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Frequency and distribution of FCN2 and FCN3 functional variants among MBL2 genotypes

Helga Bjarnadottir1, Margret Arnardottir2,3, Bjorn Runar Ludviksson2,3

  • 1Department of Immunology, Landspitali-The National University Hospital of Iceland, Hringbraut (Building 14 at Eiriksgata), 101, Reykjavik, Iceland. hbjarna@landspitali.is.

Immunogenetics
|January 23, 2016
PubMed

Insights

Mannan-binding lectin (MBL) deficiency may be compensated by other lectin pathway pattern recognition molecules (PRMs). Ficolin variants FCN2+6424 and FCN3+1637delC were investigated. MBL-deficient individuals rarely carried the FCN2+6424 variant, suggesting compensation.

Area of Science:

  • Immunology
  • Complement System
  • Genetic Epidemiology

Background:

  • The lectin pathway (LP) of complement activation relies on pattern recognition molecules (PRMs) like collectins and ficolins.
  • Mannan-binding lectin (MBL) deficiency is common, yet clinical consequences are mild, suggesting compensatory mechanisms.
  • Ficolin-2 (encoded by FCN2) and Ficolin-3 (encoded by FCN3) are other LP PRMs whose reduced levels are associated with specific genetic variants.

Purpose of the Study:

  • To investigate the hypothesis that specific variants in FCN2 and FCN3 genes are rare in MBL-deficient individuals due to compensatory roles within the LP.
  • To determine the frequency of FCN2+6424 and FCN3+1637delC variants in relation to MBL2 genotypes in healthy subjects.

Main Methods:

  • Genotyping of MBL2, FCN2+6424, and FCN3+1637delC variants in a cohort of 498 healthy individuals.
  • Analysis of allele frequencies and comparison between MBL-deficient and MBL-sufficient subgroups.
  • Assessment of combined effects of MBL deficiency and ficolin variants.

Main Results:

  • The allele frequencies for FCN2+6424 and FCN3+1637delC were 0.099 and 0.015, respectively.
  • The FCN2+6424 variant tended to be less frequent in MBL-deficient individuals (0.047) compared to MBL-sufficient individuals (0.106), P=0.057.
  • Individuals homozygous for FCN2+6424 or carrying combined heterozygous ficolin variants were sufficient MBL producers; FCN3+1637delC frequency did not differ between groups.

Conclusions:

  • The FCN2+6424 variant appears to be rare in MBL-deficient healthy individuals, supporting a compensatory role for ficolin-2.
  • MBL-deficient individuals with additional LP PRM defects may face an increased risk of morbidity.
  • Further research is warranted to elucidate the clinical implications of combined LP PRM deficiencies.
Keywords:
ComplementFCN2 + 6424FCN3 + 1637delCFicolin-2Ficolin-3Lectin pathwayMASP-2MBL2 genotypesMannan-binding lectinRedundancy

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