Amino Acid Substitution in the Cysteine-Rich Region of the Integrin f34 Subunit Causes Late- Onset Mild Junctional Epidermolysis Bullosa without Extracutaneous Involvement

Integrin a604, encoded by ITGA6 and ITGB4, is a transmembrane component of hemidesmosomes and plays an important role in connecting keratinocytes with extracellular matrix proteins. ITGB4 or ITGA6 biallelic pathogenic variants cause junctional epidermolysis bullosa (JEB) with pyloric atresia, which is associated with high lethality. Patients who survive usually develop JEB of intermediate severity and urorenal manifestations. In this study, we report a very rare subtype of late-onset, nonsyndromic JEB associated with a recurrent amino acid substitution in the highly conserved cysteine-rich tandem repeats of the integrin 04 subunit. Literature review shows that among the patients diagnosed with ITGB4 mutations, only two had no extracutaneous manifestations, and only two patients with JEB with pyloric atresia carried missense mutations located in cysteine-rich tandem repeats. We analyzed the consequences of the novel ITGB4 variant c.1642G>A, p.Gly548Arg, on the clinical phenotype, the predicted protein structure, cellular phenotype, and gene expression pattern to show its pathogenicity. The results indicated that the p.Gly548Arg amino acid substitution affected the protein structure of integrin 04 subunits and disrupted the stability of hemidesmosomes and in turn impaired the adhesion of keratinocytes. RNA-sequencing results indicated similar changes in extracellular matrix structure organization and differentiation in keratinocytes completely devoid of integrin 04 and with the amino acid substitution p.Gly548Arg, which further supports the dysregulation of the function of the integrin 04 subunit caused by p.Gly548Arg. Our results provided evidence for a late-onset, mild JEB subtype without extracutaneous manifestations and extend the ITGB4-related genotype-phenotype correlations.

Automated summary

ITGB4 mutations usually result in junctional epidermolysis bullosa (JEB) with pyloric atresia and other symptoms, but we reported a rare subtype of late-onset, nonsyndromic JEB without extracutaneous manifestations. Our study revealed the pathogenic mechanism of this JEB subtype.