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Pathophysiology of primary bile acid synthesis disorders

Failure to synthesise normal bile acids reduces the flow of bile, causing cholestasis and the retention of potentially hepatoxic compounds – for example conjugated bilirubin – which are normally excreted in the bile.1 Normally, bile acids facilitate the detachment of γ-glutamyl-transpeptidase (GGT) from the canalicular membrane. This is why BASDs, unlike other causes of cholestasis, do not lead to elevation of plasma GGT.1 As taurine and glycine conjugates of cholic acid (CA) and chenodeoxycholic acid (CDCA) are required to facilitate emulsification and absorption of fats and fat-soluble vitamins, the absence of these bile acids can lead to steatorrhoea, failure to thrive and deficiencies of fat-soluble vitamins. 1

Pathophysiology of 3β-HSD and Δ4-3-oxoR deficiencies

adapted from Jahnel 2017 2

Healthy hepatocyte

Cholesterol

Cholesterol

CYP7A1

CYP7A1

CYP727

CYP727

3β-HSD
Δ4-3-oxoR

3β-HSD
Δ4-3-oxoR

CA+CDCA

BSEP

Neutral
Pathway

Neutral
Pathway

FGFR4

FGFR4

FGF15/19

FGF15/19

Primary bile acids

Toxic bile acid intermediates

ASBT

Enterocyte

Urinary excretion

FGF15/19

FGF15/19

FXR

FXR

NTCP

NTCP

Acidic
Pathway

Acidic
Pathway

Bile acid intermediates

Absence of
primary bile acids

cholestatic

hepatotoxic

Hepatocyte with 3β-HSD
or Δ4-3-oxoR deficiency

1. Clayton PT. Disorders of bile acid synthesis. J Inherit Metab Dis 2011;34(3):593-604.

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;64:864-68.

TH-BAS11EN/01/02/2024

Content reviewed in conjunction with experts in paediatric gastroenterology and hepatology

03/2024

General condition

The gene encoding CYP7A1 is highly regulated by a negative feedback involving the farnesoid X receptor (FXR)-dependent induction of fibroblast growth factor 15/19 (FGF15/19) by bile acids in enterocytes.

FGF15/19 binds to the fibroblast growth factor receptor 4 (FGFR4)/b-klotho complex in hepatocytes, activating signaling pathways that transcriptionally repress CYP7A1 expression.

Bile acids are transported to the liver in the portal blood and enter in the hepatocytes via sodium taurocholate cotransporting polypeptide (NTCP).

Bile acids are recovered from the intestines by the apical sodium-dependent bile acid transporter (ASBT).

 Cholic acid and chenodeoxycholic acid are conjugated to glycine or taurine, which are substrates for the bile acid transport pump (BSEP). Canalicular transport of bile acid is the rate-limiting step of bile secretion.

Biosynthesis of the primary bile acids, cholic acid (CA) and chenodeoxycholic acid (CDCA), involves numerous enzymes including 3β-HSD and Δ4-3-oxoR. The neutral pathway, the major pathway in adults, is initiated by CYP7A1, which is the rate-limiting step in the conversion of cholesterol to CA and CDCA. During the first months of life, however, the acidic pathway is essential for the synthesis of primary bile acids. The acidic pathway is initiated by hydroxylation of cholesterol by the sterol 27-hydroxylase (CYP27). Its regulation is not fully understood. .

Suppression of the negative feedback loop further represses biosynthesis, increasing the production of bile acid intermediates, which are excreted in the urine.

Bile acid intermediates that are hepatotoxic and cholestatic accumulate.

Absence of primary bile acids in the intestine results in fat and fat-soluble vitamin malabsorption.

 

Biliary secretion is strongly decreased by a reduction in the bile acid-dependent fraction of bile secretion. This results in cholestasis with normal serum γ-glutamyl-transferase (GGT) activity.

Defects in the enzymes 3β-HSD and ∆4-3-oxoR, catalysing key reactions in the formation of the primary bile acids (cholic acid and chenodeoxycholic acid), lead to inadequate synthesis of primary bile acids. Consequently, primary bile acids are not synthesized but instead atypical and hepatotoxic bile acid intermediates are formed.

Tight junction protein 2 (TJP2) deficiency or progressive familial intrahepatic cholestasis type 4 (PFIC4)

TJP2 deficiency or PFIC4 is an autosomal recessive disorder caused by a mutation in the TJP2 gene, encoding the tight junction protein-2, which is involved in the organisation of epithelial and endothelial cell junctions.59 PFIC4 is characterised by early-onset cholestasis with severe progression.4

More information about tight junction protein 2 (TJP2) deficiency or progressive familial intrahepatic cholestasis type 4 (PFIC4) and references
Benign recurrent intrahepatic cholestasis type 2 (BRIC2)

BRIC2 is a hereditary liver disorder characterised by intermittent attacks of intrahepatic cholestasis, generally without progression to chronic liver damage.31,32

More information about benign recurrent intrahepatic cholestasis type 2 (BRIC2) and references

Benign recurrent intrahepatic cholestasis type 1 (BRIC1)

BRIC1 is a hereditary liver disorder characterised by intermittent attacks of intrahepatic cholestasis, generally without progression to chronic liver damage. 31,32

More information about benign recurrent intrahepatic cholestasis type 1 (BRIC1) and references

Progressive familial intrahepatic cholestasis type 1 (PFIC1)

PFIC1 is an autosomal recessive childhood bile formation disorder of hepatocellular origin associated with extrahepatic features.31

More information about progressive familial intrahepatic cholestasis type 1 (PFIC1) and references

Progressive familial intrahepatic cholestasis type 2 (PFIC2)

PFIC2 is an autosomal recessive childhood disorder of bile formation in hepatocytes that is not associated with extrahepatic features.32 It is caused by impaired bile salt secretion due to defects in ABCB11 encoding the bile salt export pump protein (BSEP).58

More information about progressive familial intrahepatic cholestasis type 2 (PFIC2) and references

Choledochal cysts

Choledochal cysts are rare congenital bile duct abnormalities. 33,34

More information about choledochal cysts and references

Biliary lithiasis

Biliary lithiasis or gallstone disease is characterised by the presence of stones in the gallbladder, the biliary ducts, or both.24,25

More information about the biliary lithiasis and references
PRIMARY BILE ACID SYNTHESIS DEFECTS (3β-HYDROXY-Δ5-C27-STEROID DEHYDROGENASE (3β-HSD) DEFICIENCY, OR Δ4-3-OXOSTEROID 5β-REDUCTASE (Δ4-3-OXO-R) DEFICIENCY)

These inborn errors of primary bile acid synthesis are rare autosomal recessive cholestatic disorders, leading to inadequate synthesis (or complete absence) of the primary bile acids and resulting in the build-up of atypical and hepatotoxic bile acid intermediates.52

More information about primary bile acid synthesis defects 3β-HSD and Δ4-3-oxoR deficiencies and references

Cystic fibrosis

Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. CFTR is expressed in the apical surface of cholangiocytes.42

More information about cystic fibrosis and references

Alpha-1-antitrypsin deficiency (AATD)

AATD is a rare autosomal recessive condition caused by a mutation in the SERPINA1 gene leading to decreased production of the neutrophil-elastase protective protein alpha-1 antitrypsin, thereby increasing the risk of serious lung and liver disease.4,5

More information about alpha-1-antitrypsin deficiency (AATD) and references

Drug toxicity

Drug-induced liver injury (DILI) is a major cause of paediatric liver disease including cholestasis, accounting for almost 20% of cases of acute liver failure in children, and is a major reason for liver transplantation.45

More information about drug toxicity and references 

Cortisol deficiency

Cortisol deficiency may result from a primary adrenal process, owing to maldevelopment, malfunction, or destruction of the gland or be secondary to dysfunction of the hypothalamic-pituitary-adrenal axis.39

More information about cortisol deficiency and references 

Other extrahepatic causes

Such as spontaneous perforation of the common bile duct or congenital stenosis, etc1

  1. Adapted from, Protocole national de diagnostic et de soins : Déficits de synthèse des acides biliaires primaires. In: Génétiques CdRCdlAdVBedC, ed., 2019.

Choledochal cysts

Choledochal cysts  are rare congenital bile duct abnormalities. 21,22

More information about choledochal cysts and references

Cholestasis and / or cholestatic jaundice

In newborns:

First, confirm the aetiology:1

  Those requiring urgent treatment:

       Biliary atresia

        Urinary infection or sepsis

        Cortisol deficiency

  Those with an easily detectable aetiology:

     Alagille syndrome

       Choledochal cyst

       Cystic fibrosis

       Alpha-1-antitrypsine deficiency 

 

Neonatal sclerosing cholangitis

Neonatal sclerosing cholangitis is a rare biliary tract disease characterised by severe neonatal-onset cholangiopathy with patent bile ducts.4

More information about neonatal sclerosing cholangitis and references 

Biliary Lithiasis

Biliary lithiasis or gallstone disease is characterised by the presence of concretions in the gallbladder, the biliary ducts, or both.15,16

More information about biliary lithiasis and references

Alpha-1-antitrypsin deficiency (AATD)

AATD is a rare autosomal recessive condition caused by a mutation in the SERPINA1 gene leading to decreased production of the neutrophil-elastase protective protein alpha-1 antitrypsin, thereby increasing the risk of serious lung and liver disease.1,5

More information about alpha-1-antitrypsin deficiency and references

Cystic fibrosis

Cystic fibrosis is an autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR is expressed in the apical surface of cholangiocytes.30

More information about cystic fibrosis and references 

Cortisol deficiency

Cortisol deficiency may result from a primary adrenal process, owing to maldevelopment, malfunction, or destruction of the gland, or be secondary to dysfunction of the hypothalamic-pituitary-adrenal axis.27

More information about cortisol deficiency and references 

Biliary atresia

Biliary atresia is a progressive obliterative cholangiopathy of the intrahepatic and extrahepatic bile ducts. It occurs in the perinatal period causing severe, persistent jaundice and acholic stool and, if untreated, is associated with a poor prognosis.4

More information about biliary atresia and references 

Arthrogryposis-renal dysfunction-cholestasis syndrome (ARC syndrome)

ARC syndrome is an autosomal recessive disease characterised by immobility of the limbs and fixation of joints with muscle wasting (neurogenic arthrogryposis multiplex congenita), renal tubular dysfunction and neonatal cholestasis.8

More information about arthrogryposis-renal dysfunction-cholestasis syndrome (ARC syndrome) and references 

Hepatitis A

Hepatitis A virus (HAV) is an RNA picornavirus which is transmitted through faecal-oral contamination.47

More information about hepatitis A and references

Progressive familial intrahepatic cholestasis type 3 (PFIC3)

PFIC3 is an autosomal recessive childhood disorder of bile formation in hepatocytes caused by mutations in the ABCB4 gene coding for the phospholipid transporter MDR3, which is expressed in the canalicular membrane of hepatocytes.32,58

More information about progressive familial intrahepatic cholestasis type 3 (PFIC3) and references

Autoimmune cholangitis

Autoimmune cholangitis (AIC), also known as autoimmune cholangiopathy, is a chronic inflammation of the liver and a variant syndrome of autoimmune hepatitis.9

More information about autoimmune cholangitis and references

Biliary atresia

Biliary atresia is a progressive obliterative cholangiopathy of the intrahepatic and extrahepatic bile ducts. It occurs in the perinatal period causing severe, persistent jaundice and acholic stool and, if untreated, is associated with a poor prognosis.3

More information about biliary atresia and references 

sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a rare, idiopathic, heterogeneous, chronic, cholestatic liver disease characterised by inflammation and fibrosis of both the intrahepatic and extrahepatic bile ducts, leading to the formation of multifocal bile duct strictures.54-56

More information about primary sclerosing cholangitis and references 

Alagille syndrome (AGS)

Alagille syndrome is a multisystemic, autosomal dominant disorder caused by a defect in the Notch signalling pathway leading to intrahepatic bile duct paucity and resulting in significant cholestasis.2

More information about Alagille syndrome and references

Progressive familial intrahepatic cholestasis type 5 (PFIC5)

PFIC5 is a severe autosomal recessive liver disorder caused by a mutation in the NR1H4 gene.50

More information about progressive familial intrahepatic cholestasis type 5 (PFIC5) and references 

MYOSIN 5B DEFICIENCY

Myosin 5B deficiency causes microvillus inclusion disease. It is a severe autosomal recessive disease caused by a myosin 5B (MYO5B) mutation and characterised by malabsorption and diarrhoea.48

More information about myosin 5B deficiency and references

UNC45A DEFICIENCY (OSTEO-OTO-HEPATO-ENTERIC SYNDROME (O2HE SYNDROME))

UNC45A deficiency causes osteo-oto-hepato-enteric syndrome. It is an autosomal recessive syndrome secondary to loss of function mutations in the UNC45A gene.60

More information about UNC45A deficiency (osteo-oto-hepato-enteric syndrome (O2HE syndrome)) and references

Alagille syndrome

Alagille syndrome is a multisystemic, autosomal dominant disorder caused by a defect in the notch signalling pathway leading to intrahepatic bile duct paucity and resulting in significant cholestasis.1

More information about Alagille syndrome and references

Bilirubin metabolism5-7

Unconjugated
bilirubin

Bilirubin is mainly
produced from the
break down of red
blood cells.

Red cell breakdown
produces unconjugated
(“indirect”) bilirubin,
which circulates mostly
bound to albumin,
although some is
“free” and hence
able to enter the brain.

The terms “direct”
and “indirect” refer
to the way laboratories
measure the different
forms.

Unconjugated bilirubin
is metabolised in the
liver to produce
conjugated (“direct”)
bilirubin by uridine
diphosphate
glucuronosyltransferase.

The activity of this
enzyme only rises after
birth to reach adult like
values around the age
of three months.

Conjugation of bilirubin
increases its solubility
and facilitates its
secretion into bile.

Conjugated (“direct”)
bilirubin then passes
into the gut and is
largely excreted.

In the gastrointestinal
tract, bilirubin is modified
by digestive bacteria and
transformed into
urobilinogens . A large
portion remains in the
intestine and is
converted into stercobilin
(responsible for the
brown colour of faeces).
Some is reabsorbed into
the bloodstream and the
remainder is excreted in
the urine (urobilin is
responsible for the
yellow colour of urine).

Reticuloendothelial
system

Red blood cells

albumin

Haeme

Blood

“Indirect bilirubin”

“Direct bilirubin”

Liver

Intestine

Conjugated
bilirubin

Urobilinogens

Uridine
diphosphate
glucuronosyl-
transferase

Excreted in bile

Gut bacteria

Enterohepatic
circulation

Excreted in urine
(urobilin)

Excreted in faeces
(stercobilin)

Unconjugated
bilirubin-albumin
complex

​TH-BAS07EN/01/02/2024

Normal values:

Total bilirubin: 0-1.1 mg/dL

Vitamin A: 20-43 µg/dL

Vitamin E: 2.9 – 16.6 mg/L

Vitamin K1: 80-160 pg/mL

Normal values:

Serum calcium: 8.7 – 9.8 mg/dL

Serum phosphorous: 3.9 – 6.5 mg/dL

PTH: 15 – 65 pg/mL

Normal values:

Vitamin A: 30–120 μg/dL

Vitamin D: 20–100 ng/mL

Vitamin E: 5–20 μg/mL

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Enzymatic pathways of bile acid synthesis

classic pathway

adapted from Sundaram 20081 and Monte 20092

Cholesterol

Cholesterol 7α-hydroxylase
CYP7A1

3β-hydroxy-Δ5 -C27-steroid dehydrogenase
HSD3B7

Δ4-3-oxosteroid-5β-reductase
AKR1D1

Δ4-3-oxosteroid-5β-reductase
AKR1D1

3α-hydroxysteroid dehydrogenase
AKR1C4

Sterol 27-hydroxylase
CYP27A1

Bile acid CoA synthetase (BACS)
or very long chain acyl CoA
synthetase (VLCS)

Side-chain modification by
4 peroxisomal enzymes
(AMACR, BCOX, BDP, SCPx)

3α-hydroxysteroid dehydrogenase
AKR1C4

Sterol 27-hydroxylase
CYP27A1

Bile acid CoA synthetase (BACS)
or very long chain acyl CoA
synthetase (VLCS)

Side-chain modification by
4 peroxisomal enzymes
(AMACR, BCOX, BDP, SCPx)

Amino acid N-acyltransferase
(BAAT)

Amino acid N-acyltransferase
(BAAT)

7α-hydroxycholesterol

7α-hydroxy
4 cholesten-3-one

7α-12α-dihydroxy
-4 cholesten-3-one

7α-dihydroxy-5β-
cholestan-3-one

5β-cholestan-
3α,7α -diol

3α,7α-dihydroxy-5β-
cholestanoic acid (DHCA)

DHCA-CoA

Chenodeoxycholic
acid

Glyco or tauro-
chenodeoxycholic acid

Glyco or tauro-
cholic acid

Cholic acid

3α,7α,12α-trihydroxy-5β-
cholestanoic acid (THCA)

5β-cholestan-
3α,7α,12α-triol

7α-12α-dihydroxy-
5β-cholestan-3-one

THCA-CoA

Microsomes

Cytosol

Mitochondria

peroxisomes

hepatocyte

Endoplasmic
reticulum

Sterol 12α-hydroxylase
CYP8B1

AMARC: alpha methylacyl-CoA racemase

BCOX: Branched-chain acyl CoA oxydase

BDP: D-bifunctional protein hydratase 

SCPx: Sterol carrier protein

Alternative pathway

Cholesterol

Oxysterol 7α-hydroxylase
CYP7B1

3β-hydroxy-Δ5-C27-steroid dehydrogenase
HSD3B7

Side-chain modifications

Sterol 27-hydroxylase
CYP27A1

Amino acid N-acyltransferase
(BAAT)

3β-hydroxy-5-cholestanoic acid

3-oxo-7α-hydroxy-4-cholestanoic acid

3β,7α-dihydroxy-5-cholestanoic acid

Chenodeoxycholic acid

Glyco or tauro-
chenodeoxycholic acid

adapted from Sundaram 20081

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. Monte MJ, Marin JJG, Antelo A, Vazquez-Tato J. Bile acids: chemistry, physiology, and pathophysiology. World J Gastroenterol 2009;15:804-16

​TH-BAS10EN/01/02/2024

 

REMINDER ABOUT BILE ACIDS

The bile acid family is a group of acid steroids synthesised from cholesterol in the liver. Although their best-known role is to aid with the emulsion, digestion and absorption of fats and liposoluble vitamins, other important physiological roles have been identified.1

On secretion of bile acids into bile canaliculi, osmotic pressure is created that accounts for the bile-acid-dependent fraction of bile flow. Bile acids stimulate biliary lipid secretion and form mixed micelles with biliary phospholipids, allowing the solubilisation of cholesterol and other lipophilic compounds in the bile. The mixed micelles also emulsify dietary fats in the intestines, facilitating their absorption.1

Bile acid synthesis

The primary bile acids, cholic acid and chenodeoxycholic acid are synthesised from cholesterol by an enzymatic cascade involving nearly 20 enzymes and two complementary chemical pathways, the classic “neutral” pathway and the alternative “acidic” pathway.2,3 Although the neutral pathway is believed to be the major pathway for bile acid synthesis in adults, in the first months of life the acidic pathway is thought to be more important.2,5 In humans and under normal conditions, the acidic pathway contributes little (approximately 10%) to the restitution of daily loss of bile acid.1 It may become the major bile acid biosynthetic pathway in patients with liver diseases.1

The primary bile acids produced include cholic acid (CA), which accounts for approximately 70% of the circulating pool of bile acids, and chenodeoxycholic acid (CDCA), which accounts for approximately 30% of the pool.4

Enzymatic pathways of bile acid synthesis

classic pathway

adapted from Sundaram 20083 and Monte 20091

Cholesterol

Cholesterol 7α-hydroxylase
CYP7A1

3β-hydroxy-Δ5 -C27-steroid dehydrogenase
HSD3B7

Δ4-3-oxosteroid-5β-reductase
AKR1D1

Δ4-3-oxosteroid-5β-reductase
AKR1D1

3α-hydroxysteroid dehydrogenase
AKR1C4

Sterol 27-hydroxylase
CYP27A1

Bile acid CoA synthetase (BACS)
or very long chain acyl CoA
synthetase (VLCS)

Side-chain modification by
4 peroxisomal enzymes
(AMACR, BCOX, BDP, SCPx)

3α-hydroxysteroid dehydrogenase
AKR1C4

Sterol 27-hydroxylase
CYP27A1

Bile acid CoA synthetase (BACS)
or very long chain acyl CoA
synthetase (VLCS)

Side-chain modification by
4 peroxisomal enzymes
(AMACR, BCOX, BDP, SCPx)

Amino acid N-acyltransferase
(BAAT)

Amino acid N-acyltransferase
(BAAT)

7α-hydroxycholesterol

7α-hydroxy
4 cholesten-3-one

7α-12α-dihydroxy
-4 cholesten-3-one

7α-dihydroxy-5β-
cholestan-3-one

5β-cholestan-
3α,7α -diol

3α,7α-dihydroxy-5β-
cholestanoic acid (DHCA)

DHCA-CoA

Chenodeoxycholic
acid

Glyco or tauro-
chenodeoxycholic acid

Glyco or tauro-
cholic acid

Cholic acid

3α,7α,12α-trihydroxy-5β-
cholestanoic acid (THCA)

5β-cholestan-
3α,7α,12α-triol

7α-12α-dihydroxy-
5β-cholestan-3-one

THCA-CoA

Microsomes

Cytosol

Mitochondria

peroxisomes

hepatocyte

Endoplasmic
reticulum

Sterol 12α-hydroxylase
CYP8B1

AMACR: alpha methylacyl-CoA racemase

BCOX: Branched-chain acyl CoA oxydase

BDP: D-bifunctional protein hydratase 

SCPx: Sterol carrier protein

The classic pathway, also known as the “neutral” pathway because its intermediate metabolites are neutral sterols, is the main pathway for bile acid synthesis.1-3 It is present only in the liver and synthesises cholic acid and chenodeoxycholic acid.1 This pathway consists of a cascade of reactions catalysed by enzymes located in microsomes, the cytosol, mitochondria and peroxisomes.1 The final step in the synthesis of bile acid is the conjugation of cholic acid and chenodeoxycholic acid to taurine or glycine.3

Alternative pathway

Cholesterol

Oxysterol 7α-hydroxylase
CYP7B1

3β-hydroxy-Δ5-C27-steroid dehydrogenase
HSD3B7

Side-chain modifications

Sterol 27-hydroxylase
CYP27A1

Amino acid N-acyltransferase
(BAAT)

3β-hydroxy-5-cholestanoic acid

3-oxo-7α-hydroxy-4-cholestanoic acid

3β,7α-dihydroxy-5-cholestanoic acid

Chenodeoxycholic acid

Glyco or tauro-
chenodeoxycholic acid

adapted from Sundaram 20083  and Monte 20091

The alternative pathway involves C27-hydroxylation of cholesterol by sterol 27-hydroxylase as the initial step: side-chain oxidation of cholesterol precedes steroid ring modification.1,3 Thus, acidic intermediate metabolites are formed: this is why this pathway is also known as the “acidic” pathway.1 It primarily produces chenodeoxycholic acid.3

Regulation of bile acid synthesis

Bile acid synthesis is tightly regulated to ensure homeostatic levels of cholesterol are produced and to provide adequate emulsification in the intestine. An excess of bile acids has a negative feedback effect, repressing further synthesis; conversely, when bile acids levels are low, synthesis is increased.2,6

In the ‘neutral’ pathway, the rate-limiting step is the modification of the steroid nucleus, which takes place in hepatic microsomes and is catalysed by cholesterol 7α-hydroxylase (CYP7A1). The neutral pathway facilitates the transformation of cholesterol to cholic acid and chenodeoxycholic acid, which are further conjugated to glycine or taurine and used as substrates for the bile acid transport pump. The canalicular transport of bile acid is the rate-limiting step of bile secretion. Bile acids are recovered from the intestines by the apical sodium-dependent bile acid transporter and return to the liver via the portal blood. The gene encoding CYP7A1 is highly regulated by negative feedback involving farnesoid X receptor (FXR)-dependent induction of fibroblast growth factor 15/19 (FGF15/19) expression by bile acids in the enterocytes. FGF15/19 binds to the fibroblast growth factor receptor 4-β-klotho complex in hepatocytes, activating signalling pathways that transcriptionally repress CYP7A1 expression.2

Enterohepatic circulation of bile acids

Bile acids are mostly restricted to enterohepatic circulation, circulating between the liver, the biliary tree, the intestine, and the portal blood which returns them to the liver. Almost all (95%) the bile acids are recovered from the intestine, mostly in the ileum.1 The liver converts around 500 mg of cholesterol into bile acids per day. This accounts for 90% of the cholesterol that is actively metabolized by the body. The remaining 10% of cholesterol that is synthesised is biosynthesised from steroid hormones.6

Newly synthesised bile acids are secreted into the bile where they are transported to the lumen of the small intestine, where they act as lipid emulsifiers, solubilising nutrients. These nutrients are incorporated into lipoproteins, and are delivered via the portal vein to the liver and metabolised. About 95% of the bile acids are recycled and secreted back into the bile. The remaining 5% are excreted into the faeces.6-7

Enterohepatic circulation of bile acids

adapted from van Mil 20057

ENTEROHEPATIC CYCLE

  • Fichier 101 Approximately 500 mg of cholesterol is converted into bile acids each day in the adult human liver. Newly synthesized bile acids are stored in the gallbladder.
  • Fichier 102 Upon digestion of a meal, bile salts are delivered to the lumen of the small intestine where they act as emulsifiers of dietary lipids, cholesterol, and fat-soluble vitamins.
  • Fichier 104 Bile salts are converted by intestinal bacteria into secondary bile acids.
  • Fichier 105 Bile salts are transported from the intestine to the liver via the portal circulation, and subsequently resecreted into bile. Approximately 95% of bile salts are recovered in the gut during each cycle of this enterohepatic circulation.
  • Fichier 103 5% of bile acids pool that are lost via the faeces are replaced by de novo synthesis in the liver.

1. Monte MJ, Marin JJG, Antelo A, Vazquez-Tato J. Bile acids: chemistry, physiology, and pathophysiology. World J Gastroenterol 2009;15:804-16.

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. 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.

4. Ashby K, Navarro Almario EE, Tong W, Borlak J, Mehta R, Chen M. Review article: therapeutic bile acids and the risks for hepatotoxicity. Aliment Pharmacol Ther 2018;47:1623-38.

5. Clayton PT. Disorders of bile acid synthesis. J Inherit Metab Dis 2011;34:593-604.

6. Russell DW. The enzymes, regulation, and genetics of bile acid synthesis. Annu Rev Biochem 2003;72:137-74.

7. van Mil SW, Houwen RH, Klomp LW. Genetics of familial intrahepatic cholestasis syndromes. J Med Genet 2005;42:449-63.

​TH-BAS10EN/01/02/2024

Normal values:

Vitamin A: 1,09-3,07 μmol/L

Vitamin E: 25-42 μmol/L

AST: <39 U/L

ALT: <34 U/L

GGT: <38 U/L

Total bilirubin: <17 μmol/L

Conjugated bilirubin level: <5 μmol/L

Normal values:

AST: < 45 mU/mL

International normalized ratio: < 1.2

Prothrombin ratio: 70-120 %

Factor VII: 70-120 %

Factor X: 70-120 %

Vitamin E: 300-1200 μg/dL

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Causes of jaundice in newborn or infant5

Jaundice of the newborns or infants

Unconjugated hyperbilirubinaemia

Mechanical haemolysis

Other causes of haemolysis

Intramedullary haemolysis

Infection-related haemolysis

Immune haemolysis

Constitutional haemolysis

Haemolysis

Default in the conjugation of
indirect bilirubin (UGT1A gene)

Rare genetic deficiency of canalicular
or sinusoidal specific transporter of
conjugated bilirubin

Moderate or severe hereditary
deficiency of enzyme activity

Enzyme immaturity or
enzymatic inhibition

Hepatocellular insufficiency

Cholestasis (decreased bile flow)

Other (hypothyroidism, trisomy 21)

Conjugated hyperbilirubinaemia

​TH-BAS07EN/01/02/2024

Bilirubin metabolism5-7

Important things to check: the degree and duration of stool discolouration. The colour of the stool should ideally be recorded after elimination of any component likely to change the colour and with the help of a colour chart:2, 14

This chart is used with the kind permission of the AMFE, Association Maladies Foie Enfants, a French association dedicated to liver diseases in children.3

You can also refer to the stool chart provided by the Children’s Liver Disease Foundation (CLDF), a UK charity committed to fighting all childhood liver diseases :

CLDF-Yellow-Alert-Stool-Chart

Persistently pale coloured stools may indicated liver disease.14  Complete and prolonged discolouration of stools for 7 days is suggestive of biliary atresia until proven otherwise. However, the sign is not specific to biliary atresia and can also occur, among others, in conditions such as cystic fibrosis, Alagille syndrome, alpha-1 antitrypsin deficiency and neonatal sclerosing cholangitis.2

​TH-BAS08EN/01/02/2024

What causes (rare) cholestasis
in paediatric patients

?

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Content reviewed by experts in paediatric gastroenterology and hepatology.

This website was created by Theravia. Theravia is a leading international pharmaceutical laboratory specializing in rare or neglected diseases. Formed through the merger of Addmedica and CTRS, we are dedicated to address the unmet medical needs of patients with these challenging conditions

03/2024

What causes (rare) cholestasis
in paediatric patients ?

Menu

To access the platform and the
diagnostic algorithms,
please confirm:

YES, I'm a healthcare professional

If you are not a healthcare professional, please do not access the website as the content is not suitable.
We invite you to continue your research through another website

This website was created by Theravia. Theravia is a leading international pharmaceutical laboratory specializing in rare or neglected diseases. Formed through the merger of Addmedica and CTRS, we are dedicated to address the unmet medical needs of patients with these challenging conditions

Created by

Content reviewed by experts in paediatric gastroenterology and hepatology.

03/2024