56 One study showed that a complete filaggrin deficiency in ichthyosis vulgaris resulted in only moderate changes in epidermal permeability barrier function. These architectural changes include altered keratin filament organization, impaired loading of lamellar body contents, irregular extracellular distribution of secreted organelle material, and changes in lamellar bilayer architecture. 53–55 Although filaggrin is an intracellular protein, deficiencies result in alterations of keratinocyte architecture that influence extracellular matrix functions. 52 In fact, a variety of mutations of this gene have been identified, and there appear to be ethnic differences among FLG mutations found in Asians and Europeans, with some variances also among these populations. The data suggest that, as is the case with FLG mutations in patients of European origin, there is no single recurrent gene that appears to be causative of the disease. This is further supported by a study of Ethiopian patients with ichthyosis vulgaris and atopic dermatitis using whole-exome sequencing. 51 No specific gene has, as yet, been identified. 49,50 A previously unreported genetic locus for ichthyosis vulgaris has been identified in two Chinese families on chromosome 10q22.3–q24.2. 48 Childhood eczema is strongly associated with these common European mutations. 11 Mutations in the FLG gene occur in approximately 9% of individuals from European populations. 11,45–47 The gene is unusually large and repetitive, making analysis of it difficult. 44 This results from loss-of-function mutations in the gene encoding filaggrin (FLG), located at 10q21. 17,43 There are quantitative decreases in filaggrin, related to the severity of the disease. In ichthyosis vulgaris, there is a deficiency in profilaggrin, which is converted into filaggrin, the major protein of keratohyalin. There may be accentuation of palmar and plantar markings, keratosis pilaris, and features of atopy. It is characterized by fine, whitish scales involving particularly the extensor surfaces of the arms and legs, as well as the scalp. 27,37 Heterozygotes show a very mild phenotype with incomplete penetrance (semidominant) such cases may be misdiagnosed as dry skin. Ichthyosis vulgaris (OMIM 146700) is the most common disorder of keratinization (incidence 1 : 250), with an onset in early childhood and an autosomal dominant inheritance.
Translucent cells containing keratin skin#
Patterson MD, FACP, FAAD, in Weedon's Skin Pathology, 2021 Ichthyosis Vulgaris
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