Howard P. Stevens

A new mutation in the type II hair cortex keratin hHb1 involved in the inherited hair disorder monilethrix

Abstract Monilethrix is a rare dominant hair disease characterized by beaded or moniliform hair which results from the periodic thinning of the hair shaft and shows a high propensity to excess weathering and fracturing. Several cases of monilethrix have been linked to the type II keratin gene cluster on chromosome 12q13 and causative heterozygous mutations of a highly conserved glutamic acid residue (Glu 410 Lys and Glu 410 Asp) in the helix termination motif of the type II hair keratin hHb6 have recently been identified in monilethrix patients of two unrelated families. In the present study, we have investigated two further unrelated monilethrix families as well as a single case. Affected members of one family and the single patient exhibited the prevalent hHb6 Glu 410 Lys mutation. In the second family, we identified in affected individuals a lysine substitution of the corresponding glutamic acid residue, Glu 403, in the type II hair keratin hHb1, suggesting that this site represents a mutational hotspot in these highly related type II hair keratins. Both hHb1 and hHb6 are largely coexpressed in cortical trichocytes of the hair shaft. This indicates that monilethrix is a disease of the hair cortex.

RHBDF2 mutations are associated with tylosis, a familial esophageal cancer syndrome.

Tylosis esophageal cancer (TOC) is an autosomal-dominant syndrome characterized by palmoplantar keratoderma, oral precursor lesions, and a high lifetime risk of esophageal cancer. We have previously localized the TOC locus to a small genomic interval within chromosomal region 17q25. Using a targeted capture array and next-generation sequencing, we have now identified missense mutations (c.557T>C [p.Ile186Thr] and c.566C>T [p.Pro189Leu] in RHBDF2, which encodes the inactive rhomboid protease RHBDF2 (also known as iRhom2), as the underlying cause of TOC. We show that the distribution of RHBDF2 in tylotic skin is altered in comparison with that in normal skin, and immortalized tylotic keratinocytes have decreased levels of total epidermal growth factor receptor (EGFR) and display an increased proliferative and migratory potential relative to normal cells, even when normal cells are stimulated with exogenous epidermal growth factor. It would thus appear that EGFR signaling is dysregulated in tylotic cells. Furthermore, we also show an altered localization of RHBDF2 in both tylotic and sporadic squamous esophageal tumors. The elucidation of a role of RHBDF2 in growth-factor signaling in esophageal cancer will help to determine whether targeting this pathway in chemotherapy for this and other squamous cell carcinomas will be effective.

Localisation of a gene for Papillon-Lefèvre syndrome to chromosome 11q14-q21 by homozygosity mapping.

Abstract Papillon-Lefèvre syndrome is an autosomal recessively inherited palmoplantar keratoderma of unknown aetiology associated with severe periodontitis leading to premature loss of dentition. Three consanguineous families, two of Turkish and one of German origin, and three multiplex families, one of Ethiopian and two of German origin, with 11 affected and 6 unaffected siblings in all were studied. A targeted genome search was initially attempted to several candidate gene regions but failed to demonstrate linkage. Therefore a genome-wide linkage scan using a combination of homozygosity mapping and traditional linkage analysis was undertaken. Linkage was obtained with marker D11S937 with a maximum two-point lod score of Zmax = 6.1 at recombination fraction θ = 0.00 on chromosome 11q14–q21 near the metalloproteinase gene cluster. Multipoint likelihood calculations gave a maximum lod score of 7.35 between D11S901 and D11S1358. A 9.2-cM region homozygous by descent in the affected members of the three consanguineous families lies between markers D11S1989 and D11S4176 harbouring the as yet unknown Papillon-Lefèvre syndrome gene. Haplotype analyses in all the families studied support this localisation. This study has identified a further locus harbouring a gene for palmoplantar keratoderma and one possibly involved in periodontitis.

The Gene for Hypotrichosis of Marie Unna Maps between D8S258 and D8S298: Exclusion of the hr Gene by cDNA and Genomic Sequencing

Hypotrichosis of Marie Unna (MU) is an autosomal dominant hair-loss disorder with onset in childhood. A genomewide search for the gene was performed in a large Dutch family using 400 fluorescent microsatellite markers. Linkage was detected with marker D8S258, and analysis of this family and a further British kindred with additional markers in the region gave a combined maximum two-point LOD score of 13.42, with D8S560. Informative recombinants placed the MU gene in a 2.4-cM interval between markers D8S258 and D8S298. Recently, recessive mutations in the hr gene were reported in families with congenital atrichia, and this gene was previously mapped close to the MU interval. By radiation-hybrid mapping, we placed the hr gene close to D8S298 but were unable to exclude it from the MU interval. This, with the existence of the semidominant murine hr allele, prompted us to perform mutation analysis for this gene. Full-length sequencing of hr cDNA obtained from an affected individual showed no mutations. Similarly, screening of all exons of the hr gene amplified from the genomic DNA of an affected individual revealed no mutations. Analysis of expressed sequences and positional cloning of the MU locus is underway.

The palmoplantar keratodermas: much more than palms and soles

The inherited palmoplantar keratodermas (PPKs) are a diverse and often clinically confusing branch of the genetic skin diseases. As the name suggests, the lesions of PPK primarily affect the palms and soles of the feet, although a number of the PPKs are also associated with a genetic predisposition to other conditions, including cancer, hearing loss and heart failure. The mapping and identification of genes that underlie the PPKs reveal new insights into the biological interactions of the structural components of the palmoplantar epidermis and further our understanding of epidermal disease. More significantly, by genetically characterizing the PPKs, genes that have a role in life-threatening disorders might also be identified.

An autosomal recessive exfoliative ichthyosis with linkage to chromosome 12q13

Summary A new variant of congenital exfoliative ichthyosis in two related Bedouin families is reported. The ichthyosis appeared shortly after birth as a fine peeling of nonerythematous skin on the palms and soles. The prominent well‐demarcated areas of denuded skin in moist and traumatized regions resembled the ‘mauserung’ phenomenon of ichthyosis bullosa of Siemens (IBS). Unlike in IBS, epidermolysis is absent on histological examination. Electron microscopy revealed a prominent intercellular oedema and numerous aggregates of keratin filaments in basal keratinocytes. Abnormal keratin (K) 1 expression was seen in the affected epidermis; however, all other keratins, including K2e, had a distribution comparable to that seen in normal controls. A maximum two‐point LOD score of 2·53 and multipoint LOD score of 3·76 were obtained for marker D12S390, suggesting linkage to the type II keratin cluster on chromosome 12q13. Sequencing of both the K1 gene, the promotor and the 3′ calcium regulatory region did not reveal a mutation. K2e and K5 genes, as well as the genes harboured within the minimal region, such as retinoic acid receptor γ, sterol O‐acyltransferase 2, integrin β7 and insulin‐like growth factor binding protein‐6, were also excluded. This combination of clinical, histological, ultrastructural and genetic features has not been previously reported in other congenital exfoliative ichthyoses. We therefore suggest that it represents a new form of exfoliative ichthyosis.

Fine genetic mapping of diffuse non-epidermolytic palmoplantar keratoderma to chromosome 12q11-q13: exclusion of the mapped type II keratins

Abstract: Diffuse non‐epidermolytic palmoplantar keratoderma (NEPPK) belongs to the heterogeneous group of skin diseases characterized by thickening of the stratum corneum of the palms and soles (1). This autosomal dominant PPK is characterized by a diffuse pattern of palmar and plantar hyperkeratosis giving the affected areas a thickened yellowish appearance with a marked erythematous edge. Linkage of diffuse NEPPK to chromosome 12q11‐q13 has been demonstrated in two independent reports (2, 3). In this study, we describe detailed haplotyping with microsatellite markers mapping to this chromosomal region in three diffuse NEPPK pedigrees from the south of England. Fine mapping of a previously identified recombination event and the identification of a common disease haplotype segregating in the three pedigrees places the diffuse NEPPK locus proximal to the type II keratin gene cluster.