no statistically significant difference in the distribution of the polymorphism between the two groups (p = 0.10).

CONCLUSIONS

These data suggest that this IL-1beta promoter polymorphism does not act as a strong susceptibility factor for TLE+HS in a population of individuals of European ancestry.

Beta-adrenergic receptors on lymphoblasts. A study of manic-depressive illness

Beta-adrenergic receptor function has been the subject of much research in manic-depressive illness. Lymphoblast beta receptor binding was analyzed by Scatchard plot, using cell lines established from 17 unrelated bipolar subjects and 14 normals. No significant differences in affinity or density of beta receptors were found, in contrast to a previous report. Both the affinity and density of receptors appeared to be a stable characteristic of a cell line, as determined by repeated assay of the same cell lines.

Genetic factors in affective illness

Research strategies for determining genetic vulnerability markers in affective illness are delineated. Using these strategies, recent developments in the biology of manic-depressive illness are discussed, including results from association and linkage studies, pharmacologic challenge protocols, and cerebrospinal fluid (CSF) data. Several lines of evidence suggest that one genetically determined vulnerability to affective disorder may be a cholinergic supersensitivity, possibly mediated through increased numbers of cholinergic receptors.

Acute cocaine-induced seizures: differential sensitivity of six inbred mouse strains

Mature male and female mice from six inbred stains were tested for susceptibility to behavioral seizures induced by a single injection of cocaine. Cocaine was injected ip over a range of doses (50-100 mg/kg) and behavior was monitored for 20 minutes. Seizure end points included latency to forelimb or hindlimb clonus, latency to clonic running seizure and latency to jumping bouncing seizure. A range of strain specific sensitivities was documented with A/J and SJL mice being most sensitive and C57BL/6J most resistant. DBA/2J, BALB/cByJ and NZW/LacJ strains exhibited intermediate sensitivity. EEG recordings were made in SJL, A/J and C57BL/6J mice revealing a close correspondence between electrical activity and behavior. Additionally, levels of cocaine determined in hippocampus and cortex were not different between sensitive and resistant strains. Additional studies of these murine strains may be useful for investigating genetic influences on cocaine-induced seizures.

Sequence variability and candidate gene analysis in complex disease: association of mu opioid receptor gene variation with substance dependence

To analyze candidate genes and establish complex genotype-phenotype relationships against a background of high natural genome sequence variability, we have developed approaches to (i) compare candidate gene sequence information in multiple individuals; (ii) predict haplotypes from numerous variants; and (iii) classify haplotypes and identify specific sequence variants, or combinations of variants (pattern), associated with the phenotype. Using the human mu opioid receptor gene (OPRM1) as a model system, we have combined these approaches to test a potential role of OPRM1 in substance (heroin/cocaine) dependence. All known functionally relevant regions of this prime candidate gene were analyzed by multiplex sequence comparison in 250 cases and controls; 43 variants were identified and 52 different haplotypes predicted in the subgroup of 172 African-Americans. These haplotypes were classified by similarity clustering into two functionally related categories, one of which was significantly more frequent in substance-dependent individuals. Common to this category was a characteristic pattern of sequence variants [-1793T-->A, -1699Tins, -1320A-->G, -111C-->T, +17C-->T (A6V)], which was associated with substance dependence. This study provides an example of approaches that have been successfully applied to the establishment of complex genotype-phenotype relationships in the presence of abundant DNA sequence variation.

Perfectionism in anorexia nervosa: variation by clinical subtype, obsessionality, and pathological eating behavior

OBJECTIVE

The purpose of this study was to examine the role of perfectionism as a phenotypic trait in anorexia nervosa and its relevance across clinical subtypes of this illness.

METHOD

The Multidimensional Perfectionism Scale and the perfectionism subscale of the Eating Disorder Inventory were administered to 322 women with a history of anorexia nervosa who were participating in an international, multicenter genetic study of anorexia nervosa. All participants were additionally interviewed with the Yale-Brown Obsessive Compulsive Scale and the Yale-Brown-Cornell Eating Disorder Scale. Mean differences on dependent measures among women with anorexia nervosa and comparison subjects were examined by using generalized estimating equations.

RESULTS

Persons who had had anorexia nervosa had significantly higher total scores on the Multidimensional Perfectionism Scale than did the healthy comparison subjects. In addition, scores of the anorexia subjects on the Eating Disorder Inventory-2 perfectionism subscale exceeded Eating Disorder Inventory-2 normative data. For the anorexia nervosa participants, the total score on the Multidimensional Perfectionism Scale and the Eating Disorder Inventory-2 perfectionism subscale score were highly correlated. Total score on the Multidimensional Perfectionism Scale was also significantly related to the total score and the motivation-for-change subscale score of the Yale-Brown-Cornell Eating Disorder Scale.

CONCLUSIONS

These data show that perfectionism is a robust, discriminating characteristic of anorexia nervosa. Perfectionism is likely to be one of a cluster of phenotypic trait variables associated with a genetic diathesis for anorexia nervosa.

Are schizophrenic and bipolar disorders related? A review of family and molecular studies

Schizophrenic and bipolar disorders are similar in several epidemiologic respects, including age at onset, lifetime risk, course of illness, worldwide distribution, risk for suicide, gender influence (men and women at equal risk for both groups of disorders), and genetic susceptibility. Despite these similarities, schizophrenia and bipolar disorders are typically considered to be separate entities, with distinguishing clinical characteristics, non-overlapping etiologies, and distinct treatment regimens. Over the past three decades, multiple family studies are consistent with greater nosologic overlap than previously acknowledged. Molecular linkage studies (conducted during the 1990s) reveal that some susceptibility loci may be common to both nosologic classes. This indicates that our nosology will require substantial revision during the next decade, to reflect this shared genetic susceptibility, as specific genes are identified.

Temperament and character in women with anorexia nervosa

The present study examined temperament differences among anorexia nervosa (AN) subtypes and community controls, as well as the effect of body weight on personality traits in women with AN. Temperament and Character Inventory (TCI) scores were compared between 146 women with restrictor-type AN (RAN), 117 women with purging-type AN (PAN), 60 women with binge/purge-type AN (BAN), and 827 community control women (CW) obtained from an archival normative database. Women with AN scored significantly higher on harm avoidance and significantly lower on cooperativeness than CW. Subtype analyses revealed that women with RAN and PAN reported the lowest novelty seeking, RAN women the highest persistence and self-directedness, and PAN women the highest harm avoidance. Body mass index had a nominal effect on subgroup differences, suggesting that personality disturbances are independent of body weight. Findings suggest that certain facets of temperament differ markedly between women with AN, regardless of diagnostic subtype, and controls. More subtle temperament and character differences that were independent of body weight emerged that distinguish among subtypes of AN.

Sequence and genomic organization of the human G-protein Golfalpha gene (GNAL) on chromosome 18p11, a susceptibility region for bipolar disorder and schizophrenia

The sequence and genomic organization of the human Golfalpha (GNAL) gene were determined. The human GNAL gene was found to contain 12 coding exons, and it spans over 80 kb on chromosome 18p11. 5' RACE analysis suggested an additional transcription initiation start site. Sequence analysis of the putative promoter region revealed conserved binding sites for several transcription factors. Sequence analysis of the 3'-untranslated region revealed the presence of two Alu sequences and two polyadenylation signals. 3' RACE analysis confirmed the functionality of the most downstream poly-a signal. The human GNAL was found to be expressed as a single transcript of about 5.9 kb in the brain. One highly informative dinucleotide repeat was found in intron 5. Additionally, a processed pseudogene for asparagine synthetase was found about 6 kb upstream of the GNAL gene. Knowledge of the sequence and structure of the human GNAL gene provides essential information for further analysis of the GNAL locus at chromosome 18p11 which has been linked to bipolar disorder and schizophrenia.

Identification of candidate genes for psychiatric disorders on 18p11

Linkage studies have suggested a locus for bipolar disorder as well as schizophrenia in the pericentric region of chromosome 18. Several candidate genes have been identified in the region including ACTH, IMP, and G(olf), however no reports of mutations in families showing linkage to the 18p11 locus have been reported. Recently, mild linkage disequilibrium has been observed with a polymorphic marker that maps within the G(olf) gene and schizophrenia in families from Germany and Israel, suggesting that a gene mapping near G(olf) may be involved in psychiatric disorders. A BAC and cosmid contig around the G(olf) locus has been generated and BAC clones were used for cDNA selection experiments. Several novel genes have been identified which are expressed in the brain. These genes may be possible candidate genes for psychiatric illness.

Human G(olf) gene polymorphisms and vulnerability to bipolar disorder

Two intronic polymorphisms of the human alpha subunit of the olfactory G-protein (G(olf)) are described. They were detected with single-stranded conformational polymorphism (SSCP) methods and confirmed by sequencing both strands. These single base pair (bp) substitutions occur in introns 3 (an A/G at 35 bp 3' from the exon 3/intron 3 5' splice site) and 10 (an T/G at 7 bp 5' from the 3' splice site). Both polymorphisms are relatively common, with minor allele frequencies of 31% (intron 3) and 16% (intron 10). The intron 3 variant shows no linkage disequilibrium with an intron 5 (CA)n microsatellite located approximately 50 kb 3' from the intron 3 variant, among a small group of German individuals with schizophrenia. The intron 3 variant is interesting because it may create an 'in-frame' cryptic splice site which, if activated, would add 12 residues to exon 3. The intron 10 variant is interesting because a purine is substituted for a pyrimidine in the 'polypyrimidine' tract of the 3' splice site, a single base substitution of the type which has been associated with aberrant splicing in the androgen receptor gene.

Genetics of psychiatric disease

Genetic epidemiologic studies reveal that relatives of bipolar (BIP) probands are at increased risk for recurrent unipolar (RUP), BIP, and schizoaffective (SA) disorders, while relatives of schizophrenia (SZ) probands are at increased risk for SZ, SA, and RUP disorders. The overlap in familial risk may reflect shared genetic susceptibility. Recent genetic linkage studies have defined confirmed susceptibility loci for BIP disorder for multiple regions of the human genome, including 4p16, 12q24, 18p11.2, 18q22, 21q21, 22q11-13, and Xq26. Studies of SZ kindreds have yielded robust evidence for susceptibility at 18p11.2 and 22q11-13, both of which are implicated in susceptibility to BIP disorder. Similarly, confirmed SZ vulnerability loci have been mapped for 6p24, 8p and 13q32. Strong statistical evidence for a 13q32 BIP susceptibility locus has been reported. Thus, both family and molecular studies of these disorders suggest shared genetic susceptibility. These two group of disorders may not be so distinct as current nosology suggests.

Cocaine intake by rats correlates with cocaine-induced dopamine changes in the nucleus accumbens shell

Extracellular dopamine levels were determined by microdialysis in the core and shell of the nucleus accumbens and the frontal cortex of rats before and after an injection of cocaine (20 mg/kg, IP). After removal of the probes, these same animals were then tested for their voluntary intake of cocaine using the two-bottle, free-choice paradigm. Baseline dopamine levels and their responses to an injection of cocaine differed among the three brain areas. No significant correlations were found between baseline dopamine levels in any of the three brain regions and the voluntary cocaine consumption. A significant negative correlation was found between cocaine-induced increases in extracellular dopamine in the shell of the nucleus accumbens and the voluntary intake of cocaine (r = -0.73, p < 0.01). No such correlations were observed in the accumbens core region or the frontal cortex. These results provide further evidence of the role of the accumbal shell region in cocaine preference, and indicate that cocaine-induced increases in dopamine levels play a role in oral cocaine self-administration or preference. In addition, this relatively novel approach in using the same animals for both cocaine induced neurotransmitter responses and cocaine preference studies can also be applied for the study of other neurotransmitters and drugs of abuse.

A search for susceptibility loci for anorexia nervosa: methods and sample description

BACKGROUND

Eating disorders have not traditionally been viewed as heritable illnesses; however, recent family and twin studies lend credence to the potential role of genetic transmission. The Price Foundation funded an international, multisite study to identify genetic factors contributing to the pathogenesis of anorexia nervosa (AN) by recruiting affective relative pairs. This article is an overview of study methods and the clinical characteristics of the sample.

METHODS

All probands met modified DSM-IV criteria for AN; all affected first, second, and third degree relatives met DSM-IV criteria for AN, bulimia nervosa (BN), or eating disorder not otherwise specified (NOS). Probands and affected relatives were assessed diagnostically with the Structured Interview for Anorexia and Bulimia. DNA was collected from probands, affected relatives and a subset of their biological parents.

RESULTS

Assessments were obtained from 196 probands and 237 affected relatives, over 98% of whom are of Caucasian ancestry. Overall, there were 229 relative pairs who were informative for linkage analysis. Of the proband-relative pairs, 63% were AN-AN, 20% were AN-BN, and 16% were AN-NOS. For family-based association analyses, DNA has been collected from both biological parents of 159 eating-disordered subjects. Few significant differences in demographic characteristics were found between proband and relative groups.

CONCLUSIONS

The present study represents the first large-scale molecular genetic investigation of AN. Our successful recruitment of over 500 subjects, consisting of affected probands, affected relatives, and their biological parents, will provide the basis to investigate genetic transmission of eating disorders via a genome scan and assessment of candidate genes.

Genomic structure and novel variants of myo-inositol monophosphatase 2 (IMPA2)

Recently, we cloned the human myo-inositol monophosphatase 2 (IMPA2) cDNA and established its map location to chromosome 18p11.2, a region previously implicated in bipolar disorder. Because the myo-inositol monophosphatase enzyme has been shown to be inhibited by lithium, an effective therapeutic agent for bipolar disorder, IMPA2 is a plausible positional and functional candidate gene. To permit comprehensive screening for variants we characterized the genomic structure and isolated the potential promoter of IMPA2. The gene was found to encode eight exons spanning;27 kb. The proximal 1-kb 5' flanking region did not contain an obvious TATA box but multiple potential binding sites for Sp1 and consensus motifs for AP2 and other transcription factors were evident. Sequencing of the coding region and splice junctions in unrelated bipolar disorder patients detected novel variants. A missense mutation in exon 2, His76Tyr, was found in one patient. His76 is evolutionarily conserved and replacement with Tyr introduces a potential site for phosphorylation. The other polymorphisms included an RsaI polymorphism, IVS1-15G>A, and a T --> C silent mutation in the third nucleotide of codon 53 in exon 2. By Fisher's exact test the silent mutation showed a trend for association (P = 0.051) with bipolar disorder suggesting that further scrutiny of this gene is warranted.

Lack of association between temporal lobe epilepsy and a novel polymorphism in the alpha 2 subunit gene (ATP1A2) of the sodium potassium transporting ATPase

Genetic linkage studies in rodents and humans have identified specific chromosomal regions harboring seizure susceptibility genes. We have identified a novel polymorphism in the human alpha 2 subunit gene (ATP1A2) of the sodium potassium transporting ATPase (NaK-pump), a candidate gene for human temporal lobe epilepsy (TLE) based on its chromosomal location and function in ion homeostasis. The polymorphism consists of a four base pair insertion 12 base pairs upstream of the start of exon 2. We performed an association study between this polymorphism and TLE. Our study did not find a significant difference in the frequency of this polymorphism between TLE patients and controls, indicating that this variation is not a major susceptibility factor. However, since the number of patients studied so far is small and the functional consequence of the polymorphism is unknown, the variation may yet be found to play a minor role in increased risk for seizure susceptibility. In contrast to the findings in TLE patients and controls, we did find a significant difference in the frequency of the variation between African Americans and persons of European descent. This finding demonstrates the potential effect of population stratification on studies of this type and supports the growing use of parental and familial samples for controls in association studies. Further study of this polymorphism is warranted as it may be involved in other disease processes for which there are known ethnic-specific susceptibilities. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:79-83, 2000.

Susceptibility loci for bipolar disorder: overlap with inherited vulnerability to schizophrenia

Genetic epidemiological studies reveal that relatives of bipolar probands are at increased risk for recurrent unipolar, bipolar, and schizoaffective disorders, whereas relatives of probands with schizophrenia are at increased risk for schizophrenia, schizoaffective, and recurrent unipolar disorders. The overlap in familial risk may reflect shared genetic susceptibility. Recent genetic linkage studies have defined confirmed bipolar susceptibility loci for multiple regions of the human genome, including 4p16, 12q24, 18p11.2, 18q22, 21q21, 22q11-13, and Xq26. Studies of schizophrenia kindreds have yielded robust evidence for susceptibility at 18p11.2 and 22q11-13, both of which are implicated in susceptibility to bipolar disorder. Similarly, confirmed schizophrenia vulnerability loci have been mapped, too, for 6p24, 8p, and 13q32. Strong statistical evidence for a 13q32 bipolar susceptibility locus has been reported. Thus, both family and molecular studies of these disorders suggest shared genetic susceptibility. These two groups of disorders may not be as distinct as current nosology suggests.

Mapping loci for pentylenetetrazol-induced seizure susceptibility in mice

DBA/2J (D2) and C57BL/6J (B6) mice exhibit differential sensitivity to seizures induced by various chemical and physical methods, with D2 mice being relatively sensitive and B6 mice relatively resistant. We conducted studies in mature D2, B6, F1, and F2 intercross mice to investigate behavioral seizure responses to pentylenetetrazol (PTZ) and to map the location of genes that influence this trait. Mice were injected with PTZ and observed for 45 min. Seizure parameters included latencies to focal clonus, generalized clonus, and maximal seizure. Latencies were used to calculate a seizure score that was used for quantitative mapping. F2 mice (n = 511) exhibited a wide range of latencies with two-thirds of the group expressing maximal seizure. Complementary statistical analyses identified loci on proximal (near D1Mit11) and distal chromosome 1 (near D1Mit17) as having the strongest and most significant effects in this model. Another locus of significant effect was detected on chromosome 5 (near D5Mit398). Suggestive evidence for additional PTZ seizure-related loci was detected on chromosomes 3, 4, and 6. Of the seizure-related loci identified in this study, those on chromosomes 1 (distal), 4, and 5 map close to loci previously identified in a similar F2 population tested with kainic acid. Results document that the complex genetic influences controlling seizure response in B6 and D2 mice are partially independent of the nature of the chemoconvulsant stimulus with a locus on distal chromosome 1 being of fundamental importance.

A high-density genome scan detects evidence for a bipolar-disorder susceptibility locus on 13q32 and other potential loci on 1q32 and 18p11.2

Bipolar disorder is a severe mental illness characterized by mood swings of elation and depression. Family, twin, and adoption studies suggest a complex genetic etiology that may involve multiple susceptibility genes and an environmental component. To identify chromosomal loci contributing to vulnerability, we have conducted a genome-wide scan on approximately 396 individuals from 22 multiplex pedigrees by using 607 microsatellite markers. Multipoint nonparametric analysis detected the strongest evidence for linkage at 13q32 with a maximal logarithm of odds (lod) score of 3.5 (P = 0. 000028) under a phenotype model that included bipolar I, bipolar II with major depression, schizoaffective disorder, and recurrent unipolar disorder. Suggestive linkage was found on 1q31-q32 (lod = 2. 67; P = 0.00022) and 18p11.2 (lod = 2.32; P = 0.00054). Recent reports have linked schizophrenia to 13q32 and 18p11.2. Our genome scan identified other interesting regions, 7q31 (lod = 2.08; P = 0. 00099) and 22q11-q13 (lod = 2.1; P = 0.00094), and also confirmed reported linkages on 4p16, 12q23-q24, and 21q22. By comprehensive screening of the entire genome, we detected unreported loci for bipolar disorder, found support for proposed linkages, and gained evidence for the overlap of susceptibility regions for bipolar disorder and schizophrenia.

Genotyping microsatellite polymorphisms by agarose gel electrophoresis with ethidium bromide staining: application to quantitative trait loci analysis of seizure susceptibility in mice

Agarose gel electrophoresis with ethidium bromide staining (AGE/EBS) is an efficient and reliable method for analyzing microsatellite polymorphisms. We report the use of AGE/EBS for analyzing DNA microsatellite polymorphisms in a preliminary quantitative trait loci (QTL) study of seizure susceptibility in which a candidate gene strategy was used to direct initial mapping efforts. F2 intercross progeny, derived from seizure-sensitive DBA/2J (D2) and seizure-resistant C57BL/6J (B6) inbred strains of mice, were tested for their sensitivity to the seizure-inducing effect of pentylenetetrazol (PTZ), a gamma-aminobutyric acid (GABA) receptor antagonist. A semi-automated method is described, in which DNA microsatellites were amplified by polymerase chain reaction (PCR) to yield products of 100-200 base pair (bp) in length. Alleles were separated on 3-6% MetaPhor agarose gels, stained with ethidium bromide, and visualized by ultraviolet (UV) illumination. Univariate analysis of genotype and phenotype data provides evidence for a seizure-related QTL on chromosome 5, near genes coding for the GABAA receptor subunits alpha 5 and gamma 3. Interestingly, this suggestive QTL derives from the more resistant B6 strain, but it nonetheless provides impetus for the characterization of possible strain differences in these two candidate genes. Overall, these results demonstrate that AGE/EBS can be useful for rapid screening of genomic regions of special interest in QTL mapping studies.