No abstract

The nature of subtypes in schizophrenia and the meaning of heterogeneity in schizophrenia have been considered a principal controversy in psychiatric research. We addressed these issues in periodic catatonia, a clinical entity derived from Leonhard's classification of schizophrenias, in a genomewide linkage scan. Periodic catatonia is characterized by qualitative psychomotor disturbances during acute psychotic outbursts and by long-term outcome. On the basis of our previous findings of a lifetime morbidity risk of 26.9% of periodic catatonia in first-degree relatives, we conducted a genome scan in 12 multiplex pedigrees with 135 individuals, using 356 markers with an average spacing of 11 cM. In nonparametric multipoint linkage analyses (by GENEHUNTER-PLUS), significant evidence for linkage was obtained on chromosome 15q15 (P = 2.6 x 10(-5); nonparametric LOD score [LOD*] 3.57). A further locus on chromosome 22q13 with suggestive evidence for linkage (P = 1.8 x 10(-3); LOD* 1.85) was detected, which indicated genetic heterogeneity. Parametric linkage analysis under an autosomal dominant model (affecteds-only analysis) provided independent confirmation of nonparametric linkage results, with maximum LOD scores 2.75 (recombination fraction [theta].04; two-point analysis) and 2.89 (theta =.029; four-point analysis), at the chromosome 15q candidate region. Splitting the complex group of schizophrenias on the basis of clinical observation and genetic analysis, we identified periodic catatonia as a valid nosological entity. Our findings provide evidence that periodic catatonia is associated with a major disease locus, which maps to chromosome 15q15.

Serotonin receptor type 3 is a ligand-gated ion channel implicated in behavioural disorders. Our objective was to identify nucleotide variants in a specific portion of the 5' region of the serotonin receptor gene (HTR3A) containing upstream open reading frames (uORFs) and to investigate their effect on bipolar disease. Mutations in uORFs have been recently shown to cause disease by changing expression on the translational level. We identified one polymorphism, C195T, and one missense mutation, C178T (Pro16Ser) within an upstream open reading frame. No significant association was found between the C195T polymorphism and bipolar affective disorder. A significant association was, however, found between the variant C178T in 156 patients with bipolar disorder compared to 156 healthy controls (P = 0.00016). To investigate the relevance of this variant on gene expression, luciferase reporter constructs containing the C178T (Pro16Ser) allele were established and compared to the C178T plus C195T and wild-type alleles. Reporter constructs containing the C178T (Pro16Ser) allele drove 245% and 138% expression compared to the wild-type allele. These findings show that the C178T(Pro16Ser) variant in HTR3A may represent a functional variant and affect the susceptibility to bipolar disorder.

Previously reported linkage of bipolar affective disorder to DNA markers on chromosome 18 was reexamined in a large sample of German bipolar families. Twenty-three short tandem repeat markers were investigated in 57 families containing 103 individuals with bipolar I disorder (BPI), 26 with bipolar II disorder (BPII), nine with schizoaffective disorder of the bipolar type (SA/BP), and 38 individuals with recurrent unipolar depression (UPR). Evidence for linkage was tested with parametric and non-parametric methods under two definitions of the affected phenotype. Analysis of all 57 families revealed no robust evidence for linkage. Following previous reports we performed separate analyses after subdividing the families with respect to the sex of the transmitting parent. Fourteen families were classified as paternal and 12 families as maternal. In 31 families the parental lineage of transmission of the disease could not be determined ('either' families). Evidence for linkage was obtained for chromosomal region 18p11.2 in the paternal families and for 18q22-23 in the 'either' families. The findings on 18p11.2 and 18q22-23 support prior evidence for susceptibility loci in these regions. The parent-of-origin effect on 18p11.2 is confirmed in our sample. The delineation of characteristics of 'either' families requires further study.Although the etiology of bipolar affective disorder is unknown, strong support for an important genetic component comes from the results of family, twin, and adoption studies. 1 Linkage studies of bipolar disorder to date have provided suggestive evidence in favor of locus heterogeneity. Promising chromosomal regions suggested by recent linkage studies include regions on chromosome 18.Berrettini et al 2 first reported linkage of bipolar disorder to a region near the centromere on chromosome 18p in 22 families using the affected-sib-pair (ASP) method and the affected-pedigree-member (APM) method. Parametric LOD score analysis of all 22 families revealed negative LOD scores. However, individual families yielded LOD scores Ͼ1 assuming dominant or recessive genetic models. Confirmatory evidence for a bipolar susceptibility locus in this chromosomal region was found by Stine et al. 3 Both parametric LOD score analysis and ASP analysis supported linkage in their study of 28 families. In addition, the same study reported a second susceptibility locus on the long arm of chromosome 18 (18q21). Interestingly, linkage to loci on both 18p and 18q was strongest in those families, in which the father or one of the father's siblings was affected, suggesting a parent-of-origin effect operating in bipolar disorder. Gershon et al 4 re-analyzed the 18p marker data of Berrettini et al 2 by the sex of the transmitting parent. Although no kindred with limited paternal transmission was observed, ASP analysis yielded highly significant excess allele sharing in the pedigrees with mixed maternal-paternal transmission (in different pedigree branches) but not in pedigrees with exclusively maternal transmission confirmin...

The dopamine transporter (DAT) plays a central role in dopaminergic neurotransmission in the human brain. Genetic association studies have used a variable number of tandem repeat (VNTR) polymorphism in the 3Ј-flanking region of the dopamine transporter gene (DAT1) to implicate the DAT in the development of various neuropsychiatric disorders. In this study, we have examined the possibility that a mutation exists in the coding region of the DAT1 gene which through linkage disequilibrium accounts for the observed associations. The complete coding region, as well as exon-intron boundaries, was screened in 91 unrelated individuals including 45 patients with bipolar affective disorder and 46 healthy control individuals by the means of single strand conformation analysis. Our findings suggest that the DAT1 gene is highly conserved since we detected only two rare missense substitutions (Ala559Val, Glu602Gly) and three silent mutations (242C/T, 1342A/G, and 1859C/T) in the whole coding region. Five sequence variants were observed in intronic sequences but none affects known splice sites. The lack of frequent variants of possible functional relevance indicates that genetic variation in the coding region of the DAT1 gene is not responsible for the previously observed associations with neuropsychiatric disorders. The two rare missense substitutions were found in single bipolar patients but not in controls. Investigation of the patients' families revealed independent segregation between the Ala559Val variant and affective disorder. The Glu602Gly variant was inherited by the proband from an affected father. It therefore remains possible that Glu602Gly may be a rare cause of bipolar affective disorder. Molecular Psychiatry (2000) 5, 275-282.