Clinical feature and genetic analysis of a family affected by congenital bile acid synthesis defect type 2: identifcation of 2 novel mutations in AKR1D1 gene

Abstract:

Congenital bile acid synthesis defect type 2 (CBAS2) is an autosomal recessive disorder caused by biallelic mutations of AKR1D1 gene, which encodes the Δ4-3-oxo-steroid 5β-reductase. Cholestatic jaundice is the main clinical manifestation, accompanied by malabsorption of fat and fat-soluble vitamins. This paper reported the clinical and genetic features of a CBAS2 patient definitely diagnosed by AKR1D1 genetic analysis. An 8-monthold male infant was referred to the hospital with the complaint of jaundiced skin and sclera over 7 months. On physical examination, growth retardation and malnutrition were discovered besides mild jaundice of the skin and sclera. The liver was palpable 8 cm below the right subcostal margin with medium texture, and the spleen was not enlarged. On liver function test, elevated levels of bilirubin (predominantly conjugated bilirubin) and transaminases were detected, but serum total bile acids and γ-glutamyl transpeptidase levels were within the normal ranges. Liver histopathologic analysis showed disorganized bile ducts, obvious multinucleated giant cells, significant cholestasis in hepatocytes, together with portal and interstitial fibrosis and lymphocytic infiltration. Via next generation sequencing analysis and Sanger sequencing confirmation, the infant proved to be a compound heterozygote of the AKR1D1 variants c.579+2delT and c.853C > T(p.Q285X), two novel mutations originated from his mother and father, respectively. CBAS2 was thus definitely diagnosed, and chenodeoxycholic acid was given orally. As a result, the abnormal liver function and hepatomegaly were improved gradually. On a follow-up 3 months later, a soft liver was palpable 2.5 cm below the right subcostal margin, and all liver function indices recovered to normal ranges.