Accepted date: September 28, 2010; Published date: September 30, 2010
Citation: C Li, Luo Q, Li XM, Zhang XB, Han CL, et al. (2010) Filaggrin Mutations are Associated with Ichthyosis Vulgaris in the Southern Chinese Population. J Clin Exp Dermatol 1:102. doi: 10.4172/2155-9554.1000102
Copyright: © 2010 C Li, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Background: Filaggrin (FLG) plays an important role in the epidermal barrier function, which identi fi ed in patients with ichthyosis vulgaris (IV).
Objective: To study the genetics of FLG mutations in Southern Chinese patients with IV.
Methods: We evaluated the in fl uence of fi ve mutations (3321 delA, 441delA, 1249 insG, E1795X and S3296X) in a cohort of 65 IV Chinese patients and in 100 control individuals using the Sequenom ® MassARRAY ® system.
Results: The null allele frequency of 3321delA was 52.31 % (34/65). FLG mutation 441delA was only found in one IV patients. FLG mutations 1249insG, E1795X and S3296X were not found in these patients.
Conclusions: These fi ndings show that the mutation 3321delA represent the most frequent genetic cause in Southern Chinese IV patients. Our fi ndings con fi rm and extend the knowledge of the in fl uence of FLG mutations in IV.
Ichthyosis vulgaris; Southern chinese population; Filaggrin; Mutations; Polymorphism
IV (OMIM 146700) is the most common ichthyosis with an estimated prevalence of 1:250–1000, and is inherited in a semidominant pattern . Patients have light grey scaling, keratosis pilaris, increased palmoplantar markings and associated atopic manifestations. Involvement is generally mild and may vary greatly with climate and humidity. There is reduced or absence of keratohyalin granules in the epidermis.  In addition, there is a decrease or absence of profilaggrin, a major component of keratohyalin granules [3,4].
FLG is coding gene is located in the epidermal differentiation complex on chromosome 1q21 . Recently, mutations in the FLG have been shown to be a major risk factor for IV and atopic dermatitis (AD) [5,6]. The association of FLG mutations with IV in Northern European, Japanese, Bangladeshi, Korean, Taiwanese and Singaporean Chinese populations and has been confirmed in subsequent studies [7-17]. To date, more than different 20 mutations have been identified in different populations, all leading to a filaggrin deficiency. FLG mutations 3321delA, 441delA, 1249insG, E1795X and S3296X have been previously reported, from Asia including China, Japan, Korea, Taiwan . In this study, we identified five FLG mutations 3321delA, 441delA, 1249 insG, E1795X and S3296X in Southern Chinese IV patients.
Cases and controls
DNA samples from 65 IV were of Southern China origin and were recruited with ethical approval and had given their informed consent. The study was conducted according to the principles of the Declaration of Helsinki and all applicable local regulations related to protection of human subjects. The institutional review boards of the respective institutions approved the study. DNA samples from 100 healthy volunteers were available to serve as controls.
Genomic DNA was extracted from peripheral blood using standard techniques. All SNPs were genotyped by MassARRAY™ system (Sequenom, San Diego, CA, http://www.sequenom.com/). The iPLEX™ assay was followed according to manufacturers instructions (http://www.sequenom.com/) using 10 ng of genomic DNA. The primer sequences are available upon request (primer sequences in Table 1).
|Mutations||Polymerase chain reaction primer 1 sequence||Polymerase chain reaction primer 2 sequence||Extension primer sequence|
|3321del E1795X 1249 insG 441 delA S3296X||ACGTTGGATGATCAGCAGAGCCACCAAGAG ACGTTGGATGAGCACTGGAGGAAGACAAAG ACGTTGGATGGGCAAGCTTCATCTGCAGTC ACGTTGGATGCCCTCAAGTCTGGAAAGAAG ACGTTGGATGTGCATCATCCCATGAACAGG||ACGTTGGATGACCTGGTAGATGAAAGACCC ACGTTGGATGATGGTGTCCTGACCCTCTTG ACGTTGGATGTGAATGTCCCTCACTGTCAC ACGTTGGATGTTCAGAACTAGATTCATGCC ACGTTGGATGTGTCTGCTGACTGCTGGTG||TCCAGACCTTCCCCC TGTCTCGTGCCTGCT GCCTGACTACCGCTAG TCATGCCTTTTCCCCCC GTGTCTCTCTCCTGGACTT|
Table 1: Primer Sequences for all 5 FLG mutations Using iPlex Chemistry on a MassARRAY Platform.
Genotype frequencies between cases and controls were using the the continuity-adjusted chi-square test. The reported P-values are the results of two-sided tests. P-values ≤0.05 were considered to be statistically significant. All computations have been performed using SAS software version 8.01.
The assay showed good clusters and mass spectra (Figure 1 and Figure 2).The null allele frequency of FLG mutation 3321delA were 52.31%(34/65) and 4%(4/100) in cases and controls respectively. FLG mutation 441delA was only found in one IV patients. FLG mutation 441delA was not found in the controls. FLG mutations 1249insG, E1795X and S3296X were not found in these patients and contols. When comparing IV patients with controls, only 3321delA mutation showed a statistically significant association with IV (Χ2=49.1718, P<0.0001).
IV and AD are relatively common heritable skin diseases. Lack of expression of the protein filaggrin has been shown to predispose to the development of IV and atopic eczema or dermatitis [5,16]. The filaggrin gene resides on human chromosome 1q21 within the epidermal differentiation complex, a region that also harbours genes for several other proteins that are important for the normal barrier function of the epidermis .
Recent studies showed that both diseases are closely related to loss-of-function mutations in the FLG . The homozygous or compound heterozygous loss-of-function mutations p.R501X and c.2282del4 in FLG have been identified in moderate or severe IV patients from Ireland, Scotland and the USA . Meanwhile, c.3321delA mutation in FLG were identified as prevalent in Japanese and Korean IV and AD patients [7,17]. FLG mutation E1795X was identified in the Taiwanese population . Nonsense FLG mutations (p.S2889X and p.S3296X) were found in Japan . Recent reports have suggested FLG mutations 1249insG, 7945delA, Q2147X E2422X and 441delA were found in Singaporean Chinese IV patients .
In our case–control study, we investigated 3321delA, 441delA, 1249 insG, E1795X and S3296X mutations which associated with Asian IV patients. With our results, we demonstrate here that more than 52.31% of IV patients in our Southern Chinese case series carry one FLG mutation 3321delA, whereas 4% of ethnically matched control individuals carry this mutation. Mutation 3321delA was firstly reported in a Japanese population , and was absent in the European population and Singaporean Chinese patients [8,15]. One mutation, 441delA, was a previously unidentified FLG mutation which might be Singaporean Chinese specific . FLG mutation 441delA was only found in one IV patients in our case–control study. This mutation may be less common in the Asian populations. FLG mutations 1249 insG, E1795X and S3296X were not identified either in patients with IV or in healthy controls. With our results, we could not only confirm the strong influence of the FLG mutations on the pathogenesis of the disease in this population, but also exemplify differences in prevalent genetics of FLG mutations between Europe and Asia.