Mutations in SRD5B1 (AKR1D1), the gene encoding delta(4)-3-oxosteroid 5beta-reductase, in hepatitis and liver failure in infancy

Abstract

Background: A substantial group of patients with cholestatic liver disease in infancy excrete, as the major urinary bile acids, the glycine and taurine conjugates of 7alpha-hydroxy-3-oxo-4-cholenoic acid and 7alpha,12alpha-dihydroxy-3-oxo-4-cholenoic acid. It has been proposed that some (but not all) of these have mutations in the gene encoding delta(4)-3-oxosteroid 5beta-reductase (SRD5B1; AKR1D1, OMIM 604741).

Aims: Our aim was to identify mutations in the SRD5B1 gene in patients in whom chenodeoxycholic acid and cholic acid were absent or present at low concentrations in plasma and urine, as these seemed strong candidates for genetic 5beta-reductase deficiency.

Patients and subjects: We studied three patients with neonatal onset cholestatic liver disease and normal gamma-glutamyl transpeptidase in whom 3-oxo-delta(4) bile acids were the major bile acids in urine and plasma and saturated bile acids were at low concentration or undetectable. Any base changes detected in SRD5B1 were sought in the parents and siblings and in 50 ethnically matched control subjects.

Methods: DNA was extracted from blood and the nine exons of SRD5B1 were amplified and sequenced. Restriction enzymes were used to screen the DNA of parents, siblings, and controls.

Results: Mutations in the SRD5B1 gene were identified in all three children. Patient MS was homozygous for a missense mutation (662 C>T) causing a Pro198Leu amino acid substitution; patient BH was homozygous for a single base deletion (511 delT) causing a frame shift and a premature stop codon in exon 5; and patient RM was homozygous for a missense mutation (385 C>T) causing a Leu106Phe amino acid substitution. All had liver biopsies showing a giant cell hepatitis; in two, prominent extramedullary haemopoiesis was noted. MS was cured by treatment with chenodeoxycholic acid and cholic acid; BH showed initial improvement but then deteriorated and required liver transplantation; RM had advanced liver disease when treatment was started and also progressed to liver failure.

Conclusions: Analysis of blood samples for SRD5B1 mutations can be used to diagnose genetic 5beta-reductase deficiency and distinguish these patients from those who have another cause of 3-oxo-delta(4) bile aciduria, for example, severe liver damage. Patients with genetic 5beta-reductase deficiency may respond well to treatment with chenodeoxycholic acid and cholic acid if liver disease is not too advanced.

Figure 1

Negative ion liquid secondary ionisation mass spectrometry (LSIMS) analysis of a urine sample from patient BH. Identities of peaks (confirmed by gas chromatography-mass spectrometry): m/z 444 and 460, glycine conjugates of 7α-hydroxy-3-oxo-4-cholenoic acid and 7α,12α-dihydroxy-3-oxo-4-cholenoic acid; m/z 494, 510, and 552, taurine conjugates of 7α-hydroxy-3-oxo-4-cholenoic acid, 7α,12α-dihydroxy-3-oxo-4-cholenoic acid, and 7α,12α-dihydroxy-3-oxo-4-cholestenoic acid.

Figure 2

Suggested algorithm for distinguishing between primary genetic 5β-reductase deficiency and other cause of 3-oxo-Δ⁴ bile aciduria. ESI-MS/MS, electrospray ionisation tandem mass spectrometry; GC-MS, gas chromatography-mass spectrometry; FAB-MS, fast atom bombardment-mass spectrometry.