Recurrent AKR1D1 c.580-13T>A Variant: A Cause of Δ⁴-3-Oxosteroid-5β-Reductase Deficiency

Δ⁴-3-oxosteroid 5β-reductase (AKR1D1) deficiency presents with neonatal cholestasis and liver failure in early infancy and features high levels of 3-oxo-Δ⁴-bile acids in urine. Genetic analysis is needed for definitive diagnosis, because in the neonatal period it can be difficult to distinguish a primary from a secondary enzyme deficiency. By re-analysis of the gene-sequencing data, one AKR1D1 noncanonical splice-site variant (NM_005989.4: c.580-13T>A) with controversial pathogenicity was discovered to be enriched in eight families with clinical and biochemically confirmed AKR1D1 deficiency. Further RNA sequencing of liver tissue suggested this variant causes complete degradation of mRNA. An in vitro minigene experiment indicated that this variant led to partial intron retention or exon jumping, which then leads to coding sequence frameshift and nonsense-mediated mRNA decay. Thus, AKR1D1 variant c.580-13T>A was considered pathogenic and, therefore, should be screened during genetic studies in infants with a suspicion of a congenital bile acid synthetic disorder.