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Mechanobullous Disorders
Acknowledgment
The author acknowledges the prior contributions of Drs. H. Alan Arbuckle and Ronald E. Grimwood to this chapter.
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What are mechanobullous disorders?
Mechanobullous disorders, either inherited or acquired, are skin conditions characterized by blister formation (vesicles, bullae, and resultant erosions) due to mechanical trauma to the skin and/or mucous membranes. Common friction blisters that develop on the feet due to tight-fitting shoes or boots are an example of acquired lesions. Inherited mechanobullous disorders are rare, and most are classified as a form of epidermolysis bullosa (EB). In EB, deficient or abnormal proteins that hold the skin together lead to a lower threshold for blister formation. Minimal or minor trauma is needed to produce vesicles, bullae, and erosions in individuals with EB. The remainder of this chapter will focus on EB and its complications.
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Where do the blisters that form in EB occur in the skin?
The blistering of EB generally occurs at the level of the dermal-epidermal junction, where the epidermis joins with the dermis ( Fig. 6.1 ). This interface is also called the basement membrane zone (BMZ). Depending on the type of EB, the blister can arise in the basal keratinocytes just above the BMZ, through the BMZ, or in the superficial dermis below the BMZ.
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How is EB classified, and what are the major modes of inheritance?
EB is classified into four major types based on where the blister arises in relation to the BMZ. Subtypes are based on clinical characteristics, mode of inheritance, the targeted protein, and the specific genetic mutation. Table 6.1 reviews the classification and inheritance of the most common forms of EB.
Table 6.1
Classification and inheritance of the most common forms of EB.
| Major EB Type | Major EB Subtype | Minor EB Subtype | Affected gene(s) (protein) | Typical inheritance |
|---|---|---|---|---|
| Simplex | Basal | Localized | KRT5 (keratin 5), KRT14 (keratin 14) | AD |
| Generalized intermediate | KRT5 (keratin 5), KRT14 (keratin 14) | AD | ||
| Generalized severe (formerly called Dowling-Meara) | KRT5 (keratin 5), KRT14 (keratin 14) | AD | ||
| With muscular dystrophy | PLEC1 (plectin) | AR | ||
| Junctional | Generalized | Generalized severe (formerly Herlitz) | LAMA3, LAMB3, LAMC2 (laminin-332) | AR |
| Generalized intermediate (formerly non-Herlitz) | LAMA3, LAMB3, LAMC2 (laminin-332), COL17A1 (type 17 collagen) | AR | ||
| With pyloric atresia | ITGA6, ITGB4 (α 6 β 4 integrin), PLEC1 (plectin) | AR | ||
| Dystrophic | Dominant | Generalized | COL7A1 (type VII collagen) | AD |
| Recessive | Generalized severe | COL7A1 (type VII collagen) | AR | |
| Generalized intermediate | COL7A1 (type VII collagen) | AR | ||
| Kindler syndrome | FERMT1 (also called KIND1, kindlin-1) | AR |
AD, Autosomal dominant; AR, autosomal recessive; EB , epidermolysis bullosa.
Has C, Bauer JW, Bodemer C et al. Consensus reclassification of inherited epidermolysis bullosa and other disorders with skin fragility. Br J Dermatol . 2020 Feb 4. https://doi.org/10.1111/bjd.18921 .
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