Revertant Mosaicism Due to a Second-Site Mutation in COL7A1 in a Patient with Recessive Dystrophic Epidermolysis Bullosa

Abstract

Despite the high incidence of revertant mosaicism (35%) in patients with the genetic skin disease epidermolysis bullosa (EB) due to correcting mutations in the genes COL17A1 and LAMB3, revertant mosaicism has not been described for COL7A1 until recently. Mutations in COL7A1 are responsible for the most devastating form of EB in adults, which is characterized by cocooned "mitten" deformities of the hands. This report shows in vivo reversion of an inherited COL7A1 mutation in a patient with recessive dystrophic EB who was homozygous for the frameshift mutation COL7A1:c.6527insC,p.2176FsX337. The patient exhibited a patch of clinically healthy revertant skin on her left forearm. The second-site mutation c.6528delT, which is present in revertant keratinocytes, resulted in correction of the reading frame. As the new CCC codon codes for the same amino acid proline as the wild-type codon CCT, the revertant cells expressed wild-type type VII collagen polypeptide, leading to restoration of skin function. We hypothesize that, on careful examination, revertant mosaicism might be found to be more common in patients with type VII collagen-deficient EB. Furthermore, the revertant keratinocytes might offer the possibility to explore cell-based therapeutic strategies, by culturing in vitro and subsequently grafting as part of bioengineered dermo-epidermal substitutes on affected skin.

Concise Review: Transplantation of Human Hematopoietic Cells for Extracellular Matrix Protein Deficiency in Epidermolysis Bullosa

“…That such stem cell gene therapy will be effective in a nonhematopoietic disorder, and specifically in EB, is supported by the observations that a minority of individuals with EB develop self-correcting mutations in one of the genes underlying the EB pathology and that when such somatic mutations occur, the gene self-corrected skin is resistant to trauma [50][51][52]. In contrast to other conditions with prominent mosaicism, such as BM failure syndrome Fanconi anemia, where a self-correcting somatic mutation occurring in a single stem cell is capable of restoring normal hematopoiesis [53], the mosaicism in EB remains confined to small area of skin.…”

Analysis of 589,306 genomes identifies individuals resilient to severe Mendelian childhood diseases

“…For example, human genetic studies have identified rare mutations in CCR5 that confer resilience against HIV infection 12 , mutations in globin genes that modify the severity of sickle cell disease by buffering primary mutations in β-globin genes 13 , and LoF mutations in PCSK9 that protect carriers from high lipid levels and resulting heart disease 14 . Second-site mutations in disease genes have also been shown to revert clinical phenotype in patients with recessive dystrophic epidermolysis 15 and Fanconi anemia 16 , whereas LoF mutations in zinc transporter 8 have been found to protect obese individuals from diabetes 17 . Most recently, a variant Analysis of 589,306 genomes identifies individuals resilient to severe Mendelian childhood diseases A r t i c l e s identified in the gene Jagged1 was found to confer resilience to Duchenne muscular dystrophy in two dogs, implicating Jagged1 as a therapeutic target for the disorder 18 .…”

Natural Gene Therapy in Dystrophic Epidermolysis Bullosa

“…16 We performed laser dissection microscopic examination using the Leica LMD6000 laser microdissection microscope (Leica MicrosystemsGmbH,Wetzlar,Germany)on4-µmskincryo-sections from mutant and revertant skin to separate keratinocytes with normal COLVII staining from those with reduced staining and from fibroblasts. 13 Also, RNA was isolated from 5-µm sections of mutant and revertant skin (QiagenRNeasyPlusMicroKit;QiagenNV,Venlo,theNetherlands), and complementary DNA (cDNA) was synthesized as described. 13 Subsequently, nested polymerase chain reaction assays were performed on genomic DNA and cDNA (for primers, see the study by Pasmooij et al 13 ).…”

“…Almaani et al 12 identified the first patient known to have recessive DEB (RDEB) with revertant mosaicism due to an intragenic crossover within the type VII collagen (COLVII) gene, COL7A1. Pasmooij et al 13 subsequently reported on revertant mosaicism in a patient with RDEB due to a somatic nucleotide deletion within COL7A1. Herein, we describe a patient with RDEB who has revertant mosaicism due to a third type of correction, a nucleotide substitution that corrects the germline nonsense codon by changing it to a tyrosine.…”