Genotype-phenotype correlation in junctional epidermolysis bullosa

Wen, David (2023). Genotype-phenotype correlation in junctional epidermolysis bullosa. University of Birmingham. M.Res.

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Abstract

Junctional epidermolysis bullosa (JEB) is a rare autosomal recessive genodermatosis characterised by mucocutaneous cleavage within the lamina lucida of the basement membrane zone following mild mechanical trauma. Genes implicated in JEB include LAMB3, LAMA3, LAMC2 and COL17A1. A broad spectrum of JEB phenotypes exist, with severity ranging from death in infancy, to mild and localised blistering. Current genotype-phenotype paradigms are insufficient to accurately predict JEB subtype and characteristics from genotype, which has implications for clinicians, patients and their families. This study evaluated genetic and clinical findings from a cohort of individuals with JEB and systematically investigated genotype-phenotype correlations through bioinformatic analyses and comparison with mutations already reported in the literature.

Mutations were identified through Sanger sequencing, and were annotated and mapped to reference genes and proteins. Splice site mutations underwent analysis with the in-silico tools MMSplice and SpliceAI in order to predict resultant transcripts. A dedicated JEB deep phenotyping tool was developed which was used to systematically examine the clinical features of JEB individuals.

Eighteen unique mutations in LAMB3, LAMA3, LAMC2 or COL17A1 were identified from seventeen individuals (thirteen homozygotes and four compound heterozygotes). There were seven cases of severe JEB, nine intermediate JEB and one laryngoonycho- cutaneous syndrome. Seven mutations were novel, and the majority of mutations identified in the cohort were found in LAMB3 and were spread throughout the gene. LAMB3 mutations included five splice site mutations. Functional effects predicted by the in-silico tools included exon skipping and activation of cryptic splice sites, which provided potential explanations for disease severity. RT-PCR and cDNA sequencing of one case confirmed the presence of a correctly predicted transcript, and also revealed an additional transcript generated through alternate splicing. Deep phenotyping was completed for all intermediate JEB cases and demonstrated substantial variation between individuals.

Reviewing the cases together, and with other mutations reported in the literature, this study highlights the importance of investigation at the RNA level for accurate phenotype prediction, and the need for a centralised database of pathogenic variants associated with JEB and corresponding phenotypes which would be a vital resource for genetic counselling and pre-natal diagnosis.

Type of Work:

Thesis (Masters by Research > M.Res.)

Award Type:

Masters by Research > M.Res.

Supervisor(s):