Genetic Defects in Bile Acid Conjugation Cause Fat-Soluble Vitamin Deficiency

BACKGROUND & AIMS: The final step in bile acid synthesis involves conjugation with glycine and taurine, which promotes a high intraluminal micellar concentration to facilitate lipid absorption. We investigated the clinical, biochemical, molecular, and morphologic features of a genetic defect in bile acid conjugation in 10 pediatric patients with fat-soluble vitamin deficiency, some with growth failure or transient neonatal cholestatic hepatitis. METHODS: We identified the genetic defect that causes this disorder using mass spectrometry analysis of urine, bile, and serum samples and sequence analysis of the genes encoding bile acid-CoA:amino acid N-acyltransferase (BAAT) and bile acid-CoA ligase (SLC27A5). RESULTS: Levels of urinary bile acids were increased (432 +/- 248 mu mol/L) and predominantly excreted in unconjugated forms (79.4% +/- 3.9%) and as sulfates and glucuronides. Glycine or taurine conjugates were absent in the urine, bile, and serum. Unconjugated bile acids accounted for 95.7% +/- 5.8% of the bile acids in duodenal bile, with cholic acid accounting for 82.4% +/- 5.5% of the total. Duodenal bile acid concentrations were 12.1 +/- 5.9 mmol/L, which is too low for efficient lipid absorption. The biochemical profile was consistent with defective bile acid amidation. Molecular analysis of BAAT confirmed 4 different homozygous mutations in 8 patients tested. CONCLUSIONS: Based on a study of 10 pediatric patients, genetic defects that disrupt bile acid amidation cause fat-soluble vitamin deficiency and growth failure, indicating the importance of bile acid conjugation in lipid absorption. Some patients developed liver disease with features of a cholangiopathy. These findings indicate that patients with idiopathic neonatal cholestasis or later onset of unexplained fat-soluble vitamin deficiency should be screened for defects in bile acid conjugation.