Molecular basis of Kindler syndrome in Italy: novel and recurrent Alu/Alu recombination, splice site, nonsense, and frameshift mutations in the KIND1 gene.

Kindler syndrome (KS) is a rare autosomal recessive disorder characterized by skin blistering in childhood followed by photosensitivity and progressive poikiloderma. Most cases of KS result from mutations in the KIND1 gene encoding kindlin-1, a component of focal adhesions in keratinocytes. Here, we report novel and recurrent KIND1 gene mutations in nine unrelated Italian KS individuals. A novel genomic deletion of approximately 3.9 kb was identified in four patients originating from the same Italian region. This mutation deletes exons 10 and 11 from the KIND1 mRNA leading to a truncated kindlin-1. The deletion breakpoint was embedded in AluSx repeats, specifically in identical 30-bp sequences, suggesting Alu-mediated homologous recombination as the pathogenic mechanism. KIND1 haplotype analysis demonstrated that patients with this large deletion were ancestrally related. Five additional mutations were disclosed, two of which were novel. To date, four recurrent mutations have been identified in Italian patients accounting for approximately approximately 75% of KS alleles in this population. The abundance of repetitive elements in intronic regions of KIND1, together with the identification of a large deletion, suggests that genomic rearrangements could be responsible for a significant proportion of KS cases. This finding has implications for optimal KIND1 mutational screening in KS individuals.

Recurrent mutations in kindlin-1, a novel keratinocyte focal contact protein, in the autosomal recessive skin fragility and photosensitivity disorder, Kindler syndrome.

Kindler syndrome (OMIM 173650) is a rare autosomal recessive disorder characterized by trauma-induced blister formation (especially in childhood) and photosensitivity. Other features include mucocutaneous scarring and progressive poikiloderma. There is also an increased risk of skin and mucous membrane malignancy. The disorder was recently mapped to 20p12.3 and pathogenic mutations were identified in a new gene, KIND1. This gene encodes a 677 amino acid protein, kindlin-1, a component of focal contacts in keratinocytes. In this study, we identified four new recurrent mutations in KIND1 in 16 individuals with Kindler syndrome from 13 families of Pakistani (676insC), UK Caucasian (E304X), Omani (W616X), or Italian (958-1G > A) origins. Haplotype analysis demonstrated common ancestral mutant alleles for each mutation, apart from one of the six Pakistani families in which the mutation 676insC (which occurs in a repeat of seven cytosines) was present on a different genetic background. All mutations were homozygous, apart from the three UK Caucasian cases that were all compound heterozygotes (second allele mutations: L302X, 1161delA, 1909delA). All mutations were associated with markedly reduced or absent skin immunostaining with an antikindlin-1 antibody. These loss-of-function KIND1 mutations demonstrate the importance of kindlin-1 in maintaining epithelial integrity, although the mechanism linking this mutant protein to photosensitivity and poikiloderma remains to be determined. Delineation of these recurrent mutations is also relevant to optimizing mutation detection strategies in Kindler syndrome patients from particular ethnic backgrounds.

Loss of kindlin-1, a human homolog of the Caenorhabditis elegans actin-extracellular-matrix linker protein UNC-112, causes Kindler syndrome.

Kindler syndrome is an autosomal recessive disorder characterized by neonatal blistering, sun sensitivity, atrophy, abnormal pigmentation, and fragility of the skin. Linkage and homozygosity analysis in an isolated Panamanian cohort and in additional inbred families mapped the gene to 20p12.3. Loss-of-function mutations were identified in the FLJ20116 gene (renamed "KIND1" [encoding kindlin-1]). Kindlin-1 is a human homolog of the Caenorhabditis elegans protein UNC-112, a membrane-associated structural/signaling protein that has been implicated in linking the actin cytoskeleton to the extracellular matrix (ECM). Thus, Kindler syndrome is, to our knowledge, the first skin fragility disorder caused by a defect in actin-ECM linkage, rather than keratin-ECM linkage.

Extracellular matrix protein 1 gene (ECM1) mutations in lipoid proteinosis and genotype-phenotype correlation.

The autosomal recessive disorder lipoid proteinosis results from mutations in extracellular matrix protein 1 (ECM1), a glycoprotein expressed in several tissues (including skin) and composed of two alternatively spliced isoforms, ECM1a and ECM1b, the latter lacking exon 7 of this 10-exon gene (ECM1). To date, mutations that either affect ECM1a alone or perturb both ECM1 transcripts have been demonstrated in six cases. However, lipoid proteinosis is clinically heterogeneous with affected individuals displaying differing degrees of skin scarring and infiltration, variable signs of hoarseness and respiratory distress, and in some cases neurological abnormalities such as temporal lobe epilepsy. In this study, we sequenced ECM1 in 10 further unrelated patients with lipoid proteinosis to extend genotype-phenotype correlation and to add to the mutation database. We identified seven new homozygous nonsense or frameshift mutations: R53X (exon 3); 243delG (exon 4); 507delT (exon 6); 735delTG (exon 7); 785delA (exon 7); 892delC (exon 7) and 1190insC (exon 8), as well as two new compound heterozygous mutations: W160X/F167I (exon 6) and 542insAA/R243X (exons 6/7), none of which were found in controls. The mutation 507delT occurred in two unrelated subjects on different ECM1 haplotypes and may therefore represent a recurrent mutation in lipoid proteinosis. Taken with the previously documented mutations in ECM1, this study supports the view that exons 6 and 7 are the most common sites for ECM1 mutations in lipoid proteinosis. Clinically, it appears that mutations outside exon 7 are usually associated with a slightly more severe mucocutaneous lipoid proteinosis phenotype, but neurological features do not show any specific genotype-phenotype correlation.

Lipoid proteinosis maps to 1q21 and is caused by mutations in the extracellular matrix protein 1 gene (ECM1).

Lipoid proteinosis (LP), also known as hyalinosis cutis et mucosae or Urbach-Wiethe disease (OMIM 247100) is a rare, autosomal recessive disorder typified by generalized thickening of skin, mucosae and certain viscera. Classical features include beaded eyelid papules and laryngeal infiltration leading to hoarseness. Histologically, there is widespread deposition of hyaline (glycoprotein) material and disruption/reduplication of basement membrane. The aetiology of LP is currently unknown. Using DNA from three affected siblings in a consanguineous Saudi Arabian family we performed genome-wide linkage and mapped the disorder to 1q21 (marker D1S498) with a two-point LOD score of 3.45 at theta = 0. A further 28 affected individuals from five other unrelated consanguineous family groups from different geographical regions also showed complete linkage and resulted in a maximum two-point LOD score of 21.85 at theta = 0. Using available markers in the interval between D1S442 and D1S305, the observed recombinants placed the gene in a 2.3 cM critical interval between D1S2344 and D1S2343 (Marshfield genetic map) corresponding to an approximately 6.5 Mb region on the UCSC physical map. Using a candidate gene approach (comparison of control versus LP gene expression in cultured fibroblasts) and subsequent direct sequencing of genomic DNA, we identified six different homozygous loss-of-function mutations in the extracellular matrix protein 1 gene (ECM1). Although the precise function of ECM1 is not known, our findings provide the first clinical indication of its relevance to skin adhesion, epidermal differentiation, wound healing, scarring, angiogenesis/angiopathy and basement membrane physiology, as well as defining the molecular basis of this inherited disorder.

Strategies to identify disease genes.

The correlation between genes and disease began in earnest in the early 1900s with the identification of Mendelian-like inheritance of "inborn errors of metabolism." Since then, the ever-broadening field of genetics has been established as one of the most important and groundbreaking branches of science and medicine to date. With the announcement of a "working draft" sequence of the human genome in 2001, the vast array of both genomic and expressed sequence information available in the public databases alone has meant that the concept of hunting for genes is evolving. Nowadays, researchers can substitute many labor-intensive hours in the lab for less time searching on the World Wide Web. Specialization within genetics has been continuously providing subsets of the genre such as genomics, pharmacogenetics, chemogenomics, gene therapy, proteomics and functional genomics, all of which are based on the fundamental starting block, the gene. This review aims to summarize both traditional and current strategies for identifying susceptibility and monogenetic disease genes and describes how these strategies have evolved in tune with the ever-expanding wealth of information now available at our fingertips.