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Somatic Forward (Nonrevertant) Mosaicism in Recessive Dystrophic Epidermolysis Bullosa

Alexa Rose Shipman, MA (Hons Oxon), MRCP(UK)1,2; Lu Liu, PhD3; Joey E. Lai-Cheong, PhD, MRCP(UK)4; John A. McGrath, MD, FMedSci5; Adrian Heagerty, MD, FRCP1
[+] Author Affiliations
1Department of Dermatology, Solihull Hospital, Birmingham, England
2Department of Dermatology, Warwick Hospital, Warwick, England
3GSTS Pathology, St Thomas’ Hospital, London, England
4Department of Dermatology, King Edward VII Hospital, Windsor, England
5Genetic Skin Disease Group, King’s College London (Guy’s Campus), London, England
JAMA Dermatol. 2014;150(9):1025-1027. doi:10.1001/jamadermatol.2014.281.
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Revertant somatic mosaicism is a recognized phenomenon in patients with epidermolysis bullosa (EB) and other inherited diseases.1 It occurs when spontaneous mutations result in correction of a germline mutation that underlies the genodermatosis, leading to phenotypic reversion and sometimes functional improvement.2 Revertant mosaicism occurs though several mechanisms, all causing a nonreciprocal transfer of genetic information from the parent cell to the daughter cells. Gene conversions, intragenic crossover, back mutation, and second-site mutation (eg, single-base substitution) have all been described as mechanisms, and multiple mechanisms may occur in different cell populations in the same individual. True forward somatic mosaicism, however, has not to our knowledge been described previously in EB. Forward, or nonrevertant, mosaicism occurs during embryogenesis, when a mutation occurs in mitosis affecting only that subsequent cell line and not the other dividing cells of the embryo. The later it occurs during embryogenesis, the fewer cells will be affected.

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Figure 1.
Clinical Photographs Demonstrating Segmental Nature of the Patient’s Dystrophic Epidermolysis Bullosa

Clinical appearances of the abdomen (A and B), hand (C), and nails (D) showing localized erythema and scarring in contrast to the normal-appearing skin.

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Figure 2.
Immunofluorescence and Genetic Sequencing of Affected and Unaffected Skin

The photographic images across the top row represent immunofluorescence (IF) studies (scale bar = 50 μm) in affected (A), unaffected (C), and control skin (D) and a clinical image of the patient’s abdomen (B). Evident in the IF images is a reduction in type VII collagen immunoreactivity at the dermoepidermal junction in affected skin (A) compared with bright, linear labeling in unaffected skin (C) and control skin (D). A-C, The Sanger sequencing graphs of genomic DNA (gDNA) reveal compound heterozygosity for splice site/frameshift mutations in COL7A1, with both mutations clearly evident in DNA from affected skin (A) and blood (B), but the splice site mutation barely detectable in unaffected skin (C), although the heterozygous frameshift mutation is still evident. D, The Sanger sequencing graphs of gDNA from control blood are provided for comparison.

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