Renee F. Badenhop

A genome screen of 13 bipolar affective disorder pedigrees provides evidence for susceptibility loci on chromosome 3 as well as chromosomes 9, 13 and 19

Bipolar affective disorder is a severe mood disorder that afflicts approximately 1% of the population worldwide. Twin and adoption studies have indicated that genetic factors contribute to the disorder and while many chromosomal regions have been implicated, no susceptibility genes have been identified. We undertook a combined analysis of 10 cM genome screen data from a single large bipolar affective disorder pedigree, for which we have previously reported linkage to chromosome 13q14 (Badenhop et al, 2001) and 12 pedigrees independently screened using the same 400 microsatellite markers. This 13-pedigree cohort consisted of 231 individuals, including 69 affected members. Two-point LOD score analysis was carried out under heterogeneity for three diagnostic and four genetic models. Non-parametric multipoint analysis was carried out on regions of interest. Two-point heterogeneity LOD scores (HLODs) greater than 1.5 were obtained for 11 markers across the genome, with HLODs greater than 2.0 obtained for four of these markers. The strongest evidence for linkage was at 3q25–26 with a genome-wide maximum score of 2.49 at D3S1279. Six markers across a 50 cM region at 3q25–26 gave HLODs greater than 1.5, with three of these markers producing scores greater than 2.0. Multipoint analysis indicated a 20 cM peak between markers D3S1569 and D3S1614 with a maximum NPL of 2.8 (P= 0.004). Three other chromosomal regions yielded evidence for linkage: 9q31–q33, 13q14 and 19q12–q13. The regions on chromosomes 3q and 13q have previously been implicated in other bipolar and schizophrenia studies. In addition, several individual pedigrees gave LOD scores greater than 1.5 for previously reported bipolar susceptibility loci on chromosomes 18p11, 18q12, 22q11 and 8p22–23.

Novel mutations in the SDHD gene in pedigrees with familial carotid body paraganglioma and sensorineural hearing loss

Paraganglioma (PGL) is a rare disorder characterized by tumors of the head and neck region. Between 10% and 50% of cases of PGL are familial, and the disease is autosomal dominant and subject to age‐dependent penetrance and imprinting. The paraganglioma gene (PGL1) has been mapped to 11q22.3–q23, and recently germline mutations in the SDHD gene have been identified. The SDHD region contains another gene, DPP2/TIMM8B, the homolog of which causes dystonia and deafness seen in Mohr‐Tranebjaerg syndrome. Using four PGL pedigrees, two of which exhibit coinheritance of PGL and sensorineural hearing loss or tinnitus, analysis of 14 microsatellite markers provided support for linkage to the PGL1 locus. Sequence analysis identified novel mutations in exon 1 and exon 3 of the SDHD gene, including a novel two base pair deletion in exon 3 creating a premature stop codon at position 67; a novel three base pair deletion in exon 3 resulting in the loss of Tyr‐93; a missense mutation in exon 3 resulting in the substitution of Leu‐81 for Pro‐81; and a novel G‐to‐C substitution in exon 1 resulting in the substitution of Met‐1 for Ile‐1. No base changes were detected in the DPP2/TIMM8B gene. There was no apparent loss of heterozygosity at the site of the SDHD mutations. However, RT‐PCR analysis of tumor samples showed monoallelic expression of the mutant (paternal) allele as expected for imprinting. This has not previously been shown for this disorder. The inheritance and expression of the SDHD gene is consistent with the PGL1 gene being subject to genomic imprinting.

Angiotensin-Converting Enzyme Genotype in Children and Coronary Events in Their Grandparents

BACKGROUND It has been suggested that the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is an independent risk factor for coronary artery disease. The D/D genotype, which is associated with higher levels of circulating ACE than the I/D or I/I genotype, has been found significantly more frequently in patients with myocardial infarction and also in individuals with a parental history of myocardial infarction. METHODS AND RESULTS We explored the distribution of the ACE genotype in 404 school children, aged 6 to 13 years, and related the distribution to the number of their grandparents who had had vascular events. We found a significant association between the number of grandparents who had had coronary events and the ACE genotype (P = .01). In children with two or more grandparents who had had coronary events, there was an excess of both D/D (odds ratio = 2.8 [95% confidence interval = 1.16-6.56]) and I/D (odds ratio = 1.4 [95% confidence interval = 0.62-3.25]) genotypes compared with I/I genotypes. In addition, there was an association between the ACE genotype and lipoprotein(a) levels in children (P = .07). Both the ACE genotype and lipoprotein(a) were found to contribute significantly (P = .0042) and independently to family history of coronary artery disease, with the ACE genotype proving to be more predictive than lipoprotein(a) levels. CONCLUSIONS We conclude that the I/D polymorphism of the ACE gene is an important independent risk factor for coronary artery disease and is more predictive that lipoprotein(a). The I/D polymorphism is not only associated with a parental history of myocardial infarction but also with coronary artery disease in second-degree relatives. A further study to explore the relation between the I/D polymorphism and circulating levels of lipoprotein(a) is indicated.

Familial idiopathic basal ganglia calcification (Fahr's disease) without neurological, cognitive and psychiatric symptoms is not linked to the IBGC1 locus on chromosome 14q.

Abstract. Idiopathic basal ganglia calcification (IBGC) is characterised by radiological, neurological, cognitive and psychiatric abnormalities. The associations between these abnormal phenotypes and abnormal genes remain unclear despite the recent mapping to chromosome 14q of a susceptibility locus for IBGC (IBGC1). We identified two siblings, from a large multigenerational pedigree, who had both been diagnosed with radiological IBGC, dementia, bipolar affective disorder and Parkinsonism. We assessed (1) other family members to determine whether these four phenotypes were co-segregating as symptoms of IBGC, and (2) possible IBGC linkage to the IBGC1 locus on chromosome 14q or to any known or potential dementia genes. Nine second-generation and 21 third-generation members received radiological, neurological, neuropsychological and psychiatric assessments. We genotyped all family members for microsatellite markers at the IBGC1 locus and polymorphisms of the ApoE, VLDL, α1-ACT, BChE-K, APP, PS1, PS2 and tau genes and tested these for linkage to IBGC, dementia and bipolar disorder. Of the ten family members with radiological intracranial calcification, all except the two index cases were normal. There was no significant association between IBGC status and severe cognitive impairment or dementia (P=0.335) or bipolar affective disorder or Parkinsonism (P=1.0). Linkage to the IBGC1 locus was excluded. Of the eight dementia gene markers tested, the only positive LOD score was for the ApoE ε4 polymorphism and dementia/severe cognitive impairment. We have identified a form of IBGC in which calcification is inherited independently of neurological, cognitive and psychiatric symptoms. This may represent a second locus for this disorder.

New MspI polymorphism at +83 bp of the human apolipoprotein AI gene : Association with increased circulating high density lipoprotein cholesterol levels

We recently showed that loss of a MspI restriction site in the 5′‐end (intron 1) of the apolipoprotein (apo) AI gene is due to a C to T transition (+83 bp) and/or a G to A transition (+84 bp). Since this region may be relevant to the regulation of apo AI gene expression and therefore to plasma high density lipoprotein cholesterol (HDL‐C), we explored the association between this MspI polymorphic site and circulating HDL‐C levels in 243 healthy Caucasians. There were 143 aged 18–67 years (60 males and 83 females) and 100 aged 6–12 years (58 males and 42 females). We also compared this association with a known MspI polymorphic site, a G to A transition at −75 bp of the apo AI gene. The rare allele (−) frequency for the polymorphism at +83 bp was 4.1% and 22.1% for the polymorphism at −75 bp. Subjects heterozygous for the loss of the MspI restriction site at +83 bp (genotype: M2+−, n = 20) had higher HDL‐C levels than M2++ subjects (mean ± SD: 1.73 ± 0.31 vs. 1.41 ± 0.39 mmol/l, P < 0.05 for adults; 1.71 ± 0.33 vs. 1.34 ± 0.29 mmol/l, P < 0.01 for children). Adults with the G to A substitution at −75 bp also had higher HDL‐C levels (1.56 ± 0.36 mmol/l for AA, 1.53 ± 0.38 mmol/l for GA, and 1.36 ± 0.38 mmol/l for GG, P < 0.05); this difference was not observed in the children. The MspI polymorphisms at both sites were in linkage disequilibrium. Their joint effect on the HDL‐C levels was also significant and individuals with rare alleles (−) at both sites had the highest HDL‐C levels. In an analysis of variance, the MspI polymorphism at +83 bp, and at −75 bp and gender independently accounted for 6.5%, 1.7%, and 5.9%, respectively, of the variance in circulating HDL‐C levels when age was controlled as a covariate. We conclude that loss of the MspI site by the C to T (+83 bp) and/or the G to A (+84 bp) transitions is highly associated with increased HDL‐C levels. The association appears to be more significant than that of the G to A transition at −75 bp.

Positional cloning, association analysis and expression studies provide convergent evidence that the cadherin gene FAT contains a bipolar disorder susceptibility allele

A susceptibility locus for bipolar disorder was previously localized to chromosome 4q35 by genetic linkage analysis. We have applied a positional cloning strategy, combined with association analysis and provide evidence that a cadherin gene, FAT, confers susceptibility to bipolar disorder in four independent cohorts (allelic P-values range from 0.003 to 0.024). In two case–control cohorts, association was identified among bipolar cases with a family history of psychiatric illness, whereas in two cohorts of parent–proband trios, association was identified among bipolar cases who had exhibited psychosis. Pooled analysis of the case–control cohort data further supported association (P=0.0002, summary odds ratio=2.31, 95% CI: 1.49–3.59). We localized the bipolar-associated region of the FAT gene to an interval that encodes an intracellular EVH1 domain, a domain that interacts with Ena/VASP proteins, as well as putative β-catenin binding sites. Expression of Fat, Catnb (β-catenin), and the three genes (Enah, Evl and Vasp) encoding the Ena/VASP proteins, were investigated in mice following administration of the mood-stabilizing drugs, lithium and valproate. Fat was shown to be significantly downregulated (P=0.027), and Catnb and Enah were significantly upregulated (P=0.0003 and 0.005, respectively), in response to therapeutic doses of lithium. Using a protein interaction map, the expression of genes encoding murine homologs of the FAT (ft)-interacting proteins was investigated. Of 14 interacting molecules that showed expression following microarray analysis (including several members of the Wnt signaling pathway), eight showed significantly altered expression in response to therapeutic doses of lithium (binomial P=0.004). Together, these data provide convergent evidence that FAT and its protein partners may be components of a molecular pathway involved in susceptibility to bipolar disorder.

The prevalence of SDHB, SDHC, and SDHD mutations in patients with head and neck paraganglioma and association of mutations with clinical features

Paraganglioma (PGL) is a rare disorder (MIM 168000) characterised by tumours of the paraganglia, a collection of neuroendocrine tissues and small organs which are distributed throughout the body. The normal paraganglia play an important role in homeostasis either by acting directly as chemical sensors or by secreting catecholamines in response to stress. PGL is broadly categorised into two groups, those occurring in the head and neck region and those occurring elsewhere, with the adrenal medulla being the major site. Tumours in the head and neck have been detected in nearly 20 distinct locations including the jugular, vagal, tympanic, and aortic paraganglia, however the carotid body is the major site.1 The paraganglia of the head and neck region have sensory innervation and function as chemoreceptors. They are associated with the parasympathetic nervous system and are located in the vicinity of major arteries and nerves. The tumours usually present as an asymptomatic slow growing mass, lacking endocrine activity. The tumours are mostly benign but local expansion can cause cranial nerve deficit, invasion of the skull base, and eventually compression of the brain stem. The incidence of head and neck PGL is difficult to determine, however estimates range from 1 in 30 000 to 1 in 100 000 in the general population.2,3 To date, four genetic loci have been implicated in the pathogenesis of head and neck PGL. PGL1 was mapped to the long arm of chromosome 11 at 11q23 in several Dutch4,5 and North American families.6–8 Candidate gene analysis in the region revealed germline mutations in the succinate dehydrogenase subunit D ( SDHD ) gene in families carrying the PGL1 locus.9 Linkage analysis of another unrelated Dutch pedigree revealed the presence of a second more proximal locus ( PGL2 ) on 11q13.10 This locus remains unconfirmed. PGL3 …

Presenilin-1 Mutation L271V Results in Altered Exon 8 Splicing and Alzheimer's Disease with Non-cored Plaques and No Neuritic Dystrophy

The mutation L271V in exon 8 of the presenilin-1 (PS-1) gene was detected in an Alzheimers disease pedigree. Neuropathological examination of affected individuals identified variant, large, non-cored plaques without neuritic dystrophy, reminiscent of cotton wool plaques. Biochemical analysis of L271V mutation showed that it increased secretion of the 42-amino acid amyloid-β peptide, suggesting a pathogenic mutation. Analysis of PS-1 transcripts from the brains of two mutation carriers revealed a 17–50% increase in PS-1 transcripts with deletion of exon 8 (PS-1Δexon8) compared with unrelated Alzheimers disease brains. Exon trapping analysis confirmed that L271V mutation enhanced the deletion of exon 8. Western blots of brain lysates indicated that PS-1Δexon8 was overexpressed in an affected individual. Biochemical analysis of PS-1Δexon8 in COS and BD8 cells indicate the splice isoform is not intrinsically active but interacts with wild-type PS-1 to generate amyloid-β. Western blots of cell lysates immunoprecipitated with anti-Tau or anti-GSK-3β antibodies indicated that PS-1Δexon8, unlike wild-type PS-1, does not interact directly with Tau or GSK-3β, potential modifiers of neuritic dystrophy. We postulate that variant plaques observed in this family are due in part to the effects of PS-1Δexon8 and that interaction between PS-1 and various protein complexes are necessary for neuritic plaque formation.

A genome screen of a large bipolar affective disorder pedigree supports evidence for a susceptibility locus on chromosome 13q.

Bipolar affective disorder is a severe mood disorder that afflicts approximately 1% of the population worldwide. Twin and adoption studies have indicated that genetic factors contribute to the disorder and while many chromosomal regions have been implicated, no susceptibility genes have been identified. In this present study, we undertook a 10 cM genome screen using 400 microsatellite markers in a large multigenerational bipolar pedigree consisting of 40 individuals, including six affecteds. We found strongest evidence for linkage to chromosome 13q14. A maximum NPL score of 4.09 (P = 0.008) was obtained between markers D13S1272 and D13S153 using GENEHUNTER. A maximum two-point LOD score of 2.91 (θ = 0.0) was found for marker D13S153 and a maximum three-point LOD score of 3.0 was obtained between markers D13S291 and D13S153 under a recessive model with 90% maximum age-specific penetrance and including bipolar I and unipolar individuals as affected. Several other markers in the region, D13S175, D13S218, D13S263, and D13S156 had two-point LOD scores greater than 1.5. These results meet the criteria for evidence of suggestive linkage. Haplotype analysis enabled us to narrow the likely disease region to a 6 cM region between markers D13S1272 and D13S1319, which contains the serotonin 2A receptor candidate gene. Two single nucleotide polymorphisms were identified in this gene but we did not detect any significant differences in allele frequency in a case-control sample. The region on chromosome 13q14–32 has previously been implicated in other bipolar and schizophrenia cohorts. Our results provide further support for the existence of a susceptibility locus on chromosome 13q14.

C to T and/or G to A transitions are responsible for loss of a MspI restriction site at the 5'-end of the human apolipoprotein AI gene.

We detected the loss of a MspI restriction site by a C to T transition at +83 bp and a G to A transition at +84 bp of the 5′-end non-coding region of the human apolipoprotein AI gene. This base change occurred at the “hot spot” (CCGG) for methylation, which may be important in the regulation of gene expression. The population frequency for the loss of the MspI site is 6.1%.