Diagnosis of primary BILE ACID SYNTESIS DISORDERS

Early identification and diagnosis of bile acid synthesis disorders (BASDs), is vital to prevent liver damage as these disorders are eminently treatable. 1

Suspicion of primary BASD 2

Essential clues for suspicion of primary BASD:

Confirmation of primary BASD 2

Mass spectrometry analysis of urinary bile acids

AND

Genetic sequencing of the HSD3B7 and AKR1D1 genes

In practice, examinations must be carried out at the same time to exclude other possible causes with a comparable clinical picture. 4

BASDs may be suspected based on a combination of clinical and laboratory signs, and histological signs of the liver. When all these signs are observed together, a specific urinary bile acids analysis test should be performed. Genetic testing provides final confirmation of the diagnosis. Furthermore, as these diseases are inherited, it is important to investigate the patient’s family history, particularly in cases of unexplained liver problems or deaths in young children. 2-4

Other indications: 4

Specific diagnosis is based on mass spectrometry (MS) analysis of urinary bile acids showing typical bile acid profiles and on the identification of disease-causing mutations in the HSD3B7 or AKR1D1 genes.2

Bile acid analysis by mass spectrometry

Bile acid analysis in serum, urine, and bile are is usually performed with 4,5

In 3β-HSD deficiency, urinary analysis shows high excretion of bile acids, that is consistent with cholestasis, but qualitatively abnormal: 4

These assays are usually carried out by highly specialised laboratories. They provide a specific urinary excretion profile for each BASD, enabling diagnosis. 4

In Δ4-3-oxoR deficiency, urine analysis by mass spectrometry shows the absence or low concentrations (traces) of primary bile acids and the presence of atypical metabolites, with a predominance of conjugated hydroxy-oxo-bile acid and allo bile acid derivatives. However, the metabolic profile is not pathognomonic of a primary Δ4-3-oxoR deficiency as the enzyme is sensitive to any advanced liver damage, irrespective of the origin – it may result from secondary deficiency in its activity associated with a closely related urinary excretion profile. A primary genetic deficiency of Δ4-3-oxoR is very likely if the proportion of urinary Δ4-3-oxo bile acid reaches or exceeds 70%.4

Genetic analysis

Genetic sequence analysis of the HSD3B7 and AKR1D1 genes is required to confirm diagnosis.1,4 Currently, two methods are available: Sanger sequencing or targeted gene sequencing panel analysis.4 The gene encoding the enzyme HSD3B7 has been cloned, and the deleterious mutations associated with dysfunction of the enzyme have been identified. About fifteen homozygous or compound heterozygous mutations have been found to date, though no correlation has been identified between the types of mutation and the phenotypic expression of the disease.4

Following identification of the structure of the gene coding for the enzyme (AKR1D1), the primitive character of the deficiency is demonstrated by providing evidence of the mutations in affected patients.4

Suspicion of primary BASD 2

Essential clues for suspicion of primary BASD:

BASDs may be suspected based on a combination of clinical and laboratory signs, and histological signs of the liver. When all these signs are observed together, a specific urinary bile acids analysis test should be performed. Genetic testing provides final confirmation of the diagnosis. Furthermore, as these diseases are inherited, it is important to investigate the patient’s family history, particularly in cases of unexplained liver problems or deaths in young children. 2-4

Clinical signs 2-4

Laboratory signs 2-4

Other indications: 4

family history 2-4

histological signs 2-4

Confirmation of primary BASD 2

Mass spectrometry analysis of urinary bile acids

AND

Genetic sequencing of the HSD3B7 and AKR1D1 genes

In practice, examinations must be carried out at the same time to exclude other possible causes with a comparable clinical picture. 4

Specific diagnosis is based on mass spectrometry (MS) analysis of urinary bile acids showing typical bile acid profiles and on the identification of disease-causing mutations in the HSD3B7 or AKR1D1 genes.2

Bile acid analysis by mass spectrometry

Bile acid analysis in serum, urine, and bile are is usually performed with 4,5

In 3β-HSD deficiency, urinary analysis shows high excretion of bile acids, that is consistent with cholestasis, but qualitatively abnormal: 4

These assays are usually carried out by highly specialised laboratories. They provide a specific urinary excretion profile for each BASD, enabling diagnosis. 4

In Δ4-3-oxoR deficiency, urine analysis by mass spectrometry shows the absence or low concentrations (traces) of primary bile acids and the presence of atypical metabolites, with a predominance of conjugated hydroxy-oxo-bile acid and allo bile acid derivatives. However, the metabolic profile is not pathognomonic of a primary Δ4-3-oxoR deficiency as the enzyme is sensitive to any advanced liver damage, irrespective of the origin – it may result from secondary deficiency in its activity associated with a closely related urinary excretion profile. A primary genetic deficiency of Δ4-3-oxoR is very likely if the proportion of urinary Δ4-3-oxo bile acid reaches or exceeds 70%.4

Genetic analysis

Genetic sequence analysis of the HSD3B7 and AKR1D1 genes is required to confirm diagnosis.1,4 Currently, two methods are available: Sanger sequencing or targeted gene sequencing panel analysis.4 The gene encoding the enzyme HSD3B7 has been cloned, and the deleterious mutations associated with dysfunction of the enzyme have been identified. About fifteen homozygous or compound heterozygous mutations have been found to date, though no correlation has been identified between the types of mutation and the phenotypic expression of the disease.4

Following identification of the structure of the gene coding for the enzyme (AKR1D1), the primitive character of the deficiency is demonstrated by providing evidence of the mutations in affected patients.4

1. Sundaram SS, Bove KE, Lovell MA, Sokol RJ. Mechanisms of disease: Inborn errors of bile acid synthesis. Nat Clin Pract Gastroenterol Hepatol 2008;5:456-68.

2. Jahnel J, Zöhrer E, Fischler B, et al. Attempt to determine the prevalence of two inborn errors of primary bile acid synthesis: results of a European survey. J Pediatr Gastroenterol Nutr 2017;64:864-8.

3. Bove KE, Heubi JE, Balistreri WF, Setchell KD. Bile acid synthetic defects and liver disease: a comprehensive review. Pediatr Dev Pathol 2004;7:315-34.

4. Protocole national de diagnostic et de soins : Déficits de synthèse des acides biliaires primaires. Centre de Référence Coordonnateur de l’Atrésie des Voies Biliaires et des Cholestases Génétiques; 2019.

5. Gonzales E, Gerhardt MF, Fabre M, et al. Oral cholic acid for hereditary defects of primary bile acid synthesis: a safe and effective long-term therapy. Gastroenterology 2009;137:1310-20.e13203.