Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu's surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

Genome-wide association study of borderline personality disorder reveals genetic overlap with bipolar disorder, major depression and schizophrenia

Borderline personality disorder (BOR) is determined by environmental and genetic factors, and characterized by affective instability and impulsivity, diagnostic symptoms also observed in manic phases of bipolar disorder (BIP). Up to 20% of BIP patients show comorbidity with BOR. This report describes the first case-control genome-wide association study (GWAS) of BOR, performed in one of the largest BOR patient samples worldwide. The focus of our analysis was (i) to detect genes and gene sets involved in BOR and (ii) to investigate the genetic overlap with BIP. As there is considerable genetic overlap between BIP, major depression (MDD) and schizophrenia (SCZ) and a high comorbidity of BOR and MDD, we also analyzed the genetic overlap of BOR with SCZ and MDD. GWAS, gene-based tests and gene-set analyses were performed in 998 BOR patients and 1545 controls. Linkage disequilibrium score regression was used to detect the genetic overlap between BOR and these disorders. Single marker analysis revealed no significant association after correction for multiple testing. Gene-based analysis yielded two significant genes: DPYD (P=4.42 × 10-7) and PKP4 (P=8.67 × 10-7); and gene-set analysis yielded a significant finding for exocytosis (GO:0006887, PFDR=0.019; FDR, false discovery rate). Prior studies have implicated DPYD, PKP4 and exocytosis in BIP and SCZ. The most notable finding of the present study was the genetic overlap of BOR with BIP (rg=0.28 [P=2.99 × 10-3]), SCZ (rg=0.34 [P=4.37 × 10-5]) and MDD (rg=0.57 [P=1.04 × 10-3]). We believe our study is the first to demonstrate that BOR overlaps with BIP, MDD and SCZ on the genetic level. Whether this is confined to transdiagnostic clinical symptoms should be examined in future studies.

Host associations and beta diversity of fungal endophyte communities in New Guinea rainforest trees

Processes shaping the distribution of foliar fungal endophyte species remain poorly understood. Despite increasing evidence that these cryptic fungal symbionts of plants mediate interactions with pathogens and herbivores, there remain basic questions regarding the extent to which dispersal limitation and host specificity might shape fungal endophyte community composition in rainforests. To assess the relative importance of spatial pattern and host specificity, we isolated fungi from a sample of mapped trees in lowland Papua New Guinea. Sequences of the internal transcribed spacer (ITS) region were obtained for 2079 fungal endophytes from three sites and clustered into molecular operational taxonomic units (MOTUs) at 95% similarity. Multivariate analyses suggest that host affinity plays a significant role in structuring endophyte community composition whereas there was no evidence of endophyte spatial pattern at the scale of tens to hundreds of metres. Differences in endophyte communities between sampled trees were weakly correlated with variation in foliar traits but not with tree species relatedness. The dominance of relatively few generalist endophytes and the presence of a large number of rare MOTUs was a consistent observation at three sites separated by hundreds of kilometres and regional turnover was low. Host specificity appears to play a relatively weak but more important role than dispersal limitation in shaping the distribution of fungal endophyte communities in New Guinea forests. Our results suggest that in the absence of strong ecological gradients and host turnover, beta diversity of endophyte communities could be low in large areas of contiguous forest.

Estimating the heritability of reporting stressful life events captured by common genetic variants

BACKGROUND

Although usually thought of as external environmental stressors, a significant heritable component has been reported for measures of stressful life events (SLEs) in twin studies. Method We examined the variance in SLEs captured by common genetic variants from a genome-wide association study (GWAS) of 2578 individuals. Genome-wide complex trait analysis (GCTA) was used to estimate the phenotypic variance tagged by single nucleotide polymorphisms (SNPs). We also performed a GWAS on the number of SLEs, and looked at correlations between siblings.

RESULTS

A significant proportion of variance in SLEs was captured by SNPs (30%, p = 0.04). When events were divided into those considered to be dependent or independent, an equal amount of variance was explained for both. This 'heritability' was in part confounded by personality measures of neuroticism and psychoticism. A GWAS for the total number of SLEs revealed one SNP that reached genome-wide significance (p = 4 × 10-8), although this association was not replicated in separate samples. Using available sibling data for 744 individuals, we also found a significant positive correlation of R 2 = 0.08 in SLEs (p = 0.03).

CONCLUSIONS

These results provide independent validation from molecular data for the heritability of reporting environmental measures, and show that this heritability is in part due to both common variants and the confounding effect of personality.

Genome-wide association study meta-analysis of European and Asian-ancestry samples identifies three novel loci associated with bipolar disorder

Meta-analyses of bipolar disorder (BD) genome-wide association studies (GWAS) have identified several genome-wide significant signals in European-ancestry samples, but so far account for little of the inherited risk. We performed a meta-analysis of ∼750,000 high-quality genetic markers on a combined sample of ∼14,000 subjects of European and Asian-ancestry (phase I). The most significant findings were further tested in an extended sample of ∼17,700 cases and controls (phase II). The results suggest novel association findings near the genes TRANK1 (LBA1), LMAN2L and PTGFR. In phase I, the most significant single nucleotide polymorphism (SNP), rs9834970 near TRANK1, was significant at the P=2.4 × 10(-11) level, with no heterogeneity. Supportive evidence for prior association findings near ANK3 and a locus on chromosome 3p21.1 was also observed. The phase II results were similar, although the heterogeneity test became significant for several SNPs. On the basis of these results and other established risk loci, we used the method developed by Park et al. to estimate the number, and the effect size distribution, of BD risk loci that could still be found by GWAS methods. We estimate that >63,000 case-control samples would be needed to identify the ∼105 BD risk loci discoverable by GWAS, and that these will together explain <6% of the inherited risk. These results support previous GWAS findings and identify three new candidate genes for BD. Further studies are needed to replicate these findings and may potentially lead to identification of functional variants. Sample size will remain a limiting factor in the discovery of common alleles associated with BD.

A multi-tissue analysis identifies HLA complex group 9 gene methylation differences in bipolar disorder

Epigenetic studies of DNA and histone modifications represent a new and important activity in molecular investigations of human disease. Our previous epigenome-wide scan identified numerous DNA methylation differences in post-mortem brain samples from individuals affected with major psychosis. In this article, we present the results of fine mapping DNA methylation differences at the human leukocyte antigen (HLA) complex group 9 gene (HCG9) in bipolar disorder (BPD). Sodium bisulfite conversion coupled with pyrosequencing was used to interrogate 28 CpGs spanning ∼700 bp region of HCG9 in 1402 DNA samples from post-mortem brains, peripheral blood cells and germline (sperm) of bipolar disease patients and controls. The analysis of nearly 40 000 CpGs revealed complex relationships between DNA methylation and age, medication as well as DNA sequence variation (rs1128306). Two brain tissue cohorts exhibited lower DNA methylation in bipolar disease patients compared with controls at an extended HCG9 region (P=0.026). Logistic regression modeling of BPD as a function of rs1128306 genotype, age and DNA methylation uncovered an independent effect of DNA methylation in white blood cells (odds ratio (OR)=1.08, P=0.0077) and the overall sample (OR=1.24, P=0.0011). Receiver operating characteristic curve A prime statistics estimated a 69-72% probability of correct BPD prediction from a case vs control pool. Finally, sperm DNA demonstrated a significant association (P=0.018) with BPD at one of the regions demonstrating epigenetic changes in the post-mortem brain and peripheral blood samples. The consistent multi-tissue epigenetic differences at HCG9 argue for a causal association with BPD.

Identification of genomic deletions spanning the PCDH19 gene in two unrelated girls with intellectual disability and seizures

Recently, missense and truncating mutations in the gene PCDH19 have been reported to cause female-restricted epilepsy with mental retardation (EFMR). EFMR (MIM#300088) is an X-linked disorder characterized by early onset seizures and intellectual disability (ID). Interestingly, unlike typical X-linked mode of inheritance, the phenotype is restricted to females, and males are unaffected carriers. PCDH19 is highly expressed in brain, and the encoded protein belongs to the cadherin superfamily. Here we report two unrelated female patients with deletions spanning PCDH19 identified by copy number variation (CNV) analysis and validated by qPCR. In one, we have identified a 3 Mb interstitial deletion at Xq21.33-q22.1 which spans PCDH19, LOC442459 & TNMD. This patient had her first seizure at 8 months old, and also has ID and aggressive behavior. In another female patient we identified a de novo 603 kb heterozygous deletion in a female patient with fits (since 1 year of age), ID, hyperactivity and aggressive behavior. The deletion spans the entire PCDH19 gene (also TNMD, SRPX2, TSPAN6 and SYTL4). In conclusion, our results suggest that deletions at PCDH19 also cause EFMR.

Images of asteroid 21 Lutetia: a remnant planetesimal from the early Solar System

Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles.

Replicated association of the NR4A3 gene with smoking behaviour in schizophrenia and in bipolar disorder

Schizophrenia and bipolar disorder are associated with dopamine neurotransmission and show high comorbidity with tobacco dependence. Recent evidence indicates that the family of the NR4A orphan nuclear receptors, which are expressed in dopamine neurons and in dopaminoceptive brain areas, may play a role in dopamine-mediated effects. We have, therefore, analysed the association of six single nucleotide polymorphisms (SNPs) within the three genes belonging to the NR4A orphan nuclear receptor family, NR4A1 (rs2603751, rs2701124), NR4A2 (rs12803, rs834835) and NR4A3 (rs1131339, rs1405209), with the degree of smoking in a sample of 204 unrelated schizophrenia patients, which included 126 smokers and 78 non-smokers. SNPs within the NR4A3 gene (rs1131339 and rs1405209) were significantly associated with heavy smoking in this cohort, using a stepwise analysis of the escalated number of cigarettes smoked per day (P = 0.008 and 0.006, respectively; satisfying the Nyholt significance threshold of 0.009, an adjustment for multiple testing). We then repeated the association analysis of the NR4A3 markers (rs1131339 and rs1405209) in a larger cohort of 319 patients with bipolar disorder, which included 167 smokers and 152 non-smokers. We have replicated the positive association with smoking of the NR4A3 SNP rs1131339 in this group (P = 0.04), providing an important confirmation of the involvement of the NR4A3 gene in nicotine addiction in patients with mental health disease, a population significantly at risk for nicotine addiction.

Population-based linkage analysis of schizophrenia and bipolar case-control cohorts identifies a potential susceptibility locus on 19q13

Population-based linkage analysis is a new method for analysing genomewide single nucleotide polymorphism (SNP) genotype data in case-control samples, which does not assume a common disease, common variant model. The genome is scanned for extended segments that show increased identity-by-descent sharing within case-case pairs, relative to case-control or control-control pairs. The method is robust to allelic heterogeneity and is suited to mapping genes which contain multiple, rare susceptibility variants of relatively high penetrance. We analysed genomewide SNP datasets for two schizophrenia case-control cohorts, collected in Aberdeen (461 cases, 459 controls) and Munich (429 cases, 428 controls). Population-based linkage testing must be performed within homogeneous samples and it was therefore necessary to analyse the cohorts separately. Each cohort was first subjected to several procedures to improve genetic homogeneity, including identity-by-state outlier detection and multidimensional scaling analysis. When testing only cases who reported a positive family history of major psychiatric disease, consistent with a model of strongly penetrant susceptibility alleles, we saw a distinct peak on chromosome 19q in both cohorts that appeared in meta-analysis (P=0.000016) to surpass the traditional level for genomewide significance for complex trait linkage. The linkage signal was also present in a third case-control sample for familial bipolar disorder, such that meta-analysing all three datasets together yielded a linkage P=0.0000026. A model of rare but highly penetrant disease alleles may be more applicable to some instances of major psychiatric diseases than the common disease common variant model, and we therefore suggest that other genome scan datasets are analysed with this new, complementary method.

Comparison of the potential for developmental toxicity of prenatal exposure to two dietary chromium supplements, chromium picolinate and [Cr3O(O2CCH2CH3)(6(H2O)3]+, in mice

BACKGROUND

Chromium(III) is generally thought to be an essential trace element that allows for proper glucose metabolism. However, chromium(III) picolinate, Cr(pic)3, a popular dietary supplement form of chromium, has been shown to be capable of generating hydroxyl radicals and oxidative DNA damage in rats. The cation [Cr3O(O2CCH2CH3)(6(H2O)3]+, Cr3, has been studied as an alternative supplemental source of chromium. It has been shown to increase insulin sensitivity and lower glycated hemoglobin levels in rats, making it attractive as a potential therapeutic treatment for gestational diabetes. To date, no studies have been published regarding the safety of Cr3 supplementation to a developing fetus.

METHODS

From gestation days (GD) 6-17, mated CD-1 female mice were fed diets delivering either 25 mg Cr/kg/day as Cr(pic)(3), 3.3 or 26 mg Cr/kg/day as Cr3, or the diet only to determine if Cr3 could cause developmental toxicity. Dams were sacrificed on GD 17, and their litters were examined for adverse effects.

RESULTS

No signs of maternal toxicity were observed. No decrease in fetal weight or significantly increased incidence of skeletal defects was observed in the Cr3 or Cr(pic)3 exposed fetuses compared to the controls.

CONCLUSION

Maternal exposure to either Cr(pic)3 or Cr3 at the dosages employed did not appear to cause deleterious effects to the developing offspring in mice.

An inversion inv(4)(p12-p15.3) in autistic siblings implicates the 4p GABA receptor gene cluster

INTRODUCTION

We describe the case of two brothers diagnosed with autism who both carry a paracentic inversion of the short arm of chromosome 4 (46,XY, inv(4)(p12-p15.3)). We have determined that this inversion is inherited from an apparently unaffected mother and unaffected maternal grandfather. Methods/

RESULTS

Using fluorescence in situ hybridisation analysis and Southern blot hybridisation we identified the breakpoints. The proximal breakpoint (4p12) maps to a region containing a cluster of gamma-aminobutyric acid A (GABA(A)) receptor genes, and directly interrupts the GABRG1 gene, the distal-most gene of the cluster. We also identified an insertion/deletion polymorphism for a approximately 2 kb LINE1 (L1) element that occurs within intron 7 of GABRG1. Our genotype analysis amongst autism families indicated that the L1 deletion allele did not show increased transmission to affected individuals. No linkage disequilibrium was evident between the L1 and single nucleotide polymorphisms in adjacent GABA(A) receptor genes on 4p, where a recent study has identified significant association with autism.

DISCUSSION

Despite this, the identification of an inversion breakpoint disrupting GABRG1 provides solid support for the genetic involvement of the short arm of chromosome 4 in the genetic aetiology of autism, and for the hypothesis of disrupted GABA neurotransmission in autism.

Exposure of pregnant mice to chromium picolinate results in skeletal defects in their offspring

BACKGROUND

Chromium(III) picolinate, [Cr(pic)(3)], is a widely marketed dietary supplement. However, Cr(pic)(3) has been associated with oxidative damage to DNA in rats and mutations and DNA fragmentation in cell cultures. In isolated case reports, Cr(pic)(3) supplementation has been said to cause adverse effects, such as anemia, renal failure, liver dysfunction, and neuronal impairment. To date, no studies have been published regarding the safety of chromium picolinate supplementation to a developing fetus, although Cr(pic)(3) has been recommended for pregnant women who are diagnosed with gestational diabetes.

METHODS

From gestation days (GD) 6-17, pregnant CD-1 mice were fed diets containing either 200 mg/kg Cr(pic)(3), 200 mg/kg CrCl(3), 174 mg/kg picolinic acid, or the diet only to determine if Cr(pic)(3), CrCl(3), or picolinic acid could cause developmental toxicity. Dams were sacrificed on GD 17, and their litters were examined for adverse effects.

RESULTS

The incidence of bifurcated cervical arches was significantly increased in fetuses from the Cr(pic)(3) group as compared to the diet-only group. Fetuses in the picolinic acid-treated group had an incidence double that of the control group; however, this increase was not statistically significant. Fetuses in the CrCl(3) group did not differ from the controls in any variable examined. No maternal toxicity was observed in any of the treatment groups.

CONCLUSIONS

High maternal oral exposures to chromium picolinate can cause morphological defects in developing offspring of mice.

The unstable trinucleotide repeat story of major psychosis

New hopes for cloning susceptibility genes for schizophrenia and bipolar affective disorder followed the discovery of a novel type of DNA mutation, namely unstable DNA. One class of unstable DNA, trinucleotide repeat expansion, is the causal mutation in myotonic dystrophy, fragile X mental retardation, Huntington disease and a number of other rare Mendelian neurological disorders. This finding has led researchers in psychiatric genetics to search for unstable DNA sites as susceptibility factors for schizophrenia and bipolar affective disorder. Increased severity and decreased age at onset of disease in successive generations, known as genetic anticipation, was reported for undifferentiated psychiatric diseases and for myotonic dystrophy early in the twentieth century, but was initially dismissed as the consequence of ascertainment bias. Because unstable DNA was demonstrated to be a molecular substrate for genetic anticipation in the majority of trinucleotide repeat diseases including myotonic dystrophy, many recent studies looking for genetic anticipation have been performed for schizophrenia and bipolar affective disorder with surprisingly consistent positive results. These studies are reviewed, with particular emphasis placed on relevant sampling and statistical considerations, and concerns are raised regarding the interpretation of such studies. In parallel, molecular genetic investigations looking for evidence of trinucleotide repeat expansion in both schizophrenia and bipolar disorder are reviewed. Initial studies of genome-wide trinucleotide repeats using the repeat expansion detection technique suggested possible association of large CAG/CTG repeat tracts with schizophrenia and bipolar affective disorder. More recently, three loci have been identified that contain large, unstable CAG/CTG repeats that occur frequently in the population and seem to account for the majority of large products identified using the repeat expansion detection method. These repeats localize to an intron in transcription factor gene SEF2-1B at 18q21, a site named ERDA1 on 17q21 with no associated coding region, and the 3' end of a gene on 13q21, SCA8, that is believed to be responsible for a form of spinocerebellar ataxia. At present no strong evidence exists that large repeat alleles at either SEF2-1B or ERDA1 are involved in the etiology of schizophrenia or bipolar disorder. Preliminary evidence suggests that large repeat alleles at SCA8 that are non-penetrant for ataxia may be a susceptibility factor for major psychosis. A fourth, but much more infrequently unstable CAG/CTG repeat has been identified within the 5' untranslated region of the gene, MAB21L1, on 13q13. A fifth CAG/CTG repeat locus has been identified within the coding region of an ion transporter, KCNN3 (hSKCa3), on 1q21. Although neither large alleles nor instability have been observed at KCNN3, this repeat locus has been extensively analyzed in association and family studies of major psychosis, with conflicting findings. Studies of polyglutamine containing genes in major psychosis have also shown some intriguing results. These findings, reviewed here, suggest that, although a major role for unstable trinucleotides in psychosis is unlikely, involvement at a more modest level in a minority of cases cannot be excluded, and warrants further investigation.

Multiple binding sites for tetrahedral oxyanion inhibitors of bovine spleen purple acid phosphatase

The theory of multiple inhibition kinetics has been extended to enzymes for which one inhibitor is noncompetitive and the other exhibits mixed inhibition. Plots of reciprocal velocity versus the concentration of either inhibitor at various fixed concentrations of the second inhibitor are predicted to give parallel lines if binding of the inhibitors is mutually exclusive and intersecting lines if the inhibitors interact at different sites on the enzyme. Application of this analysis to the purple acid phosphatase from bovine spleen in the presence of molybdate (a noncompetitive inhibitor) and phosphate (which exhibits mixed inhibition) results in parallel lines in the reciprocal velocity plots, indicating that phosphate and molybdate compete for a common site; since molybdate is a noncompetitive inhibitor, this site is inferred to be distinct from the site at which substrate binds and is hydrolyzed. Extension of these ideas suggests that phosphate ester substrates should be capable of binding to the molybdate-binding site as well as to the active site, and evidence for substrate inhibition at high substrate concentrations has been obtained. The implications of these findings for interpretation of previous spectroscopic studies of purple acid phosphatase complexes with tetrahedral oxyanions are discussed.

Identification of the human cortactin-binding protein-2 gene from the autism candidate region at 7q31

Human chromosome 7q31 contains putative susceptibility loci for autism (AUTS1) and speech and language disorder (SPCH1). We report here the identification and characterization of a novel gene encoding cortactin-binding protein-2 (CORTBP2), which is located 45 kb telomeric to the cystic fibrosis transmembrane conductance regulator gene (CFTR) at 7q31.3. The full-length (5975-bp) gene was isolated and found to be composed of 23 exons encompassing 170 kb of DNA. In addition to being a positional candidate for AUTS1, CORTBP2 was expressed at highest levels in the brain, as shown by northern blot analysis. Subsequent mutation analysis of CORTBP2 in 90 autistic patients identified two polymorphisms, including a leucine to valine change caused by a T to G substitution in exon 15. However, comparison of allele frequencies between autistic and control populations (n=96) showed no significant difference, suggesting that this variant is not a susceptibility factor for autism.

The trail of chromium(III) in vivo from the blood to the urine: the roles of transferrin and chromodulin

The chromium-binding oligopeptide chromodulin (also known as low-molecular-weight chromium-binding substance) has been shown to activate the tyrosine kinase activity of the insulin receptor in response to insulin and has been proposed to be part of a novel autoamplification mechanism for insulin signaling. The model requires that Cr3+ be moved from the blood to insulin-sensitive tissues in response to insulin and subsequently be lost in the urine as chromodulin; however, the model has not been tested by in vivo studies. In vivo studies with rats have shown that the iron transport protein transferrin serves as the major chromic ion transport agent and that this transport is stimulated by insulin. The ion is transported to a variety of tissues, while liver and kidneys are the major target. In hepatocytes, chromodulin occurs in appreciable levels in the cytosol and in the nucleus. Apochromodulin levels appear to be maintained under homeostatic control, although the only detectable form of urinary chromium is probably chromodulin. Increases in urinary chromium loss in response to insulin are reflected by increases in chromodulin, establishing a direct link between carbohydrate metabolism and the oligopeptide.

Disruption of a novel gene (IMMP2L) by a breakpoint in 7q31 associated with Tourette syndrome

Gilles de la Tourette syndrome (GTS) is a complex neuropsychiatric disorder characterized by multiple motor and phonic tics. We identified a male patient with GTS and other anomalies. It was determined that he carried a de novo duplication of the long arm of chromosome 7 [46,XY,dup(7)(q22.1-q31.1)]. Further molecular analysis revealed that the duplication was inverted. The distal chromosomal breakpoint occurred between the two genetic markers D7S515 and D7S522, which define a region previously shown to be disrupted in a familiar case of GTS. Yeast and bacterial artificial chromosome clones spanning the breakpoints were identified by means of FISH analysis. To further characterize the distal breakpoint for a role in GTS, we performed Southern blot hybridization analysis and identified a 6.5-kb SacI junction fragment in the patient's genomic DNA. The DNA sequence of this fragment revealed two different breaks in 7q31 within a region of approximately 500 kb. IMMP2L, a novel gene coding for the apparent human homologue of the yeast mitochondrial inner membrane peptidase subunit 2, was found to be disrupted by both the breakpoint in the duplicated fragment and the insertion site in 7q31. The cDNA of the human IMMP2L gene was cloned, and analysis of the complete 1,522-bp transcript revealed that it encompassed six exons spanning 860 kb. The possible role of IMMP2L and several other candidate genes within the region of chromosomal rearrangement, including NRCAM, Leu-Rch Rep, and Reelin, is discussed. The 7q31 breakpoint interval has also been implicated in other neuropsychiatric diseases that demonstrate some clinical overlap with GTS, including autism and speech-language disorder.

Human secretin (SCT): gene structure, chromosome location, and distribution of mRNA

Secretin is an endocrine hormone that stimulates the secretion of bicarbonate-rich pancreatic fluids. Recently, it has been discussed that secretin deficiency may be implicated in autistic syndrome, suggesting that the hormone could have a neuroendocrine function in addition to its role in digestion. In the present study, the human secretin gene (SCT) was isolated from a bacterial artificial chromosome genomic library. SCT contains four exons, with the protein coding regions spanning 713 bp of genomic DNA. Human SCT is similar structurally to the secretin genes of other species. Amino acid conservation, however, is most pronounced within the exon encoding the biologically active mature peptide. Northern blot analysis shows that human SCT transcripts are located in the spleen, intestinal tract, and brain. Radiation hybrid mapping places the SCT locus on chromosome 11p15.5.

Detection of expansion regions in Portuguese bipolar families

We have studied 24 families with multiple affected members with bipolar disorder to test the hypothesis that in those families clinically showing genetic anticipation [Macedo et al., 1999] we would find large repeat expansions. The families meeting inclusion criteria had a minimum of two affected members over two generations and showed marked anticipation both in terms of age of onset and disease severity. We used the repeat expansion detection (RED) method to test patients (n = 24) and controls from these families and unrelated controls (n = 53). We also genotyped patients and family members from two families with large expansions at the known expansion loci on chromosomes 13, 17, and 18. The RED method revealed a higher number of large expansions in patients compared with controls (t-test; P < 0.0055: Mann-Whitney U; P = 0.02). The patients with the largest expansions were typed at the specific loci on chromosomes 13, 17, and 18 and the chromosome 18 expansion locus segregated with disease in one family, and a second family showed segregation with the expansion located at the SCA8 locus on chromosome 13. Genetic anticipation had been analyzed in this cohort of families, with correction for potential ascertainment bias, possible proband effects, cohort effects, regression to the mean, gender effects, and maternal vs. paternal transmission. None of these potential confounds appeared to account for the observed anticipation. We also identified that the presence of large expansions in affected family members derives primarily from two families from the genetically isolated Azores population. One family shows segregation with the chromosome 18 locus, whereas the other family segregates with expansions at the SCA8 locus. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:854-857, 2000.

Long repeat tracts at SCA8 in major psychosis

Expansion at a recently identified unstable trinucleotide repeat on chromosome 13q21 has been reported as the molecular cause for spinocerebellar ataxia type 8 (SCA8). The trinucleotide repeat, which consists of a [CTA]n repeat and adjacent [CTG]n repeat, was reported to have a pathogenic range of 107-127 CTG repeats (or 110-130 combined CTA and CTG repeats) in a large ataxia kindred. This repeat region was also cloned by our group from a bipolar affective disorder (BPAD) patient, who has approximately 600 combined repeats, and large alleles (>100 repeats) were reported to be present in 0.7% of controls and 1.5% of major psychosis patients (n = 710 and n = 1,120, respectively). We have followed up these findings by screening three new samples of BPAD and schizophrenia (SCZ) patients and controls, including 272 individuals from 14 BPAD families from Sweden, 130 individuals from 32 SCZ and BPAD families/trios from the Azores Islands, and 206 SCZ individuals from the United Kingdom and Ireland, and 219 matched controls. We found large repeat alleles above the SCA8 pathogenic range in individuals from 3 of 32 Azorean pedigrees and in 1 of 206 SCZ individuals from the United Kingdom, and repeat alleles within the SCA8 pathogenic range in 1 of 14 Swedish families. Although the rarity of major psychosis patients carrying the SCA8 expansion mutation would require a much larger sample size to reach statistical significance, these results support the previously reported observation of increased occurrence of large repeats at SCA8 in major psychosis. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:873-876, 2000.

Elucidating a biological role for chromium at a molecular level

Chromium is an essential trace element for mammals and is required for maintenance of proper carbohydrate and lipid metabolism. However, elucidating its function at a molecular level has proved to be problematic. Recent research has revealed that the chromium-binding oligopeptide chromodulin may play a unique role in the autoamplification of insulin signaling. Attempts to develop chromium-containing nutritional supplements and therapeutics are described.

Reversal of charge selectivity in transmembrane protein pores by using noncovalent molecular adapters

In this study, the charge selectivity of staphylococcal alpha-hemolysin (alphaHL), a bacterial pore-forming toxin, is manipulated by using cyclodextrins as noncovalent molecular adapters. Anion-selective versions of alphaHL, including the wild-type pore and various mutants, become more anion selective when beta-cyclodextrin (betaCD) is lodged within the channel lumen. By contrast, the negatively charged adapter, hepta-6-sulfato-beta-cyclodextrin (s(7)betaCD), produces cation selectivity. The cyclodextrin adapters have similar effects when placed in cation-selective mutant alphaHL pores. Most probably, hydrated Cl(-) ions partition into the central cavity of betaCD more readily than K(+) ions, whereas s(7)betaCD introduces a charged ring near the midpoint of the channel lumen and confers cation selectivity through electrostatic interactions. The molecular adapters generate permeability ratios (P(K+)/P(Cl-)) over a 200-fold range and should be useful in the de novo design of membrane channels both for basic studies of ion permeation and for applications in biotechnology.

The biochemistry of chromium

Chromium has been known to be a micronutrient for mammals for four decades, but progress in elucidating the role of chromium has proceeded slowly. However, recent studies have shed light on a potential role of chromium in maintaining proper carbohydrate and lipid metabolism at a molecular level. The oligopeptide chromodulin binds chromic ions in response to an insulin-mediated chromic ion flux, and the metal-saturated oligopeptide can bind to an insulin-stimulated insulin receptor, activating the receptor's tyrosine kinase activity. Thus, chromodulin appears to play a role in an autoamplification mechanism in insulin signaling. The molecular agent responsible for transporting chromium from mobile pools to insulin-sensitive cells is probably the metal transport protein transferrin. Chromium from the popular dietary supplement chromium picolinate enters cells via a different mechanism. Release of chromium from chromium picolinate for use in cells requires reduction of the chromic center, a process that can lead potentially to the production of harmful hydroxyl radicals.

Quest for the molecular mechanism of chromium action and its relationship to diabetes

Despite forty years of research on the potential role of chromium in carbohydrate and lipid metabolism, significant progress has only recently been made regarding the mode of action of chromium at a molecular level. The oligopeptide low-molecular-weight chromium-binding substance (LMWCr) may function as part of a novel insulin-signaling autoamplification mechanism. The proposed mechanism of action also sheds some light on the potential of chromium-containing compounds as nutritional supplements or in the treatment of adult-onset diabetes and other conditions. The potential relationship between the results of recent studies on diabetic patients and the proposed mode of action of LMWCr are discussed.

An unstable trinucleotide-repeat region on chromosome 13 implicated in spinocerebellar ataxia: a common expansion locus

Larger CAG/CTG trinucleotide-repeat tracts in individuals affected with schizophrenia (SCZ) and bipolar affective disorder (BPAD) in comparison with control individuals have previously been reported, implying a possible etiological role for trinucleotide repeats in these diseases. Two unstable CAG/CTG repeats, SEF2-1B and ERDA1, have recently been cloned, and studies indicate that the majority of individuals with large repeats as detected by repeat-expansion detection (RED) have large repeat alleles at these loci. These repeats do not show association of large alleles with either BPAD or SCZ. Using RED, we have identified a BPAD individual with a very large CAG/CTG repeat that is not due to expansion at SEF2-1B or ERDA1. From this individual's DNA, we have cloned a highly polymorphic trinucleotide repeat consisting of (CTA)n (CTG)n, which is very long ( approximately 1,800 bp) in this patient. The repeat region localizes to chromosome 13q21, within 1.2 cM of fragile site FRA13C. Repeat alleles in our sample were unstable in 13 (5.6%) of 231 meioses. Large alleles (>100 repeats) were observed in 14 (1. 25%) of 1,120 patients with psychosis, borderline personality disorder, or juvenile-onset depression and in 5 (.7%) of 710 healthy controls. Very large alleles were also detected for Centre d'Etude Polymorphisme Humaine (CEPH) reference family 1334. This triplet expansion has recently been reported to be the cause of spinocerebellar ataxia type 8 (SCA8); however, none of our large alleles above the disease threshold occurred in individuals either affected by SCA or with known family history of SCA. The high frequency of large alleles at this locus is inconsistent with the much rarer occurrence of SCA8. Thus, it seems unlikely that expansion alone causes SCA8; other genetic mechanisms may be necessary to explain SCA8 etiology.

Repeat sizes at CAG/CTG loci CTG18.1, ERDA1 and TGC13-7a in schizophrenia

A number of studies using the repeat expansion detection (RED) technique have suggested an association between unknown large CAG/CTG repeats and schizophrenia. The polymorphic CAG/CTG repeat loci CTG18.1 and ERDA1 have been reported to account for a high proportion (approximately 90%) of the large repeats detected by RED and may therefore be responsible for the cited association. The recently described locus TGC13-7a contains a highly polymorphic CTA/TAG and CAG/CTG composite repeat, and is thus another authentic candidate. In the present investigation, each locus was analysed for association with schizophrenia in a sample of 206 patients and 219 group-matched controls. No evidence for association of CTG18.1, ERDA1 and/or TGC13-7a with schizophrenia was found. The combined data accounted for only 54% of the CAG/CTG arrays of > 40 repeats found in our previous RED analysis.

The binding of trivalent chromium to low-molecular-weight chromium-binding substance (LMWCr) and the transfer of chromium from transferrin and chromium picolinate to LMWCr

A recent model for the role of chromium in insulin signaling requires that the oligopeptide low-molecular-weight chromium-binding substance (LMWCr) tightly bind four chromic ions before the oligopeptide obtains a conformation required for binding to the tyrosine kinase active site of the insulin receptor. To test this model, the chromium-binding constant of LMWCr was determined, and the ability of LMWCr to remove chromium from Cr2-transferrin and the nutritional supplement chromium picolinate, Cr(pic)3, was examined. These results are consistent with the model of the mode of action of LMWCr; a Hill study indicates the four chromic ions bind to apoLMWCr in a highly cooperative fashion (n =3.47) with a binding constant of 1.54x 10(21). Chromium is readily transferred from transferrin to apoLMWCr at near neutral pH. The results also suggest that reduction of the chromic center of Cr(pic)3 may be required for the supplement to release chromium; thus, release of chromium is related to a mechanism by which Cr(pic)3 may generate hydroxyl radicals in cells.

The biomimetic [Cr3O(O2CCH2CH3)6(H2O)3]+ decreases plasma cholesterol and triglycerides in rats: towards chromium-containing therapeutics

The in vivo effects of administration of the synthetic, functional biomimetic [Cr3O(O2CCH2CH3)6(H2O)3]+ 1 and a naturally occurring, biologically active form of chromium, low-molecular-weight chromium-binding substance (LMWCr), to rats are described. Given that the complexes are proposed to function by interacting with insulin receptor, trapping it in its active conformation, in contrast to current chromium-containing nutrition supplements, which only serve as sources of absorbable chromium, changes in lipid and carbohydrate metabolism would be expected. After 12 weeks administration (20 micrograms/kg body mass), compound 1 results in 40% lower levels of blood plasma LDL cholesterol, 33% lower levels of total cholesterol, and significantly lower HDL cholesterol and triglyceride; these results are in stark contrast to those of administration of other forms of Cr(III) to rats, which have no effect on these parameters. LMWCr, in contrast to 1, has no effect as it probably is degraded in vivo or excreted. These results are interpreted in terms of the mechanism of chromium action in response to insulin and the activation of insulin receptor, and the potential for the rational design of chromium-containing therapeutics is discussed.

Clinical characteristics of bipolar disorder subjects with large CAG/CTG repeat DNA

BACKGROUND

Unstable DNA has been implicated in a variety of neuropsychiatric disorders, with increasing severity of disease associated with larger DNA repeats. We examined the unstable DNA hypothesis for bipolar disorder by looking for increased severity of symptoms and earlier age of onset amongst bipolar individuals with large CAG/CTG repeats.

METHODS

From a sample of 91 bipolar subjects, eight with large CAG/CTG (> or = 270bp) trinucleotide repeats were matched to eight bipolar individuals with small repeats (< or = 150bp). Medical charts were reviewed for age of onset and a number of severity indicators. Candidate CAG/CTG expansions on chromosomes 17 and 18 were also genotyped.

RESULTS

No obvious differences were noted for the clinical indices, however seven out of eight individuals with large Repeat Expansion Detection (RED) products had expansions at the CTG18.1 locus, while four out of eight had large repeats at ERDA1. Both of these sites are unlikely to be related to disease.

LIMITATIONS

Our total sample size is small and less than 9% have large repeats.

CONCLUSIONS

The lack of increased severity or earlier age of onset amongst bipolar subjects with large CAG/CTG repeats suggests these repeats are unlikely to have a major etiological role in bipolar disorder.

The nutritional supplement chromium(III) tris(picolinate) cleaves DNA

Chromium(III) tris(picolinate) [Cr(pic)3] is currently a very popular nutritional supplement; however, its safety has recently been questioned, especially with regard to its ability to act as a clastogen. At physiologically relevant concentrations, Cr(pic)3 is reduced by biological reductants, including ascorbate and thiols, to Cr(II)-containing species. These species are susceptible to air oxidation, resulting in the catalytic generation of the potent DNA-damaging agent hydroxyl radical. In the absence of reductants, H2O2 can interact with Cr(pic)3 to produce hydroxyl radicals by a second, less efficient mechanism. Cr(pic)3 is extremely stable, which allows the complex to be readily absorbed but also to potentially be incorporated into cells intact. In this form, Cr(pic)3 is primed by its redox potential to enter into the generation of hydroxyl radicals. This study suggests that investigation of the long-term effects of supplementation of the diet with Cr(pic)3 are needed to assess the safety of this material.

Analysis of genome-wide CAG/CTG repeats, and at SEF2-1B and ERDA1 in schizophrenia and bipolar affective disorder

A shift towards larger CAG/CTG triplet repeats and schizophrenia (SCZ) and bipolar affective disorder (BPAD) has been detected by several recent studies, using the Repeat Expansion Detection (RED) technique, however no specific loci have been shown to be responsible for this shift. Further analyses by our group of RED (CTG)10 ligation products amongst an extended sample of patients and comparison with controls matched for age, sex and ethnicity show no significant differences in distribution (P= 0.23, n=95; P=0.93, n=91, for SCZ and BPAD respectively). Alleles at two recently discovered unstable trinucleotide repeat loci at 18q21.1 (SEF2-1B) and 17q21.3 (ERDA1) have also been analysed in affecteds and matched controls. We observed no increase in frequency of larger alleles (>37 repeats) in affected individuals at SEF2-1B (BPAD: P=0.95, n= 100; SCZ: P=0.61, n=97) or at ERDA1 (BPAD: P= 0.4, n = 101; SCZ: P= 0.05, n = 151, with larger alleles more frequent in controls). Our findings suggest that larger CAG/CTG repeats at these loci are neither major contributory factors to the etiology of psychosis, nor in linkage disequilibrium with a gene that is. Furthermore, when the RED results were compared to allele sizes at SEF2-1B and ERDA1, it was observed that a majority of SCZ, BPAD and control individuals with large RED products had a large allele at either or both sites (78% for RED products > or =270 bp; 62% for RED products > or =180 bp).

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.

Mechanisms of chromium action: low-molecular-weight chromium-binding substance

Chromium has long been known to be essential for proper lipid and carbohydrate metabolism in mammals, with chromium deficiency leading to symptoms associated with adult-onset diabetes and cardiovascular disease. Elucidating the structure, function, and mode of action of the biologically active form of chromium has proved enigmatic. However, a naturally-occurring oligopeptide, low-molecular-weight chromium-binding substance (LMWCr), has been found in our laboratory to activate insulin receptor kinase activity up to 7-fold with a dissociation constant of 250 picomolar in the presence of 100 nanomolar insulin, and it has been partially characterized in terms of structural and spectroscopic properties. LMWCr may function in a manner similar to that of the calcium-binding signal protein calmodulin. In other words, LMWCr is maintained in its active apo-oligopeptide form; in response to a chromium flux, LMWCr binds 4 chromic ions. The holoprotein is then capable of binding to insulin receptor (and perhaps other enzymes) activating the enzyme. Establishing a link between the nutrient chromium, LMWCr's activation of insulin receptor kinase activity, and adult-onset diabetes and related conditions could result in a new treatment for these conditions.

Genetic association analysis of serotonin system genes in bipolar affective disorder

OBJECTIVE

This study examined the putative role of serotonin genes in the etiology of bipolar affective disorder.

METHOD

Genetic association analysis was performed for individuals with bipolar affective disorder and unaffected subjects closely matched in age, sex, and ethnic background (N=103 in each group). The allele and genotype frequencies of polymorphisms at the genes for serotonin receptors HTR1A, HTR1Dalpha, HTR1Dbeta, HTR2A, HTR2C, HTR7, tryptophan hydroxylase (TPH), and the serotonin transporter (hSERT) were compared in the two groups of subjects.

RESULTS

Statistically significant positive associations were found for HTR2A and hSERT polymorphisms. However, results from an independent replication group of over 100 patients with bipolar affective disorder and their matched comparison subjects failed to confirm these associations.

CONCLUSIONS

These results suggest that the serotonin genes studied are not associated with bipolar affective disorder, although transmission disequilibrium studies are required in order to confirm this conclusion.

No evidence of expansion of CAG or GAA repeats in schizophrenia families and monozygotic twins

Many diseases caused by trinucleotide expansion exhibit increased severity and decreased age of onset (genetic anticipation) in successive generations. Apparent evidence of genetic anticipation in schizophrenia has led to a search for trinucleotide repeat expansions. We have used several techniques, including Southern blot hybridization, repeat expansion detection (RED) and locus-specific PCR to search for expanded CAG/CTG repeats in 12 families from the United Kingdom and 11 from Iceland that are multiplex for schizophrenia and demonstrate anticipation. The unstable DNA theory could also explain discordance of phenotype for schizophrenia in pairs of monozygotic twins, where the affected twin has a greater number of repeats than the unaffected twin. We used these techniques to look for evidence of different CAG/CTG repeat size in 27 pairs of monozygotic twins who are either concordant or discordant for schizophrenia. We have found no evidence of an increase in CAG/CTG repeat size for affected members in the families, or for the affected twins in the MZ twin sample. Southern hybridization and RED analysis were also performed for the twin and family samples to look for evidence of expansion of GAA/TTC repeats. However, no evidence of expansion was found in either sample. Whilst these results suggest that these repeats are not involved in the etiology of schizophrenia, the techniques used for detecting repeat expansions have limits to their sensitivity. The involvement of other trinucleotide repeats or other expandable repeat sequences cannot be ruled out.

Chromium oligopeptide activates insulin receptor tyrosine kinase activity

A possible new mechanism for the amplification of insulin receptor tyrosine kinase activity in response to insulin has been identified. The chromium-containing oligopeptide low molecular weight chromium-binding substance (LMWCr) does not effect the tyrosine protein kinase activity of rat adipocytic membrane fragments in the absence of insulin; however, insulin-stimulated kinase activity in the membrane fragments is increased up to 8-fold by the oligopeptide. Using isolated rat insulin receptor, LMWCr has been shown to bind to insulin-activated insulin receptor with a dissociation constant of circa 250 pM, resulting in the increase of its tyrosine protein kinase activity. The ability of LMWCr to stimulate insulin receptor tyrosine kinase activity is dependent on its chromium content. The results appear to explain the previously poorly understood relationship between chromium and adult-onset diabetes and cardiovascular disease.

Isolation and characterization of a biologically active chromium oligopeptide from bovine liver

Low-molecular-weight chromium-binding substance (LMWCr), the only known naturally occurring Cr-containing polypeptide from mammals and candidate for the biologically active form of chromium, has been isolated for the first time in yields sufficient for spectroscopic studies capable of providing structural and mechanistic data on a molecular level. The results of paramagnetic 1H NMR, electron paramagnetic resonance, and electronic spectroscopic studies indicate that the four chromic ions per polypeptide are probably arranged in an integer-spin tetranuclear assembly, although an alternate possibility, the presence of two dinuclear assemblies, could not be ruled out. This assembly (or assemblies) is bridged by anionic ligands and supported by carboxylates provided by the polypeptide.

Search for unstable DNA in schizophrenia families with evidence for genetic anticipation

Evidence for genetic anticipation has recently become an important subject of research in clinical psychiatric genetics. Renewed interest in anticipation was evoked by molecular genetic findings of a novel type of mutation termed "unstable DNA." The unstable DNA model can be construed as the "best fit" for schizophrenia twin and family epidemiological data. We have performed a large-scale Southern blot hybridization, asymmetrical PCR-based, and repeat expansion-detection screening for (CAG)n/(CTG)n and (CCG)n/(CGG)n expansions in eastern Canadian schizophrenia multiplex families demonstrating genetic anticipation. There were no differences in (CAG)n/(CTG)n and (CCG)n/(CGG)n pattern distribution either between affected and unaffected individuals or across generations. Our findings do not support the hypothesis that large (CAG)n/(CTG)n or (CCG)n/(CGG)n expansions are the major etiologic factor in schizophrenia. A separate set of experiments directed to the analysis of small (30-130 trinucleotides), Huntington disease-type expansions in individual genes is required in order to fully exclude the presence of (CAG)n/(CTG)n- or (CCG)n/(CGG)n-type unstable mutation.

A biologically active form of chromium may activate a membrane phosphotyrosine phosphatase (PTP)

Chromium is essential for proper carbohydrate and lipid metabolism in mammals, although the mechanism of this action has previously proved elusive. Low-molecular-weight chromium-binding protein (LMWCr), a biologically active form of chromium in mammals, potentiates the effect of insulin on the conversion of glucose into lipid and into carbon dioxide in isolated adipocytes. Kinetics studies indicate that LMWCr isolated from bovine liver activates phosphotyrosine phosphatase (PTP) activity in adipocyte membranes while having no intrinsic phosphatase activity. This activation is directly proportional to the amount of added LMWCr. The pattern of inhibition of this activity in the presence of a number of known phosphatase inhibitors suggests the involvement of a membrane phosphotyrosine phosphatase similar to PTP1A' or PTP1B. We propose that chromium plays a biological role in the activation of a membrane phosphotyrosine phosphatase.

Immobilization of conalbumin onto polystyrene/divinylbenzene co-polymers: towards finding the best support for MAMC

Immediately after the successful immobilization of conalbumin onto CNBr-activated Sepharose, efforts were begun to find a less expensive support and a more benign chemistry of activation. The potential of the Sepharose-conalbumin conjugate for decontamination of several metal-containing waste-waters has been established, and a new method of chromatography has emerged, named metalloprotein affinity metal chromatography (MAMC). Efforts to immobilize conalbumin onto polystyrene/divinylbenzene co-polymers, using the well known and commercially available Merrifield, aminomethyl and plain polystyrene resins are presented here. Immobilizations of conalbumin were carried out on the Merrifield and Aminomethyl resins, but the procedures were time consuming and complicated by polymer aggregation. Because of high cost of these materials, research was directed towards the activation and functionalization of plain polystyrene/divinylbenzene co-polymers. Chlorosulfonation followed by sulfonamide formation was attempted on three commercially available polymers. Successful polysulfonamide formation was achieved with bislysine copper(II) acting as a diamine. Removal of the copper allows the unblocking of the alpha amino group of the immobilized lysine which in turn is treated with glutaraldehyde, affording an activated support for immobilization of proteins. To date, approximately 46 mg transferrin/g dry matrix have been successfully immobilized. The chemical and biological inertness of this support makes it a good candidate to scale up the procedure and continue the optimization of MAMC.

Point mutation analysis of the FMR-1 gene in autism

We have analysed all 17 exons of the human FMR-1 gene for mutations in autistic individuals using single-stranded conformational polymorphism (SSCP) analysis. We have identified three new polymorphisms. SSCP DNA fragment shifts were found for exons, 5, 10 and 11 in autistic individuals and in normal controls. Sequence analysis showed the exon 10 and 11 polymorphisms to result from base substitutions within introns, 14 and 73 bp downstream from the splice site respectively. In exon 5, a G to A base substitution at codon 138 has no effect on amino acid sequence. The intronic polymorphism adjacent to exon 10 was analysed amongst two groups of unrelated autistic individuals-one from the UK and one from Germany- and amongst a control population. Comparison of allele frequencies between Caucasian autism cases and Caucasian controls show a significant increase in the presence of the polymorphic intronic sequence 3' to exon 10 (Fisher's exact test, P = 0.01). The base change is at a position where it is unlikely to affect splicing of the FMR-1 transcript and is most likely a neutral variant that has only a spurious false positive association with autism. However further linkage disequilibrium analyses are justifiable. The positive association with autism should be explored in further samples to determine whether it has any validity as a genetic marker for autism.

Frequency analysis of large CAG/CTG trinucleotide repeats in schizophrenia and bipolar affective disorder

Much interest has recently been focussed on the possibility of the involvement of unstable DNA in the etiology of schizophrenia and bipolar affective disorder (BPAD), following several publications that report increases in frequency of large CAG/CTG repeats in affected individuals. Using the Repeat Expansion Detection (RED) technique, we have performed a matched control pair analysis for both disorders. No significant differences in CAG/CTG repeat sizes were observed for 52 bipolar affecteds and matched controls (P = 0.15), and borderline significance was observed for 54 schizophrenia affecteds and matched controls (P = 0.05), using a (CTG)10 oligonucleotide (one-tailed t-tests for paired samples). Furthermore, using a (CTG)17 oligonucleotide, no significant differences were observed for 58 bipolar affecteds and 55 schizophrenia affecteds compared to 81 unmatched controls. No significant sex effect was observed for either group, and no significant differences in repeat size were found for responders and non-responders to drug treatments. More importantly, there was no significant correlation (either positive or negative) between age of onset of disease and size of repeat. We thus cannot conclude that CAG/CTG trinucleotides are involved in psychotic disorders and that either the differences observed in similar studies may be the result of population stratification, or that the increased frequency of larger repeats amongst affected individuals is a much smaller effect than previously thought.