Mannan-binding lectin deficiency increases the risk of recurrent infections in children with Down's syndrome.

Down syndrome (DS) is the most frequent cause of intellectual disability worldwide. DS individuals present abnormalities in the immune system that include high susceptibility to recurrent infections (RI) as well as to autoimmune diseases. Respiratory tract infections remain one of the major causes of death in DS individuals. Mannan-binding lectin (MBL) functions as an opsonina and initiates the lectin complement pathway. MBL deficiency was shown to increase the susceptibility to different infectious diseases, notably by extracellular pathogens. In the present study, MBL circulating levels were evaluated in 150 children with DS from Brazil, to clarify whether MBL deficiency is associated with the presence of RI in these patients. According to the clinical history 30.7% (46/150) of the DS children experienced RI, and MBL deficiency was seen in 34.8% (16/46) of them compared with 13.5% (14/104) of the DS children without RI (p = 0.005, odds ratio = 3.43, 95% confidence interval = 1.5-7.85). Moreover, MBL deficiency was significantly associated with the occurrence of pneumonia when compared with DS without RI (37.5%, 12/32 vs. 13.5% 14/104, p = 0.005, odds ratio = 3.68, 95% confidence interval = 1.5-6.95). These findings demonstrated that MBL deficiency increases the susceptibility to RI in DS patients and that, in the future, they could potentially benefit from MBL therapy.