Mutations in SPINK5, encoding a serine protease inhibitor, cause Netherton syndrome

Prenatal diagnosis of a lethal form of Netherton syndrome by SPINK5 mutation analysis

Netherton syndrome (NS) is a severe autosomal recessive ichthyosis with no specific treatment or prenatal diagnosis available at present. The recent identification of SPINK5, which encodes a serine protease inhibitor, as the defective gene enables DNA based prenatal diagnosis to be carried out. Here we report the first direct molecular prenatal diagnosis of a lethal form due to a recurrent SPINK5 mutation in three consanguineous Turkish families. XmnI restriction enzyme digestion and DNA sequencing demonstrated that each deceased affected child was homozygous for mutation 153delT inherited from each parent. Analysis of fetal DNA from amniotic fluid cells in Family 1 and from a chorionic villus sampling in Family 3 showed that the fetus was heterozygous for 153delT in both cases. The pregnancies were carried to term and the newborns were unaffected. In Family 2, fetal DNA analysis from chorionic villus biopsy showed in a first pregnancy that the fetus was homozygous for 153delT. The pregnancy was terminated at 13 weeks and DNA analysis of fetal keratinocytes confirmed the prenatal prediction. In a second pregnancy in Family 2, fetal DNA analysis showed heterozygosity for 153delT, and the pregnancy was continued. Direct SPINK5 mutation analysis in families at risk for NS represents the first early, rapid and reliable method for prenatal diagnosis of this life threatening form of ichthyosis.

Netherton syndrome: disease expression and spectrum of SPINK5 mutations in 21 families

Netherton syndrome is a severe autosomal recessive skin disorder characterized by congenital erythroderma, a specific hair-shaft abnormality, and atopic manifestations with high IgE levels. Recently, we identified SPINK5, which encodes the serine protease inhibitor Kazal-type 5 protein (LEKTI), as the defective gene in Netherton syndrome. Here we describe the intron-exon organization of the gene and characterize the SPINK5 mutations in patients from 21 families of different geographic origin, using denaturing high performance liquid chromatography and direct sequencing. We identified 18 mutations, of which 13 were novel and seven (39%) were recurrent. The majority of the mutations were clustered between exons 1-8 and exons 21-26. They comprised four nonsense mutations (22%), eight frameshift insertions or deletions (44%), and six splice-site defects (33%). All mutations predict the formation of premature termination codons. Northern blot analysis showed variable reduction of SPINK5 mutant transcript levels, suggesting variable efficiency of nonsense-mediated mRNA decay. Seven patients were homozygotes, eight were compound heterozygotes, and five were heterozygotes with only one identifiable SPINK5 mutation. Five mutations, one of which resulted in perinatal lethal disease in three families, were associated with certain ethnic groups. We also describe 45 intragenic polymorphisms in the patients studied. The clinical features of erythroderma, trichorrhexis invaginata, and atopic manifestations were present in the majority of affected individuals and ichthyosis linearis circumflexa was seen in 12 out of 24 patients. Interfamilial and intrafamilial variation in disease severity was observed, with no clear correlation between mutations and phenotype, suggesting that the degree of severity may be affected by other factors.

Computational analysis of human disease-associated genes and their protein products

The complete genome sequences for human, Drosophila melanogaster and Arabidopsis thaliana have been reported recently. With the availability of complete sequences for many bacteria and archaea, and five eukaryotes, comparative genomics and sequence analysis are enabling us to identify counterparts of many human disease genes in model organisms, which in turn should accelerate the pace of research and drug development to combat human diseases. Continuous improvement of specialized protein databases, together with sensitive computational tools, have enhanced the power and reliability of computational prediction of protein function.

Gene polymorphism in Netherton and common atopic disease

Atopic dermatitis (AD) and asthma are characterized by IgE-mediated atopic (allergic) responses to common proteins (allergens), many of which are proteinases. Loci influencing atopy have been localized to a number of chromosomal regions, including the chromosome 5q31 cytokine cluster. Netherton disease is a rare recessive skin disorder in which atopy is a universal accompaniment. The gene underlying Netherton disease (SPINK5) encodes a 15-domain serine proteinase inhibitor (LEKTI) which is expressed in epithelial and mucosal surfaces and in the thymus. We have identified six coding polymorphisms in SPINK5 (Table 1) and found that a Glu420-->Lys variant shows significant association with atopy and AD in two independent panels of families. Our results implicate a previously unrecognized pathway for the development of common allergic illnesses.

The spectrum of pathogenic mutations in SPINK5 in 19 families with Netherton syndrome: implications for mutation detection and first case of prenatal diagnosis

The Comèl-Netherton syndrome is an autosomal recessive multisystemic disorder characterized by localized or generalized congenital ichthyosis, hair shaft abnormalities, immune deficiency, and markedly elevated IgE levels. Life-threatening complications during infancy include temperature and electrolyte imbalance, recurrent infections, and failure to thrive. To study the clinical presentations of the Comèl-Netherton syndrome and its molecular cause, we ascertained 19 unrelated families of various ethnic backgrounds. Results of initial linkage studies mapped the Comèl-Netherton syndrome in 12 multiplex families to a 12 cM interval on 5q32, thus confirming genetic homogeneity of Comèl-Netherton syndrome across families of different origins. The Comèl-Netherton syndrome region harbors the SPINK5 gene, which encodes a multidomain serine protease inhibitor (LEKTI) predominantly expressed in epithelial and lymphoid tissues. Recently, recessive mutations in SPINK5 were identified in several Comèl-Netherton syndrome patients from consanguineous families. We used heteroduplex analysis followed by direct DNA sequencing to screen all 33 exons and flanking intronic sequences of SPINK5 in the affected individuals of our cohort. Mutation analysis revealed 17 distinct mutations, 15 of which were novel, segregating in 14 Comèl-Netherton syndrome families. The nucleotide changes included four non-sense mutations, eight small deletions or insertions leading to frameshift, and five splice site defects, all of which are expected to result in premature terminated or altered translation of SPINK5. Almost half of the mutations clustered between exons 2 and 8, including two recurrent mutations. Genotype-phenotype correlations suggested that homozygous nucleotide changes resulting in early truncation of LEKT1 are associated with a severe phenotype. For the first time, we used molecular data to perform prenatal testing, thus demonstrating the feasibility of molecular diagnosis in the Comèl-Netherton syndrome.

Clinico-immunological heterogeneity in Comèl-Netherton syndrome

BACKGROUND

Comèl-Netherton syndrome (CN) is characterized by atopic-eczema-like skin abnormalities combined with linear ichthyotic lesions, hair shaft abnormalities and atopy with high IgE levels.

OBJECTIVE

Five children with CN are described. In 2 of the 3 CN patients still alive, analysis of cytokines regulating IgE synthesis was performed.

METHODS

In peripheral blood mononuclear cells and cultures of purified T cells, mRNA expression and protein production of interleukin 4 (IL-4), IL-13, IL-5 and interferon gamma were analysed. The results were compared with the values in age-matched atopic dermatitis patients and healthy children.

RESULTS

The 5 CN patients showed striking differences in disease severity and evolution. Marked differences were found in several cytokines in the 2 analysed CN patients. Low percentages of natural killer cells were observed in both CN patients.

CONCLUSION

The regulation of IgE production in patients with CN is varied and complex. The CN patients were heterogeneous in terms of Th2 skewing.

Towards a molecular understanding of hair loss and its treatment

Most common forms of hair loss (alopecia) are caused by aberrant hair follicle cycling and changes in hair follicle morphology. However, current treatments for alopecia do not specifically target these processes. We are now beginning to identify the molecules and molecular pathways that control normal hair follicle formation, cycling and growth. In parallel, new techniques are being developed for delivering molecules to hair follicles. Here, we outline the characteristics of common hair loss diseases, and discuss ways in which recent advances in hair follicle biology could be translated into effective therapies for these conditions.

Human papillomavirus infection in Netherton's syndrome

BACKGROUND

Netherton's syndrome (NS) is a hereditary disorder with dermatological signs (e.g. ichthyosis) and a complex immunological dysfunction. In immunodeficient individuals human papillomavirus (HPV) types are associated with carcinomas on non-mucosal sites.

OBJECTIVES

To study the presence of HPV infection in different skin lesions of three male NS patients and to investigate a possible association between HPV and malignancies in NS.

METHODS

Patient 1 had extraordinary widespread multiple skin carcinomas on sunlight-exposed areas, as well as common viral warts. Patient 2 showed disseminated viral plane warts that resolved spontaneously, and patient 3 was free of skin lesions suspicious for HPV infection; only pseudoepitheliomatous wart-like lesions as a symptom of ichthyosis were apparent. We performed nested polymerase chain reaction analysis of DNA from benign and malignant skin lesions and HPV-8 serology in these three patients.

RESULTS

Antibodies to HPV-8 were not detectable in our patients; however, seven of 22 (31%) biopsies of the three NS patients were positive for HPV DNA. Epidermodysplasia verruciformis (EV) -associated HPV types and normal cutaneous types (HPV-2, HPV-28) were detected. Interestingly, only the patient with cutaneous carcinomas harboured, preferentially in malignant lesions, EV-HPV types (HPV-19, 23, 38 and HPV-RTRX9, closely related to EV-HPVs), whereas plane warts of patient 2 were positive for HPV-28. The pseudoepitheliomatous skin lesions were HPV-DNA negative in all investigated probes.

CONCLUSIONS

These data in NS patients further confirm an association of EV-HPVs with non-melanoma skin cancer (NMSC) and suggest a possible carcinogenic role similar to that assumed for NMSC in transplant recipients. A complex immunological disorder facilitating EV-HPV infection, negative HPV serology and photochemotherapy may all have contributed to the unusual occurrence of multiple cancers in one of our NS patients.

Searching for candidate genes in the new millennium

Completion of the entire sequence of the human genome is having a profound effect on the strategies biological scientists use to identify disease-associated genes. Laborious positional cloning approaches and traditional functional studies are gradually being transformed by emerging genomic and proteomic databases. Some of the exciting challenges investigators now face are the identification of new genes, determining the function of these genes, defining disease associations, and elucidating correlation between genotype and phenotype. To demonstrate how investigative methods for single-gene disorders are changing, we illustrate one possible approach in the search for the gene underlying the autosomal recessive genodermatosis, acrodermatitis enteropathica.

Purification and partial amino acid sequence of proteins from human epidermal keratinocyte conditioned medium

Keratinocytes are the main cell type of the epidermis. They secrete a variety of proteins and peptides that have diverse roles in epidermal physiology. In this report, we present purification and partial amino acid sequence of LEKTI, a serine proteinase inhibitor, and DAN (NO3) zinc-finger protein, a tumor suppressor protein of neuroblastoma, from human keratinocyte conditioned medium. Epidermal keratinocytes were isolated from human foreskin and serially passaged in a defined medium (MSBM). At confluence of the fourth passage, MSBM medium was replaced with protein-free Dulbecco's modified Eagle medium/F12 (DMEM:F12) 3:1 base medium and collected every 24 h for 4 days. Medium was pooled and concentrated using a stirred cell concentrator. Concentrated medium was diluted 1:1 in 50 mM sodium phosphate, pH 8 buffer, and loaded onto a preparative heparin affinity column. Proteins/peptides were purified from heparin column passthrough by the combination of preparative and analytical FPLC-based gel filtration chromatography and reversed-phase HPLC. Samples electroblotted onto a PVDF support were sequenced by Edman degradation in a gas-phase sequencing system.

The balance between CD45RChigh and CD45RClow CD4 T cells in rats is intrinsic to bone marrow-derived cells and is genetically controlled

The level of CD45RC expression differentiates rat CD4 T cells in two subpopulations, CD45RC(high) and CD45RC(low), that have different cytokine profiles and functions. Interestingly, Lewis (LEW) and Brown Norway (BN) rats, two strains that differ in their ability to mount type 1 and type 2 immune responses and in their susceptibility to autoimmune diseases, exhibit distinct CD45RC(high)/CD45RC(low) CD4 T cell ratios. The CD45RC(high) subpopulation predominates in LEW rats, and the CD45RC(low) subpopulation in BN rats. In this study, we found that the antiinflammatory cytokines, IL-4, IL-10, and IL-13, are exclusively produced by the CD45RC(low) CD4 T cells. Using bone marrow chimeras, we showed that the difference in the CD45RC(high)/CD45RC(low) CD4 T cell ratio between naive LEW and BN rats is intrinsic to hemopoietic cells. Furthermore, a genome-wide search for loci controlling the balance between T cell subpopulations was conducted in a (LEW x BN) F(2) intercross. Genome scanning identified one quantitative trait locus on chromosome 9 (approximately 17 centiMorgan (cM); log of the odds ratio (LOD) score 3.9). In addition, two regions on chromosomes 10 (approximately 28 cM; LOD score 3.1) and 20 (approximately 40 cM; LOD ratio score 3) that contain, respectively, a cytokine gene cluster and the MHC region were suggestive for linkage. Interestingly, overlapping regions on these chromosomes have been implicated in the susceptibility to various immune-mediated disorders. The identification and functional characterization of genes in these regions controlling the CD45RC(high)/CD45RC(low) Th cell subpopulations may shed light on key regulatory mechanisms of pathogenic immune responses.

Linkage and allelic association of chromosome 5 cytokine cluster genetic markers with atopy and asthma associated traits

Linkage and association of polymorphic markers in the chromosome 5q31-q33 cytokine cluster to atopy and asthma associated phenotypes have been reported by a number of groups. To investigate this region, 29 polymorphic markers were used to genotype a combined set of 233 families. These markers were ordered based upon the genetic data, supplemented by published genetic and physical maps. Significant two-point linkage was observed for asthma (most significant marker IRF1, P = 0.0002) and atopy (CD14SNP, P = 0.0001). Allelic association was observed between D5S463 and atopy (P = 0.002) and the skin prick test index (P = 0.04). The data support the possibility of three asthma/atopy loci in the 5q31-q33 region, each with a relatively small effect.

Hair on a gene string: recent advances in understanding the molecular genetics of hair loss

The hair follicle is finally, after remaining a mystery for many years, beginning to yield some of its molecular secrets. The past decade has seen unprecedented and ever quickening advances in understanding the molecular genetics of the many single gene disorders, which have alopecia as a major feature. This article reviews recent novel clinical and experimental observations, which have shed new light on the basic molecular mechanisms underlying hair morphogenesis, differentiation, keratinization and cycling. We consider recent progress in understanding structural hair defects and complex traits and consider where future developments are likely to occur.

The genodermatoses: candidate diseases for gene therapy

Tremendous progress has been made in understanding the genetic basis of different forms of genodermatoses, a group of heritable diseases displaying a spectrum of phenotypic manifestations and clinical severity. The information about the underlying mutations in the candidate gene/protein systems has provided the basis for initial development of cutaneous gene therapy, and these heritable conditions appear to serve as appropriate candidate diseases for such efforts. Because of its accessibility and the fact that resident skin cells, such as epidermal keratinocytes and dermal fibroblasts, can be readily propagated in culture, skin serves as an appropriate target tissue for gene therapy. Various strategic considerations, including the use of in vivo or ex vivo approaches, gene replacement versus gene repair, utilization of different delivery systems, etc., require careful prioritization depending on the type of mutations and their pathogenetic consequences at the mRNA and protein levels.