Bile Acid Synthesis Disorders (BASDs)

What are BASDs?

Bile acid synthesis disorders (BASDs) are a group of disorders characterized by defects in the creation of bile acids. Bile acids are chemicals found in the liver that play several key functions such as promoting the flow and excretion of bile and assisting in the intestinal absorption of fat.

Bile acids are formed from cholesterol, so BASDs interfere with the process of breaking down and eliminating cholesterol from the body, as well other abnormal bile acids.

Different types of BASDs include:

• 3-beta-hydroxy-delta-5-C27-steroid oxidoreductase deficiency
• alpha-methylacyl-CoA racemase (AMACR) deficiency
• amino acid n-acyltransferase deficiency
• bile acid CoA ligase deficiency
• cholesterol 7alpha-hydroxylase deficiency
• delta4-3-oxosteroid 5-beta-reductase deficiency
• oxysterol 7-alpha-hydroxylase deficiency
• Sterol 27-hydroxylase deficiency (cerebrotendinous xanthomatosis)
• trihydroxycholestanoic acid CoA oxidase deficiency

What are the symptoms of BASDs?

• Jaundice (yellowing of the skin)
• Stunted growth
• Vitamin deficiencies
• Enlarged liver or spleen
• Liver diseases

 What causes BASDs?

BASDs result from improper synthesis of bile acids, particularly cholic acid and chenodeoxycholic acid. Bile acids are synthesized by the liver through a series of chemical reactions involving enzymes. When one enzyme is missing or deficient, it leads to diminished production of bile and makes way for a bile acid synthesis disorder.

The root cause of this is mutations in specific genes.  In all known BASDs, these mutations are believed to be inherited as autosomal recessive traits.

How are BASDs diagnosed?

A BASD is often diagnosed after clinical evaluation, detailed patient history, and identification of characteristic symptoms.

A diagnosis may be confirmed through:

• Serologic tests
• Liver biopsy
• Blood, bile, or urine analysis
• Fast atom bombardment-mass spectrometry (FABS-MS)
• Eelectrospray ionization mass spectrometry (ESI-MS)
• Gas chromatography-mass spectrometry (GC-MS)
• Molecular genetic testing

What are the treatments for BASDs?

The drug Cholbam (cholic acid) is the first approved treatment indicated for certain BASDs.

Other general treatments and therapies include:

• Bile acid replacement therapy
• Vitamins
• Liver transplant for severe cases

Where can I find out more about BASDs?

• The National Organization for Rare Disorders (NORD)
• NIH