P0188 SRD5B1 (AKR1D1) GENE ANALYSIS IN DELTA4???3-OXOSTEROID 5BETA-REDUCTASE DEFICIENCY: EVIDENCE FOR PRIMARY GENETIC DEFECT

Abstract

Introduction: Delta4–3-oxosteroid 5beta-reductase deficiency, an inborn error in primary bile acid synthesis, is diagnosed on the basis of abnormal urinary bile acids with 3-oxo-delta4 nuclear structure. Diagnosis on this basis alone must be approached with extreme caution as other patients with severe liver disease have been described who excrete these compounds in urine but do not have a primary genetic defect. We have searched for delta4–3-oxosteroid 5beta-reductase gene (SRD5B1 or AKR1D1) mutations in 2 sisters with clinical and biochemical features of delta4–3-oxosteroid 5beta-reductase deficiency. Methods: The twin sisters had a history of neonatal cholestasis of unknown cause with normal serum gamma glutamyl-transferase activity, normal serum total bile acid concentration, and steatorrhea. Evolution was characterized by chronic cholestasis without pruritus, and by liver failure. Analysis of urinary bile acids performed by GC-MS showed 3-oxo-delta4 precursors of chenodeoxycholic and cholic acids (90% of urinary bile acids) associated with 5 % of allo-bile acids and low or undetectable levels of primary bile acids. Cholic acid therapy allowed normalization of liver function and was associated with a strong decrease of bile acid precursors. Five years later, both girls have a normal clinical exam with normal liver function tests and improved liver histology. The 9 exons and adjoining intronic junctions of SRD5B1 were sequenced. Results: In both sisters, we found a compound heterozygous status represented by two nonconservative missense mutations, P133R (467C>G) in exon 4, that deletes a BfaI restriction site, and R261C (850C>T ) in exon 7. These mutations were not detected by sequencing or restriction analysis in 100 chromosomes of control individuals of same ethnicity. Each parent harboured a heterozygous status for one of the mutations. Conclusion: Together with the biochemical data and the evolution profile under primary bile acid therapy, these molecular data provide strong indications for a SRD5B1 primary genetic defect. SRD5B1 mutation analysis allows to establish the diagnosis of genetic delta4–3-oxosteroid 5beta-reductase deficiency and in presence of 3-oxo-delta4 bile aciduria it should help to distinguish a genetic defect from a secondary defect.