CACNA1C SNP rs1006737 associates with bipolar I disorder independent of the Bcl-2 SNP rs956572 variant and its associated effect on intracellular calcium homeostasis

Objectives. Intracellular calcium (Ca²⁺) dyshomeostasis (ICDH) has been implicated in bipolar disorder (BD) pathophysiology. We previously showed that SNP rs956572 in the B-cell CLL/lymphoma 2 (Bcl-2) gene associates with elevated B lymphoblast (BLCL) intracellular Ca²⁺ concentrations ([Ca²⁺]_B) differentially in BD-I. Genome-wide association studies strongly support the association between BD and the SNP rs1006737, located within the L-type voltage-dependent Ca²⁺ channel α1C subunit gene (CACNA1C). Here we investigated whether this CACNA1C variant also associates with ICDH and interacts with SNP rs956572 on [Ca²⁺]_B in BD-I. Methods. CACNA1C SNP rs1006737 was genotyped in 150 BD-I, 65 BD-II, 30 major depressive disorder patients, and 70 healthy subjects with available BLCL [Ca²⁺]_B and Bcl-2 SNP rs956572 genotype measures. Results. SNP rs1006737 was significantly associated with BD-I. The [Ca²⁺]_B was significantly higher in BD-I rs1006737 A compared with healthy A allele carriers and also in healthy GG compared with A allele carriers. There was no significant interaction between SNP rs1006737 and SNP rs956572 on [Ca²⁺]_B. Conclusions. Our study further supports the association of SNP rs1006737 with BD-I and suggests that CACNA1C SNP rs1006737 and Bcl-2 SNP rs956572, or specific causal variants in LD with these proxies, act independently to increase risk and ICDH in BD-I.