Positive and negative symptoms in affected sib pairs with schizophrenia: implications for genetic studies in an African Xhosa sample

Careful phenotyping and the identification of subtypes of schizophrenia can contribute significantly to the success of genetic studies in schizophrenia. The phenomenology of schizophrenia in affected sib pairs has been well-described in Caucasian populations, however a paucity of data exists for African populations. This study therefore investigated symptom dimensions in a sizeable group of affected Xhosa sib pairs as a means of evaluating the role of shared familial factors in the psychosis of schizophrenia. Five hundred and thirteen participants were interviewed with the Diagnostic Interview for Genetic Studies (DIGS), which included the Schedules for the Assessment of Negative and Positive symptoms (SANS/SAPS). One hundred and four sib pairs were then extracted (N = 208) for analysis of concordance for lifetime psychotic symptoms and an exploratory factor analysis of the SANS/SAPS. Concordance analysis of life-time symptoms indicated a significant concordance for olfactory hallucinations, persecutory delusions, jealousy, somatic, reference and control delusions as well as thought insertion and withdrawal. The factor analysis of the global scores of the SAPS and SANS revealed a five factor best-fit model and accounted for 92.5% of variance. The factors included a negative symptom factor, a positive symptom factor, a positive thought disorder and a bizarre behaviour component. The core symptomatology of schizophrenia in this sib pair sample was similar to that reported in Caucasian populations with the exception of higher rates of auditory hallucinations and delusions of persecution. In summary therefore; although the factor analysis only supported the concept of the universality of psychotic symptoms in schizophrenia, the concordance analysis of these symptoms did reveal hallucinations as well as delusions of control as possible candidates relevant for future research into genotype-phenotype relationships.

Obsessive compulsive disorder--prevalence in Xhosa-speaking schizophrenia patients

Obsessive compulsive disorder (OCD) has been reported in up to 31% of schizophrenia sufferers. This study evaluated the presence of OCD in a Xhosa-speaking schizophrenia group. Xhosa patients (N = 509, including 100 sibships) with schizophrenia were recruited from hospital and community settings. The patients underwent a structured clinical interview for the presence of lifetime co-morbid schizophrenia and OCD. Only 3 patients (0.5%) fulfilled criteria for OCD. No concordance for OCD was noted in the sibship group. Our findings differ from those in other parts of the world, and if replicated, might suggest unique protective environmental or genetic factors for OCD in certain ethnic groups.

Association studies in candidate genes: strategies to select SNPs to be tested

OBJECTIVE

When numerous single nucleotide polymorphisms (SNPs) have been identified in a candidate gene, a relevant and still unanswered question is to determine how many and which of these SNPs should be optimally tested to detect an association with the disease. Testing them all is expensive and often unnecessary. Alleles at different SNPs may be associated in the population because of the existence of linkage disequilibrium, so that knowing the alleles carried at one SNP could provide exact or partial knowledge of alleles carried at a second SNP. We present here a method to select the most appropriate subset of SNPs in a candidate gene based on the pairwise linkage disequilibrium between the different SNPs.

METHOD

The best subset is identified through power computations performed under different genetic models, assuming that one of the SNPs identified is the disease susceptibility variant.

RESULTS

We applied the method on two data sets, an empirical study of the APOE gene region and a simulated study concerning one of the major genes (MG1) from the Genetic Analysis Workshop 12. For these two genes, the sets of SNPs selected were compared to the ones obtained using two other methods that need the reconstruction of multilocus haplotypes in order to identify haplotype-tag SNPs (htSNPs). We showed that with both data sets, our method performed better than the other selection methods.

Examination of IMPA1 and IMPA2 genes in manic-depressive patients: association between IMPA2 promoter polymorphisms and bipolar disorder

Manic-depressive (bipolar) illness is a serious psychiatric disorder with a strong genetic predisposition. The disorder is likely to be multifactorial and etiologically complex, and the causes of genetic susceptibility have been difficult to unveil. Lithium therapy is a widely used pharmacological treatment of manic-depressive illness, which both stabilizes the ongoing episodes and prevents relapses. A putative target of lithium treatment has been the inhibition of the myo-inositol monophosphatase (IMPase) enzyme, which dephosphorylates myo-inositol monophosphate in the phosphatidylinositol signaling system. Two genes encoding human IMPases have so far been isolated, namely myo-inositol monophosphatase 1 (IMPA1) on chromosome 8q21.13-21.3 and myo-inositol monophosphatase 2 (IMPA2) on chromosome 18p11.2. In the present study, we have scanned for DNA variants in the human IMPA1 and IMPA2 genes in a pilot sample of Norwegian manic-depressive patients, followed by examination of selected polymorphisms and haplotypes in a family-based bipolar sample of Palestinian Arab proband-parent trios. Intriguingly, two frequent single-nucleotide polymorphisms (-461C>T and -207T>C) in the IMPA2 promoter sequence and their corresponding haplotypes showed transmission disequilibrium in the Palestinian Arab trios. No association was found between the IMPA1 polymorphisms and bipolar disorder, neither with respect to disease susceptibility nor with variation in lithium treatment response. The association between manic-depressive illness and IMPA2 variants supports several reports on the linkage of bipolar disorder to chromosome 18p11.2, and sustains the possible role of IMPA2 as a susceptibility gene in bipolar disorder.

In-Depth Haplotype Analysis of ABCA1 Gene Polymorphisms in Relation to Plasma ApoA1 Levels and Myocardial Infarction

OBJECTIVE

By regulating the cellular cholesterol efflux from peripheral cells to high-density lipoprotein, the ABCA1 protein is suspected to play a key role in lipid homeostasis and atherosclerosis. Twenty-six polymorphisms of the ABCA1 gene were genotyped and tested for association with plasma levels of ApoA1 and myocardial infarction (MI) in the ECTIM study.

METHODS AND RESULTS

In addition to single-locus analysis, a systematic exploration of all possible haplotype effects was performed, with this exploration being performed on a minimal set of "tag" polymorphisms that define the haplotype structure of the gene. Two polymorphisms were associated with plasma levels of ApoA1, 1 in the promoter (C-564T) and 1 in the coding (R1587K) regions, whereas only 1 polymorphism (R219K) was associated with the risk of MI. However, no haplotype effect was detected on ApoA1 variability or on the risk of MI.

CONCLUSIONS

ABCA1 gene polymorphisms but not haplotypes are involved in the variability of plasma ApoA1 and the susceptibility to coronary artery disease.

The factor structure for positive and negative symptoms in South African Xhosa patients with schizophrenia

Most studies investigating the symptom dimensions of schizophrenia utilising the Scale for the Assessment of Negative Symptoms (SANS) and the Scale for the Assessment of Positive Symptoms (SAPS) favour a three factor model. This study sought to investigate the factor structure of both the global and individual items of the SANS and SAPS in a large sample of South African Xhosa patients with schizophrenia. A total of 422 subjects participated. Both principal components and factor analytical procedures were applied. For the global items, a two-factor solution representing positive and negative symptoms accounted for 59.9% of the variance. Alternatively, the three-dimensional model of negative, psychotic and disorganisation factors was supported by a five-factor solution if the more heterogeneous items of attention and alogia were ignored. Analysis of the individual items yielded a five-factor solution with the negative symptoms splitting into diminished expression and disordered relating, and the positive symptoms separating into factors for psychosis, thought disorder and bizarre behaviour. Our findings are very similar to those from other parts of the world, providing evidence that the factor structure for the symptoms of schizophrenia is relatively resistant to cultural influences. This is particularly true for negative symptoms.

Evidence for linkage by transmission disequilibrium test analysis of a chromosome 22 microsatellite marker D22S278 and bipolar disorder in a Palestinian Arab population

A number of linkage studies suggest a schizophrenia susceptibility locus on chromosome 22, particularly with microsatellite marker D22S278 (22q12). In addition to some evidence for linkage to schizophrenia in this region, linkage to bipolar disorder using this marker has also been reported. We tested a group of 60 Bipolar I triads and an expanded group of 79 Bipolar I and Bipolar II triads recruited from a Palestinian Arab population for linkage with the D22S278 marker. Significant linkage was observed using the extended transmission disequilibrium test for multiallelic markers (ETDT) for both Bipolar I (P = 0.031) and the expanded group of Bipolar I and Bipolar II (P = 0.041). These weakly positive results are at least consistent with the hypothesis that this region of chromosome 22 might harbor a susceptibility locus for both major psychoses and should be considered for more intensive study. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:836-838, 2000.

Tangier disease is caused by mutations in the gene encoding ATP-binding cassette transporter 1

Tangier disease (TD) was first discovered nearly 40 years ago in two siblings living on Tangier Island. This autosomal co-dominant condition is characterized in the homozygous state by the absence of HDL-cholesterol (HDL-C) from plasma, hepatosplenomegaly, peripheral neuropathy and frequently premature coronary artery disease (CAD). In heterozygotes, HDL-C levels are about one-half those of normal individuals. Impaired cholesterol efflux from macrophages leads to the presence of foam cells throughout the body, which may explain the increased risk of coronary heart disease in some TD families. We report here refining of our previous linkage of the TD gene to a 1-cM region between markers D9S271 and D9S1866 on chromosome 9q31, in which we found the gene encoding human ATP cassette-binding transporter 1 (ABC1). We also found a change in ABC1 expression level on cholesterol loading of phorbol ester-treated THP1 macrophages, substantiating the role of ABC1 in cholesterol efflux. We cloned the full-length cDNA and sequenced the gene in two unrelated families with four TD homozygotes. In the first pedigree, a 1-bp deletion in exon 13, resulting in truncation of the predicted protein to approximately one-fourth of its normal size, co-segregated with the disease phenotype. An in-frame insertion-deletion in exon 12 was found in the second family. Our findings indicate that defects in ABC1, encoding a member of the ABC transporter superfamily, are the cause of TD.

No evidence for involvement of KCNN3 (hSKCa3) potassium channel gene in familial and isolated cases of schizophrenia

Several studies have reported in schizophrenia a decrease of age of onset in successive family generations, and this observation is consistent with anticipation. Anticipation is known to result from expansion of CAG repeats in several neurodegenerative disorders. Longer alleles of the KCNN3 gene, which contains a highly polymorphic CAG repeat, and encodes a neuronal small conductance calcium-activated potassium channel, have recently been shown to be over-represented in sporadic cases of schizophrenia. In this report, we tested the hypothesis of an association between longer alleles of CAG repeat in the KCNN3 gene and schizophrenia in 20 families with clinical evidence for anticipation and in 151 unrelated schizophrenic cases. No significant difference in the distributions of allele frequencies was observed between familial cases of schizophrenia and controls, and between unrelated cases and controls. Furthermore, no intergenerational CAG repeat instability was detected in the 20 families. Our results do not support the involvement of the KCNN3 (hSKCa3) gene in the etiology of schizophrenia.

Mutations in the MDR3 gene cause progressive familial intrahepatic cholestasis

Class III multidrug resistance (MDR) P-glycoproteins (P-gp), mdr2 in mice and MDR3 in man, mediate the translocation of phosphatidylcholine across the canalicular membrane of the hepatocyte. Mice with a disrupted mdr2 gene completely lack biliary phospholipid excretion and develop progressive liver disease, characterized histologically by portal inflammation, proliferation of the bile duct epithelium, and fibrosis. This disease phenotype is very similar to a subtype of progressive familial intrahepatic cholestasis, hallmarked by a high serum gamma-glutamyltransferase (gamma-GT) activity. We report immunohistochemistry for MDR3 P-gp, reverse transcription-coupled PCR sequence analysis, and genomic DNA analysis of MDR3 from two progressive familial intrahepatic cholestasis patients with high serum gamma-GT. Canalicular staining for MDR3 P-gp was negative in liver tissue of both patients. Reverse transcription-coupled PCR sequencing of the first patient's sequence demonstrated a homozygous 7-bp deletion, starting at codon 132, which results in a frameshift and introduces a stop codon 29 codons downstream. The second patient is homozygous for a nonsense mutation in codon 957 (C --> T) that introduces a stop codon (TGA). Our results demonstrate that mutations in the human MDR3 gene lead to progressive familial intrahepatic cholestasis with high serum gamma-GT. The histopathological picture in these patients is very similar to that in the corresponding mdr2(-/-) mouse, in which mdr2 P-gp deficiency induces complete absence of phospholipid in bile.

Defect of multidrug-resistance 3 gene expression in a subtype of progressive familial intrahepatic cholestasis

Disruption of the murine mdr2 (multidrug-resistance) gene, which encodes a phosphatidylcholine flippase, leads to a hepatic disorder because of loss of biliary phospholipid secretion. Among the hereditary human cholestasis, a subtype of progressive familial intrahepatic cholestasis with high gamma-glutamyltranspeptidase (GGT) serum activity shares histological, biochemical, and genetic features with mice lacking mdr2 gene expression (mdr2 -/- mice). No MDR3 (human mdr2 homolog) messenger RNA (mRNA) was detected by Northern blotting in the liver of a patient suffering from this form of PFIC, and the biliary phospholipid level in a second patient was substantially decreased. Thus, the absence of the MDR3 P-glycoprotein may be responsible for this type of PFIC, which, as in the murine model, may be due to a toxic effect of bile acids on the biliary epithelium in absence of biliary phospholipids.

Construction of a 3.7-Mb physical map within human chromosome 20p12 ordering 18 markers in the Alagille syndrome locus

Alagille syndrome (AGS, MIM 118450) is associated with human chromosome band 20p12. To study this region, we constructed a 3.7-Mb physical map using 36 YACs isolated from the CEPH YAC library with three sequence-tagged sites (STS): D20S503, D20S41, and D20S188. New STSs were obtained from 6 isolated YAC end-fragments. Eighteen markers were ordered on the contig as follows:20ptel-D20S177-D20S175-D20S509- D20S5/D20S503-D20S506-D20S162-D20S504- D20S505-D20S507-D20S188-(D20S6-D20S27- D20S189)-D20S186-D20S41-D20S61-D20S492- D20S508-20pcen. A restriction map with the enzymes AscI, MluI, NotI, SacII, and SfiI was generated, revealing seven putative CpG islands. We established a YAC contig that spans the AGS region and thus will be valuable for cloning candidate genes and searching for DNA polymorphisms segregating with this syndrome.

Deleted chromosome 20 from a patient with Alagille syndrome isolated in a cell hybrid through leucine transport selection: study of three candidate genes

Alagille syndrome (AGS) is a well-defined genetic entity assigned to the short arm of Chromosome (Chr) 20 by a series of observations of AGS patients associated with microdeletions in this region. By fusing lymphoblastoid cells of an AGS patient that exhibited a microdeletion in the short arm of Chr 20 encompassing bands p11.23 to p12.3 with rodent thermosensitive mutant cells (CHOtsH1-1) deficient in-leucyl-tRNA synthetase, we isolated a somatic cell hybrid segregating the deleted human Chr 20. This hybrid clone, designated NR2, was characterized by several methods, including PCR, with eight pairs of oligonucleotides mapped to Chr 20: D20S5, D20S41, D20S42, D20S56, D20S57, D20S58, adenosine deaminase (ADA), and Prion protein (PRIP); Restriction Fragment Length Polymorphism (RFLP) analyses with four genomic anonymous probes (D20S5, cD3H12, D20S17, D20S18); and fluorescent in situ hybridization (FISH) with total human DNA and D20Z1, a sequence specific to the human Chr 20 centromere, as probes. The NR2 hybrid allowed us to exclude three candidate genes for AGS: hepatic nuclear factor 3 beta (HNF3 beta), paired box 1 (PAX1), and cystatin C (CST3) as shown by their localization outside of the deletion. The NR2 hybrid is a powerful tool for the mapping of new probes of this region, as well as for obtaining new informative probes specific for the deletion by subtractive cloning of the region. Such markers will be useful for linkage analysis and screening of cDNA libraries.

Segregation analysis of Alagille syndrome

Alagille syndrome (AGS) is a well defined genetic disorder characterised by five major features. An autosomal dominant mode of transmission with reduced penetrance has been suggested by the analysis of a limited number of families. However there has been no statistical analysis. We report here the first segregation analysis of AGS, using 33 families collected through 43 probands. Segregation analysis of these families allowed us to conclude that AGS is transmitted as a dominant disorder with 94% penetrance and 15% of cases are sporadic. The expressivity of the phenotype was variable and 26 persons (15 parents and 11 sibs) were identified as presenting minor forms of the disease. These results are valuable for genetic counselling.

Mapping of microsatellite markers in the Alagille region and screening of microdeletions by genotyping 23 patients

Alagille syndrome (AGS) has been assigned to 20p11.23-20p12.2 according to minimum overlap between deletions observed on the chromosome 20 short arm of 9 patients. We report here the localisation of 5 microsatellite markers (D20S41, D20S48, D20S50, D20S56, and D20S58) within the deletion of one AGS patient. This study allows an estimation of the genetic extent of this deletion as being between 30 and 36 cM, and demonstrates its paternal origin. The search for submicroscopic deletions in 23 AGS patients, by typing these 5 markers, failed to reveal allelic loss. However, these results lead to the proposition that the AGS locus lies in one of the seven intervals defined by the six microsatellite markers in the region flanked by D20S5 and D20S18.

Infantile neuropathy with unstable myelin: study of the P0 protein

An unusual form of hereditary motor and sensory neuropathy characterized by a prominent disruption of the myelin lamellae is reported. In addition to detailed morphological analysis, we investigated the protein P0, which is the major protein of peripheral myelin involved in adhesion. No major gene rearrangement and no differences in P0 protein expression were observed in the present case.

Screening of microdeletions of chromosome 20 in patients with Alagille syndrome

We report a cytogenetic and molecular study of a series of patients with Alagille syndrome. All 14 patients were studied with high resolution banding techniques and eight of them were also analysed with non-radioactive in situ hybridisation of the cosmid probe D20S6. Seven of these eight patients were also studied for allelic losses at the D20S6 locus. No microdeletion of chromosome 20 was found in this series.

Pelizaeus-Merzbacher disease: a valine to phenylalanine point mutation in a putative extracellular loop of myelin proteolipid

In the central nervous system, myelin proteolipid protein isoforms (PLP and DM20) play an essential structural role in myelination. It has been shown in several species that myelination is impaired by molecular defects resulting from single base mutations in the PLP gene. We have used DNA amplification by polymerase chain reaction to study the PLP gene coding regions from 17 patients in 15 unrelated families with similar Pelizaeus-Merzbacher phenotype. In one case amplification of peripheral nerve PLP/DM20 cDNAs revealed that a silent T----C transition was unrelated to the disease. In one family a nonsilent mutation was identified that leads to a phenylalanine substitution for valine-218 in PLP/DM20 proteins. We investigated the inheritance of the mutant allele in 19 subjects of this four-generation family and found a strict cosegregation of the Phe218 substitution with transmission and expression of the disease. The effect of the Val218----Phe mutation is discussed in the frame of a recently suggested topological model of PLP/DM20, according to which Val218 is part of an extracellular loop that connects the last two of four membrane-spanning alpha-helices.

Interstitial deletion of the short arm of chromosome 20 in arteriohepatic dysplasia (Alagille syndrome)

An autosomal dominant transmission of arteriohepatic dysplasia, or Alagille syndrome, with reduced penetrance and variable expressivity has been suggested from familial pedigrees, but the nature of the genetic defect and its chromosomal localization are not firmly established. We report the case of an 8-year-old boy with arteriohepatic dysplasia, in whom high-resolution chromosome study showed a partial deletion of the short arm of chromosome 20, which encompasses subbands p11.23 to p12.3. In situ hybridization and Southern blotting localized four restriction fragment length polymorphism probes within the deletion and another one distal to the deletion. Because one patient has already been reported to have arteriohepatic dysplasia and deletion of the short arm of chromosome 20, and six additional patients with such a deletion had major features of Alagille syndrome, this syndrome should now be assigned to chromosome 20p.