A clinical and genetic study of X-linked recessive ichthyosis and contiguous gene defects

RNA sequencing and lipidomics uncovers novel pathomechanisms in recessive X-linked ichthyosis

Recessive X-linked ichthyosis (RXLI), a genetic disorder caused by deletion or point mutations of the steroid sulfatase (STS) gene, is the second most common form of ichthyosis. It is a disorder of keratinocyte cholesterol sulfate retention and the mechanism of extracutaneous phenotypes such as corneal opacities and attention deficit hyperactivity disorder are poorly understood. To understand the pathomechanisms of RXLI, the transcriptome of differentiated primary keratinocytes with STS knockdown was sequenced. The results were validated in a stable knockdown model of STS, to confirm STS specificity, and in RXLI skin. The results show that there was significantly reduced expression of genes related to epidermal differentiation and lipid metabolism, including ceramide and sphingolipid synthesis. In addition, there was significant downregulation of aldehyde dehydrogenase family members and the oxytocin receptor which have been linked to corneal transparency and behavioural disorders respectively, both of which are extracutaneous phenotypes of RXLI. These data provide a greater understanding of the causative mechanisms of RXLI's cutaneous phenotype, and show that the keratinocyte transcriptome and lipidomics can give novel insights into the phenotype of patients with RXLI.

Prevalence and Phenotypic Effects of Copy Number Variants in Isolated Hypogonadotropic Hypogonadism

CONTEXT

The genetic architecture of isolated hypogonadotropic hypogonadism (IHH) has not been completely defined.

OBJECTIVE

To determine the role of copy number variants (CNVs) in IHH pathogenicity and define their phenotypic spectrum.

METHODS

Exome sequencing (ES) data in IHH probands (n = 1394) (Kallmann syndrome [IHH with anosmia; KS], n = 706; normosmic IHH [nIHH], n = 688) and family members (n = 1092) at the Reproductive Endocrine Unit and the Center for Genomic Medicine of Massachusetts General Hospital were analyzed for CNVs and single nucleotide variants (SNVs)/indels in 62 known IHH genes. IHH subjects without SNVs/indels in known genes were considered "unsolved." Phenotypes associated with CNVs were evaluated through review of patient medical records. A total of 29 CNVs in 13 genes were detected (overall IHH cohort prevalence: ~2%). Almost all (28/29) CNVs occurred in unsolved IHH cases. While some genes (eg, ANOS1 and FGFR1) frequently harbor both CNVs and SNVs/indels, the mutational spectrum of others (eg, CHD7) was restricted to SNVs/indels. Syndromic phenotypes were seen in 83% and 63% of IHH subjects with multigenic and single gene CNVs, respectively.

CONCLUSION

CNVs in known genes contribute to ~2% of IHH pathogenesis. Predictably, multigenic contiguous CNVs resulted in syndromic phenotypes. Syndromic phenotypes resulting from single gene CNVs validate pleiotropy of some IHH genes. Genome sequencing approaches are now needed to identify novel genes and/or other elusive variants (eg, noncoding/complex structural variants) that may explain the remaining missing etiology of IHH.

Tracing skin aging process: a mini- review of in vitro approaches

Skin is a rather complex, yet useful organ of our body. Besides, skin aging is a complicated process that gains a growing interest as mediates many molecular processes in our body. Thus, an efficient skin model is important to understand skin aging function as well as to develop an effective innovative product for skin aging treatment. In this mini review, we present in vitro methods for assessments of skin aging in an attempt to pinpoint basic molecular mechanisms behind this process achieving both a better understanding of aging function and an effective  evaluation of potential products or ingredients that counteract aging. Specifically, this study presents in vitro assays such as 2D or 3D skin models, to evaluate skin aging-related processes such as skin moisturization, photoaging, wound healing, menopause, and skin microbiome as novel efforts in the designing of efficacy assessments in the development of skincare products.

Clinico-epidemiological Study of Congenital Ichthyosis in a Tertiary Care Center of Eastern India

Background

Congenital ichthyoses comprises various specific genetic diseases and can range from mild to very severe presentation. Furthermore, these may be associated with various syndromes. There is scanty data regarding the demographic profile and clinical features of patients with congenital ichthyosis in India.

Aims and Objectives

The aim is to evaluate the epidemiology and clinical characteristics of various types of congenital ichthyoses.

Materials and Methods

The study was conducted for 1 year from April 2013 to March 2014. Patients were evaluated for epidemiological profile and clinical features.

Results

During the study of 1 year, 106 patients of congenital ichthyoses were identified. The most common of the various ichthyoses was ichthyosis vulgaris, followed by lamellar ichthyosis, X-linked recessive ichthyosis. One case of Netherton syndrome and one of ichthyosis hystrix were also identified.

Conclusion

Various types of congenital ichthyoses present with different clinical features which range from mild to severe. These present with significant psychological stress to both patients and their families. Furthermore, all these diseases have significant implications of transmission to their offspring.

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.

Steroid-resistant nephrotic syndrome associated with steroid sulfatase deficiency-x-linked recessive ichthyosis: a case report and review of literature

Nephrotic syndrome associated with X-linked recessive ichthyosis due to steroid sulfatase deficiency has rarely been reported in English literature. We describe a 4 and a half-year-old boy presenting with steroid-resistant nephrotic syndrome (SRNS) with an underlying ichthyotic skin present since birth. Renal biopsy revealed minimal change disease. As many of the male members of the family also showed similar skin manifestations, genetic analysis was done on the patient, which revealed deletion of the steroid sulfatase (STS) gene spanning both the 3' as well as the 5'ends. The patient was thus diagnosed with SRNS associated with X-linked recessive ichthyosis. He was started on cyclosporine regimen, and remission was achieved in 5 weeks. We speculate that the deficiency of STS resulting in increased cholesterol sulfate accumulation interferes with the integrity of adherens junctions present between glomerular epithelial cells of the slit diaphragm, and this results in proteinuria and nephrotic syndrome. The nephrotic syndrome remitted with a calcineurin inhibitor medication.

CONCLUSION

We suggest that the deficiency of STS is another one in an increasing list of genetic causes of podocytopathy and nephrotic syndrome. Remission of proteinuria in such a case may be achieved with immunosuppressive medication.

Large contiguous gene deletions in Sjögren-Larsson syndrome

Sjögren-Larsson syndrome (SLS) is an autosomal recessive disorder characterized by ichthyosis, mental retardation, spasticity and mutations in the ALDH3A2 gene for fatty aldehyde dehydrogenase, an enzyme that catalyzes the oxidation of fatty aldehyde to fatty acid. More than 70 mutations have been identified in SLS patients, including small deletions or insertions, missense mutations, splicing defects and complex nucleotide changes. We now describe 2 SLS patients whose disease is caused by large contiguous gene deletions of the ALDH3A2 locus on 17p11.2. The deletions were defined using long distance inverse PCR and microarray-based comparative genomic hybridization. A 24-year-old SLS female was homozygous for a 352-kb deletion involving ALDH3A2 and 4 contiguous genes including ALDH3A1, which codes for the major soluble protein in cornea. Although lacking corneal disease, she showed severe symptoms of SLS with uncommon deterioration in oral motor function and loss of ambulation. The other 19-month-old female patient was a compound heterozygote for a 1.44-Mb contiguous gene deletion and a missense mutation (c.407C>T, P136L) in ALDH3A2. These studies suggest that large gene deletions may account for up to 5% of the mutant alleles in SLS. Geneticists should consider the possibility of compound heterozygosity for large deletions in patients with SLS and other inborn errors of metabolism, which has implications for carrier testing and prenatal diagnosis.

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.

Maternal urine and serum steroid measurements to identify steroid sulfatase deficiency (STSD) in second trimester pregnancies

OBJECTIVE

To document the performance of second trimester maternal urine and serum steroid measurements for detecting fetal steroid sulfatase deficiency (STSD).

METHODS

We studied detection rate and false positive rate (DR, FPR) of analytes in maternal urine [combinations of 16alpha-OH-dehydroepiandrosterone sulfate (16alpha-OH-DHEAS), 11beta-hydroxyandrosterone, total estriol] and serum [combinations of 16alpha-OH-DHEAS, 11beta-hydroxyandrosterone, total estriol, unconjugated estriol (uE3)]. Samples were obtained from pregnancies which were screen positive for Smith-Lemli-Opitz syndrome (SLOS).

RESULTS

Among 1 079 301 pregnancies, 3083 (0.29%) were screen positive for SLOS. Urine and/or serum samples were available from 917 viable pregnancies with known gender. We assigned likelihood ratios (LRs) to steroid measurements from male fetuses with known STSD and unaffected female fetuses. An LR > or = 100 was present in urine from 84 of 86 STSD pregnancies (98% DR, 95% CI 92-99), along with 0 of 198 pregnancies with normal female fetuses (0.0% FPR, CI 0-1.9). LRs were > or = 100 in 4 of 129 female fetuses with major abnormalities (3% FPR). In maternal serum, steroid measurements performed less effectively, achieving a 71% DR for STSD at a 1.6% FPR.

CONCLUSION

Maternal urine steroid measurements are effective for detecting STSD, including those with point mutations and those with full deletions.

Ichthyoses - Part 1: Differential diagnosis of vulgar ichthyoses and therapeutic options

Ichthyoses are a group of genetic disorders with defective cornification, clinically characterized by scaling of the skin. Additionally, distinctive cutaneous inflammation can often be observed. For most of the patients these diseases lead to a significant restriction in quality of life. The diagnostic criteria include clinical and histological findings, often confirmed by specialized tests. Because many of the ichthyoses are extremely rare, their accurate diagnosis is often carried out in specialized centers. We summarize isolated vulgar and congenital ichthyoses both with and without associated symptoms and focus on the common genetic changes and their clinical phenotype. Specific therapies are still not available for most of these genetic disorders. The use of different topical agents (e. g. urea, retinoids and salicylic acid) and baths followed by mechanical keratolysis (sometimes in combination with systemic retinoids) reduce symptoms. Patients with uncommon congenital ichthyoses often benefit from interdisciplinary management which involves specialized dermatological centers. In this first part of the paper the vulgar ichthyoses as well as the diagnostic and therapeutic options are discussed. The second part focuses on the congenital ichthyoses and their differential diagnosis.

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.

End-stage renal failure in a child with X-linked ichthyosis

We describe an 8-year-old boy who presented with steroid-resistant nephrotic syndrome (SRNS) associated with X-linked ichthyosis (XLI). At birth, the patient exhibited scaly skin, cryptorchidism, and steroid sulfatase (STS) deficiency. DNA analysis showed deletion of exons 1-10 of the STS gene. Proteinuria developed at 6 years and was resistant to steroid therapy. Kidney biopsy findings prior to steroid therapy were compatible with minimal change nephrotic syndrome. By immunofluorescence, glomerular basement membranes exhibited diffuse linear staining for the alpha5 chain of collagen IV, making X-linked Alport syndrome an unlikely explanation for the association of SRNS and ichthyosis. Despite immunosuppressive therapy together with oral prednisolone, no clinical response was achieved. He rapidly reached end-stage renal failure and finally underwent renal transplantation. We propose that SRNS should be considered as one of the highly variable phenotypes associated with XLI.

Molecular advances in genetic skin diseases

The genes for several genetic skin diseases have been identified in recent years. This development improves diagnostic capabilities and genetic counseling, and investigators can now turn to the molecular mechanisms involved in the pathogenesis of these diseases. The identification of the causative genes has led to the generation of mouse models for some genetic skin diseases. A study of the keratin 10 deficient mouse, a model for epidermolytic hyperkeratosis, and a mouse model for Bloom syndrome are reviewed in this article. Several studies also evaluate the relation between genotype and phenotype. In this article, the clinical findings and molecular advances in tuberous sclerosis complex, neurofibromatosis type 1, Bloom syndrome, epidermolytic hyperkeratosis, X-linked ichthyosis, Netherton syndrome, and Hermansky-Pudlak syndrome are reviewed.

Brachytelephalangic dwarfism due to the loss of ARSE and SHOX genes resulting from an X;Y translocation

Here we report an 8-year-old male patient who had mesomelic shortening of forearms and legs, brachytelephalangia and ichthyotic skin lesions. Chromosomal analysis showed an X;Y translocation involving the short arm of the X chromosome (Xp). Fluorescence in situ hybridization (FISH) and molecular studies localized the breakpoints on Xp22.3 in the immediate vicinity of the KAL gene demonstrating deletions of steroid sulfatase (STS), arylsulfatase E (ARSE), and short stature homeo box (SHOX) genes. It was suspected that the patient was suffering from chondrodysplasia punctata because of a loss of the arylsulfatase E (ARSE) gene. However, no stippled epiphyses were to be seen in the neonatal radiograph. Interestingly, this patient is the first case with a proven loss of the ARSE gene without chondrodysplasia punctata, assuming that chondrodysplasia punctata is not an obligatory sign of ARSE gene loss. Brachytelephalangia was the only result of ARSE gene deletion in this case. The patient's mother also had dwarfism and showed Madelung deformity of the forearms. She was detected as a carrier of the same aberrant X chromosome. The male patient did not show Madelung deformity, demonstrating that Lerri-Weill syndrome phenotype may be still incomplete in children with SHOX gene deletion. The wide clinical spectrum in the male and the Leri-Weill phenotype in his mother are the results of both a deletion involving several sulfatase genes in Xp22.3 and the SHOX gene located in the pseudoautosomal region. Nevertheless, there is no explanation for the absence of chondrodysplasia punctata despite the total loss of the ARSE gene. Further studies are necessary to investigate genotype/phenotype correlation in cases with translocations or microdeletions on Xp22.3, including the ARSE and the SHOX gene loci.

X-linked ichthyosis: an update

X-linked ichthyosis is a genetic disorder of keratinization characterized by a generalized desquamation of large, adherent, dark brown scales. Extracutaneous manifestations include corneal opacity and cryptorchidism. Since 1978 it has been known that a deficit in steroid sulphatase enzyme (STS) is responsible for the abnormal cutaneous scaling, although the exact physiological mechanism remains uncertain. The STS gene has been mapped to the distal part of the short arm of the X chromosome. Interestingly, this region escapes X chromosome inactivation and has the highest ratio of chromosomal deletions among all genetic disorders, complete deletions having been found in up to 90% of patients. Diagnosis of patients with X-linked ichthyosis and female carriers is based on biochemical and genetic analysis. The latter currently seems to be the most accurate method in the majority of cases.

An atypical contiguous gene syndrome: molecular studies in a family with X-linked Kallmann's syndrome and X-linked ichthyosis

BACKGROUND AND OBJECTIVE

Kallmann's syndrome (KS) is characterized by hypogonadotrophic hypogonadism in association with anosmia or hyposmia. This entity can be associated with X-linked ichthyosis (XLI) in a contiguous gene syndrome. Genetic defects have been demonstrated on the Xp22.3 region explaining the presence of one or both entities in affected individuals. In this report we describe the molecular findings in four patients, pertaining to a three generation family, with KS which was associated with XLI in two of them.

MEASUREMENTS

Enzymatic activity of steroid sulphatase was measured in leucocytes. Polymerase chain reaction of the 14 exons of the Kallmann gene (KAL) and of the 5' and 3' extremes of the steroid sulphatase gene was performed in genomic DNA. PCR products of the 14 exons of the KAL gene were purified and sequenced.

RESULTS

Absence of steroid sulphatase activity and a complete deletion of the STS gene were demonstrated in both patients with XLI. In all subjects, the 14 KAL gene exons amplified in a normal fashion; no mutation was documented after sequencing all exons.

CONCLUSIONS

Although it has been proposed recently that the X-linked form of the disease accounts for the minority of patients with Kallman's syndrome, the pedigree chart of this family demonstrates this inheritance pattern. Various possibilities are mentioned in order to explain the absence of mutation in the KAL gene. The coexistence, in this family, of Kallman's syndrome individuals and patients with Kallman's syndrome and X-linked ichthyosis is discussed.

Ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome: clinical and neuropathological observations in a 33-year-old man

The syndrome of ichthyosis follicularis, alopecia, and photophobia (IFAP) is an uncommon neuroichthyosis described in only 10 males so far. We report on a man with congenital ichthyosis and alopecia with apparently normal development in early infancy. Photophobia and generalized myoclonicastatic seizures began during or after the first year of age and were associated with progressive impairment of motor skills and mental abilities. He died at 33 years of age. Neuropathological findings showed an unusual deformation of the temporal lobes and olivocerebellar atrophy. Cytogenetic and molecular studies did not uncover deletions in either Xp22.2 to 3 or in Xq27.3 to qter.

X-linked dominant chondrodysplasia punctata: a peroxisomal disorder?

X-linked dominant chondrodysplasia punctata is characterised by resolving irregular punctate calcifications of epiphyses, variable ichthyosis and atrophoderma, short stature, and cataracts. We report on a patient with this syndrome who had transiently abnormal peroxisomal function tests. We review the literature and propose that X-linked dominant chondrodysplasia punctata is a peroxisomal disorder and that its phenotype can be explained by X chromosome lyonisation and the relative proliferation of cells expressing the normal X allele.

Analysis of an interstitial deletion in a patient with Kallmann syndrome, X-linked ichthyosis and mental retardation

Contiguous gene syndromes are an interesting clinical phenomenon, resulting from interstitial or terminal deletions of several adjacent genes. The phenotype results in a combination of two or more monogenic disorders and relates clinical findings to corresponding genotypes. We present the case of a male patient with Kallmann syndrome (KS), X-linked ichthyosis (XLI) and X-linked mental retardation (MRX). He was referred at the age of 15.4 years for delayed puberty and obesity. He had a previous history of pyloric stenosis, bilateral orchidopexy and surgical correction of a pes equinovarus adductus. On physical examination, generalised ichthyosis and hypoplastic external genitalia were found. KS was evident with hypogonadotropic hypogonadism, hyposmia and a hypoplastic anlage of the olfactory tract in magnetic resonance imaging. Lipoprotein electrophoresis, and lack of steroid sulfatase and arylsulfatase-C activity in leucocytes confirmed XLI. DNA investigation established an interstitial deletion in Xp22.3 involving the Kallmann (KAL) gene, the steroid sulfatase (STS) gene and a putative mental retardation locus (MRX). The novel MRX locus maps to a 1-Mb region between DXS1060 and GS1.

Contiguous gene syndrome due to deletion of the first three exons of the Kallmann gene and complete deletion of the steroid sulphatase gene

OBJECTIVE

Large terminal or interstitial deletions of the 22.3 region on the short arm of the X chromosome cause contiguous gene syndromes. Kallmann syndrome (hypogonadotrophic hypogonadism with anosmia or hyposmia) associated with X-linked ichthyosis, due to a contiguous gene syndrome, is an uncommon finding. Genetic defects have been demonstrated in the Xp22.3 region, explaining the presence of one or both entities in affected individuals. In this report we describe the molecular findings of a patient with Kallmann syndrome and X-linked ichthyosis.

PATIENT

A 20-year-old subject with hypogonadism, anosmia and generalized ichthyosis was studied endocrinologically, biochemically and molecularly.

MEASUREMENTS

Levels of LH, FSH, GH, testosterone, oestradiol and cortisol were determined basally and after specific stimulation tests. Enzymatic activity of steroid sulphatase was measured in leucocytes. Polymerase chain reaction of the 14 exons of the Kallmann gene and of the 5' and 3' extremes of the steroid sulphatase gene was performed in genomic DNA.

RESULTS

A partial deletion from exon 1 to exon 3 of the Kallmann gene, as well as a complete deletion of the steroid sulphatase gene were observed.

CONCLUSIONS

A patient bearing a contiguous gene syndrome with partial deletion of the Kallmann syndrome gene and complete deletion of the steroid sulphatase gene is described. This is the first time a mutation in the conserved cysteine-rich N-terminal region which corresponds to the whey acidic protein motif of the Kallmann gene has been characterized, thus demonstrating the importance of this specific region for the function of the gene.

A recurrent missense mutation in the KAL gene in patients with X-linked Kallmann's syndrome

Kallmann's syndrome (KS) is defined by the association of hypogonadotropic hypogonadism and anosmia or hyposmia. Segregation analysis in familial cases has demonstrated diverse inheritance patterns, suggesting the existence of several genes regulating GnRH secretion. Genetic defects have been demonstrated in the KAL gene, located on the Xp22.3 region, explaining the X-linked form of the disease. We report molecular findings regarding the KAL gene in 12 unrelated males with X-linked KS. PCR of the 14 exons of the KAL gene was performed on genomic DNA. PCR products of all exons were purified and sequenced. Genetic defects in the KAL gene were found in 7 patients. One exhibits a deletion from exon 3 to exon 5. Six individuals present a previously unidentified missense mutation in exon 11, consisting of a G to A substitution at codon 514 (GAA to AAA). In the remaining 5 individuals, no mutations were observed. We also found three different polymorphic changes. The first one, in exon 2, had not been reported previously. The other two were located at exons 11 and 12. The deletion described, comprises only part (exon 5) of the coding region of the first fibronectin type III-like repeat of the KAL protein. The rest of the deletion comprises part of the conserved cysteine-rich N-terminal region that corresponds to the whey acidic protein motif. The same missense mutation was found in 6 of the 12 patients, indicating the possibility that it derived from a common ancestor or suggesting the presence of a hot spot in this region of the gene.

Biology and function of the reversible sulfation pathway catalysed by human sulfotransferases and sulfatases

Sulfation and sulfate conjugate hydrolysis play an important role in metabolism, and are catalysed by members of the sulfotransferase and sulfatase enzyme super-families. In general, sulfation is a deactivating, detoxication pathway, but for some chemicals the sulfate conjugates are much more reactive than the parent compound. The range of compounds which are sulfated is enormous, yet we still understand relatively little of the function of this pathway. This review summarises current knowledge of the sulfation system and the enzymes involved, and illustrates how heterologous expression of sulfotransferases (SULTs) and sulfatases is aiding our appreciation of the properties of these important proteins. The role of sulfation in the bioactivation of procarcinogens and promutagens is discussed, and new data on the inhibition of the sulfotransferase(s) involved by common dietary components such as tea and coffee are presented. The genetic and environmental factors which are known to influence the activity and expression of human SULTs and sulfatases are also reviewed.

Protein processing: a role in the pathophysiology of genetic disease

Genetic diseases associated with an enzyme deficiency frequently have reduced intracellular levels of the mutant protein, despite apparently normal levels of message and protein synthesis. It has been suggested that the endoplasmic reticulum (ER) can recognise mutant protein as incorrectly folded and invoke 'quality control' processes which cause the retention and degradation of this protein. This process may occur, even for mutations which do not abrogate protein activity, contributing directly to pathophysiology. Genetic diseases associated with defects in ER and Golgi processing proteins have also been reported and generally result in impaired processing of multiple protein products. In this review the role of the ER and Golgi in the pathogenesis of genetic diseases relating to the vacuolar network are discussed.

A model of corrective gene transfer in X-linked ichthyosis

Single gene recessive genetic skin disorders offer attractive prototypes for the development of therapeutic cutaneous gene delivery. We have utilized X-linked ichthyosis (XLI), characterized by loss of function of the steroid sulfatase arylsulfatase C (STS), to develop a model of corrective gene delivery to human skin in vivo. A new retroviral expression vector was produced and utilized to effect STS gene transfer to primary keratinocytes from XLI patients. Transduction was associated with restoration of full-length STS protein expression as well as steroid sulfatase enzymatic activity in proportion to the number of proviral integrations in XLI cells. Transduced and uncorrected XLI keratinocytes, along with normal controls, were then grafted onto immunodeficient mice to regenerate full thickness human epidermis. Unmodified XLI keratinocytes regenerated a hyperkeratotic epidermis lacking STS expression with defective skin barrier function, effectively recapitulating the human disease in vivo. Transduced XLI keratinocytes from the same patients, however, regenerated epidermis histologically indistinguishable from that formed by keratinocytes from patients with normal skin. Transduced XLI epidermis demonstrated STS expression in vivo by immunostaining as well as a normalization of histologic appearance at 5 weeks post-grafting. In addition, transduced XLI epidermis demonstrated a return of barrier function parameters to normal. These findings demonstrate corrective gene delivery in human XLI patient skin tissue at both molecular and functional levels and provide a model of human cutaneous gene therapy.

Inherited ichthyoses: a review of the histology of the skin

The histology of skin biopsies from 46 cases of different forms of congenital ichthyosis was reviewed. Sections were examined for hyperkeratosis, follicular keratosis, appearance of the granular layer, epidermal thickness, tonofilament clumps, epidermal vacuolation, spongiosis, bullae and dyskeratosis, appearance of the basal layer, inflammation, mitoses, and adnexae. A detailed description of the histological features of each type of ichtnyosis studied is presented. Some ichthyoses can be recognized on routine hematoxylin and eosin staining (bullous ichthyosiform erythroderma, Netherton's syndrome, and neutral lipid storage disease); some forms require frozen sections to demonstrate fat (neutral lipid storage disease) or enzyme activity (Sjögren-Larsson syndrome). Protein electrophoresis and enzymology are necessary for X-linked recessive ichthyosis. A close liaison with the clinicians is essential for the diagnosis of all types of ichthyosis, and combined studies including routine histopathology, electron microscopy, and frozen sections may be required for the diagnosis.