G H S Ashton

α6β4 integrin abnormalities in junctional epidermolysis bullosa with pyloric atresia

Junctional epidermolysis bullosa with pyloric atresia (JEB‐PA) (MIM 226730) is an autosomal recessive disorder resulting from mutations in the genes encoding α6β4 integrin (ITGA6 and ITGB4). Clinically, it is characterized by mucocutaneous fragility and gastrointestinal atresia, which most commonly affects the pylorus. Additional features of JEB‐PA include involvement of the urogenital tract, aplasia cutis and failure to thrive. While most affected individuals have a poor prognosis resulting in death in infancy, others have milder clinical features and a better prognosis. We report two previously undescribed homozygous ITGB4 mutations in two unrelated families, which resulted in severe skin blistering, pyloric atresia and lethality in infancy. Delineation of the mutations was used to undertake DNA‐based prenatal diagnosis in subsequent pregnancies at risk for recurrence in both families. We review all previously published ITGA6 and ITGB4 mutation reports to help define genotype–phenotype correlation in this rare genodermatosis.

Dilemmas in distinguishing between dominant and recessive forms of dystrophic epidermolysis bullosa

Background  Dystrophic epidermolysis bullosa (DEB) is a heterogeneous inherited blistering skin disorder. The mode of inheritance may be autosomal dominant or recessive but all forms of DEB result from mutations in the gene encoding the anchoring fibril protein, type VII collagen, COL7A1. Consequently, in spite of careful clinical and skin biopsy examination, it may be difficult to distinguish mild recessive cases from de novo dominant disease in families with clinically normal parents and no other affected siblings; this distinction has significant implications for the accuracy of genetic counselling.

EEC (Ectrodactyly, Ectodermal dysplasia, Clefting) syndrome: heterozygous mutation in the p63 gene (R279H) and DNA-based prenatal diagnosis.

Summary Background Germline mis‐sense mutations in the DNA‐binding domain of the p63 gene have recently been established as the molecular basis for the autosomal dominant EEC (Ectrodactyly, Ectodermal dysplasia, Clefting) syndrome.

A recurrent laminin 5 mutation in British patients with lethal (Herlitz) junctional epidermolysis bullosa: evidence for a mutational hotspot rather than propagation of an ancestral allele

The three genes (LAMA3, LAMB3 and LAMC2) that encode the anchoring filament protein, laminin 5, may all harbour pathogenetic mutations in the autosomal recessive blistering skin disorder, junctional epidermolysis bullosa (JEB). Recently, one particular mutation, R635X in the LAMB3 gene, has been found to account for approximately 40% of all JEB laminin 5 mutations (Kivirikko et al., Hum Mol Genet 1996; 5: 231‐7). In this study, we assessed the frequency of this mutation in 12 British patients with lethal (Herlitz) JEB using PCR amplification of genomic DNA and restriction endonuclease digestion. The mutation R635X was found in seven of 24 (29%) mutant alleles, confirming its relative frequency within the British gene pool. In addition, haplotype analysis using intragenic polymorphisms showed that the mutation arose on at least four different haplotype backgrounds, suggesting it represents a mutational hotspot rather than propagation of a common British ancestral allele. These findings support the hypermutable nature of this CpG dinucleotide and have implications in screening for laminin 5 gene mutations in British and other patients with JEB.

An Indian child with Kindler syndrome resulting from a new homozygous nonsense mutation (C468X) in the KIND1 gene

Kindler syndrome is an inherited skin condition that presents with blistering followed by photosensitivity and a progressive poikiloderma. The disorder results from mutations in the KIND1 gene, encoding the protein kindlin‐1, a recently characterized 677‐amino acid protein involved in anchorage of the actin cytoskeleton to the extracellular matrix. We report the clinical features of an 11‐year‐old boy with Kindler syndrome from a consanguineous Indian family and the identification of a homozygous nonsense mutation (C468X) in exon 12 of the KIND1 gene in his genomic DNA. This mutation has not been described previously but is similar to the 17 previously published KIND1 mutations that are all predicted to lead to loss of kindlin‐1 protein expression and function. The clinical features in this boy highlight the relevance of kindlin‐1 in skin biology, specifically to epidermal adhesion and response to acute and chronic sun exposure. Delineation of this new pathogenic mutation in KIND1 is also useful for genetic counselling in this family and in assessing carrier status in unaffected family members.

Prenatal diagnosis of Herlitz junctional epidermolysis bullosa in nonidentical twins

Advances in molecular diagnostics have led to the feasibility of DNA‐based prenatal testing in families at risk for recurrence of severe forms of both dystrophic and junctional epidermolysis bullosa. In this report, we describe prenatal testing in a woman who previously had a child affected with Herlitz junctional epidermolysis bullosa. However, in her second pregnancy, she was found to have dichorionic diamniotic twins. DNA analysis of a pathogenic mutation and informative intragenic polymorphisms (LAMB3 gene) predicted one fetus to be affected and the other unaffected. Selective termination of the affected fetus was performed, and pregnancy with the unaffected fetus was continued, leading to full term delivery of a healthy girl with no skin blisters. This is the first reported case of DNA analysis in a twin pregnancy at risk of Herlitz junctional epidermolysis bullosa, with successful diagnosis and selective termination of one affected twin.

Genomic localization, organization and amplification of the human zinc transporter protein gene, ZNT4, and exclusion as a candidate gene in different clinical variants of acrodermatitis enteropathica

Abstract Acrodermatitis enteropathica is an inherited disorder of zinc metabolism, the molecular basis of which is currently unknown. Recent transgenic mouse studies have highlighted the potential significance of certain zinc transport proteins, for example ZnT4, in providing clues to the pathogenesis of zinc-related disorders such as acrodermatitis enteropathica. Specifically, mice of any genotype suckled on ZnT4-deficient mice fail to absorb intestinal zinc and ZnT4-deficient mice also develop dermatitis, alopecia and stunted growth. Therefore, to assess human ZnT4 as a candidate gene/protein in acrodermatitis enteropathica or related disorders, we characterized the intron-exon organization of the human ZNT4 gene, which comprises seven distinct exons spanning approximately 38.7 kb. High-resolution radiation hybrid mapping placed ZNT4 on 15q21.1. We also developed a PCR-based mutation detection strategy using primers placed on flanking introns followed by direct sequencing of the PCR products. Using this approach, we sequenced DNA from five individuals with acrodermatitis enteropathica; no mutations were identified. Thus, ZNT4 is unlikely to be the correct candidate gene for this disorder. We also identified and characterized two common single nucleotide polymorphisms in exon 5 and in the 3′ UTR of ZNT4 , which will be useful for future genetic linkage studies in assessing ZNT4 as a candidate gene for other inherited disorders of zinc metabolism.

Human Ro60 (SSA2) genomic organization and sequence alterations, examined in cutaneous lupus erythematosus

Background The Ro 60 kDa protein (Ro60 or SSA2) is the major component of the Ro ribonucleoprotein (Ro RNP) complex, to which an immune response is a specific feature of several autoimmune diseases. The genomic organization and any sequence variation within the DNA encoding Ro60 are unknown.