Two novel mutations on exon 8 and intron 65 of COL7A1 gene in two Chinese brothers result in recessive dystrophic epidermolysis bullosa

Novel biallelic variants in COL7A1 cause recessive dystrophic epidermolysis bullosa

Background

Autosomal recessive dystrophic epidermolysis bullosa (RDEB) is an incurable and severe inherited skin disorder characterized by recurrent blistering at the sublamina densa beneath the cutaneous basement membrane. It is caused by biallelic loss‐of‐function mutation in the gene encoding type VII collagen (COL7A1). This study aimed to identify the causative variants of a Chinese RDEB patient and further provide prenatal diagnosis for the ongoing risk pregnancy of the proband's mother.

Methods

Clinical exome sequencing (CES) has been performed and an in‐house pipeline was used to conduct a phenotype‐driven data analysis. A minigene assay was used to verify the pathogenicity of a novel splice site variant in the COL7A1.

Results

Here we report two compound heterozygous variants in COL7A1, c.3867delT (p.G1290Efs*35) and c.5532+4_5532+5delAG, identified in a RDEB patient by CES. The minigene assay confirmed that thec.5532+4_5532+5delAGchange was a noncanonic splice site variant leading to in an in‐frame deletion of exon 64. Prenatal diagnosis indicated that the present pregnancy of the patient's mother was not affected.

Conclusion

Our study expands the mutation spectrum of COL7A1 and demonstrated that CES and minigene assays were efficient tools for RDEB molecular diagnoses.

Treatment of keratinocytes with 4-phenylbutyrate in epidermolysis bullosa: Lessons for therapies in keratin disorders

Background

Missense mutations in keratin 5 and 14 genes cause the severe skin fragility disorder epidermolysis bullosa simplex (EBS) by collapsing of the keratin cytoskeleton into cytoplasmic protein aggregates. Despite intense efforts, no molecular therapies are available, mostly due to the complex phenotype of EBS, comprising cell fragility, diminished adhesion, skin inflammation and itch.

Methods

We extensively characterized KRT5 and KRT14 mutant keratinocytes from patients with severe generalized EBS following exposure to the chemical chaperone 4-phenylbutyrate (4-PBA).

Findings

4-PBA diminished keratin aggregates within EBS cells and ameliorated their inflammatory phenotype. Chemoproteomics of 4-PBA-treated and untreated EBS cells revealed reduced IL1β expression- but also showed activation of Wnt/β-catenin and NF-kB pathways. The abundance of extracellular matrix and cytoskeletal proteins was significantly altered, coinciding with diminished keratinocyte adhesion and migration in a 4-PBA dose-dependent manner.

Interpretation

Together, our study reveals a complex interplay of benefits and disadvantages that challenge the use of 4-PBA in skin fragility disorders.

Neonatal epidermolysis bullosa: lessons to learn about genetic counseling

BACKGROUND

Epidermolysis Bullosa (EB) is a heterogeneous group of congenital blistering diseases that usually presents in the neonatal period. EB is classified into three major categories, each with many subtypes based on the precise location at which separation or blistering occurs, namely epidermolysis bullosa simplex (EBS), junctional epidermolysis bullosa (JEB) and dystrophic epidermolysis bullosa (DEB).

METHODS

We describe genetics of neonatal EB in Hong Kong.

RESULTS

Two neonates of consanguineous Pakistani parents had the EB-Pyloric Atresia (EB-PA) variant. One had a 4 kb homozygous deletion of exon 19-25 of the ITGB4 gene, and the other with only a histopathological diagnosis. Both died of sepsis in infancy. Aberrant COL7A1 mutations in the dominant and recessive EB were described. Genetic analysis, together with histopathological classification is important to aid prognosis and counseling. JEB and EB-PA are associated with consanguinity and mortality during infancy. Morbidity and prognosis of the autosomal dominant DEB are optimistic. The autosomal recessive DEB is more severe, with neonatal onset and recurrent blistering. It is also associated with chronicity and malignant changes when the child reaches adulthood.

CONCLUSION

Exact genetic diagnosis aids in counseling of the family concerning the prognosis in the affected child and the risk of affected children in future pregnancies.

Minor collagens of the skin with not so minor functions

The structure and function of the skin relies on the complex expression pattern and organisation of extracellular matrix macromolecules, of which collagens are a principal component. The fibrillar collagens, types I and III, constitute over 90% of the collagen content within the skin and are the major determinants of the strength and stiffness of the tissue. However, the minor collagens also play a crucial regulatory role in a variety of processes, including cell anchorage, matrix assembly, and growth factor signalling. In this article, we review the expression patterns, key functions and involvement in disease pathogenesis of the minor collagens found in the skin. While it is clear that the minor collagens are important mediators of normal tissue function, homeostasis and repair, further insight into the molecular level structure and activity of these proteins is required for translation into clinical therapies.

A novel deletion and two recurrent substitutions on type VII collagen gene in seven Iranian patients with epidermolysis bullosa

OBJECTIVES

Epidermolysis bullosa is one of the most important series of mechano-bullous heritable skin disorders which is categorized into four major types according to the layer that bullae forms within basement membrane zone. In dystrophic form of the disease, blisters are made in the sublamina densa zone, at the level of type VII collagen protein which produce anchoring fibrils. Type VII collagen gene is the only responsible gene for this form. The aim of this study was to survey causative mutations of type VII collagen gene among Iranian patients with epidermolysis bullosa.

MATERIALS AND METHODS

For this purpose, exons 73-75 were investigated by polymerase chain reaction followed by direct sequencing.

RESULTS

In current study, we found three different point mutations in type VII collagen alleles in 7 out of 50 patients. Four patients were homozygous for a new deletion which resulted in frame shift (p.Pro2089fs). Two patients were homozygous for a recurrent glycine substitution (p.G2031S) and one patient was detected with an allele carrying a substitution (p.R2069C).

CONCLUSION

The results emphasized heterogeneity in the type VII collagen gene and will provide a sign for early diagnosis and future study of the disease pathogenesis.

Recessive dystrophic epidermolysis bullosa: a review of disease pathogenesis and update on future therapies

OBJECTIVE

Review the pathogenesis of recessive dystrophic epidermolysis bullosa and provide an update on research currently underway that is aimed at treating and potentially curing this severe skin disorder.

DESIGN

Review article.

SETTING

Private practice and large teaching hospital.

PARTICIPANTS

None.

MEASUREMENTS

N/A.

RESULTS

Currently, patients with recessive dystrophic epidermolysis bullosa are managed with only supportive care. However, there are several promising new treatment avenues that may help patients in the future. These include gene therapy, cell therapy, and protein-based therapy. Each approach offers distinct advantages and disadvantages.

CONCLUSIONS

The advances in understanding the molecular basis for epidermolysis bullosa over the last few decades has led to significant progress in devising new treatment options. Though many of these approaches remain several years away from regular implementation, it is an exciting time for research in the field.