Exacerbation of X-linked ichthyosis phenotype in a female by inheritance of filaggrin and steroid sulfatase mutations

Background

X-linked ichthyosis (XLI) is a relatively common, recessive condition caused by mutations in the steroid sulfatase (STS) gene. Common loss-of-function mutations in the filaggrin gene (FLG) cause ichthyosis vulgaris and predispose individuals to atopic eczema.

Objective

To test the hypothesis that co-inheritance of FLG mutations can act as a genetic modifier in XLI.

Methods

An unusually severe XLI phenotype in addition to eczema and mild childhood asthma was investigated in a female Indian patient by fluorescent in situ hybridization (FISH) for the common STS gene deletion. Direct sequencing of the entire FLG gene was also performed.

Results

FISH analysis revealed that the proband was homozygous for the common STS genomic deletion mutation. Further investigation revealed a frame-shift mutation 3672del4 in the gene encoding filaggrin (FLG), leading to premature termination of profilaggrin translation. Interestingly, her father, who had a very typical mild presentation of XLI, did not carry this FLG mutation in addition to his STS deletion. Her mother was a heterozygous carrier of the FLG mutation and consistent with this, had mild symptoms of ichthyosis vulgaris; she was also a heterozygous carrier of the STS deletion.

Conclusion

This is the second reported case of the modifying effects of FLG null alleles on XLI and strengthens the hypothesis that filaggrin defects can synergize with STS deficiency to exacerbate the ichthyosis phenotype.     

X-性连锁鱼鳞病一家系类固醇硫酸酯酶基因研究

目的 检测一个中国汉族人X-性连锁鱼鳞病家系的类固醇硫酸酯酶(STS)基因突变情况.方法 收集1个X-性连锁鱼鳞病家系的临床资料,提取外周血DNA,通过PCR扩增外周血基因组DNA类固醇硫酸酯酶基因的第1和第10外显子,以表型正常家系成员及50例健康人为正常对照.结果 家系内全部患者均存在STS基因的完全缺失,即10个外显子均缺失,家系中正常人及对照者未发现上述缺失.结论 STS基因的完全缺失可能为导致该家系临床表型的主要原因.

Abstract：

Objective To detect the steroid sulfatase (STS) gene mutation in a Chinese pedigree with X-linked ichthyosis (XLI). Methods Genomic DNA was extracted from the peripheral blood of 3 affected patients and unaffected members in this family and 50 unrelated healthy volunteers followed by the amplification of the exon 1 and exon 10 of STS gene by PCR. Results Complete deletion of the exon 1 to 10 of STS gene was detected in all the patients in this pedigree with XLI, while no mutation was found in this gene in unaffected members of this family or normal human controls. Conclusion The complete deletion of STS gene is likely to be the main cause of the phenotype of XLI in this family.     

四种遗传性鱼鳞病基因型与临床表型的相关性分析

目的对四种鱼鳞病(寻常型鱼鳞病;X性-联鱼鳞病;板层状鱼鳞病;大疱性鱼鳞病)的致病基因进行精细定位,并分析其基因型与临床表型的关系。方法对四种鱼鳞病各1例患者进行临床表型分析以及外周血DNA直接测序检测鱼鳞病FLG基因、STS基因、TGM1基因和K1,K10角蛋白基因的突变位点。结果①寻常型鱼鳞病患者在FLG基因的外显子5的第278位有G-T突变,613位有G-A突变。②板层状鱼鳞病患者TGM1基因外显子3的第504位碱基有C-T突变,使第142位氨基酸由精氨酸(R)转变为半胱氨酸(C),即R142C错义突变;外显子7的第1122位碱基有C-T突变,使348位氨基酸由精氨酸(R)突变为终止密码(R348X),导致其编码的蛋白缺失了C端的470个氨基酸。③X-性联鱼鳞病患者STS基因完全缺失。④大疱性鱼鳞病患者外显子5的第242碱基存在A-C突变,外显子6的第599位碱基均存在A-G突变,导致K1蛋白第633位氨基酸由赖氨酸(Lys)变为精氨酸(Arg)。结论鱼鳞病患者临床表型的不同与致病基因的突变位点密切相关。     

Novel FLG mutations associated with ichthyosis vulgaris in the Chinese population

Loss-of-function mutations in the gene encoding filaggrin (FLG) can cause the semidominant keratinizing disorder ichthyosis vulgaris (OMIM 146700). To identify FLG mutations in three Chinese pedigrees with ichthyosis vulgaris, we sequenced the entire coding region of FLG in the proband of each pedigree. We found two novel FLG null mutations (c.477-478insA and c.6218-6219delAA) and a known mutation (c.3321delA). Both novel mutations were identified in the proband of pedigree 1; c.477-478insA was inherited from the proband's father, and the other was a de novo mutation. Neither of these two mutations was found in 200 unrelated controls. These findings extend the spectrum of functional FLG variants possibly causing ichthyosis vulgaris. Interestingly, the proband of pedigree 1 was compound heterozygous for these mutations, but had a mild phenotype, suggesting that an incomplete penetrance factor and perhaps other unknown factors may be involved in the pathogenesis of ichthyosis vulgaris.     

X性联锁遗传鱼鳞病一家系的STS基因研究

目的 研究一 X性联锁遗传鱼鳞病(XLI)家系基因突变,探讨基因突变与临床表现的关系,为进一步开展基因诊断和基因治疗奠定基础。方法 应用PCR方法扩增家系中的先证者及其母亲及与该家系无关的50例正常人外周血基因组DNA STS基因的第一外显子和第十外显子。以角蛋白hHb6为引物,作内对照。结果 家系中先证者的STS基因全部缺失,而先证者之母和与该家系无关的50例正常人未发现缺失。先证者及先证者之母的内对照引物PCR扩增后都有产物。结论 该XLI家系存在STS基因缺失,该缺失引发出XLI特有的皮肤病变。     

Deletion of distal promoter of VCXA in a patient with X-linked ichthyosis associated with borderline mental retardation

BACKGROUND: X-linked ichthyosis (XLI) is caused by deficiency of steroid sulfatase (STS) activity. About 90% XLI patients have large deletions involving the entire STS gene and flanking regions. Recently, VCXA, which is located approximately 0.7Mb telomeric to the STS gene, was reported as a candidate gene for mental retardation (MR) in patients with XLI. OBJECTIVE: To delineate the X-chromosomal deletion of a XLI patient with borderline mental retardation. METHODS: We carried out FISH analysis to show that the whole STS gene is deleted, and PCR analysis for fine-scale deletion mapping. RESULTS: The deleted segment is approximately 1.6Mb in size, and includes the entire STS and VCXB1 genes. VCXA itself is intact, but its promoter is deleted. CONCLUSION: A deletion that includes the VCXA promoter is associated with borderline mental retardation in a patient with XLI.     

X‐linked ichthyosis: Clinical and molecular findings in 35 Italian patients

Recessive X‐linked ichthyosis (XLI), the second most common ichthyosis, is caused by mutations in the STS gene encoding the steroid sulfatase enzyme. A complete deletion of the STS gene is found in 85%‐90% of cases. Rarely, larger deletions involving contiguous genes are detected in syndromic patients. We report the clinical and molecular genetic findings in a series of 35 consecutive Italian male patients. All patients underwent molecular testing by MLPA or aCGH, followed, in case of negative results, by next‐generation sequencing analysis. Neuropsychiatric, ophthalmological and paediatric evaluations were also performed. Our survey showed a frequent presence of disease manifestations at birth (42.8%). Fold and palmoplantar surfaces were involved in 18 (51%) and 7 (20%) patients, respectively. Fourteen patients (42%) presented neuropsychiatric symptoms, including attention‐deficit hyperactivity disorder and motor disabilities. In addition, two patients with mental retardation were shown to be affected by a contiguous gene syndrome. Twenty‐seven patients had a complete STS deletion, one a partial deletion and 7 carried missense mutations, two of which previously unreported. In addition, a de novo STS deletion was identified in a sporadic case. The frequent presence of palmoplantar and fold involvement in XLI should be taken into account when considering the differential diagnosis with ichthyosis vulgaris. Our findings also underline the relevance of involving the neuropsychiatrist in the multidisciplinary management of XLI. Finally, we report for the first time a de novo mutation which shows that STS deletion can also occur in oogenesis.     

Analysis of Taiwanese ichthyosis vulgaris families further demonstrates differences in FLG mutations between European and Asian populations

Background  Mutations in the gene encoding filaggrin ( FLG ) were identified to underlie ichthyosis vulgaris (IV) and also shown to predispose to atopic eczema. Until now, no FLG mutations have been described in the Taiwanese population.
Objectives  To elucidate filaggrin mutations in the Taiwanese population and further to clarify the population genetics of filaggrin gene mutations in the Asian populations.
Methods  In the present study, 12 individuals from four unrelated Taiwanese IV families were examined for FLG mutations. We carried out comprehensive sequencing of the entire FLG coding region using an overlapping polymerase chain reaction strategy.
Results  We identified three FLG mutations in the Taiwanese IV families. One mutation E1795X was a previously unidentified FLG mutation, which might be specific to the Taiwanese. Interestingly, another FLG mutation 3321delA is prevalent in the Japanese population and the other mutation Q2417X was found in the Singaporean Chinese population. No FLG mutation identified in the white European population was found in the Taiwanese population.
Conclusions  The present findings suggest that the Taiwanese population, as an East Asian group, share FLG mutations with both the Japanese and the Singaporean Chinese population. In addition, these results exemplify differences in the population genetics of filaggrin between Europe and Asia.     

X linked recessive ichthyosis: Current concepts

In the present review, we describe the most importantaspects of the X-linked ichthyosis(XLI) and make a compilation of the some historic details of the disease. The aim of the present study is an update of the XLI. Historical, clinical, epidemiological, and molecular aspects are described through the text. Recessive XLI is a relatively common genodermatosis affecting different ethnic groups. With a high spectrum of the clinical manifestations due to environmental factors, the disease has a genetic heterogeneity that goes from a point mutation to a large deletion involving several genes to produce a contiguous gene syndrome. Most XLI patients harbor complete STS gene deletion and flanked sequences; seven intragenic deletions and 14 point mutations with a complete loss of the steroid sulfatase activity have been reported worldwide. In this study, we review current knowledge about the disease.     

应用多重连接探针扩增技术检测X-性连锁鱼鳞病一家系STS基因

目的：检测X-性连锁鱼鳞病一家系STS基因突变情况。方法：提取先证者(男，31岁)及其父母外周血DNA，父母均无鱼鳞病临床表现，运用多重连接探针扩增技术检测所有成员的STS基因是否存在外显子缺失，若无外显子缺失，运用聚合酶链式反应特异性扩增STS基因，检测是否存在基因突变。结果：家系中先证者为STS基因半合子缺失，其母为STS基因杂合子缺失，其父亲未发现STS基因突变。家系中仅先证者出现鱼鳞病的临床表现。结论：STS基因缺失是该X-性连锁鱼鳞病患者发病的遗传因素。     

Analysis of the VCX3A, VCX2 and VCX3B genes shows that VCX3A gene deletion is not sufficient to result in mental retardation in X-linked ichthyosis

BACKGROUND: X-linked ichthyosis (XLI), an inborn error of metabolism, is due to steroid sulphatase (STS) deficiency. Most patients with XLI harbour complete deletion of the STS gene and flanking sequences. The presence of low copy number repeats on either side of the STS gene seems to have a major role in the high frequency of these deletions. Some patients with XLI with terminal deletions of Xp22.3 involving marker DXS1139 and the STS gene show mental retardation (MR); VCX3A is the only gene located on this critical region. OBJECTIVES: To analyse the VCX3A, VCX, VCX2 and VCX3B genes in 80 unrelated Mexican patients with XLI with normal intelligence. METHODS: STS activity was measured in the leucocytes using 7-[3H]-dehydroepiandrosterone sulphate as a substrate. Amplification of the regions from telomeric DXS89 to centromeric DXS1134 including both extremes of the STS and the VCX3A, VCX, VCX2 and VCX3B genes was performed using polymerase chain reaction. RESULTS: No STS activity was detected in the patients with XLI (0.00 pmol mg(-1) protein h(-1)). We observed two different deletion patterns: the first group included 62 patients with deletion of VCX3A and VCX genes. The second group included 18 patients with breakpoints at several regions on either side of the STS gene not including the VCX3A gene. CONCLUSIONS: These data indicate that more complex mechanisms, apart from possible VCX3A gene participation, are occurring in the genesis of MR in XLI, at least in the sample of Mexican patients analysed.     

X-linked ichthyosis and ichthyosis vulgaris: comparison of their clinical features based on biochemical analysis

Thirty cases of X-linked ichthyosis (XLI) and 32 cases of ichthyosis vulgaris (IV) were diagnosed by measuring the steroid sulphatase activity of peripheral blood lymphocytes or the electrophoretic mobility of serum LDL or both. The clinical features of the two conditions were then compared. In both diseases 60-66% of patients had a family history of the condition. Ichthyosis was noted at birth or immediately afterwards in 59% of the patients with XLI while it appeared in infancy in 68% of those with IV. Scales were mostly large and brown or dark brown in patients with XLI, while the majority of patients with IV had small brown or light brown scales. The distribution of the ichthyotic lesions differed in the two types of ichthyosis. On the trunk, the abdomen was more severely involved than the back in 63% of the cases with the XLI, whereas the back was more scaly than the abdomen in 44% of those with IV. On the extremities, the extensor surface was more severely affected than the flexor surface in both types. X-linked ichthyosis was characterized by the presence of lesions in the pre-auricular area, which were found in 93% of the cases with XLI, while only 17% of the IV patients had ichthyotic lesions at this site. Involvement of the preauricular area could be an important clinical feature for distinguishing XLI from IV.     

Deletion patterns of the STS gene and flanking sequences in Israeli X-linked ichthyosis patients and carriers: analysis by polymerase chain reaction and fluorescence in situ hybridization techniques

BACKGROUND: Deletion of the entire steroid sulfatase (STS) gene is the most common molecular defect in X-linked ichthyosis (XLI) patients. Usually, additional flanking sequences are also missing. The aim of this study was to estimate the extent of deletions in an ethnically heterogeneous population of Israeli XLI patients. METHODS: Multiplex polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH) techniques were applied in the analysis of blood samples of 24 patients and amniotic cells of seven affected fetuses from 22 unrelated families. RESULTS: In 19 families, a large deletion of the 2-3 megabase was found. It included the whole STS gene and spanned adjacent areas up- and downstream between the loci DXS 1139 and DXS 1132. Two unrelated families of Iraqi ancestry had a partial deletion of the gene and its centromeric adjacent sequence. In another family, the telomeric end of the extragenic segment was only partially missing. Application of FISH on metaphase blood cells and interphase amniotic cells confirmed the diagnosis of XLI in all patients, except the three with partial intragenic deletion. In those cases, the remaining fraction of the gene was sufficient to provide a false negative result. Diagnosis of carriers and prenatal diagnosis in uncultured cells was applicable only by FISH. CONCLUSIONS: Our study revealed a remarkable heterogeneity in the deletion pattern among Israeli patients with XLI. This heterogeneity could not be attributed to specific ethnic groups because of the small size of the study group. More studies involving patients of various ancestries should be carried out. In addition, this study demonstrated the usefulness of the FISH technique in the prenatal diagnosis of fetuses with suspected XLI.     

X-linked recessive ichthyosis

A 13-year-old boy presented with a lifelong history of tightly-adherent, brown, polygonal scales that covered the extensor surfaces of the extremities, lateral aspects of the trunk, and neck. The clinical presentation and the history of a similar skin condition in the patient's male maternal relatives helped establish the diagnosis of X-linked recessive ichthyosis (XLI). Systemic manifestations of the steroid sulfatase (STS) deficiency underlying XLI include cryptorchidism, asymptomatic corneal opacities, and maternal failure to progress during labor. Most cases of XLI are caused by deletions of the STS gene, and contiguous gene syndromes may occur when the deletions extend to neighboring genes on the distal short arm of the X chromosome.     

寻常型鱼鳞病一家系Filaggrin基因突变检测

目的探讨一家系寻常型鱼鳞病(ichthyosis vulgaris,IV)丝聚合蛋白(filaggrin,FLG)基因的突变。方法提取IV患者及其家庭成员和100例健康对照者基因组DNA,采用PCR及直接测序法,对FLG基因已报道的13个突变位点(3321delA,441delA,1249insG,E1795X,S3296X,R501X,2282del4,R2447X,S2889X,7945delA,3702delG,Q2417X,R4307X)进行测序。结果三代7位成员中4例IV患者同时检测到FLG(441delA)基因突变。结论患者FLG(441delA)基因突变可能导致其发病。     

Specific filaggrin mutations cause ichthyosis vulgaris and are significantly associated with atopic dermatitis in Japan

Mutations in the gene encoding filaggrin (FLG) have been identified as the cause of ichthyosis vulgaris (IV) and shown to be major predisposing factors for atopic dermatitis (AD). However, these studies have been mainly carried out in European populations. In early 2007, we identified two Oriental-specific FLG mutations in four Japanese families with IV and reported that filaggrin mutations were also significant predisposing factors for AD in Japan. However, the frequency of FLG mutations observed in our Japanese AD cohort (5.6%), was much lower than that seen in Europeans (up to 48%). Here, we studied a further seven Japanese families with IV and identified two additional nonsense mutations in FLG, S2889X, and S3296X. We found that more than 20% of patients in our Japanese AD case series carry FLG mutations, and there is significant statistical association between the four mutations and AD (chi(2) P=8.4 x 10(-6); heterozygote odds ratio 7.57, 95% CI 2.84-23.03). These data emphasize that skin-barrier impairment due to reduced filaggrin expression plays an important role in the pathogenesis of AD and sheds further light on the genetic architecture of atopy in Japan.     

丝聚蛋白与相关皮肤病发病机制的研究进展

丝聚蛋白通过参与角质形成细胞的终末角化过程,在表皮屏障中发挥重要作用.中间丝聚合蛋白基因突变引起蛋白表达下降,导致多种过敏性疾病.丝聚蛋白基因突变导致特应性皮炎,也是欧洲和亚洲人种寻常型鱼鳞病的主要诱发因素.丝聚蛋白基因与特应性皮炎发病的婴儿期或早期儿童期关系密切,而与晚期儿童期和成人期无关.有研究发现,小鼠体内缺氧诱导因子引起丝聚蛋白表达降低,提示丝聚蛋白可能不是疾病的单一致病因素.     

上海某中学青少年特应性皮炎和鱼鳞病FLG基因型的研究

目的 探讨青少年FLG基因型、了解特应性疾病患病率、发展进程及其FLG基因的关系。 方法 上海某中学334例11 ~ 19岁青少年作为研究样本,进行鱼鳞病、特应性皮炎（AD）、哮喘、鼻炎等特应性疾病的临床病史及体征观察、记录。285例进行了外周血采样及FLG基因高频突变筛查。5年后,进行样本人群随访,观察并记录各特应性疾病的临床症状及体征。 结果 5年前,334例青少年中AD19例（5.69%）,寻常性鱼鳞病14例（4.19%）,过敏性鼻炎36例（10.78%）,哮喘4例（1.20%）。在完成FLG基因测序的285例样本中,携带FLG基因高频突变者24例（8.42%）。5年后完成随访265例,失访69例（20.66%）,AD、鱼鳞病、过敏性鼻炎及哮喘的患病人数分别为13例（4.89%）、15例（5.64%）、27例（10.15%）、1例（0.38%）,原19例AD中6例进入完全缓解期,13例SCORAD评分明显下降,原36例过敏性鼻炎中9例症状消失。单纯AD、单纯鱼鳞病、AD合并鱼鳞病的FLG基因高频突变率分别为10.0%、55.6%、40.0%,且患鱼鳞病与FLG基因突变有关（P < 0.001）。结论 青少年中,FLG基因高频突变率为8.42%。FLG基因是寻常性鱼鳞病的半显性遗传因素,中间丝聚合蛋白的表达受多因素影响。     

Deletion pattern of the steroid sulphatase gene in Japanese patients with X-linked ichthyosis

Most caucasian patients with X-linked ichthyosis (XLI) reportedly display large genomic deletions involving the entire steroid sulphatase (STS) gene and flanking regions. In this study, we investigated the deletion patterns of the STS gene and flanking regions in 12 unrelated Japanese patients with XLI using the polymerase chain reaction method with 10 markers, including the 5' and 3' ends of the STS gene. Eleven of the 12 patients exhibited deletion of this entire gene, whereas the twelfth patient showed no evidence of deletion. In 10 of the 12 patients, the entire region from DXS1139 to DXF22S1 was deleted, the most common deletion pattern observed in caucasian patients, indicating that there are no racial or ethnic differences.     

Filaggrin and the great epidermal barrier grief

One of the principal functions of human skin is to form an effective mechanical barrier against the external environment. This involves the maturation and death of epidermal keratinocytes as well as the assembly of a complex network of differentially and spatially expressed proteins, glycoproteins and lipids into the keratinocyte cell membrane and surrounding extracellular space. In 2006, the key role of the granular cell layer protein filaggrin (filament-aggregating protein) in maintaining the skin barrier was determined with the identification of loss-of-function mutations in the profilaggrin gene (FLG). These mutations have been shown to be the cause of ichthyosis vulgaris and a major risk factor for the development of atopic dermatitis, asthma associated with atopic dermatitis as well as systemic allergies. Mutations in the FLG gene are extremely common, occurring in approximately 9% of individuals from European populations. The remarkable discovery of these widespread mutations is expected to have a major impact on the classification and management of many patients with ichthyosis and atopic disease. It is also hoped that the genetic discovery of FLG mutations will lead to the future development of more specific, non-immunosuppressive treatments capable of restoring effective skin barrier function and alleviating or preventing disease in susceptible individuals.