Compound heterozygosity for a point mutation and a deletion located at splice acceptor sites in the LAMB3 gene leads to generalized atrophic benign epidermolysis bullosa

Clinical and molecular features in a cohort of Middle Eastern patients with epidermolysis bullosa

BACKGROUND

Epidermolysis bullosa (EB) features skin and mucosal fragility due to pathogenic variants in genes encoding components of the cutaneous basement membrane. Based on the level of separation within the dermal-epidermal junction, EB is sub-classified into four major types including EB simplex (EBS), junctional EB (JEB), dystrophic EB (DEB), and Kindler EB (KEB) with 16 EB-associated genes reported to date.

METHODS

We ascertained a cohort of 151 EB patients of various Middle Eastern ethnic backgrounds.

RESULTS

The cohort was comprised of EBS (64%, 97/151), DEB (21%, 31/151), JEB (12%, 18/151), and KEB (3%, 5/151). KRT14 and KRT5 variants were most common among EBS patients with 43% (42/97) and 46% (45/97) of EBS patients carrying mutations in either of these two genes, respectively. Truncal involvement was more common in KRT14-associated EBS as compared to EBS due to KRT5 mutations (p < .05). Mutations in COL17A1 and laminin 332-encoding genes were identified in 55% (10/18) and 45% (8/18) of JEB patients. Scarring alopecia, caries, and EB nevi were most common among JEB patients carrying COL17A1 mutations as compared to laminin 332-associated JEB (p < .05). Abnormal nails were evident in most DEB and JEB patients while poikiloderma was exclusively observed in KEB (p < .001).

CONCLUSIONS

EB patients of Middle Eastern origin were found to feature specific phenotype-genotype correlations of relevance to the diagnosis and genetic counseling of patients in this region.

Spatial and temporal control of laminin-332 (5) and -511 (10) expression during induction of anagen hair growth

Basement membrane plays important roles in hair growth. We characterized changes in laminin isoform expression during hair cycling. At the mRNA level, laminin-511 (10) expression underwent a steady increase during anagen stages. In contrast, laminin-332 (5) expression was initially upregulated in outer root sheath (ORS) keratinocytes at anagen II and then transiently downregulated. Laminin-332 significantly increased coincident with the signal in inner root sheath and hair matrix cells after anagen IV. Levels of laminin-332 proteins were also upregulated at late anagen I-III but dropped after anagen IV. This decrease coincided with increased levels of mRNA encoding the two proteases, membrane type 1 metalloproteinase and bone morphogenetic protein 1, involved in laminin-332 processing. Immunohistochemistry demonstrated that laminin-332 and alpha6 beta4 integrin were well colocalized, but their signals were remarkably decreased in the lower half of follicles after anagen VI. Consistent with these data, ultrastructurally mature hemidesmosomes were seen in ORS keratinocytes at anagen II, whereas at anagen VI, only fragmental hemidesmosomes were present. In hair follicle culture, laminin-511 (10)/521 (11)-rich human placental laminin enhanced hair growth, whereas recombinant laminin-332 antagonized hair growth induced by laminin-511. Our results indicate a positive role for laminin-511 and a negative role for laminin-332 on hair growth.

Epidermal basement membrane: its molecular organization and blistering disorders

The epidermal basement membrane is a specialized structure localized between the epidermis and the dermis. Recent studies have elucidated the biological roles of the basement membrane and its pathophysiological involvement in bullous diseases. To understand the functions of the basement membrane, it is essential to have clear and precise information regarding the ultrastructural molecular organization of the epidermal basement membrane. Immunoelectron microscopy is a powerful technique and the only method available for the clarification of the ultrastructural localization or orientation of molecules. This review summarizes the latest information regarding the molecular organization of the epidermal basement membrane as determined by immunoelectron microscopy as well as the blistering diseases that occur in the epidermal basement membrane zone.

Genetic abnormalities and clinical classification of epidermolysis bullosa

Genetic abnormalities for different subtypes of epidermolysis bullosa (EB) have been described. In dominant simplex type EB, mutations of the K5 or K14 gene lead to disruption of basal cells and the formation of bullae. The recessive simplex types include EB with muscular dystrophy due to abnormal plectin, EB without muscular dystrophy in patients homozygous for K14 gene abnormalities, and skin fragility syndrome, with formation of acantholytic vesicles within the epidermis due to PKP1 gene mutations. In junctional EB, mutations of the laminin 5, type XVII collagen, and alpha 6 beta 4 integrin genes have been reported. Dystrophic type EB is associated with various abnormalities of the type VII collagen gene. A new classification of EB based on these genetic abnormalities has been proposed. However, some concern has been voiced regarding the clinical utility of a classification based solely on genetic abnormalities. Although the reasons are unclear, identical genetic abnormalities have been known to be associated with different clinical features. A classification including a component based on clinical features would therefore be preferable. This article describes recently discovered genetic abnormalities and offers a new classification scheme for EB.