Investigation of the male pattern baldness major genetic susceptibility loci AR/EDA2R and 20p11 in female pattern hair loss

BACKGROUND

The aetiology of female pattern hair loss (FPHL) is largely unknown. However, it is hypothesized that FPHL and male pattern baldness (AGA) share common susceptibility alleles. The two major susceptibility loci for AGA are the androgen receptor (AR)/ectodysplasin A2 receptor (EDA2R) locus on the X-chromosome, and a locus on chromosome 20p11, for which no candidate gene has yet been identified.

OBJECTIVES

To examine the role of the AR/EDA2R and 20p11 loci in the development of FPHL using 145 U.K. and 85 German patients with FPHL, 179 U.K. supercontrols and 150 German blood donors.

METHODS

Patients and controls were genotyped for 25 single nucleotide polymorphisms (SNPs) at the AR/EDA2R locus and five SNPs at the 20p11 locus.

RESULTS

Analysis of the AR/EDA2R locus revealed no significant association in the German sample. However, a nominally significant association for a single SNP (rs1397631) was found in the U.K. sample. Subgroup analysis of the U.K. patients revealed significant association for seven markers in patients with an early onset (P = 0·047 after adjustment for the testing of multiple SNPs by Monte Carlo simulation). No significant association was obtained for the five 20p11 variants, either in the overall samples or in the analysis of subgroups.

CONCLUSIONS

The observed association suggests that the AR/EDA2R locus confers susceptibility to early-onset FHPL. Our results do not implicate the 20p11 locus in the aetiology of FPHL.

The autoimmune regulator gene (AIRE) is strongly associated with vitiligo

BACKGROUND

Vitiligo is an autoimmune disorder that occurs with greatly increased frequency in the rare recessive autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy syndrome (APECED) caused by mutations of the autoimmune regulator (AIRE) gene on chromosome 21q22.3. We have previously detected an association between alopecia areata and single nucleotide polymorphisms (SNPs) in the AIRE gene.

OBJECTIVES

To report the findings of an extended study including haplotype analysis on six AIRE polymorphisms (AIRE C-103T, C4144G, T5238C, G6528A, T7215C and T11787C) in vitiligo, another APECED-associated disease.

METHODS

A case-control analysis was performed.

RESULTS

Results showed a strong association between AIRE 7215C and vitiligo [P = 1.36 x 10(-5), odds ratio (OR) 3.12, 95% confidence interval (CI) 1.87-5.46]. We found no significant association with the other polymorphisms individually. However, haplotype analysis revealed that the AIRE haplotype CCTGCC showed a highly significant association with vitiligo (P = 4.14 x 10(-4), OR 3.00, 95% CI 1.70-5.28). To select the most informative minimal haplotypes, we tagged the polymorphisms using SNP tag software. Using AIRE C-103T, G6528A, T7215C and T11787C as tag SNPs, the haplotype AIRE CGCC was associated with vitiligo (P = 0.003, OR 2.49, 95% CI 1.45-4.26).

CONCLUSIONS

The link between vitiligo and AIRE raises the possibility that defective skin peripheral antigen selection in the thymus is involved in the changes that result in melanocyte destruction in this disorder.

Genetic analysis of autoimmune regulator haplotypes in alopecia areata

Alopecia areata is an immune-mediated disorder, occurring with the highest observed frequency in the rare recessive autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) syndrome caused by mutations of the autoimmune regulator (AIRE) gene on chromosome 21q22.3. We have previously detected association between alopecia areata and a single nucleotide polymorphism (SNP) in the AIRE gene in patients without APECED, and we now report the findings of an extended examination of the association of alopecia areata with haplotype analysis including six SNPs in the AIRE gene: C-103T, C4144G, T5238C, G6528A, T7215C and T11787C. In Caucasian groups of 295 patients and 363 controls, we found strong association between the AIRE 7215C allele and AA [P = 3.8 x 10(-8), OR (95% CI): 2.69 (1.8-4.0)]. The previously reported association between AA and the AIRE 4144G allele was no longer significant on correction for multiple testing. The AIRE haplotypes CCTGCT and CGTGCC showed a highly significant association with AA [P = 6.05 x 10(-6), 9.47 (2.91-30.8) and P = 0.001, 3.51 (1.55-7.95), respectively]. To select the haplotypes most informative for analysis, we tagged the polymorphisms using SNPTag software. Employing AIRE C-103T, G6528A, T7215C and T11787C as tag SNPs, two haplotypes were associated with AA; AIRE CGCT and AIRE CGCC [P = 3.84 x 10(-7), 11.40 (3.53-36.9) and P = 3.94 x 10(-4), 2.13 (1.39-3.24) respectively]. The AIRE risk haplotypes identified in this study potentially account for a major component of the genetic risk of developing alopecia areata.

Nine procaspases are expressed in normal human epidermis, but only caspase-14 is fully processed

BACKGROUND

During normal stratification of the epidermis, keratinocytes undergo a complex programme of terminal differentiation. This programmed cell death results in corneocyte accumulation to form the stratum corneum (SC). Terminal differentiation and apoptosis share numerous features such as elimination of nuclei and organelles, changes in cell shape, and activation of transglutaminases and proteases. Caspases are cysteine proteases that play a central role in apoptosis. Therefore they may also be involved in the terminal differentiation of keratinocytes.

OBJECTIVES

To identify the caspases expressed in normal human epidermis and to define their pattern of expression and activation.

METHODS

We analysed mRNAs from human epidermis by reverse transcription-polymerase chain reaction (RT-PCR), skin cryosections by immunohistological methods, and epidermal protein extracts by Western blotting.

RESULTS

The mRNAs encoding caspase-1, -2, -3, -4, -6, -7, -8, -9, -10 and -14 were detected by RT-PCR. Accordingly, the immunohistological analyses showed clear expression in the epidermis of the corresponding proteins except caspase-2 and caspase-8, with only a weak expression of caspase-9. Moreover, procaspase-1, -2, -3, -4, -6, -7, -9, -10 and -14, and the fully processed caspase-14, were immunodetected in total epidermis extracts. However, only procaspase-1 and the processed caspase-14 were detected in extracts of superficial SC. In addition to these two proteins, procaspase-4 was detected in extracts of superficial SC obtained from lesional psoriatic skin.

CONCLUSIONS

This study, the first exhaustive description of caspase expression and processing in normal human epidermis, indicates that in vivo granular keratinocytes express nine procaspases, and in addition the activated form of caspase-14. This confirms that only caspase-14 is involved in keratinocyte differentiation, and suggests that keratinocytes are ready to induce apoptosis in response to cutaneous damage.

A nonsynonymous substitution of cystatin A, a cysteine protease inhibitor of house dust mite protease, leads to decreased mRNA stability and shows a significant association with atopic dermatitis

BACKGROUND

Cystatin A (CSTA) is a strong candidate for atopic dermatitis (AD) because it maps to AD susceptibility locus on chromosome 3q21 and it does inhibit Der p 1 and Der f 1, major house dust mite cysteine proteases and environmental triggers for AD and asthma.

OBJECTIVE

To examine any association between polymorphisms in CSTA and AD and study the effect on the CSTA mRNA expression level.

METHODS

We identified three polymorphisms and characterized the linkage disequilibrium mapping of the CSTA gene. All three CSTA polymorphisms were genotyped in 100 AD patients and 203 matched controls. Subsequently, we performed transfection-based RNA stability assays.

RESULTS

We found a significant association between the CSTA +344C variant and AD [odds ratio (OR) = 1.91; P = 0.024]. When further 61 control samples were genotyped. The association with CSTA +344C allele was enhanced OR = 2.13; P = 0.006. To test whether the CSTA +344 affected the CSTA transcriptional activity, the decay rates of RNAs transcribed from the CSTA +344C and CSTA +344T variants were investigated. COS-7 cells were transfected with a pcDNA3.1-CSTA+344C or a pcDNA3.1-CSTA+344T construct and cultured in the presence or absence of actinomycin D. Real-time RT-PCR revealed that CSTA +344C mRNA is more than two times less stable than the CSTA +344T mRNA (P < 0.001).

CONCLUSION

These results suggest that the CSTA +344C allele associated with unstable mRNA could result in failing to protect the skin barrier in AD patients from both exogenous and endogenous proteases.

Genetic association between an AACC insertion in the 3'UTR of the stratum corneum chymotryptic enzyme gene and atopic dermatitis

Atopic dermatitis is a disease with an impaired skin barrier that affects 15%-20% of children. In the normal epidermis, the stratum corneum chymotryptic enzyme (SCCE) thought to play a central role in desquamation by cleaving proteins of the stratum corneum (e.g., corneodesmosin and plakoglobin). Genetic variations within the SCCE gene could be associated with dysregulation of SCCE activity leading to an abnormal skin barrier. We screened the SCCE gene for variations and performed a case-control study on 103 atopic dermatitis patients and 261 matched controls. 16 synonymous single nucleotide polymorphisms (SNPs) have been identified and a 4 bp (AACC) insertion has been found in the 3'UTR. We performed an association study of the SCCE AACC insertion in the 3'UTR, and found a significant trend between the AACC allele with the two insertions and disease in the overall data set [odds ratio (OR)=2.31; p=0.0007]. The AACC insertion in the SCCE gene may result in a change to SCCE activity within the skin barrier. These findings suggest that SCCE could have an important role in the development of atopic dermatitis.

Identification of novel single nucleotide polymorphisms within the NOTCH4 gene and determination of association with MHC alleles

Mapping of disease susceptibility loci within the MHC has been partly hampered by the high degree of polymorphism of the HLA genes and the high level of linkage disequilibrium (LD) between markers within the MHC region. It is therefore important to identify new markers and determine the level of LD between HLA alleles and non-HLA genes. The NOTCH4 gene lies at the centromeric end of the MHC class III region, approximately 335 kb telomeric of the DRB1 locus. The encoded protein is an oncogene that is important in regulating vascular development and remodelling. A recent report has linked polymorphisms within NOTCH4 with risk of developing schizophrenia. We have investigated if coding polymorphisms exist within this gene and have identified three single nucleotide polymorphisms; a synonomous T to C transition at +1297 (HGBASE accession number SNP000064386), a synonomous A to G transition at +3061 (SNP000064387) and an A to G transition at +3063 which results in a replacement of glycine with aspartic acid at amino acid 279 (SNP000064388). The allele frequencies of +1297T, +3061A and +3063G were 0.65, 0.66 and 0.66, respectively. Linkage disequilibrium was detected both between these markers and with MHC alleles. These findings can be used in the fine mapping of disease susceptibility alleles within the MHC.

Notch4, a non-HLA gene in the MHC is strongly associated with the most severe form of alopecia areata

Alopecia areata (AA) is a disorder primarily affecting the hair and nails in which associated autoimmune or atopic disease is common. Genetically, it is a complex trait with evidence of a role for genes of the major histocompatibility complex (MHC), the interleukin-1 cluster and chromosome 21 in the pathogenesis. The strongest association is with HLA class II alleles, although whether this indicates a direct contribution to the pathogenesis or results merely from linkage disequilibrium with nearby disease genes is unknown. Notch4 is a recently defined gene in the HLA class III region. Notch signalling is a direct determinant of keratinocyte growth arrest and entry into differentiation. A possible role for Notch in hair growth has been indicated by transgenic mouse findings that activation of the Notch pathway in the hair cortex leads to aberrant differentiation of adjacent hair-shaft layers. Notch4 is therefore a plausible candidate gene for AA. We have examined two polymorphisms in the coding sequence of the Notch4 gene at positions +1297 and +3063 in a case-control study of 116 AA patients and 142 ethnically matched, healthy control subjects. The initial analysis showed a significant association of AA in the overall data set with the Notch4(T+1297C) polymorphism (P<0.001) but not with Notch4(A+3063G). To confirm this association, we genotyped an additional 62 patients and found that the risk for disease was higher in Notch4(+1297C) homozygotes [odds ratio (OR) 3.43 (1.63, 7.19)] than in heterozygotes [OR 2.58 (1.57, 4.24)]. On classifying the patients by severity of disease, the association appeared to be confined to the severest form (alopecia universalis) [OR 4.02 (1.64, 9.88), P=0.0014]. These results support previous findings showing that different HLA susceptibility alleles are associated with mild and severe AA.

Role of the autoimmune regulator (AIRE) gene in alopecia areata: strong association of a potentially functional AIRE polymorphism with alopecia universalis

Alopecia areata is characterized by a reversible form of patchy or complete hair loss associated with T-cell infiltration of hair follicles. The lifetime disease risk of approximately 1.4% in the general population is increased to more than 30% in autoimmune polyendocrinopathy candidiasis ectodermal dysplasia syndrome (APECED), a recessive condition resulting from a mutation of the autoimmune regulator (AIRE) gene on chromosome 21q22.3. Aire protein is thought to have transcriptional regulatory activity but its role is not well defined at present. In this study, we have examined the possible involvement of AIRE in the pathogenesis of alopecia areata. On screening the AIRE coding sequence, we identified 20 variants. Two of these at positions, G961C and T1029C, give rise to amino acid changes, S278R and V301A, located in the DNA-binding segment (SAND) and PHD1 zinc finger motif, respectively. We found no difference in the frequency of the AIRE T1029C polymorphism between the control and patient groups. We genotyped 202 alopecia areata patients and 175 matched Caucasian controls for the AIRE G961C alleles. The frequency of the rare allele (961G) was 0.08 in the controls and there was a significant increase to 0.13 in alopecia areata overall and 0.20 in severe disease (alopecia universalis). We found no association between the AIRE G961G variant and mild (patchy) alopecia areata or alopecia totalis. However, the AIRE 961G allele is a potent risk factor (> 3) for the severest form of alopecia areata, and for disease of early age at onset (at 30 years). The change from serine to arginine in the SAND domain of AIRE protein may have a significant effect on AIRE DNA-binding activity. Moreover, our results could provide a rational explanation of the unusually high frequency of AA in APECED patients, supporting the concept of AA as an autoimmune disease.

Epidemiology and genetics of alopecia areata

The frequency of alopecia areata and observed patterns of heritability are in keeping with a polygenic inheritance model but the genetics of alopecia areata is still poorly understood. The role of environmental factors in triggering disease initiation or exacerbation remains almost entirely speculative. Using the candidate gene approach, three susceptibility/severity factors have been identified. HLA alleles were the first to show a strong association with alopecia areata and some DQB and DR alleles have been demonstrated to confer a high risk for disease by both case-control and family-based studies. Interleukin (IL)-1 cluster genes, mainly the IL-1 receptor antagonist, show a strong association with disease severity in alopecia areata and a number of other autoimmune and inflammatory diseases. Finally, the association of alopecia areata with Down's syndrome, the high frequency of alopecia areata in autoimmune polyglandular syndrome type I due to mutations of the autoimmune regulator (AIRE) gene on chromosome 21q22.3 and the finding of association with MX1, another gene in the Down's syndrome region of chromosome 21 indicate this area of the genome as a promising target for future-family based investigations. The role of individual genes of the MHC, IL-1 cluster or chromosome 21q22.3 is difficult to establish and further genetic and functional investigations are needed to confirm their involvement in the pathogenesis of alopecia areata.

Genetic analysis of the interleukin-1 receptor antagonist and its homologue IL-1L1 in alopecia areata: strong severity association and possible gene interaction

Alopecia areata is an inflammatory hair loss disease with a major genetic component. The presence of focal inflammatory lesions with perifollicular T-cell infiltrates reflects the importance of local cytokine production in the pathogenesis. In addition to its fundamental pro-inflammatory role, the interleukin-1 (IL-1) system has major effects on hair growth regulation in vitro, with the inhibitory actions of IL-1alpha and IL-1beta being opposed by the receptor antagonist IL-1ra. The novel interleukin-1 like molecule 1 (IL-1L1) which has greatest gene sequence homology with IL1RN, the gene encoding IL-1ra, is another potential IL-1 antagonist. In view of previous studies suggesting a significant role for IL1RN polymorphisms in the pathogenesis of autoimmune/inflammatory disease, we have analysed polymorphisms of IL-1ra (IL1RN+2018) and its homologue IL-1L1 (IL1L1+4734) in a case-control association study on 165 patients and a large number of matched controls. Homozygosity for the rare allele of IL1RN (IL1RN*2) was significantly associated with alopecia areata [odds ratio (OR) = 1.89, 95% CI (1.09, 3.28); P = 0.02], confirming our previous findings of significant association with the IL1RN variable number tandem repeat (VNTR). The results also revealed a novel association involving a polymorphism of the interleukin-1 receptor antagonist homologue IL1L1 at position + 4734, IL1RN+2018, and alopecia areata. The effect of a genotype combining three copies of the rare alleles at the IL1RN and IL1L1 loci conferred a more than additive increase in the risk of disease compared to IL1RN+2018 or IL1L1+4734 alone [OR 3.37 (1.60, 7.06); P = 0.002], suggesting possible synergy between the IL1RN and IL1L1 genes. This effect was stronger in patients with severe disease (alopecia totalis/universalis) [OR 4.62 (1.87, 11.40), P = 0.0022], and in those with early age at onset (< 20 years) [OR = 6.38 (2.64, 15.42), P = 0.0002]. Our results suggest that these polymorphisms within IL1RN and IL1L1 themselves or a gene in linkage disequilibrium with IL1RN and IL1L1 predispose to the more severe forms of alopecia areata.

Association analysis of IL1A and IL1B variants in alopecia areata

Alopecia areata is an inflammatory hair loss disease with a major genetic component. The disease is characterized by focal inflammatory lesions with perifollicular T-cell infiltrates, reflecting the role of local cytokine production in the development of patchy hair loss. IL-1 alpha and IL-1 beta are important inhibitors of hair growth in vitro. Their effect is opposed by the interleukin-1 receptor antagonist, IL-1ra. Genes of the IL-1 cluster are candidate genes in the pathogenesis of alopecia areata. To investigate the role of the IL-1 system in alopecia areata we examined three biallelic polymorphisms within the IL-1 gene cluster (IL1A+4845, IL1B+3954 and IL1B-511) in 165 patients and a large number of matched controls (n=1150). There was no significant association of IL1B-511 or IL1B+3954 genotypes with the overall dataset, or with disease severity or age at onset, in contrast with a previous report. The results suggested the possibility of an association with IL1A+4845 in the overall dataset [OR 1.39 (95% CI 1.00, 1.93)] although this was not statistically significant. This was due mainly to the contribution from mild cases of alopecia areata [OR 1.48 (0.96, 2.29)], suggesting that IL-1 alpha may have a particular role in the pathogenesis of this subgroup.

Structure and polymorphism of the human gene for the interferon-induced p78 protein (MX1): evidence of association with alopecia areata in the Down syndrome region

Alopecia areata (AA) is a chronic inflammatory disease characterised by patchy hair loss with T cell infiltration of hair follicles. AA occurs in approximately 0.1% of the general population, but this is increased to 9% in Down syndrome (DS). DS is associated with an additional copy (full or partial) of chromosome 21, and the DS region may potentially include genes involved in the pathogenesis of AA. MX1 is the gene encoding the interferon-induced p78 protein (MxA). MxA protein confers resistance to influenza viruses, and we have previously shown that MxA protein is strongly expressed in lesional anagen hair bulbs from patients with AA but not in normal follicles. We therefore studied the possible involvement of MX1 in the pathogenesis of AA. To establish markers in the MX1 region which could be screened by PCR-based methods, we defined the human MX1 exon/intron organisation and screened the exons and the introns by conformation-sensitive gel electrophoresis. We found that the MX1 gene contains 17 exons extending over 33 kb. The size and sequence of the region from exon 6 to exon 16 are highly conserved between human and mouse. Screening of 4747 bp within the MX1 gene revealed four single nucleotide polymorphisms in intron 6. These polymorphisms are concentrated within 147 bp and show strong linkage disequilibrium. In a case-control association study for the MX1 (+9959) polymorphism in 165 AA patients and 510 controls we found a significant association of this marker with AA (odds ratio 1.79, 95% CI 1.21-2.66, chi2 = 8.464, P = 0.0036). The risk of disease was greater for patchy AA (mild disease) and with early age at onset (odds ratio 2.34, 95% CI 1.24-4.43, P = 0.0072), providing new evidence of genetic heterogeneity in AA. Our demonstration of genetic association between the MX1 gene and disease supports the hypothesis that this is a new candidate gene in AA.

Cloning, localization, and structure of new members of the butyrophilin gene family in the juxta-telomeric region of the major histocompatibility complex

New members of the butyrophilin (BT) gene family have been identified by cDNA and genomic cloning. Six genes are described: BT2. 1, 2.2, 2.3, and BT3.1, 3.2, and 3.3. BT2, BT3, and BT form three distinct subfamilies sharing about 95% amino acid identity at the intra subfamily level and 50% identity at the interfamily level. All the BT2 and BT3 subfamily members map close to BT in the juxta-telomeric region of the major histocompatibility complex. The BT2 members have the canonical structural organization of BT, i.e., two immunoglobulin domains followed by a transmembrane anchor and a B30.2 intracytoplasmic domain. In the BT3 subfamily, only BT3.3 has the structural organization of BT. The two other genes, BT3.1 and BT3.2, code for putative protein without the B30.2 domain. In the case of BT3.2, this is due to an Alu insertion in the B30.2 coding exon, leading to a new polyadenylation site.

A first map of the porcine major histocompatibility complex class I region

A map of the SLA complex, or swine major histocompatibility complex (MHC), class I region was constructed by alignment of yeast artificial chromosomes (YACs) harboring MHC class I genes as well as anchor genes already mapped within the human MHC complex (HLA). Five YACs containing 9 anchor genes built a contig of about 1.0-1.2 Mb between the SLA class III BAT1 locus and the olfactory receptor-like genes OLF42. Ten different SLA class I sequences, including putative allelic forms of published classical and non-classical SLA class I genes, were assigned to the 400-kb enclosing centromeric part of the contig. Three additional YACs comprising the OLF89 genes and two YACs containing the butyrophilin gene were located telomeric to the contig. Comparison between the human and porcine MHC complexes showed a perfect conserved order of anchor genes, whereas no orthologous relationships were found for the class I loci.

Cloning, structural analysis, and mapping of the B30 and B7 multigenic families to the major histocompatibility complex (MHC) and other chromosomal regions

We present the cloning, structural analysis, and mapping of new members belonging to two multigenic families, the B30-RING finger family and the B7.1-B7.2 family, as well as two genes derived by exon shuffling from members of these families. Eight new members were found and three of them map to the human major histocompatibilitiy complex (MHC) region. Phylogenic and physical mapping analysis allowed us to decipher the evolutionary story of these two multigenic families and to shed light on the evolution of the MHC region. We also show that a deductive analysis can be used to predict the existence of a given gene.