Cloning of a cDNA for steroid sulfatase: frequent occurrence of gene deletions in patients with recessive X chromosome-linked ichthyosis

Clinical and molecular diagnosis of genodermatoses: Review and perspectives

Genodermatoses are a complex and heterogeneous group of genetic skin disorders characterized by variable expression and clinical and genetic heterogeneity, rendering their diagnosis challenging. DNA-based techniques, like whole-exome sequencing, can establish a diagnosis in 50% of cases. RNA-sequencing is emerging as an attractive tool that can obtain information regarding gene expression while integrating functional genomic data with regard to the interpretation of variants. This increases the diagnostic rate by an additional 10-15%. In the present review, we detail the clinical steps involved in the diagnosis of genodermatoses, as well as the current DNA-based technologies available to clinicians. Herein, the intention is to facilitate a better understanding of the possibilities and limitations of these diagnostic technologies. In addition, this review could guide dermatologists through new emerging techniques, such as RNA-sequencing and its applications to familiarizing them with future techniques. Currently, this multi-omics approach is likely the best strategy designed to promote the diagnosis of patients with genodermatoses and discover new skin disease genes that could result in novel targeted therapies.

Genetic Heterogeneity of X-Linked Ichthyosis in the Republic of North Ossetia-Alania, Case Series Report

North Caucasus has always been a residence of a lot of different authentic ethnic groups speaking different languages and still living their traditional lifestyle. The diversity appeared to be reflected in the accumulation of different mutations causing common inherited disorders. X-linked ichthyosis represents the second most common form of genodermatoses after ichthyosis vulgaris. Eight patients from three unrelated families of different ethnic origin, Kumyk, Turkish Meskhetians, and Ossetian, with X-linked ichthyosis from the North Caucasian Republic of North Ossetia-Alania were examined. NGS technology was implied for searching for disease-causing variants in one of the index patients. Known pathogenic hemizygous deletion in the short arm of chromosome X encompassing the STS gene was defined in the Kumyk family. A further analysis allowed us to establish that likely the same deletion was a cause of ichthyosis in a family belonging to the Turkish Meskhetians ethnic group. In the Ossetian family, a likely pathogenic nucleotide substitution in the STS gene was defined; it segregated with the disease in the family. We molecularly confirmed XLI in eight patients from three examined families. Though in two families, Kumyk and Turkish Meskhetian, we revealed similar hemizygous deletions in the short arm of chromosome X, but their common origin was not likely. Forensic STR markers of the alleles carrying the deletion were defined to be different. However, here, common alleles haplotype is hard to track for a high local recombination rate. We supposed the deletion could arise as a de novo event in a recombination hot spot in the described and in other populations with a recurrent character. Defined here are the different molecular genetic causes of X-linked ichthyosis in families of different ethnic origins sharing the same residence place in the Republic of North Ossetia-Alania which could point to the existing reproductive barriers even inside close neighborhoods.

A novel nonsense mutation in the STS gene in a Pakistani family with X-linked recessive ichthyosis: including a very rare case of two homozygous female patients

Background

X-linked ichthyosis (XLI; OMIM# 308100) is a recessive keratinization disorder characterized by the presence of dark brown, polygonal, adherent scales on different parts of the body surface. It almost exclusively affects males and the estimated prevalence ranges from 1:2000–6000 in males worldwide. Extracutaneous manifestations are frequent including corneal opacities, cryptorchidism, neuropsychiatric symptoms or others. Up to 90% of XLI cases are caused by recurrent hemizygous microdeletion encompassing entire STS gene on chromosome Xp22.3, while only a minority of patients shows partial deletions or loss of function point mutations in STS. Larger deletions also involving contiguous genes are identified in syndromic patients.

Methods

Here, we report clinical and genetic findings of a large Pakistani family having 16 affected individuals including 2 females with XLI. Molecular karyotyping and direct DNA sequencing of coding region of the STS gene was performed.

Results

The clinical manifestations in affected individuals involved generalized dryness and scaling of the skin with polygonal, dark scales of the skin on scalp, trunk, limbs, and neck while sparing face, palms and soles. There were no associated extra-cutaneous features such as short stature, cryptorchidism, photophobia, corneal opacities, male baldness, and behavioral, cognitive, or neurological phenotypes including intellectual disability, autism or attention deficit hyperactivity disorder. Molecular karyotyping was normal and no copy number variation was found. Sanger sequencing identified a novel hemizygous nonsense mutation (c.287G > A; p.W96*), in exon 4 of STS gene in all affected male individuals. In addition, two XLI affected females in the family were found to be homozygous for the identified variant.

Conclusions

This study is useful for understanding the genetic basis of XLI in the patients studied, for extending the known mutational spectrum of STS, diagnosis of female carriers and for further application of mutation screening in the genetic counseling of this family.

Cord blood Per- and polyfluoroalkyl substances, placental steroidogenic enzyme, and cord blood reproductive hormone

BACKGROUND

Per- and polyfluoroalkyl substances (PFASs) are widely used in China, but little is known about the association between prenatal PFASs exposure and fetal reproductive development as well as its potential mechanism.

OBJECTIVE

We investigated the effects of cord blood PFASs on fetal reproductive hormones and its potential mechanism in relation to steroidogenic enzymes.

METHODS

Ten selected PFASs (n = 351) including PFOS, PFOA, PFBS, PFDA, PFDoA, PFHpA, PFHxS, PFNA, PFOSA, and PFUA, and two reproductive hormones estradiol (E2) (n = 351) and testosterone (T) (n = 349) were measured in 351 cord blood serum samples from a Chinese birth cohort between 2010 and 2013. Three steroidogenic enzymes including P450arom (n = 125), 3β-HSD1 (n = 123), and 17β-HSD1 (n = 116) were measured in 125 placental tissue samples. Linear regression tested the associations between cord blood PFASs and reproductive hormones in cord blood. Mediation analysis assessed the role of placental steroidogenic enzymes between cord blood PFASs and reproductive hormones.

RESULTS

The positive associations between PFOA, PFHxS and E2 levels, PFOS, PFUA, PFNA and T levels, and PFOS, PFUA and T/E2 ratio were significant. PFUA, PFNA, PFDA, PFHxS, and ∑PFASs were associated with higher P450arom levels. PFHxS was also associated with increased 3β-HSD1 and 17β-HSD1 levels. These associations were more pronounced in females than males when stratified by gender. Furthermore, 17β-HSD1 demonstrated mediating effects in the positive association between cord blood PFHxS and E2 levels in females.

CONCLUSION

Our findings suggested the potential impacts of cord blood PFASs on fetal reproductive hormones, in which steroidogenic enzymes may play important roles. These associations were more pronounced in females than males.

The Morbid Anatomy of the Dermatologic Genome: An Update for the Third Millennium

Background:

Much progress has been made in recent years in the identification of genes underlying many hereditary skin diseases.

Objective:

To provide an update on the status of the identification of genes involved in hereditary skin disorders and to compare the current standing with that in the last decade.

Methods:

A review of the literature is presented here in a series of lists describing the chromosomal location, specific gene, clinical relevance, and availability of molecular-based genetic tests for each genodermatosis.

Results:

Progress has been made in identifying the genes underlying many disorders of cornification, genodermatoses with malignant potential, bullous disorders, pigmentary disorders, disorders affecting the epidermal appendages and the dermis, and other miscellaneous genodermatoses.

Conclusion:

The great progress made toward the completion of the human gene sequence and the continued efforts of many clinical and molecular scientists to identify disease genes will make diagnosis of hereditary dermatological disorders more precise and allow accurate family counseling as well as possibly leading to more targeted therapies during this millennium.

Steroid Sulfatase Deficiency and Androgen Activation Before and After Puberty

CONTEXT

Steroid sulfatase (STS) cleaves the sulfate moiety off steroid sulfates, including dehydroepiandrosterone (DHEA) sulfate (DHEAS), the inactive sulfate ester of the adrenal androgen precursor DHEA. Deficient DHEA sulfation, the opposite enzymatic reaction to that catalyzed by STS, results in androgen excess by increased conversion of DHEA to active androgens. STS deficiency (STSD) due to deletions or inactivating mutations in the X-linked STS gene manifests with ichthyosis, but androgen synthesis and metabolism in STSD have not been studied in detail yet.

PATIENTS AND METHODS

We carried out a cross-sectional study in 30 males with STSD (age 6-27 y; 13 prepubertal, 5 peripubertal, and 12 postpubertal) and 38 age-, sex-, and Tanner stage-matched healthy controls. Serum and 24-hour urine steroid metabolome analysis was performed by mass spectrometry and genetic analysis of the STS gene by multiplex ligation-dependent probe amplification and Sanger sequencing.

RESULTS

Genetic analysis showed STS mutations in all patients, comprising 27 complete gene deletions, 1 intragenic deletion and 2 missense mutations. STSD patients had apparently normal pubertal development. Serum and 24-hour urinary DHEAS were increased in STSD, whereas serum DHEA and testosterone were decreased. However, total 24-hour urinary androgen excretion was similar to controls, with evidence of increased 5α-reductase activity in STSD. Prepubertal healthy controls showed a marked increase in the serum DHEA to DHEAS ratio that was absent in postpubertal controls and in STSD patients of any pubertal stage.

CONCLUSIONS

In STSD patients, an increased 5α-reductase activity appears to compensate for a reduced rate of androgen generation by enhancing peripheral androgen activation in affected patients. In healthy controls, we discovered a prepubertal surge in the serum DHEA to DHEAS ratio that was absent in STSD, indicative of physiologically up-regulated STS activity before puberty. This may represent a fine tuning mechanism for tissue-specific androgen activation preparing for the major changes in androgen production during puberty.

X-linked ichthyosis and Crigler-Najjar syndrome I: Coexistence in a male patient with two copy number variable regions of 2q37.1 and Xp22.3

X-linked ichthyosis (XLI) is an X-linked recessive skin disorder generally restricted to males, which arises from mutations in the steroid sulfatase (STS) gene located on Xp22.3. Crigler-Najjar syndrome (CN-I) is a rare autosomal recessive disease caused by the homozygous or compound heterozygous mutations in the UPD-glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) gene on chromosome 2q37. A male patient was referred to the Department of Medical Genetics with of severe icterus and ichthyosis. The patient and his family members underwent genetic tests related to XLI and CN-I. Quantitative polymerase chain reaction on genomic DNA was performed to determine the gene copy number, while single nucleotide polymorphism array analysis was conducted to identify deletion mutations. Family pedigree analysis showed that the patient and his two cousins were all affected by ichthyosis, which was in accordance with the inheritance pattern of an X-linked recessive disease. In addition, the patient's serum bilirubin concentration (>340 mmol/l) was markedly greater than the normal level. The patient presented with kernicterus and phenobarbital treatment was ineffective. The clinical diagnosis of XLI was confirmed molecularly by laboratory evidence of a maternal 1.61 M deletion (including the STS gene) on ChrXp22.31. Coincidentally, the male patient was also confirmed to carry a rare maternal inherited microdeletion (374 Kb) comprising the entire UGT1A1 gene combined with a paternal UGT1A1 mutation (c.1253delT), a causative event of CN-I. To the best of our knowledge, this study reported for the first time the comorbidity of XLI and CN-I in a male patient. The results suggested that co-occurrence of these two recessive diseases in a patient may be incidental.

The Regulation of Steroid Action by Sulfation and Desulfation

Steroid sulfation and desulfation are fundamental pathways vital for a functional vertebrate endocrine system. After biosynthesis, hydrophobic steroids are sulfated to expedite circulatory transit. Target cells express transmembrane organic anion-transporting polypeptides that facilitate cellular uptake of sulfated steroids. Once intracellular, sulfatases hydrolyze these steroid sulfate esters to their unconjugated, and usually active, forms. Because most steroids can be sulfated, including cholesterol, pregnenolone, dehydroepiandrosterone, and estrone, understanding the function, tissue distribution, and regulation of sulfation and desulfation processes provides significant insights into normal endocrine function. Not surprisingly, dysregulation of these pathways is associated with numerous pathologies, including steroid-dependent cancers, polycystic ovary syndrome, and X-linked ichthyosis. Here we provide a comprehensive examination of our current knowledge of endocrine-related sulfation and desulfation pathways. We describe the interplay between sulfatases and sulfotransferases, showing how their expression and regulation influences steroid action. Furthermore, we address the role that organic anion-transporting polypeptides play in regulating intracellular steroid concentrations and how their expression patterns influence many pathologies, especially cancer. Finally, the recent advances in pharmacologically targeting steroidogenic pathways will be examined.

Role of cholesterol sulfate in epidermal structure and function: lessons from X-linked ichthyosis

X-linked ichthyosis is a relatively common syndromic form of ichthyosis most often due to deletions in the gene encoding the microsomal enzyme, steroid sulfatase, located on the short area of the X chromosome. Syndromic features are mild or unapparent unless contiguous genes are affected. In normal epidermis, cholesterol sulfate is generated by cholesterol sulfotransferase (SULT2B1b), but desulfated in the outer epidermis, together forming a 'cholesterol sulfate cycle' that potently regulates epidermal differentiation, barrier function and desquamation. In XLI, cholesterol sulfate levels my exceed 10% of total lipid mass (≈1% of total weight). Multiple cellular and biochemical processes contribute to the pathogenesis of the barrier abnormality and scaling phenotype in XLI. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Cognitive, behavioural and psychiatric phenotypes associated with steroid sulfatase deficiency

The enzyme steroid sulfatase (STS) desulfates a variety of steroid compounds thereby altering their activity. STS is expressed in the skin, and its deficiency in this tissue has been linked to the dermatological condition X-linked ichthyosis. STS is also highly expressed in the developing and adult human brain, and in a variety of steroidogenic organs (including the placenta and gonads); therefore it has the potential to influence brain development and function directly and/or indirectly (through influencing the hormonal milieu). In this review, we first discuss evidence from human and animal model studies suggesting that STS deficiency might predispose to neurobehavioural abnormalities and certain psychiatric disorders. We subsequently discuss potential mechanisms that may underlie these vulnerabilities. The data described herein have potential implications for understanding the complete spectrum of clinical phenotypes associated with X-linked ichthyosis, and may indicate novel pathogenic mechanisms underlying psychological dysfunction in developmental disorders such as attention deficit hyperactivity disorder and Turner syndrome.

Functional characterization of seven single-nucleotide polymorphisms of the steroid sulfatase gene found in a Japanese population

Steroid sulfatase (STS) is an enzyme that hydrolyzes steroid sulfates such as dehydroepiandrosterone sulfate (DHEA-S) and estrone sulfate. STS has a key role in the synthesis of steroid hormones in placenta and breast cancer cells. Recently, we have identified six novel single-nucleotide polymorphisms (SNPs) and one nonsynonymous SNP (V476M) in the STS gene in a Japanese population. To clarify the effects of SNPs in the 5'-flanking region or 5' untranslated region on transcriptional activity, a reporter gene assay was conducted. In addition, DHEA-S desulfatase activity of a variant (Met at codon 476)-type enzyme was compared with that of the wild (Wd)-type enzyme in COS-1 cells. The transcriptional activities were significantly decreased (155A) and increased (-2837A and -1588C) in MCF-7 cells. On the other hand, no significant difference was found in expression levels of STS protein or specific activities of DHEA-S desulfation between Wd and the variant enzymes. This is the first report on the effects of various SNPs in the STS gene detected in Japanese healthy subjects.

Ichthyosis in the newborn

The ichthyoses encompass a variety of genetic disorders marked by abnormal epidermal differentiation. The neonatal period is critical for patients with ichthyosis because of the risk for significant associated morbidity and mortality, with the majority of complications arising as a result of impaired barrier function. This article reviews presentations of ichthyosis in the neonate, outlines risks and complications, and provides strategies for management.

A case of 9.7 Mb terminal Xp deletion including OA1 locus associated with contiguous gene syndrome

Terminal or interstitial deletions of Xp (Xp22.2→Xpter) in males have been recognized as a cause of contiguous gene syndromes showing variable association of apparently unrelated clinical manifestations such as Leri-Weill dyschondrosteosis (SHOX), chondrodysplasia punctata (CDPX1), mental retardation (NLGN4), ichthyosis (STS), Kallmann syndrome (KAL1), and ocular albinism (GPR143). Here we present a case of a 13.5 yr old boy and sister with a same terminal deletion of Xp22.2 resulting in the absence of genes from the telomere of Xp to GPR143 of Xp22. The boy manifested the findings of all of the disorders mentioned above. We began a testosterone enanthate monthly replacement therapy. His sister, 11 yr old, manifested only Leri-Weill dyschondrosteosis, and had engaged in growth hormone therapy for 3 yr. To the best of our knowledge, this is the first report of a male with a 9.7 Mb terminal Xp deletion including the OA1 locus in Korea.

Double trouble: homozygous dominant mutations and hair loss in pachyonychia congenita

In this issue, Wilson et al. report the first case of homozygous dominant negative mutations in KRT17 in pachyonychia congenita (PC). Homozygous dominant negative mutations are a rare occurrence in keratin disorders and this is a first report in PC. These mutations cause a distinct sub-phenotype of PC that is more severe in the offspring of affected parents and has associated alopecia.

Familial X;Y translocation with distinct phenotypic consequences: Characterization using FISH and array CGH

X;Y translocation is a relatively rare event in humans. Analyzed cytogenetically, the majority of these aberrations have breakpoints at Xp22 and Yq11. Females with t(X;Y)(p22;q11) are phenotypically normal except for short stature, while the males may have abnormalities. Aberrations that lead to nullisomy of the deleted region and complete loss of the respective genes have been recognized as a cause of variable contiguous gene syndromes in males. The phenotype depends on the extent and position of the deletion showing the variable association of apparently unrelated clinical manifestations such as ichthyosis, chondrodysplasia punctata, hypogonadotropic hypogonadism with anosmia, ocular albinism, short stature, and mental retardation. In addition, some patients have been reported with symptoms of attention deficit hyperactivity disorder. The extent of terminal Xp deletions is limited by the presence of male lethal genes in Xp22.2 at about 10-11 Mb from the telomere. The deletions in the majority of viable reported male patients extend to the STS ( approximately 7.0 Mb) or to the KAL1 ( approximately 8.5 Mb) loci. We present a clinical, cytogenetic, FISH, and array CGH study of a family with an Xp;Yq translocation. The chromosomal status is also discussed in the light of their phenotypic traits. The final karyotypes of the patients were designated as: Patient 1: 46,Y,der(X),t(X;Y)(p22;q12).ish der(X)(Xpter-,DXZ1+,Xqter+)mat.arr cgh Xp22.31p22.33(RP11-60P14 --> RP13-391G2)x0;arr cgh Yq11.221qter (RP11-235I1 --> RP11-270H4)x2.Patient 2: 46,X,der(X),t(X;Y)(p22;q12).ish der(X)(Xpter-,DXZ1+,Xqter+)mat.arr cgh Xp22.31p22.33(RP11-60P14 --> RP13-391G2)x1;arr cgh Yq11.221qter (RP11-235I1 --> RP11-270H4)x1.

Specific estradiol biosynthetic pathway in choriocarcinoma (JEG-3) cell line

Estradiol (E2) plays a crucial role in all reproduction processes. In the placenta, it is well recognized that E2 is synthesized from fetal dehydroepiandrosterone sulfate (DHEAS). However, there is some controversy about the biosynthetic pathway involved, some authors suggest that E2 is produced by aromatization of testosterone (T), while others suggest that E2 is produced by the conversion of estrone (E1) into E2 by type 1 17beta-HSD, subsequent to the aromatization of 4-androstenedione (4-dione) into E1. In the present report, using the precursor [(14)C]DHEA, inhibitors of steroidogenic enzymes (chemical inhibitors and siRNA) and a choriocarcinoma (JEG-3) cell line that expresses all the enzymes necessary to transform DHEA into E2, we could determine the sequential steps and the specific steroidogenic enzymes involved in the transformation of DHEA into E2. Quantification of mRNA expression levels using real-time PCR, strongly suggests that type 1 3beta-hydroxysteroid dehydrogenase (3beta-HSD1), aromatase and type 1 17beta-HSD (17beta-HSD1) that are highly expressed in JEG-3 cells are the enzymes responsible for the transformation of DHEA into E2. Analysis of the intermediates produced in the absence and presence of 3beta-HSD, aromatase and 17beta-HSD1 inhibitors permits to determine the following sequential steps: DHEA is transformed into 4-dione by 3beta-HSD1, then 4-dione is aromatized into E1 by aromatase and E1 is finally transformed into E2 by 17beta-HSD1. Our data are clearly in favor of the pathway in which the step of aromatization precedes the step of reduction by 17beta-HSD.

GS2 as a retinol transacylase and as a catalytic dyad independent regulator of retinylester accretion

GS2 (PNPLA4; iPLAeta) is the smallest member of the patatin-like family of phospholipases (PNPLA). It was initially identified by its ability to hydrolyze retinylesters (RE) in cell homogenates, and was later found to esterify retinol using a variety of acyl donors. In the present study we set out to determine its cellular function and examined its impact on RE status in 293T cells transfected with GS2, GS2-M1 (a non-translatable mutant of GS2) and empty vector, in fibroblasts isolated from normal and GS2-null donors and in SCC12b and in a somatic cell knock-out of GS2 (SCC12b-GS2(neo/-)), that we generated by homologous recombination. At 50nM medium retinol, GS2 had no significant impact on RE accumulation. However, at 2muM retinol, GS2 promoted a 1.6- to 5-fold increase in RE accumulation. To verify role of GS2 as a catalyst, RE levels were measured in 293T transfected wild type GS2, catalytic dyad mutants devoid of enzymatic activity, or alanine substitution mutants spanning the entire GS2 sequence. Surprisingly, every GS2 mutant promoted RE accumulation. This activity was also observed in the GS2 paralogues and rat orthologue. The data demonstrate that within the context of the cell GS2 promotes RE accumulation and may do so either as a catalyst or as a regulatory protein that enhances RE formation catalyzed by other acyl transferases.

Contiguous gene syndrome due to a maternally inherited 8.41 Mb distal deletion of chromosome band Xp22.3 in a boy with short stature, ichthyosis, epilepsy, mental retardation, cerebral cortical heterotopias and Dandy-Walker malformation

Microdeletions of Xp22.3 are associated with contiguous gene syndromes, the extent and nature of which depend on the genes encompassed by the deletion. Common symptoms include ichthyosis, mental retardation and hypogonadism. We report on a boy with short stature, ichthyosis, severe mental retardation, cortical heterotopias and Dandy-Walker malformation. The latter two abnormalities have so far not been reported in terminal Xp deletions. MLPA showed deletion of SHOX and subsequent analysis using FISH and SNP-arrays revealed that the patient had an 8.41 Mb distal deletion of chromosome region Xp22.31 --> Xpter. This interval contains several genes whose deletion can partly explain our patient's phenotype. His cortical heterotopias and DWM suggest that a gene involved in brain development may be in the deleted interval, but we found no immediately obvious candidates. Interestingly, further analysis of the family revealed that the patient had inherited his deletion from his mother, who has a mos 46,X,del(X)(p22)/45,X/46, XX karyotype.

Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism

Many of the ichthyoses are associated with inherited disorders of lipid metabolism. These disorders have provided unique models to dissect physiologic processes in normal epidermis and the pathophysiology of more common scaling conditions. In most of these disorders, a permeability barrier abnormality "drives" pathophysiology through stimulation of epidermal hyperplasia. Among primary abnormalities of nonpolar lipid metabolism, triglyceride accumulation in neutral lipid storage disease as a result of a lipase mutation provokes a barrier abnormality via lamellar/nonlamellar phase separation within the extracellular matrix of the stratum corneum (SC). Similar mechanisms account for the barrier abnormalities (and subsequent ichthyosis) in inherited disorders of polar lipid metabolism. For example, in recessive X-linked ichthyosis (RXLI), cholesterol sulfate (CSO(4)) accumulation also produces a permeability barrier defect through lamellar/nonlamellar phase separation. However, in RXLI, the desquamation abnormality is in part attributable to the plurifunctional roles of CSO(4) as a regulator of both epidermal differentiation and corneodesmosome degradation. Phase separation also occurs in type II Gaucher disease (GD; from accumulation of glucosylceramides as a result of to beta-glucocerebrosidase deficiency). Finally, failure to assemble both lipids and desquamatory enzymes into nascent epidermal lamellar bodies (LBs) accounts for both the permeability barrier and desquamation abnormalities in Harlequin ichthyosis (HI). The barrier abnormality provokes the clinical phenotype in these disorders not only by stimulating epidermal proliferation, but also by inducing inflammation.

Filaggrin mutations are genetic modifying factors exacerbating X-linked ichthyosis

Mutations inactivating the STS gene cause X-linked ichthyosis (XLI), whereas null mutations in the FLG gene cause ichthyosis vulgaris. Two brothers presented with XLI. One had a typical fine scaling, and the other was much more severely affected. Both patients carried STS missense mutation T165I. Furthermore, the more severely affected patient also carried heterozygous FLG mutation R501X, which was absent from his mildly affected brother. These data suggest that disrupting epidermal differentiation via different pathways can increase phenotypic severity. Owing to the high population frequency of FLG mutations, filaggrin is a possible genetic modifier in other genodermatoses.

Filaggrin mutations p.R501X and c.2282del4 in ichthyosis vulgaris

Ichthyosis vulgaris (IV) is the most common hereditary disorder of cornification in humans, characterized by generalized fine scaling of the skin, palmar hyperlinearity with or without keratosis pilaris and atopy. Recently, the molecular basis of IV was ascribed to loss-of-function mutations in the gene encoding filaggrin (FLG), namely p.R501X and c.2282del4. Homozygotes and compound heterozygotes were severely affected whereas heterozygotes showed mild disease or were asymptomatic, suggesting semidominant inheritance with incomplete penetrance in heterozygotes. We report the presence of FLG mutations in 15 out of 21 IV patients with a marked generalized scaling phenotype, including eight affected members of a four-generation family. In this group of patients not only homozygous and compound heterozygous, but also heterozygous patients for p.R501X and c.2282del4 display a pronounced phenotype, whereas in none of six individuals these two mutations were detectable despite decreased filaggrin expression on immunohistochemistry in two patients, indicating that other mutations in FLG and/or in other genes remain to be identified. In contrast, two additional p.R501X heterozygotes from the extended family are asymptomatic. In a control population from west-Austria a combined p.R501X and c.2282del4 carrier frequency of 6/110 (5.45%) was observed. We confirm that these FLG variants are common, but our results point to the existence of additional modifiers.

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.

Dehydroepiandrosterone sulphate sulphohydrolase [correction of sulphoydrolase] from human placenta microsomes--properties of the purified enzyme

A form of steroid sulphate sulphohydrolase (EC 3.1.6.2) hydrolysing the dehydroepiandrosterone sulphate (DHEAS-ase) was purified from human placenta microsomes. During the purification procedure the DHEAS-ase was separated from the oestrone sulphate sulphohydrolase (OS-ase). The purified DHEAS-ase revealed specific activity of 1520 nmolxmin-1xmgprotein-1 and exhibited optimal activity at pH 8.4. The Km value was established to be 3.3+/-0.07x10(-5) M. The pI value was around 8.7. The molecular weight estimated by gel filtration was 7.4 kDa. The purified DHEAS-ase was not sensitive to the common sulphohydrolase inhibitors, such as phosphate, sulphate and sulphide ions, but was inhibited by several phosphohydrolase inhibitors (ammonium molybdate, vanadium oxide(V), zinc acetate). Steroids effected inhibition or activation of the purified enzyme. The data concerning substances reacting with -SH groups suggest that in the physiological conditions DHEAS-ase is controlled by the redox status of the cell.

Avances biomoleculares en los trastornos epidérmicos hereditarios

In recent years, the genes responsible for many hereditary skin diseases have been discovered. These genes encode different proteins that participate in the terminal differentiation of the epidermis, so their alteration or absence causes a keratinization disorder and/or an increase in skin fragility. Thanks to genetic analyses, we have been able to understand the physiopathology of numerous genodermatoses and we have become closer to diagnosing many others. In the not-too-distant future, biomolecular techniques may foreseeably help us prevent and treat these processes, which include skin diseases as serious as epidermolysis bullosa or epidermolytic hyperkeratosis. In this article, we will study the most recent biomolecular findings referring to keratinization and epidermal disorders, mentioning the altered genes and/ or the defective proteins that cause them.

Molecular genetics of the ichthyoses

The ichthyoses are a large, clinically, genetically, and etiologically heterogeneous group of disorders of cornification due to abnormal differentiation and desquamation of the epidermis. Although they differ in clinical features, inheritance, and structural and biochemical abnormalities of the epidermis, they often pose a diagnostic challenge. For each of the 12 ichthyoses and related disorders described here, the major disease genes have been identified and genotype-phenotype correlation have begun to emerge. The molecular findings reveal the functional importance and interactions of many different epidermal proteins and metabolic pathways, including major structural proteins (keratins, loricrin), enzymes involved in lipid metabolism (transglutaminase 1, lipoxygenases, fatty aldehyde dehydrogenase, steroid sulfatase, glucocerebrosidase, Delta8-Delta7 sterol isomerase, 3beta-hydroxysteroid dehydrogenase), and protein catabolism (LEKTI), peroxisomal transport and processing (Peroxin 7 receptor, Phytanoyl-CoA hydroxylase) and DNA repair (proteins of the transcription repair complex). This review highlights the spectacular advances in the molecular genetics and biology of heritable ichthyoses over the past decade. It illustrates the power of molecular diagnostics for refining disease classification, providing prenatal diagnosis, improving genetic counseling, and clinical management.

Phylogenomic approaches to common problems encountered in the analysis of low copy repeats: the sulfotransferase 1A gene family example

Background

Blocks of duplicated genomic DNA sequence longer than 1000 base pairs are known as low copy repeats (LCRs). Identified by their sequence similarity, LCRs are abundant in the human genome, and are interesting because they may represent recent adaptive events, or potential future adaptive opportunities within the human lineage. Sequence analysis tools are needed, however, to decide whether these interpretations are likely, whether a particular set of LCRs represents nearly neutral drift creating junk DNA, or whether the appearance of LCRs reflects assembly error. Here we investigate an LCR family containing the sulfotransferase (SULT) 1A genes involved in drug metabolism, cancer, hormone regulation, and neurotransmitter biology as a first step for defining the problems that those tools must manage.

Results

Sequence analysis here identified a fourth sulfotransferase gene, which may be transcriptionally active, located on human chromosome 16. Four regions of genomic sequence containing the four human SULT1A paralogs defined a new LCR family. The stem hominoid SULT1A progenitor locus was identified by comparative genomics involving complete human and rodent genomes, and a draft chimpanzee genome. SULT1A expansion in hominoid genomes was followed by positive selection acting on specific protein sites. This episode of adaptive evolution appears to be responsible for the dopamine sulfonation function of some SULT enzymes. Each of the conclusions that this bioinformatic analysis generated using data that has uncertain reliability (such as that from the chimpanzee genome sequencing project) has been confirmed experimentally or by a "finished" chromosome 16 assembly, both of which were published after the submission of this manuscript.

Conclusion

SULT1A genes expanded from one to four copies in hominoids during intra-chromosomal LCR duplications, including (apparently) one after the divergence of chimpanzees and humans. Thus, LCRs may provide a means for amplifying genes (and other genetic elements) that are adaptively useful. Being located on and among LCRs, however, could make the human SULT1A genes susceptible to further duplications or deletions resulting in 'genomic diseases' for some individuals. Pharmacogenomic studies of SULT1Asingle nucleotide polymorphisms, therefore, should also consider examining SULT1A copy number variability when searching for genotype-phenotype associations. The latest duplication is, however, only a substantiated hypothesis; an alternative explanation, disfavored by the majority of evidence, is that the duplication is an artifact of incorrect genome assembly.

Steroid hormone synthesis in pregnancy

The goal of this article is to summarize what is known about the pathways of steroid hormone synthesis and metabolism in human pregnancy. Emphasis is placed on the distinctions between steroidogenic pathways in adults and those that are operative during human pregnancy.

Basis For Abnormal Desquamation And Permeability Barrier Dysfunction in RXLI

Mutations in the gene for steroid sulfatase (SSase), are responsible for recessive x-linked ichthyosis (RXLI). As a consequence of SSase deficiency, its substrate, cholesterol sulfate (CSO4), accumulates in the epidermis. Accumulation of this amphipathic lipid in the outer epidermis provokes both a typical scaling phenotype and permeability barrier dysfunction. Research on RXLI has illuminated several, potentially overlapping pathogenic mechanisms and provided insights about the role of SSase and CSO4 in normal differentiation, barrier maintenance, and desquamation. We now show here that SSase is concentrated in lamellar bodies (LB), and secreted into the SC interstices, along with other LB-derived lipid hydrolases. There, it degrades CSO4, generating some cholesterol for the barrier, while the progressive decline in CSO4 (a serine protease (SP) inhibitor) permits corneodesmosome (CD) degradation leading to normal desquamation. Two molecular pathways contribute to disease pathogenesis in RXLI: 1) excess CSO4 produces nonlamellar phase separation in the stratum corneum (SC) interstices, explaining the barrier abnormality. 2) The increased CSO4 in the SC interstices inhibit activity sufficiently to delay CD degradation, leading to corneocyte retention. We also show here that increased Ca++ in the SC interstices in RXLI could contribute to corneocyte retention, by increasing CD and interlamellar cohesion. RXLI represents one of the best understood diseases in dermatology--from the gene to the SC interstices, its etiology and pathogenesis are becoming clear, and assessment of disease mechanisms in RXLI led to new insights about the role of SSase and CSO4 in epidermis terminal differentiation.

A familial contiguous gene deletion syndrome at Xp22.3 characterized by severe learning disabilities and ADHD

We describe a mother and two sons with a 6-Mb terminal deletion of the short arm of the X chromosome. The breakpoint was localized to a region between DXS6837 and sAJ243947 in Xp22.33. The two boys were shown to be deleted for the SHOX and ARSE genes on their X chromosome. Both sons were short in stature and showed mild to moderate skeletal abnormalities. The most significant findings in the younger son were severe learning disabilities and attention deficit hyperactivity disorder (ADHD). The older son tested in the mild mental retardation range and was also affected by ADHD. The VCX-A gene, implicated recently in X-linked nonspecific mental retardation, was found to be present in both boys. The mother's stature was greater than one standard deviation below her target height and she had only subtle radiographic evidence of Madelung deformity. Our findings indicate that loss of the Xp22.3 region is not always associated with the classic presentations of Léri-Weill syndrome, or chondrodysplasia punctata, and that one or more genes involved in learning and attention may reside in Xp22.3.

The molecular genetics of the genodermatoses: progress to date and future directions

The Human Genome Mapping Project and allied rapid advances in genetic technology over the past decade have facilitated accurate association of allelic variations in several genes with specific skin phenotypes. Currently the genetic bases of the majority of the more common genodermatoses have been elucidated. In scientific terms this work has been extraordinarily successful and has yielded many new biological insights. These advances, although exciting, have yet to be translated into direct benefit for patients with these diseases. Genetic counselling has been greatly aided by gene identification, by the better understanding of genotype-phenotype correlation and by the disclosure of unexpected genetic mechanisms in some families. Knowledge of the molecular basis of these disorders has also been vital in enabling DNA-based prenatal diagnosis in several conditions and DNA-based preimplantation diagnosis has been used in a selected few. While this successful period of gene mapping is now nearing completion, progress towards the next goal, that of developing therapeutic strategies based on the knowledge of these underlying genetic mechanisms, has proven frustratingly slow. Despite the ready access to the skin compared with solid internal organs, the challenges of cutaneous gene therapy are legion and many technical issues need to be surmounted to enable gene replacement or modification of gene expression to have a useful role in these disorders. In this article we make a comprehensive review of progress to date in gene identification, genotype-phenotype correlation, prenatal diagnosis and cutaneous gene therapy, and we examine future directions for research in this field.

Progress in molecular genetics of heritable skin diseases: the paradigms of epidermolysis bullosa and pseudoxanthoma elasticum

The 42nd Annual Symposium on the Biology of the Skin, entitled "The Genetics of Skin Disease", was held in Snowmass Village, Colorado, in July 1993. That meeting presented the opportunity to discuss how modern approaches to molecular genetics and molecular biology could be applied to understanding the mechanisms of skin diseases. The published proceedings of this meeting stated that "It is an opportune time to examine the genetics of skin disease" (Norris et al, 1994). Indeed, this meeting just caught the wave of early pioneering studies that have helped us to understand the molecular basis of a large number of genodermatoses. This overview presented in the 50th Annual Symposium on the biology of the skin, highlights the progress made in the molecular genetics of heritable skin diseases over the past decade.

Somatic and germinal mosaicism for the steroid sulfatase gene deletion in a steroid sulfatase deficiency carrier

Steroid sulfatase deficiency results in X-linked ichthyosis, an inborn error of metabolism in which the principal molecular defect is the complete deletion of the steroid sulfatase gene and flanking markers. Mosaicism for the steroid sulfatase gene has not yet been reported in X-linked ichthyosis. In this study we describe an X-linked ichthyosis patient with complete deletion of the steroid sulfatase gene and his mother with somatic and germinal mosaicism for this molecular defect. The family (X-linked ichthyosis patient, grandmother, mother, and sister) was analyzed through steroid sulfatase enzyme assay, polymerase chain reaction, DNA markers, and fluorescence in situ hybridization of the steroid sulfatase gene. Steroid sulfatase activity was undetectable in the X-linked ichthyosis patient, very low in the mother, and normal in the grandmother and sister. The X-linked ichthyosis patient showed a 2 Mb deletion of the steroid sulfatase gene and flanking regions from 5'DXS1139 to 3'DXF22S1. The mother showed one copy of the steroid sulfatase gene in 98.5% of oral cells and in 80% of leukocytes. The grandmother and sister showed two copies of the steroid sulfatase gene. The origin of the X chromosome with the deletion of the steroid sulfatase gene corresponded to the grandfather of the proband. We report the first case of somatic and germinal mosaicism of the steroid sulfatase gene in an X-linked ichthyosis carrier and propose DNA slippage as the most plausible mechanism in the genesis of this mosaicism.

Segmental duplications: an 'expanding' role in genomic instability and disease

The knowledge that specific genetic diseases are caused by recurrent chromosomal aberrations has indicated that genomic instability might be directly related to the structure of the regions involved. The sequencing of the human genome has directed significant attention towards understanding the molecular basis of such recombination 'hot spots'. Segmental duplications have emerged as a significant factor in the aetiology of disorders that are caused by abnormal gene dosage. These observations bring us closer to understanding the mechanisms and consequences of genomic rearrangement.

Carrier identification by FISH analysis in isolated cases of X-linked ichthyosis

X-linked ichthyosis (XLI) is an inborn error of metabolism due to steroid sulfatase (STS) deficiency. STS assay and FISH are useful in diagnosing carrier status of XLI. Biochemical analysis appears to indicate that most sporadic cases are inherited. Since this method does not seem to be completely reliable in recognizing XLI-carriers, the aim of the present study was to corroborate by FISH whether or not most sporadic cases of XLI had de novo mutations. XLI patients were classified through STS assay and PCR amplification of 5'-3' ends of the STS gene. XLI patients had undetectable levels of STS activity and complete deletion of the STS gene. Patients' mothers were studied through STS assay and FISH. Nine out of 12 mothers presented an STS activity compatible with XLI-carrier state. These mothers also had only one copy of the STS gene, indicating that they carry the primary gene defect. One mother had normal STS activity but only one copy of the STS gene. This data corroborated that most sporadic cases do not represent de novo mutations, and that FISH must be included in the analysis of mothers of sporadic cases when they present with normal STS activity, in order to correctly diagnose the XLI carrier state.

Deletion of exons 1-5 of the STS gene causing X-linked ichthyosis

X-linked ichthyosis is an inherited disorder due to steroid sulfatase deficiency. It is clinically characterized by dark, adhesive, and regular scales of the skin. Most X-linked ichthyosis patients present large deletions of the STS gene and flanking markers; a minority show a point mutation or partial deletion of the STS gene. In this study we analyzed the STS gene in a family with simultaneous occurrence of X-linked ichthyosis and ichthyosis vulgaris. X-linked ichthyosis diagnosis was confirmed through steroid sulfatase assay in leukocytes using 7-[3H]-dehydroepiandrosterone sulfate as a substrate. Exons 1, 2, 5, and 6-10, and the 5' flanking markers DXS1130, DXS1139, and DXS996 of the STS gene were analyzed by polymerase chain reaction. X-linked ichthyosis patients of the family (n = 4 males) had undetectable levels of STS activity (0.00 pmol per mg protein per h). The DNA analysis showed that only exons 6-10 and the 5' flanking markers of the STS gene were present. We report the first partial deletion of the STS gene spanning exons 1-5 in X-linked ichthyosis patients.

The morbid anatomy of the dermatologic genome: an update for the third millennium

BACKGROUND

Much progress has been made in recent years in the identification of genes underlying many hereditary skin diseases.

OBJECTIVE

To provide an update on the status of the identification of genes involved in hereditary skin disorders and to compare the current standing with that in the last decade.

METHODS

A review of the literature is presented here in a series of lists describing the chromosomal location, specific gene, clinical relevance, and availability of molecular-based genetic tests for each genodermatosis.

RESULTS

Progress has been made in identifying the genes underlying many disorders of cornification, genodermatoses with malignant potential, bullous disorders, pigmentary disorders, disorders affecting the epidermal appendages and the dermis, and other miscellaneous genodermatoses.

CONCLUSION

The great progress made toward the completion of the human gene sequence and the continued efforts of many clinical and molecular scientists to identify disease genes will make diagnosis of hereditary dermatological disorders more precise and allow accurate family counseling as well as possibly leading to more targeted therapies during this millennium.