Copy number variants encompassing Mendelian disease genes in a large multigenerational family segregating bipolar disorder

Abstract

Background: Bipolar affective disorder (BP) is a common, highly heritable psychiatric disorder characterized by periods of depression and mania. Using dense SNP genotype data, we characterized CNVs in 388 members of an Old Order Amish Pedigree with bipolar disorder. We identified CNV regions arising from common ancestral mutations by utilizing the pedigree information. By combining this analysis with whole genome sequence data in the same individuals, we also explored the role of compound heterozygosity.

Results: Here we describe 541 inherited CNV regions, of which 268 are rare in a control population of European origin but present in a large number of Amish individuals. In addition, we highlight a set of CNVs found at higher frequencies in BP individuals, and within genes known to play a role in human development and disease. As in prior reports, we find no evidence for an increased burden of CNVs in BP individuals, but we report a trend towards a higher burden of CNVs in known Mendelian disease loci in bipolar individuals (BPI and BPII, p = 0.06).

Conclusions: We conclude that CNVs may be contributing factors in the phenotypic presentation of mood disorders and co-morbid medical conditions in this family. These results reinforce the hypothesis of a complex genetic architecture underlying BP disorder, and suggest that the role of CNVs should continue to be investigated in BP data sets.

Figure 1

Flowchart outlining the quality control and analysis pipeline of this study. SNP data from the control and Old Order Amish populations was used to call CNVs using the PennCNV program. The pedigree structure in the Amish allowed family based calls to be made, and the CNV frequency in the control data allowed us to determine whether the Amish CNV calls were common, rare, or exclusive to the Amish population. We sought to determine CNVs in bipolar individuals, burden in individuals, and CNVs in disease loci. In addition, we utilized the whole genome sequence data to find CNVs and SNPs within the same gene in the same individual.

Figure 2

Location of CNV Regions, burden of rare CNVs, and disease genes. CNV regions are shown as red and green lines (green: heterozygous duplication, dark green: homozygous duplication, red: heterozygous deletion, dark red: homozygous deletion). Stacked histogram bars represent the location of specific rare CNVs, and the number, split by phenotype (green background: duplications, red background: deletions; dark grey: bipolar, mid-grey: unknown, light grey: unaffected). Inner line plot (blue) shows location and number of disease genes. Genes of interest are labeled around the outside of the plot.