A novel deep intronic EIF2AK3 variant disrupts splicing and causes Wolcott-Rallison syndrome.
AIM: Deep intronic variants can disrupt splicing and cause monogenic disease but are missed by routine genetic testing. This study assessed the contribution of deep intronic variants to Wolcott-Rallison syndrome (WRS), a recessive disorder characterized by early-onset diabetes and progressive multisystem disease caused by loss-of-function EIF2AK3 variants. METHODS: We investigated a cohort of 116 individuals referred to the Exeter Genomics Laboratory for genetic testing who had diabetes diagnosed at ≤2 years and at least one additional feature consistent with WRS: hepatic dysfunction, skeletal abnormalities or developmental delay. No genetic cause had been identified after testing all known early-onset diabetes genes. We screened genome-sequencing data for rare homozygous intronic EIF2AK3 variants. Candidate variants predicted to affect splicing by SpliceAI were assessed using a minigene exon-trapping assay. RESULTS: We identified two rare homozygous intronic EIF2AK3 variants in two siblings. Only one variant, c.1651-180G>T, was predicted to disrupt splicing in silico. The two children, born to consanguineous parents, were diagnosed with early-onset diabetes (diagnosed at 1 year and 21 weeks), hepatic dysfunction, skeletal abnormalities, developmental delay, thyroid dysfunction, hip dysplasia and gait abnormalities. The minigene assay showed that c.1651-180G>T creates a cryptic donor splice site within intron 9, resulting in inclusion of a 79-nucleotide pseudoexon, causing a frameshift and premature stop codon. Using this evidence, the variant was reclassified as likely pathogenic according to ACMG/ACGS guidelines. CONCLUSIONS: We report the first deep intronic EIF2AK3 variant causing WRS, highlighting the need to consider systematic intronic analysis in unresolved cases.