Brandão LAC, Guimarães RL, Carrera M, Milanese M, Segat L, Luiz de Lima-Filho J, Arraes LC, Crovella S. MBL2 Functional Allelic Variants and Increased Risk for the Development of Atopic Dermatitis in Brazilian Children. Arch Dermatol. 2008;144(3):412-413. doi:10.1001/archderm.144.3.412
Atopic dermatitis (AD) is a chronic inflammatory skin disease.
Patients with AD have a cutaneous immune defect, and innate immunity has been suggested to play a possible role in the cause of AD.1
Mannose-binding lectin (MBL) is an important molecule of the immune system able to activate the complement system and induce phagocytosis.
Deficiencies of MBL have been associated with increased susceptibility to infections, autoimmunity, and other diseases.2
In the present article, we analyze functional allelic variants in the MBL2 gene (GenBank 4153) (namely, allele A/0
in exon 1 and H/L and X/Y in the promoter) in 165 Brazilian children with AD and adult controls. Our aim was to investigate an association between MBL defective-producer genotypes and susceptibility to develop AD.
We enrolled 165 children with AD (84 boys and 81 girls; median age, 7 years; age range, 2-12 years) at the dermatologic day hospital of the Instituto Materno Infantil do Pernambuco, Recife, Brazil. Clinical diagnosis and disease severity were assessed by using the SCORAD index.3 We also recruited as controls 165 healthy adult blood donors (83 men and 82 women; median age, 31 years; age range, 18-49 years) from the same geographical area as the pediatric patients with AD. In responses to a questionnaire completed in the presence of a clinician, the control subjects reported no dermatologic problems. Informed consent was obtained from patients (or their parents)
DNA was extracted from peripheral blood following standard procedures.
Genotyping of MBL2 exon 1 was performed by melting temperature assay using specific primers (forward 5′-GGCTTCCCAGGCAAAGATG-3′;
reverse 5′- AGCCCAACACGTACCTGGTT-3′) and SYBR Green I reagents (Applied Biosystems, Foster City, California). Melting curve profiles were obtained by using the dissociation software of the ABI 7900 HT (Applied Biosystems).
For the promoter H/L and X/Y allelic variants, we developed 2 allele-specific polymerase chain reactions using the following primers:
(1) for H/L, we used 5′-TGCTTCCCCTTGGTGTTTTTAC-3′ and 5′-TGCTTCCCCTTGGTGTTTTTAG-3′ as reverse allele-specific primers and 5′-GCCAGGGCCAACGTAGTAAG-3′ as the common forward primer; (2) for X/Y, we used 5′-CTGGAAGACTATAAACATGCTTTC-3′
and 5′-CTGGAAGACTATAAACATGCTTTG-3′ as the reverse allele-specific primers and 5′-CCGAAGAGGACATGGAGAGA-3′ as the common forward primer. Allelic variants in the MBL2 exon 1 and promoter regions were double checked by direct sequencing.
The 3 MBL2 exon 1 allelic variants (at positions 52, 54, and 57) were grouped together into 1 category (allele 0) because they have a similar functional effect on serum MBL levels,4 while the combination of 3 wild-type alleles were grouped as allele A.
Allele and genotype frequencies were calculated by direct gene counting. The Fisher exact test was used for pairwise comparison using 2 × 2 and 3 × 2 contingency tables.
Haplotype and linkage disequilibrium were estimated using downloadable Arlequin software, version 3.01 (http://cmpg.unibe.ch/software/arlequin3/, hosted by University of Geneva, Geneva, Switzerland).
The results of our analysis are summarized in Table 1 and Table 2. We genotyped the 3 exon 1 MBL2 allelic variants and the H/L and X/Y promoter variants in 165 children with AD and 165 adult controls and compared them. The 0 allele occurred significantly more frequently in patients with AD (P<.001) (odds ratio [OR], 2.42; 95% confidence interval [CI],1.68-3.50). This is reflected in genotype frequencies, where genotype 00 was seen significantly more frequently in patients with AD than in controls (P<.001).
We then computed MBL genotypes considering also the promoter variants H/L and X/Y. Resulting genotypes were then ranked into 3
classes according to MBL production as high (HP), low (LP), and deficient (DP).2 The HP genotype was seen significantly more frequently in controls than in patients with AD. The DP genotype was found more frequently in patients than in controls (P<.001). In addition, the globally considered combination defective producers category (LP plus DP) was also more common among patients than controls (P<.05). Promoter and exon 1 single-nucleotide allelic variations were, as expected,
found to be in linkage disequilibrium in both patients and controls.
An association between undetectable MBL levels and recurrent cutaneous abscesses, pruritus, and AD has already been described.5 While Hashimoto et al6 did not find an association between the MBL2 allelic variant at codon 54 and susceptibility to AD in Japanese patients, our findings clearly demonstrate that MBL2 allele 0, responsible for defective MBL protein levels as well as the MBL2 00 genotype, occurs significantly more frequently in children with AD than in healthy adults (OR, 2.42).
The H/L and X/Y allelic variants influence protein expression as well. Genotyping H/L and X/Y allelic variants allowed us to characterize MBL-deficient genotypes that are found more frequently in patients with AD than in controls.
While the role of MBL in the development of AD is still debated in the literature, we were able to demonstrate that the presence of an MBL-defective producer genotype is associated with an increased susceptibility to AD in Brazilian children.
Correspondence: Dr Segat, Genetic Unit, Department of Reproduction and Development Sciences, University of Trieste, Via dell'Istria 65/1, 34100 Trieste, Italy (email@example.com).
Financial Disclosure: None reported.
Funding/Support: This study was supported by a FACEPE grant (Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco, Recife, Brazil) (Dr Crovella)
and by grant RC2007 from Children's Hospital Burlo Garofolo, Trieste,
Italy (Dr Crovella).