Bipolar and panic disorders may be associated with hereditary defects in the innate immune system.

Background: Mannan-binding lectin (MBL) and mannan-binding lectin-associated serine protease-2 (MASP-2) represent important arms of the innate immune system, and different deficiencies may result in infections or autoimmune diseases. Both bipolar and panic disorders are associated with increased inflammatory response, infections and mutual comorbidity. However, associations with MBL, MASP-2 or the gene, MBL2, coding for MBL, have not been investigated thoroughly.

Methods: One hundred patients with bipolar disorder, 100 with panic disorder and 349 controls were included. Serum concentrations of MBL and MASP-2 were measured and seven single nucleotide polymorphisms (SNPs) influencing these concentrations were genotyped. Disease association with genetic markers and serum levels were investigated.

Results: In panic disorder, we observed a large proportion (30%) of MBL deficient (<100ng/ml) individuals and significantly lower levels of MBL and MASP-2 plus association with the MBL2 YA two-marker haplotype. Bipolar disorder was associated with the MBL2 LXPA haplotype and lower MASP-2 levels.

Limitations: No information on course or severity of disorders was included, and only MBL and MASP-2 were measured, excluding other components from the complement pathway. Restrictions defined by ethnical committees preclude information of control׳s ethnic origin.

Conclusions: Significant differences in MBL and MASP-2 concentrations were observed between cohorts, especially an intriguing finding associating panic disorder with MBL deficiency. These differences could not be fully explained by allele or haplotype frequency variations. Since MBL deficiency is highly heterogeneous and associated with both infectious and autoimmune states, more research is needed to identify which complement pathway components could be associated with bipolar respectively panic disorder.