ARTICLE
Auteur(s) : Huseyin OnayHuseyin Onay1,
Mustafa Pehlivan2, Sibel Alper3, Ferda
Ozkinay1,4, Sacide Pehlivan1,5
1Department of Medical Genetics, Faculty of Medicine,
Ege Universitesi, 35100, Bornova Izmir, Turkey
2Department of Internal Medicine, Ataturk Education and
Research Hospital, Izmir, Turkey
3Department of Dermatology, Faculty of Medicine, Ege
University, Izmir, Turkey
4Department of Pediatrics, Faculty of Medicine, Ege
University, Izmir, Turkey
5Department of Biology, Faculty of Science, Ege
University, Izmir, Turkey
accepté le 20 Decembre 2006
Vitiligo is a skin disorder with progressive depigmentation of the
skin. It effects approximately 2% of the world’s population,
without preference for a specific skin tone or gender [1]. Although
the exact etiology of vitiligo has not yet been established, the
abnormal immune responses frequently observed in vitiligo patients
have led to suggestion that, in some cases, the condition has an
autoimmune component [2].Mannose binding lectin (MBL) is a calcium
dependent lectin that plays an important role in innate immunity by
activating the classical complement pathway and phagocytosis. One
of the functions of MBL is modulation of the inflammation [3]. The
structure and the biological properties of MBL resemble those of
C1q in the complement pathway [4]. MBL activates complement via the
MBL associated serine protease (MASP) [5]. There are wide
variations in serum MBL levels in humans due to genomic
polymorphisms in the MBL2 gene. The single nucleotide polymorphisms
[codon 52 (allele D), codon 54 (allele B), codon 57 (allele C),
normal (allele A)] in exon 1 of the MBL2 gene disrupt the assembly
of MBL trimers or accelerate the degradation of the protein. MBL
protein concentrations decrease by about 10 times in individuals
with the heterozygote phenotype whereas no protein could be
detected in homozygous or compound heterozygous state [6]. As a
consequence, functional MBL decreases in the circulation and this
causes predisposition to infections and autoimmune diseases [6]. In
the literature the relationships between serum MBL concentration
and autoimmune diseases (such as Systemic Lupus Erythematosus (SLE)
[7], dermatomyositis (DM) [8], Sjögren’s Syndrome (SJS) [9] and
rheumatoid arthritis (RA) [10] were investigated. All these studies
showed that the frequencies of MBL2 gene polymorphisms were higher
in SLE, DM, SJS, RA patient groups compared to control groups.The
aim of this study was to examine any association between the MBL2
gene variants and vitiligo.
Materials and methods
Codon 54 (allele B) and codon 57 (allele C) polymorphisms in the
exon 1 of the MBL2 gene, were investigated in samples belonging to
50 healthy controls and 40 patients diagnosed as having vitiligo in
the Department of Dermatology, Medical School Hospital, Ege
University, Izmir/Turkey. Analysis of the MBL2 gene at the
polymorphic sites 54 and 57 was performed after amplification of
exon 1. Polymerase Chain Reaction (PCR) was performed using forward
(5’-TAG GAC AGA GGG CAT GCT C-3’) and reverse (5’-CAG GCA GTT TCC
TCT GGA AGG-3’) primers in a 25 μl volume containing 50 ng DNA, 2
mM dNTPs, 2 nmol of each primer, 1.5 mM MgCl2 and 3U Taq
polymerase. The 349 bp PCR product was digested with restriction
enzymes Ban I and Mbo II to identify codon 54 and codon 57
variants, respectively. Ban I digestion was performed at
50 °C for 60 minutes with 5 U enzyme and Mbo II
digestion was performed at 37 °C for 90 minutes
with 3.5 U enzyme. After enzyme digestion, products were visualized
by electrophoresis on 2% agarose gel. The DNA fragments of patients
and normal controls on agarose gel electrophoresis are illustrated
in figure 1.
Results
Codon 57 polymorphism was not detected in any subject from either
group. MBL2 codon 54 genotype and allele frequencies are given in
Table 1. B allele frequency was
significantly higher in the patient group (20%) compared to the
control group (3%). AB genotype was found 35% and 6% in the patient
group and the healthy control group, respectively. The difference
was statistically significant. AA genotype was found to be 62% and
94% in patient group and healthy control group, respectively. The
frequency of AA genotype was significantly lower in the patient
group.
Table 1 Comparison of the MBL2 codon 54 genotype and
allele frequencies between patients with vitiligo and control
subjects
|
MBL2
|
Vitiligo patients n (%)a
|
Control n (%)b
|
Chi-Square test p
|
|
Genotypes
|
|
|
|
|
AA
|
25 (62.5)
|
47 (94)
|
|
|
AB
|
14 (35)
|
3 (6)
|
0.001
|
|
BB
|
1 (2.5)
|
–
|
|
|
AB+BB
|
15 (37.5)
|
3 (6)
|
|
|
Alleles
|
|
|
|
|
A
|
64 (80)
|
97 (97)
|
0.0001
|
|
B
|
16 (20)
|
3 (3)
|
|
|
na = 40, nb = 50
|
Discussion
The etiology of vitiligo has not yet been established, the abnormal
immune responses frequently observed in vitiligo patients have led
to the suggestion that, in some cases, the condition has an
autoimmune component [2].
MBL, as one of the key molecules in innate immunity, is involved
in the first line defense mechanism before antibody production [11,
12]. It has been suggested that MBL has four functions in the host
defense. These functions are: 1) complement activation, 2)
opsonophagocytosis, 3) Modulation of inflammatory response 4) the
promotion of apoptosis [13]. Recently there have been a number of
reports showing an association between MBL deficiency and increased
susceptibility to autoimmune diseases such as systemic lupus
erythematosus (SLE) [4, 14], dermatomyositis [8] and cutaneous
lupus erythematosus [8]. Senaldi et al. reported that patients with
SLE had a higher frequency of low levels of MBL than controls [7].
The frequency of the MBL B allele was found to be significantly
higher in British SLE patients [14]. Low MBL concentration was
found to be very strongly associated with adult dermatomyositis
[8]. In a recent report it was shown that absence of the MBL
protein increased the prevalence of RA [10]. Tsutsumi et al. stated
that a homozygous mutation of the MBL2 gene might be associated
with increased risk of having autoimmune disorders, especially SLE
and SJS [4]. Werth et al. hypothesized the role of MBL in the
pathophysiology of the autoimmune diseases. Defects in the
clearance of apoptotic cells substantially contribute to triggering
autoimmune responses and MBL is one of the proteins shown to be
involved in the clearance of apoptotic cells [8]. MBL has also been
shown to be involved in controlling proinflammatory cytokines,
clearance of immune complexes and adhesion molecules on
inflammatory cells, thus making it particularly relevant in
cutaneous autoimmunity [8, 15]. It is known that there is a
perturbed calcium homeostasis in vitiliginous melanocytes, as
defective calcium uptake has been demonstrated in both keratinocyte
cell cultures [16] and melanocytes from vitiliginous skin [17]. It
may be hypothesized that in vitiligo patients who carry MBL2 gene
polymorphisms, perturbed calcium homeostasis could cause decreased
MBL concentration, because MBL is a calcium dependent lectin.
Therefore it may also be considered that the normal MBL allele
plays a protective role in susceptibility to vitiligo.
Conclusion
This is the first time in the literature that an association
between MBL2 gene polymorphisms and vitiligo has been investigated.
We found B allele frequency to be significantly higher in the
patient group. This finding has led us to consider that codon 54
polymorphism in the MBL2 gene may play a role in susceptibility to
vitiligo.
Acknowledgements
Financial support: none. Conflict of interest: none.
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