Lemonde H A, Custard E J, Bouquet J, Duran M, Overmars H, Scambler P J, Clayton P T
Biochemistry, Endocrinology, and Metabolism Unit, Institute of Child Health, University College London with Great Ormond Street Hospital for Children NHS Trust, London, UK.
Gut. 2003 Oct;52(10):1494-9. doi: 10.1136/gut.52.10.1494.
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).
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.
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.
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.
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.
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.
相当一部分婴儿胆汁淤积性肝病患者排泄的主要尿胆汁酸为7α-羟基-3-氧代-4-胆烯酸和7α,12α-二羟基-3-氧代-4-胆烯酸的甘氨酸和牛磺酸共轭物。有人提出，其中一些患者（但不是全部）在编码δ(4)-3-氧代类固醇5β-还原酶（SRD5B1；AKR1D1，OMIM 604741）的基因中存在突变。
我们的目的是在血浆和尿液中鹅去氧胆酸和胆酸缺乏或浓度较低的患者中鉴定SRD5B1基因的突变，因为这些患者似乎是遗传性5β-还原酶缺乏的有力候选者。
我们研究了3例新生儿期起病的胆汁淤积性肝病且γ-谷氨酰转肽酶正常的患者，其尿液和血浆中的主要胆汁酸为3-氧代-δ(4)胆汁酸，饱和胆汁酸浓度较低或检测不到。在其父母、兄弟姐妹以及50名种族匹配的对照受试者中寻找SRD5B1基因中检测到的任何碱基变化。
从血液中提取DNA，对SRD5B1的9个外显子进行扩增和测序。使用限制性内切酶筛选父母、兄弟姐妹和对照的DNA。
在所有3名儿童中均鉴定出SRD5B1基因的突变。患者MS为错义突变（662 C>T）的纯合子，导致Pro198Leu氨基酸替代；患者BH为单碱基缺失（511 delT）的纯合子，导致第5外显子移码并出现提前终止密码子；患者RM为错义突变（385 C>T）的纯合子，导致Leu106Phe氨基酸替代。所有患者的肝活检均显示巨细胞性肝炎；其中2例可见明显的髓外造血。MS经鹅去氧胆酸和胆酸治疗后治愈；BH起初有所改善，但随后病情恶化，需要进行肝移植；RM在开始治疗时已有晚期肝病，也进展为肝衰竭。
检测血液样本中的SRD5B1突变可用于诊断遗传性5β-还原酶缺乏，并将这些患者与其他导致3-氧代-δ(4)胆汁酸尿症的患者（例如严重肝损伤患者）区分开来。如果肝病不太严重，遗传性5β-还原酶缺乏患者可能对鹅去氧胆酸和胆酸治疗反应良好。
