Recessive dystrophic epidermolysis bullosa caused by COL7A1 hemizygosity and a missense mutation with complex effects on splicing

Loss-of-function mutations in the gene encoding type VII collagen, COL7A1, are the molecular basis of the blistering skin disorder, recessive dystrophic epidermolysis bullosa (RDEB). COL7A1 maps to a region of the short arm of chromosome 3 that has been found to be deleted in many types of malignancies. We have characterized the first case of a large genomic deletion in chromosome 3p21.31 that removes COL7A1 entirely in an RDEB patient. This interstitial deletion spans 255 to 520 kb and encompasses 9 to 15 genes, but seems to have no pathological consequences other than RDEB. We show that the second, hemizygous allele of COL7A1 in this patient bears a base substitution within exon 94, c.7245G>A. This translates into an amino acid substitution, p.M2415I, and leads to a complex splicing abnormality that allows marginal levels of functional mRNA and protein to be synthesized. We propose that the leakiness of the splicing defect enables the partial rescue of collagen VII deficiency. This is consistent with the diagnosis of the moderately severe form of RDEB in the proband, at variance with the most severe form, RDEB Hallopeau-Siemens, that would arise from complete collagen VII deficiency.     

伴斑点状色素沉着的单纯性大疱性表皮松解症1例国内首报

患儿男,15岁。躯干、四肢反复发生水疱和大疱,伴色素沉着和色素减退15年。皮损组织病理示:棘层下部棘细胞间裂隙和陈旧性表皮内水疱,部分基底细胞液化或空疱变性及基底层色素增加,真皮血管周围多数淋巴和嗜酸粒细胞浸润。直接免疫荧光检查阴性。透射电镜下超微结构示角质形成细胞间水肿,基底细胞内裂隙和空泡形成,并见大量张力微丝排列为均质化团块,部分呈漩涡状;基底细胞及细胞间可见黑素小体。诊断:单纯性大疱性表皮松解症,斑点状色素沉着。经云南省医学信息研究所查证证实该例为国内首例报道。     

痒疹样营养不良型大疱性表皮松解症一家系调查

先证者女,18岁。躯干、四肢反复水疱、丘疹、结节伴痒6年。皮肤科情况:双下肢胫前多发密集米粒至花生米大小扁平丘疹、结节,色泽淡红至暗红,部分呈脐样凹陷,上覆白色糠状鳞屑,见点状糜烂、结痂;躯干及双上肢散在粟粒至黄豆大小淡白色、淡红色丘疹及萎缩性疤痕,部分皮损表面糜烂、结痂;指趾甲及黏膜未见受累。皮损组织病理示:角化过度,颗粒层、棘层中度不规则增厚,表皮下见裂隙及大疱,真皮浅层毛细血管扩张,血管内皮细胞及纤维组织明显增生,血管周围少许淋巴细胞浸润。诊断:痒疹样营养不良型大疱性表皮松解症。家系调查4代39人,共有24人患病,每代均有发病,其中男17人、女7人患病,符合常染色体显性遗传。     

The Human Intermediate Filament Database: comprehensive information on a gene family involved in many human diseases

We describe a revised and expanded database on human intermediate filament proteins, a major component of the eukaryotic cytoskeleton. The family of 70 intermediate filament genes (including those encoding keratins, desmins, and lamins) is now known to be associated with a wide range of diverse diseases, at least 72 distinct human pathologies, including skin blistering, muscular dystrophy, cardiomyopathy, premature aging syndromes, neurodegenerative disorders, and cataract. To date, the database catalogs 1,274 manually-curated pathogenic sequence variants and 170 allelic variants in intermediate filament genes from over 459 peer-reviewed research articles. Unrelated cases were collected from all of the six sequence homology groups and the sequence variations were described at cDNA and protein levels with links to the related diseases and reference articles. The mutations and polymorphisms are presented in parallel with data on protein structure, gene, and chromosomal location and basic information on associated diseases. Detailed statistics relating to the variants records in the database are displayed by homology group, mutation type, affected domain, associated diseases, and nucleic and amino acid substitutions. Multiple sequence alignment algorithms can be run from queries to determine DNA or protein sequence conservation. Literature sources can be interrogated within the database and external links are provided to public databases. The database is freely and publicly accessible online at www.interfil.org (last accessed 13 September 2007). Users can query the database by various keywords and the search results can be downloaded. It is anticipated that the Human Intermediate Filament Database (HIFD) will provide a useful resource to study human genome variations for basic scientists, clinicians, and students alike.     

PDGFRalpha-positive cells in bone marrow are mobilized by high mobility group box 1 (HMGB1) to regenerate injured epithelia

The role of bone marrow cells in repairing ectodermal tissue, such as skin epidermis, is not clear. To explore this process further, this study examined a particular form of cutaneous repair, skin grafting. Grafting of full thickness wild-type mouse skin onto mice that had received a green fluorescent protein-bone marrow transplant after whole body irradiation led to an abundance of bone marrow-derived epithelial cells in follicular and interfollicular epidermis that persisted for at least 5 mo. The source of the epithelial progenitors was the nonhematopoietic, platelet-derived growth factor receptor α-positive (Lin(-)/PDGFRα(+)) bone marrow cell population. Skin grafts release high mobility group box 1 (HMGB1) in vitro and in vivo, which can mobilize the Lin(-)/PDGFRα(+) cells from bone marrow to target the engrafted skin. These data provide unique insight into how skin grafts facilitate tissue repair and identify strategies germane to regenerative medicine for skin and, perhaps, other ectodermal defects or diseases.     

Genome‐wide single nucleotide polymorphism‐based autozygosity mapping facilitates identification of mutations in consanguineous families with epidermolysis bullosa

Autozygosity mapping (AM) is a technique utilised for mapping homozygous autosomal recessive (AR) traits and facilitation of genetic diagnosis. We investigated the utility of AM for the molecular diagnosis of heterogeneous AR disorders, using epidermolysis bullosa (EB) as a paradigm. We applied this technique to a cohort of 46 distinct EB families using both short tandem repeat (STR) and genome‐wide single nucleotide polymorphism (SNP) array‐based AM to guide targeted Sanger sequencing of EB candidate genes. Initially, 39 of the 46 cases were diagnosed with homozygous mutations using this method. Independently, 26 cases, including the seven initially unresolved cases, were analysed with an EB‐targeted next‐generation sequencing (NGS) panel. NGS identified mutations in five additional cases, initially undiagnosed due to the presence of compound heterozygosity, deep intronic mutations or runs of homozygosity below the set threshold of 2 Mb, for a total yield of 44 of 46 cases (95.7%) diagnosed genetically.