Herlitz's junctional epidermolysis bullosa is linked to mutations in the gene (LAMC2) for the gamma 2 subunit of nicein/kalinin (LAMININ-5).

We have linked Herlitz's junctional epidermolysis bullosa (H-JEB) to the gene (LAMC2) encoding the gamma 2 subunit of nicein/kalinin, an isolaminin (laminin-5) expressed by basal keratinocytes. In four H-JEB kindreds, a maximum two-point lod score of 5.33 at theta = 0 was observed between a microsatellite near LAMC2 at 1q25-31 and the disease. In one family, a homozygous point mutation leading to a premature stop codon (CGA to TGA) was identified in exon 3 of the gene. The segregation of the mutated allele implicates the mutation in the pathology of the disorder and corroborates the linkage results.

Mutations in ATP2C1, encoding a calcium pump, cause Hailey-Hailey disease.

Hailey-Hailey disease (HHD, MIM 16960) is inherited in an autosomal dominant manner and characterized by persistent blisters and erosions of the skin. Impaired intercellular adhesion and epidermal blistering also occur in individuals with pemphigus (which is due to autoantibodies directed against desmosomal proteins) and in patients with Darier disease (DD, MIM 124200), which is caused by mutations in a gene encoding a sarco/endoplasmic reticulum (ER)-Golgi calcium pump. We report here the identification of mutations in ATP2C1, encoding the human homologue of an ATP-powered pump that sequesters calcium into the Golgi in yeast, in 21 HHD kindreds. Regulation of cytoplasmic calcium is impaired in cultured keratinocytes from HHD patients, and the normal epidermal calcium gradient is attenuated in vivo in HHD patients. Our findings not only provide an understanding of the molecular basis of HHD, but also underscore the importance of calcium control to the functioning of stratified squamous epithelia.

Mutations in the human connexin gene GJB3 cause erythrokeratodermia variabilis.

Erythrokeratodermia variabilis (EKV, OMIM 133200) is an autosomal dominant genodermatosis with considerable intra- and interfamilial variability. It has a disfiguring phenotype characterized by the independent occurrence of two morphologic features: transient figurate red patches and localized or generalized hyperkeratosis. Both features can be triggered by external factors such as trauma to the skin. After initial linkage to the RH locus on 1p, EKV was mapped to an interval of 2.6 cM on 1p34-p35, and a candidate gene (GJA4) encoding the gap junction protein alpha-4 (connexin 31, Cx31) was excluded by sequence analysis. Evidence in mouse suggesting that the EKV region harbours a cluster of epidermally expressed connexin genes led us to characterize the human homologues of GJB3 (encoding Cx31) and GJB5 (encoding Cx31.1). GJB3, GJB5 and GJA4 were localized to a 1.1-Mb YAC in the candidate interval. We detected heterozygous missense mutations in GJB3 in four EKV families leading to substitution of a conserved glycine by charged residues (G12R and G12D), or change of a cysteine (C86S). These mutations are predicted to interfere with normal Cx31 structure and function, possibly due to a dominant inhibitory effect. Our results implicate Cx31 in the pathogenesis of EKV, and provide evidence that intercellular communication mediated by Cx31 is crucial for epidermal differentiation and response to external factors.

Genetic polymorphism in Methylenetetrahydrofolate Reductase chloride transport protein 6 (MTHFR CLCN6) gene is associated with keratinocyte skin cancer in a cohort of renal transplant recipients.

Background: Renal transplant recipients (RTRs) are at increased risk of keratinocyte cancer (KC), especially cutaneous squamous cell carcinoma (cSCC). Previous studies identified a genetic variant of the Methylenetetrahydrofolate Reductase (MTHFR) gene, C677T, which conferred a risk for diagnosis of cSCC in Irish RTRs. Objective: We sought to find further genetic variation in MTHFR and overlap genes that may be associated with a diagnosis of KC in RTRs. Methods: Genotyping of a combined RTR population (n = 821) from two centres, Ireland (n = 546) and the USA (n = 275), was performed. This included 290 RTRs with KC and 444 without. Eleven single nucleotide polymorphisms (SNPs) in the MTHFR gene and seven in the overlap gene MTHFR Chloride transport protein 6 (CLCN6) were evaluated and association explored by time to event analysis (from transplant to first KC) using Cox proportional hazards model. Results: Polymorphism at MTHFR CLCN6 (rs9651118) was significantly associated with KC in RTRs (HR 1.50, 95% CI 1.17-1.91, p < 0.00061) and cSCC (HR 1.63, 95% CI 1.14-2.34, p = 0.007). A separate SNP, MTHFR C677T, was also significantly associated with KC in the Irish population (HR 1.31, 95% CI 1.05-1.63, p = 0.016), but not American RTRs. Conclusions: We report the association of a SNP in the MTHFR overlap gene, CLCN6 and KC in a combined RTR population. While the exact function of CLCN6 is not known, it is proposed to be involved in folate availability. Future applications could include incorporation in a polygenic risk score for KC in RTRs to help identify those at increased risk beyond traditional risk factor assessment.

Ultraviolet and ionizing radiation enhance the growth of BCCs and trichoblastomas in patched heterozygous knockout mice.

Basal cell carcinomas, the commonest human skin cancers, consistently have abnormalities of the hedgehog signaling pathway and often have PTCH gene mutations. We report here that Ptch+/- mice develop primordial follicular neoplasms resembling human trichoblastomas, and that exposure to ultraviolet radiation or ionizing radiation results in an increase in the number and size of these tumors and a shift in their histologic features so that they more closely resemble human basal cell carcinoma. The mouse basal cell carcinomas and trichoblastoma-like tumors resemble human basal cell carcinomas in their loss of normal hemidesmosomal components, presence of p53 mutations, frequent loss of the normal remaining Ptch allele, and activation of hedgehog target gene transcription. The Ptch mutant mice provide the first mouse model, to our knowledge, of ultraviolet and ionizing radiation-induced basal cell carcinoma-like tumors, and also demonstrate that Ptch inactivation and hedgehog target gene activation are essential for basal cell carcinoma tumorigenesis.

Molecular genetics of epidermolysis bullosa.

Blisters following minor trauma characterize epidermolysis bullosa, a group of hereditary diseases of the skin. In the simplex type, epidermal basal cells are fragile, and mutations of genes encoding keratin intermediate filament proteins underlie that fragility. In the dystrophic types, the causative mutation appears to be in the gene encoding type VII collagen, which is the major component of anchoring fibrils. These recent findings afford solid evidence that at least one function of the cytoskeletal intermediate filament network is the provision of mechanical stability and that anchoring fibrils indeed do anchor the epidermis to the underlying dermis.

X-linked ichthyosis: increased blood cholesterol sulfate and electrophoretic mobility of low-density lipoprotein.

Plasma cholesterol sulfate concentration is increased in patients with recessive X-linked ichthyosis, a disease in which steroid sulfatase activity is absent. In these patients, cholesterol sulfate is found primarily in the low-density lipoprotein fraction of plasma, and the electrophoretic mobility of these lipoproteins is greatly increased.

Epidermolysis bullosa simplex: evidence in two families for keratin gene abnormalities.

Epidermolysis bullosa simplex (EBS) is characterized by skin blistering due to basal keratinocyte fragility. In one family studied, inheritance of EBS is linked to the gene encoding keratin 14, and a thymine to cytosine mutation in exon 6 of keratin 14 has introduced a proline in the middle of an alpha-helical region. In a second family, inheritance of EBS is linked to loci that map near the keratin 5 gene. These data indicate that abnormalities of either of the components of the keratin intermediate filament heterodipolymer can impair the mechanical stability of these epithelial cells.

Basal cell carcinomas in mice overexpressing sonic hedgehog.

Mutations in the tumor suppressor gene PATCHED (PTC) are found in human patients with the basal cell nevus syndrome, a disease causing developmental defects and tumors, including basal cell carcinomas. Gene regulatory relationships defined in the fruit fly Drosophila suggest that overproduction of Sonic hedgehog (SHH), the ligand for PTC, will mimic loss of ptc function. It is shown here that transgenic mice overexpressing SHH in the skin develop many features of basal cell nevus syndrome, demonstrating that SHH is sufficient to induce basal cell carcinomas in mice. These data suggest that SHH may have a role in human tumorigenesis.

Human homolog of patched, a candidate gene for the basal cell nevus syndrome.

The basal cell nevus syndrome (BCNS) is characterized by developmental abnormalities and by the postnatal occurrence of cancers, especially basal cell carcinomas (BCCs), the most common human cancer. Heritable mutations in BCNS patients and a somatic mutation in a sporadic BCC were identified in a human homolog of the Drosophila patched (ptc) gene. The ptc gene encodes a transmembrane protein that in Drosophila acts in opposition to the Hedgehog signaling protein, controlling cell fates, patterning, and growth in numerous tissues. The human PTC gene appears to be crucial for proper embryonic development and for tumor suppression.

The genetics of human skin diseases.

Molecular genetic analyses during the past half-decade have brought unexpected insights into the molecular defects underlying a wide variety of abnormal skin phenotypes. Highlights of the efforts in the past year include the identification of mutations in an epidermal transglutaminase gene in lamellar ichthyosis as well as mutations in an additional five keratin genes causing four different abnormal phenotypes, and mutations in beta 4 integrin and bullous pemphigoid antigen 2 genes in junctional epidermolysis bullosa and in the p16NK-4a gene in 50% of kindreds with familial melanoma.

Steroid sulfatase of human leukocytes and epidermis and the diagnosis of recessive X-linked ichthyosis.

Patients with recessive X-linked ichthyosis, one of the inherited types of excessive stratum corneum cohesion, have deficient steroid sulfatase in fibroblasts grown from their dermis. Because of the expense and long period required to grow such cells, we have assayed this enzyme in peripheral blood leukocytes and found it to be undetectable in those from patients with this type of ichthyosis, but normal in those from patients with other hereditary or acquired types of ichthyosis. In addition, steroid sulfatase activity is less in leukocytes from women who are carriers of this disease than normal women, and this assay can be used to detect such carriers. Despite previous studies demonstrating that the gene for this enzyme escapes the inactivation of other x-chromosome genes, normal women have leukocyte steroid sulfatase activity only 1.3 times that of normal men, suggesting that some gene dosage compensation occurs. Normal human epidermis, the tissue most affected clinically, also expresses steroid sulfatase activity. The epidermal enzyme is similar in its subcellular localization, its molecular size, and kinetically to that of placenta, leukocytes, and fibroblasts.

Stratum corneum lipids in disorders of cornification. Steroid sulfatase and cholesterol sulfate in normal desquamation and the pathogenesis of recessive X-linked ichthyosis.

The pathological scaling in recessive x-linked ichthyosis is associated with accumulation of abnormal quantities of cholesterol sulfate in stratum corneum (J. Clin. Invest. 68:1404-1410, 1981). To determine whether or not cholesterol sulfate accumulates in recessive x-linked ichthyosis as a direct result of the missing enzyme, steroid sulfatase, we quantitated both steroid sulfatase and its substrate, we quantitated both steroid sulfatase and its substrate, cholesterol sulfate, in different epidermal strata, as well as within stratum corneum subcellular fractions obtained from normal human and neonatal mouse epidermis and from patients with recessive x-linked ichthyosis. In normal human and mouse epidermis, steroid sulfatase activity peaked in the stratum granulosum and stratum corneum, and negligible activity was detectable in lower epidermal layers. In contrast, in recessive x-linked ichthyosis epidermis, enzyme levels were virtually undetectable at all levels. In normal human stratum corneum, up to 10 times more steroid sulfatase activity was present in purified peripheral membrane preparations than in the whole tissue. Whereas in normal human epidermis cholesterol sulfate levels were lowest in the basal/spinous layer, and highest in the stratum granulosum, in recessive x-linked ichthyosis the levels were only slightly higher in the lower epidermis, but continued to climb in the stratum corneum. In both normal and in recessive x-linked ichthyosis stratum corneum, cholesterol sulfate appeared primarily within membrane domains, paralleling the pattern of steroid sulfatase localization. Finally, the role of excess cholesterol sulfate in the pathogenesis of recessive x-linked ichthyosis was directly tested by topical applications of this substance, which produced visible scaling in hairless mice in parallel to an increased cholesterol sulfate content of the stratum corneum. These results demonstrate an intimate relationship between steroid sulfatase and cholesterol sulfate in normal epidermis: both are concentrated in the outer epidermis (stratum corneum and stratum granulosum), and both are localized to membrane domains. Presumably, as a result of this distribution pattern, continued enzymatic degradation of substrate occurs in normal epidermis, thereby preventing excessive accumulation of cholesterol sulfate. In contrast, in recessive x-linked ichthyosis, degradation of cholesterol sulfate does not occur and cholesterol sulfate accumulates specifically in the stratum corneum, where it produces visible scale.

Differing tumor-suppressor functions of Arf and p53 in murine basal cell carcinoma initiation and progression.

Human basal cell carcinomas (BCCs) very frequently carry p53 mutations, and p53 loss markedly accelerates murine BCC carcinogenesis. We report here our studies of the mechanism by which p53 is activated to suppress BCC carcinogenesis. We find that aberrant hedgehog signaling in microscopic BCCs activates p53 in part via Arf (that is, the oncogene-induced stress pathway) but not via the DNA damage response pathway. However, Arf loss and p53 loss produce differing outcomes-loss of p53 promotes both tumor initiation and progression; loss of Arf promotes tumor progression but not initiation. Intriguingly, increased expression of Arf in tumor stromal cells, as in tumor keratinocytes themselves, contributes to suppression of BCC carcinogenesis.

Loss of heterozygosity at chromosome 1q22 in basal cell carcinomas and exclusion of the basal cell nevus syndrome gene from this site.

Basal cell carcinomas, the most common human tumors, generally appear sporadically and in small numbers. Rarely, they may appear in great numbers and at an earlier age as a manifestation of the basal cell nevus syndrome, an autosomal dominant inherited disorder. Drawing on the retinoblastoma paradigm, we have begun a search for tumor suppressor genes important in the development of basal cell carcinomas by comparing DNA of tumors and normal cells. Loss of heterozygosity, a frequent marker of the site of tumor suppressor genes, was found at chromosome 1q in one-third of the tumors studied. However, comparison of the inheritance of DNA markers versus the inheritance of the basal cell nevus syndrome is one large kindred excluded this area of chromosome 1q as the site of the gene whose abnormality causes this hereditary disease. These data suggest that large deletions may accompany the development of cutaneous, low grade tumors just as they accompany the development of visceral, high grade cancers.

Mutations of the PATCHED gene in several types of sporadic extracutaneous tumors.

Patients with basal cell nevus syndrome have a high incidence of multiple basal cell carcinomas, medulloblastomas, and meningiomas. Because somatic PATCHED (PTCH) mutations have been found in sporadic basal cell carcinomas, we have screened for PTCH mutations in several types of sporadic extracutaneous tumors. We found that 2 of 14 sporadic medulloblastomas bear somatic nonsense mutations in one copy of the gene and also deletion of the other copy. In addition, we identified missense mutations in PTCH in two of seven breast carcinomas, one of nine meningiomas, and one colon cancer cell line. No PTCH gene mutations were detected in 10 primary colon carcinomas and eighteen bladder carcinomas.

Mycosis fungoides: clinical course and cellular abnormalities.

Mycosis fungoides is a lymphoma that appears to begin in skin. Although variable in its clinical course, it tends to affect middle-aged people, is present for a median of 4 yr before diagnosis, and generally results in death of the patient 4 to 5 yr after diagnosis. Cutaneous tumors and palpably enlarged lymph nodes are associated with shortened survival, and each of these frequently is accompanied by extracutaneous dissemination of the disease. The malignant cells are T lymphocytes with highly infolded nuclei, and they frequently express a helper cell function. Their chromosome complement has been found to be abnormal in karyotyping studies, and measurement of the amount of DNA by cytophotometry may permit diagnosis of the disease before the histological characteristics are detectable by light microscopy.

New cell formation in human sebaceous glands.

Intradermal injection of thymidine-H3 fol- lowed by biopsy removal 40 minutes to 36 days later revealed a characteristic pattern of human sebaceous gland activity. Cells lying on or near the basement membrane divide, and daughter cells move centrally, produce lipid, and undergo nuclear degeneration. The steady state replenishment from the periphery con- tinues for at least 2 to 4 weeks. The average renewal time for the human sebaceous gland in the 4 specimens examined is 7.4 days.

Glucocorticoid receptors of normal human epidermis.

Epidermal cytosol of adult humans can bind dexamethasone, and this binding resembles that by glucocorticoid receptors of other tissues as judged by 4 criteria: affinity of binding, specificity of binding, molecular size of receptor-steroid complexes, and ability of these complexes to bind to nuclei. For demonstration of these receptors, epidermis can be separated by trypsinization but only after preliminary incubation of the skin with molybdate ion, which prevents inactivation of receptors when heated to 22 degree C. The presence of these receptors suggest that glucocorticoids may act directly on the epidermis. Five glucocorticoids that are used topically all displaced 3H-dexamethasone from the receptor in vitro but the affinity of this binding correlates imperfectly with the potency of the steroids when used in vivo.