Syed Ashraf Uddin, Nicole Cesarato, Aytaj Humbatova, Axel Schmidt, Fazal ur Rehman, Muhammad Naeem, Abdul Samad Tareen, Sabrina Wolf, Muhammad Anwar Panezai, Holger Thiele, Abdul Wali, Regina Fölster-Holst, Sulman Basit, Muhammad Ayub, Regina C. Betz
DOI: 10.2340/00015555-3634

Dystrophic epidermolysis bullosa is an inherited skin disorder characterized by fragile skin that is prone to blistering. We report here a consanguineous Pakistani family with two siblings, in whom a severe recessive dystrophic epidermolysis bullosa was suspected. Using whole-exome sequencing for one sibling, the homozygous base substitution c.7249C>G in COL7A1 was identified, and could be confirmed in the other sibling by Sanger sequencing. In our exome data, this mutation was annotated as a missense substitution (p.Gln2417Glu), but in silico tools indicated a possible effect on splicing. Using the ExonTrap vector it was verified that the mutation leads to activation of a cryptic donor splice site, which leads to loss of 26 nucleotides, and a frame­shift event predicted to result in a truncated protein (p.Q2417Sfs*57). The present report de­scribes an apparent COL7A1 missense substitution with an unexpected consequence on splicing that leads to a severe recessive dystrophic epidermolysis bullosa phenotype.

This study examined the genetic cause of a severe form of the blister-forming disease epidermolysis bullosa in 2 affected siblings from Pakistan. Exchange of a single base on gene copies from both parents was found in the COL7A1 gene, which should affect the protein properties. However, computer programs predicted a so-called splice effect (altered removal of the introns of a gene). This was proved experimentally in cell culture. Thus, the study shows that a new splice site was created in exon 94, which resulted in a truncated protein.