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Monilethrix is an uncommon hereditary disorder of hair and nail which produces hair fragility and a variable alopecia. Many of the dystrophic hairs have a unique beaded morphology. Ultrastructural changes suggest a defect in the microfilament structure of the cortex of the hair shaft,and hence the cysteine-rich trichocyte keratins are candidate genes. Here, in two families with autosomal dominant monilethrix, we have excluded linkage to the type I keratin gene cluster on chromosome 17q, but show that the disorder is closely linked to the type II keratin cluster on 12q, where genes for basic trichocyte keratins are found. The combined maximum lod score for D12S96 was 12.27 at theta=0.0. This is the first mapping of a primary human hair disorder and the first evidence implicating a defect of the word 'hard' keratins of hair and nail disease.

White sponge nevus (WSN) is a benign autosomal dominant disorder which affects non-cornifying stratified squamous epithelia (MIM 193900) (ref. 1). Phenotypically it presents as white 'spongy' plaques (oral leukokeratoses), most commonly in the mouth but also reported in the esophagus and anogenital mucosa. Histologically, the plaques show evidence of hyperproliferation, acanthosis and tonofilament aggregation. These types of pathogenic changes are characteristic of many of the epidermal keratin disorders. Keratins are expressed in pairs by epithelial cells in a tissue and cell specific manner. The major differentiation specific keratins of the buccal mucosa, nasal, esophageal and anogenital epithelia are K4 and K13 (ref. 7). The tissue distribution and nature of the lesions in patients affected by WSN suggested that mutations in K4 and/or K13 might be responsible for this disorder. We have now confirmed this hypothesis and report here a three base-pair (bp) deletion in the helix initiation peptide of K4 in affected members from two families with this condition.

Keratins K6 and K16 are expressed in suprabasal interfollicular epidermis in wound healing and other pathological conditions associated with hyperproliferation, such as psoriasis and are induced when keratinocytes are cultured in vitro. However, these keratins are also constitutively expressed in normal suprabasal mucosal and palmoplantar keratinocytes. Mutations in keratins have been reported in the basal keratin pair K5 and K14 in epidermolysis bullosa simplex and in suprabasal epidermal keratins K1, K2 and K10 in epidermolytic ichthyoses. Two families with autosomal dominant disorder of focal non epidermolytic palmoplantar keratoderma, have oral mucosal and follicular lesions in addition to the palmoplantar hyperkeratosis. Previous studies have shown linkage in these families to the type I keratin gene cluster at 17q12-q21 and this report shows that the cDNA of affected members of both families have novel heterozygous mutations in the expressed keratin 16 gene. These mutations (R10C and N8S) lie in the helix initiation motif of the 1A domain. These mutations do not appear to cause epidermolysis on light or electron microscopy, which may reflect differences in function, assembly or interaction of the 'hyperproliferative' or 'mucoregenerative' keratins from other major types of keratins. The mutations reported here are the first to describe the molecular pathology of focal non epidermolytic palmoplantar keratoderma.

Palmoplantar keratoderma of Voerner type (or epidermolytic palmoplantar keratoderma) is an autosomal dominant inherited disorder of keratinization with histologic features of epidermolytic hyperkeratosis. We studied members of two large unrelated kindreds with epidermolytic palmoplantar keratoderma, and biopsy specimens of lesional palmar skin from both families confirmed the histologic changes of epidermolytic hyperkeratosis. Whorls of abnormally aggregated keratin filaments were seen ultrastructurally to be associated with signs of cellular disintegration in spinous and granular cells. Direct sequencing of genomic DNA samples obtained from several members of each family established the substitution of a highly conserved arginine by tryptophan (R162W) in the 1A region of the alpha-helical rod domain of keratin 9. This arginine residue in a highly conserved region of keratins 1 and 10 is affected by disruptive missense point mutations in many patients with bullous ichthyosiform erythroderma. An equivalent position in the sole and palm restricted keratin 9 appears to be the mutation hot spot in epidermolytic palmoplantar keratoderma. To date, R162W is the most prevalent genetic defect reported in this genodermatosis.

Pachyonychia congenita (PC) is a group of autosomal dominant disorders characterized by dystrophic nails and other ectodermal aberrations. A gene for Jackson-Lawler PC was recently mapped to the type I keratin cluster on 17q. Here, we show that a heterozygous missense mutation in the helix initiation motif of K17 (Asn92Asp) co-segregates with the disease in this kindred. We also show that Jadassohn-Lewandowsky PC is caused by a heterozygous missense mutation in the helix initiation peptide of K16 (Leu130Pro). The known expression patterns of these keratins in epidermal structures correlates with the specific abnormalities observed in each form of PC.

Intermediate filaments are major structural proteins encoded by a large multigene family. Their tissue-specific expression makes them important in studies of development, differentiation and pathology. Most intermediate filaments are keratins; recent discoveries of keratin mutations in a range of genetic skin disorders have clarified their role as providing essential structural support for cells in different physical settings.

The importance of keratins and other intermediate filaments in the maintenance of tissue structure is emphasized by the discovery that many hereditary skin-blistering diseases are caused by mutations in keratin genes. Here, we describe a situation in which keratin 14 (K14) is missing altogether in the epidermis: A homozygous 2-nucleotide deletion in exon I of the K14 gene causes premature termination of the mRNA transcripts upstream from the start of the rod domain and results in a K14 null phenotype. In this individual no keratin intermediate filaments are visible in basal epidermal cells, although filaments are present in the upper layers of the epidermis. No compensating keratin expression is detected in vivo, and K14 mRNA is down-regulated. The individual, diagnosed as Köbner (generalized) EBS, suffers from severe widespread keratinocyte fragility and blistering at many body sites, but although the phenotype is severe, it is not lethal. This K14-/- phenotype confirms that only one K14 gene is expressed in human epidermis and provides an important model system for examining the interdependence of different keratin filament systems and their associated structures in the skin.

Ichthyosis bullosa of Siemens is a blistering disorder with autosomal dominant inheritance. The disease resembles bullous congenital ichthyosiform erythroderma but is less severe. Keratins K1 and K10 have been implicated in bullous congenital ichthyosiform erythroderma. Linkage analysis pointed to the involvement of a keratin type II gene (12q11-13) in ichthyosis bullosa of Siemens. Mutations in the highly conserved regions of K1, a member of the type II gene cluster, were excluded. The gene coding for keratin 2e is also located in the type II gene cluster and the expression of the gene coincides with the occurrence of epidermolytic hyperkeratosis. Sequence analysis revealed the presence of mutations in the K2e gene in patients with ichthyosis bullosa of Siemens. Three different mutations were detected, one in the 1A domain and two in the 2B domain of the rod. Furthermore, histologic and ultrastructural examination of skin biopsies indicated that ichthyosis exfoliativa is identical to ichthyosis bullosa of Siemens. This was confirmed by the results of the molecular analysis. In the family diagnosed as ichthyosis exfoliativa, a mutation was detected that was identical to the mutation found in one of the families with ichthyosis bullosa of Siemens.

Ichthyosis bullosa of Siemens (IBS) is a congenital bullous ichthyosis without erythroderma. In contrast to bullous congenital ichthyosiform erythroderma (BCIE), there is a relatively mild involvement of the skin and epidermolytic hyperkeratosis (EHK) is restricted to the upper suprabasal layers of the epidermis. Tonofilament aggregation was observed by EM in suprabasal cells from affected patients in the two families under study, indicative of a keratin abnormality. Keratin 2e is a differentiation specific type II keratin expressed suprabasally in the epidermis. Part of the K2e gene was amplified by polymerase chain reaction using genomic DNA from affected and unaffected individuals from two IBS families. Direct sequencing of polymerase chain reaction products revealed a point mutation in the highly conserved helix termination motif, producing the protein sequence change LLEGEE-LLEGKE. This mutation was found in all affected members of a five-generation kindred and also in a sporadic case in a second unrelated family. No mutation was seen in unaffected individuals. The mutation destroys a MnlI restriction site, which allowed exclusion of the mutation from a population of 50 unaffected unrelated individuals by restriction fragment analysis of K2e PCR products. This is the sixth keratin gene found to be involved in an inherited epidermal disorder.

Bullous congenital ichthyosiform erythroderma is a human hereditary skin disorder in which suprabasal keratinocytes rupture. Recent reports have implicated keratins K1 and K10 in this disease. Here we describe four diverse keratin mutations that are all significantly associated with this disease. Two of these are in the helix 1A subdomain of the type II keratin 1, giving a serine-to-proline substitution in codon 185 and an asparagine-to-serine substitution in codon 187. In the analogous region of type I keratin 10, an arginine-to-proline and an arginine-to-serine transition in codon 156 have been identified. All four mutations create restriction fragment length polymorphisms that were used exclude the mutations from 120 normal chromosomes. Insertional polymorphism (in the V2 subdomains of the non-helical tails of K1 and K10) was excluded as the cause of the phenotypic heterogeneity observed within one family.

Darier's disease is a dominantly inherited skin disorder in which there is abnormal adhesion between keratinocytes. We and others have recently mapped the disease gene to chromosome 12q23-q 24.1. In the present study we have established that the disease gene lies between the loci D12S78 and D12S79 which are 12cM apart. We have also obtained direct evidence that the disease is unlikely to result from a mutation in one of the members of the keratin gene cluster on chromosome 12q.

Human skin fibroblasts secrete over 50 proteins into the culture medium. In this paper these are characterised using two-dimensional polyacrylamide gel electrophoresis and peptide mapping of proteins metabolically labelled in the presence and absence of tunicamycin. Thirty of these proteins have been shown to be N-glycosides, 4 are O-glycosides and 10 are not glycosylated. Of the major proteins, groups 1-4 have previously been shown to be fibroblast specific. Peptide mapping and tunicamycin treatment has identified that groups 1 and 2, and 3 and 4 are closely related and that groups 1 and 3 arise by N-glycosylation of 2 and 4, respectively. The unglycosylated precursor forms of several other proteins have also been identified. This approach to the analysis of protein secretion provides an abundance of information on many proteins simultaneously and can be used to assess the changes in protein secretion associated with development, and to identify extracellular growth factors and other regulatory proteins.