Several common mutations (listed below) of the MBL2 gene can lead to a condition called mannose-binding lectin deficiency. People with this condition have low levels of mannose-binding lectin and may be susceptible to recurrent infections. Mannose-binding lectin deficiency is thought to affect approximately 5 to 10 percent of people worldwide; however, many affected individuals have no signs or symptoms related to low mannose-binding lectin levels. In addition, the mode of inheritance (dominant or recessive) is unclear. Therefore, this is not a Mendelian condition, and it is important to note that people (only) inherit an increased risk of developing mannose-binding lectin deficiency, and do not inherit the condition itself.GHR
The infectious conditions associated with MBL2 deficiency, discussed in detail in OMIM, may be summarized as follows:
- HIV infection; perhaps 10 fold higher risk for homozygous (minor) compared to homozygous (major)
- Meningococcal disease; about 4 fold higher risk for homozygotes
- Tuberculosis; heterozygotes seems to have a lower risk than either homozygote
- Lung infections in cystic fibrosis patients; generally worse in carriers of one or two MBL2 variant alleles
- Vascular disease; about 4 fold higher risk for double minor homozygotes at the three major variants
- Cardiovascular disease (arterial thrombosis) in systemic lupus erythematosus (SLE) patients; perhaps 7 fold higher risk
The three most common MBL2 gene variants studied are:
- rs1800450, aka Gly54Asp, G54D or the "B" allele
- rs1800451, aka Gly57Glu, G57E or the "C" allele
- rs5030737, aka Arg52Cys, R52C or the "D" allele
The A allele refers to the wildtype alleles at these three SNPs; in papers about the MBL2 gene, generally the "O" allele refers to a haplotype consisting of one or more of the B, C and D alleles.
A variant in the promoter region known as c.-221G>C (rs7096206) has also been associated with MBL2 deficiency, together with or independently of the B/C/D variants.