Multiple Correcting COL17A1 Mutations in Patients with Revertant Mosaicism of Epidermolysis Bullosa

Abstract

Revertant mosaicism by somatic reversion of inherited mutations has been described for a number of genetic diseases. Several mechanisms can underlie this reversion process, such as gene conversion, crossing-over, true back mutation, and second-site mutation. Here, we report the occurrence of multiple corrections in two unrelated probands with revertant mosaicism of non-Herlitz junctional epidermolysis bullosa, an autosomal recessive genodermatosis due to mutations in the COL17A1 gene. Immunofluorescence microscopy and laser dissection microscopy, followed by DNA and RNA analysis, were performed on skin biopsy specimens. In patient 1, a true back mutation, 3781T-->C, was identified in the specimen from the arm, and a second-site mutation, 4463-1G-->A, which compensated for the frameshift caused by the inherited 4424-5insC mutation, was identified in the 3' splice site of exon 55 in a specimen from the middle finger. Patient 2 showed--besides two distinct gene conversion events in specimens from the arm and hand sites, both of which corrected the 1706delA mutation--a second-site mutation (3782G-->C) in an ankle specimen, which prevented the premature ending of the protein by the 3781C-->T nonsense mutation (R1226X). Thus, both inherited mutations, paternal as well as maternal, reverted at least once by different reversion events in distinct cell clusters in the described patients. The occurrence of multiple correcting mutations within the same patient indicates that in vivo reversion is less unusual than was generally thought. Furthermore, in the male patient, mosaic patterns of type XVII collagen-positive keratinocytes were present in clinically unaffected and affected skin. This latter observation makes it likely that reversion may be overlooked and may happen more often than expected.

A reversion of an IL2RG mutation in combined immunodeficiency providing competitive advantage to the majority of CD8+ T cells

“…Mosaicism due to somatic gene reversion has been observed in the immune system as well as in various other disease entities. [1][2][3][4][5][6]17,[35][36][37] Here we report a novel X-(S)CID family with a unique mutation in the extracellular part of CD132.…”

“…Most spontaneous reversions have been found to occur in severe skin disease and hematologic or immunological diseases. [2][3][4][5][6] The growth advantage of revertant cells has been the central dogma for the success of gene therapy in severe combined immunodeficiency (SCID). 7,8 SCID is a collection of various gene defects that result in the absence of T lymphocytes with or without the involvement of B cells and/or NK cells.…”

The Genetics of Human Skin Disease

“…Second-site and true back-mutations (correction of the original mutation) have also been reported in the reverted skin of patients with the non-Herlitz form of JEB, where DNA sequencing of reverted skin from different regions of the body in two JEB patients revealed multiple second-site mutations in the LAMB3 and COL17A1 genes that negate the effects of the original germline mutations (Pasmooij et al 2005(Pasmooij et al , 2007. Moreover, immunofluorescence staining on the reverted and nonreverted areas of the skin convincingly show these corrections and full restoration of protein levels.…”

Pigmentation and melanocyte supply to the epidermis depend on type XVII collagen

“…Type XVII collagen, lam-332 and C7, along with 11 other macroproteins, are synthesized by keratinocytes and involved in the group of genetic blistering diseases called epidermolysis bullosa (EB) (7)(8)(9). Revertant mosaicism (RM) refers to the coexistence of cells carrying the original germline mutation and cells that spontaneously have corrected the germline mutation by a somatic reverse mutation in one individual (4).…”

“…This patch was more pigmented than the surrounding, mutant (affected) skin. Interestingly, revertant skin manifested as hyperpigmented patches in several patients (8,9).…”