Revertant mosaicism: partial correction of a germ-line mutation in COL17A1 by a frame-restoring mutation
Thomas N. Darling, … , Helmut Hintner, Kim B. Yancey
Thomas N. Darling, … , Helmut Hintner, Kim B. Yancey
Published May 15, 1999
Citation Information: J Clin Invest. 1999;103(10):1371-1377. https://doi.org/10.1172/JCI4338.
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Revertant mosaicism: partial correction of a germ-line mutation in COL17A1 by a frame-restoring mutation

Abstract

Generalized atrophic benign epidermolysis bullosa is an autosomal recessive subepidermal blistering disease typified by null mutations in COL17A1. In 1 large kindred, affected individuals were homozygous for a 2-bp deletion in COL17A1, 4003delTC, which resulted in a downstream premature termination codon, nonsense-mediated mRNA decay, and abrogation of type XVII collagen synthesis. Interestingly, 1 of these patients, although phenotypically identical to her affected siblings, showed focal expression of type XVII collagen in epidermal basement membrane in a pattern suggestive of revertant mosaicism. When studies of randomly obtained epidermal, oromucosal, and peripheral blood cells failed to identify the genetic basis of this apparent mosaicism, microscopic subpopulations of potentially revertant epidermal cells (i.e., those overlying basement membrane containing type XVII collagen) were selectively isolated using laser capture microdissection. Analysis of DNA and RNA from these cells revealed a second mutation, 4080insGG, on 1 allele of COL17A1. This 2-bp insertion corrected the reading frame just proximal to the premature termination codon, countered nonsense-mediated mRNA decay, and allowed protein production by patient keratinocytes in vivo and in vitro. These studies elucidate the molecular basis of a novel form of revertant mosaicism in humans.

Authors

Thomas N. Darling, Carole Yee, Johann W. Bauer, Helmut Hintner, Kim B. Yancey

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Figure 1

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Type XVII collagen was present only at focal sites in the proband’s epid...
Type XVII collagen was present only at focal sites in the proband’s epidermal BM. (a) IF microscopy studies of normal human skin cryosections stained with an mAb to type XVII collagen (see Methods) showed continuous expression of this protein in epidermal BM (shown in red). (b) IF microscopy studies of the proband’s skin cryosections stained in the same manner found that type XVII collagen (when detected) was present in epidermal BM only in a focal, interrupted distribution (shown in red; an intervening segment of nonreactive BM is delineated by arrows). (c) The proband’s epidermal BM was otherwise intact. For purposes of documentation, the cryosection shown in b was double stained with an antibody to type IV collagen. This antibody (as well as antibodies to bullous pemphigoid antigen 1, laminin 5, and type VII collagen; ref. 9) showed normal reactivity (shown in green) along the entire epidermal BM of the proband. Type IV collagen in microvascular BMs was also stained.