A study of patients with suspected immunodeficiency found a higher number of homozygous and compound heterozygous patients with abnormal mannan-binding protein (MBP) alleles (variants B, C, and D). In the case group of 227 patients, 12 patients were homozygous for B and 6 were compound heterozygous for B/C or B/D. One patient in the control population of 123 patients was homozygous or compound heterozygous.