A mannosyltransferase gene at 11q23 is disrupted by a translocation breakpoint that co-segregates with bipolar affective disorder in a small family
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Bipolar affective disorder (BPAD) is a complex neuropsychiatric disease characterized by extreme mood swings. Genetic influences affect the disease susceptibility substantially, yet the underlying mechanisms are unknown. We previously described a pedigree in which all five individuals with BPAD and one individual with recurrent major depression were carriers of a reciprocal chromosomal translocation t(9;11)(p24;q23). Gene content analyses of the breakpoint junctions revealed disruption of a gene (DIBD1) at 11q23, a genomic region that has also been implicated in schizophrenia and Tourette syndrome. DIBD1 is predicted to encode a mannosyltransferase similar to Saccaromyces cerevisiae Alg9p of the protein N-glycosylation pathway. The inborn errors of protein N-glycosylation cause congenital disorders of glycosylation in humans. DIBD1 shows uniform expression in the tested subregions of the brain by Northern analysis. Sequence analysis revealed four intra-genic single nucleotide polymorphisms. The valine residue at V289I was conserved in other eukaryotic species, whereas its frequency was approximately 65% in humans. We performed linkage and linkage disequilibrium analyses in two NIMH bipolar pedigree series using four tightly linked simple tandem repeat polymorphisms (STRPs) and the V289I. These analyses overall failed to support a role for DIBD1 in disease susceptibility. The most-significant finding was a lod score of 1.18 (P=0.0098), obtained by an intronic STRP D11S5025, in the subset of 22 multiplex pedigrees. In conclusion, we found that a mannosyltransferase gene at 11q23 is disrupted by a translocation breakpoint co-segregating with BPAD in a family. However, its role in the disease susceptibility remains unconfirmed.
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