Journal of Gastroenterology and Hepatology (2005) 20, 807–817 DOI: 10.1111/j.1400-1746.2005.03743.x
Blackwell Science, LtdOxford, UKJGHJournal of Gastroenterology and Hepatology0815-93192004 Blackwell Publishing Asia Pty Ltd206807817Review Article Progressive familial intrahepatic cholestasisMJ Harris et al.
Correspondence: Dr Irwin M Arias, National Institute of Health and National Institute of Child Health and Human
Development, Cell Biology and Metabolism Branch, Bethesda, MD 20892, USA. Email: firstname.lastname@example.org
Accepted for publication 27 May 2004.
Progressive familial intrahepatic cholestasis: Genetic disorders of
MATTHEW J HARRIS,* DAVID G LE COUTEUR* AND IRWIN M ARIAS†
*ANZAC Research Institute, University of Sydney and Center for Education and Research on Aging, Concord
Repatriation General Hospital, Sydney, NSW , Australia and †National Institute of Health and National Institute
of Child Health and Human Development, Cell Biology and Metabolism Branch, Bethesda, MD, USA
liver. Benign recurrent intrahepatic cholestasis is predominantly an adult form with similar clinical symp-
toms that spontaneously resolve. These genetic disorders have significantly helped to unravel the basic
mechanisms of the canalicular bile transport processes. Progressive familial intrahepatic cholestasis type
1 involves a gene also linked to benign recurrent intrahepatic cholestasis. The gene codes for an ami-
nophospholipid translocase protein that maintains the integrity of the membrane. How a mutation in this
protein causes cholestasis is unknown but is thought to involve the enterohepatic recirculation of bile
acids. Progressive familial intrahepatic cholestasis types 2 and 3 involve the canalicular bile salt export
pump and a phospholipid translocase, respectively, both of which are fundamental to bile secretion. This
review covers the clinical manifestations, genetics, treatment and mechanism of each disease.
© 2005 Blackwell Publishing Asia Pty Ltd
Progressive familial intrahepatic cholestasis types 1, 2 and 3 are childhood diseases of the
Key words: ABC transporters, biliary secretion, hereditary cholestasis, intrahepatic, PFIC.
The discovery of genes involved in hereditary intrahe-
patic cholestasis has advanced the understanding of
molecular mechanisms of bile secretion. Mutations in
three canalicular membrane proteins have been identi-
fied that result in cholestasis and progress to chronic
liver disease. These three diseases are progressive famil-
ial intrahepatic cholestasis (PFIC) types 1, 2 and 3 and
are caused by mutations in the genes coding for the
familial intrahepatic cholestasis 1 protein (FIC1), the
bile salt export pump (BSEP) and the phospholipid
translocase (MDR3), respectively. This review covers
the clinical manifestations, genetics, treatment and
mechanism of each disease.
BILE ACID TRANSPORT AND
Cholestasis is a liver disease caused by impaired bile
secretion, associated with and often secondary to the
intracellular accumulation of bile acids in the hepato-
cyte. Bile acids are natural detergents that are
secreted from the liver to facilitate emulsification and
absorption of fats in the intestine. Ninety percentof
bile acids are taken up from the intestine into the por-
tal blood stream where they are recycled by the liver
in a process called ‘enterohepatic re-circulation’. In
the liver, the BSEP is an adenosine triphosphate
(ATP)-dependent transporter localized in the canalic-
ular membrane that mediates bile acid transport into
the bile ducts. The detergent effects of bile acids in
the bile ducts are abrogated by the formation of
mixed micelles with phospholipid. These phospholip-
ids are translocated into bile by the canalicular phos-
pholipid translocase, MDR3. Hereditary and acquired
forms of cholestasis ultimately involved impairment of
BSEP or MDR3 transport activity. A third gene,
FIC1, also has a function in biliary transport, because
cholestasis develops when this gene is mutated
(PFIC1). The precise mechanism for PFIC1 disease
remains elusive, although recent advances have
unravelled the role of FIC1 in maintaining bile salt
MJ Harris et al.
Named after the Amish descendents of Jacob Byler,
PFIC1 was known as ‘Byler’s disease’ or, for those non-
Byler descendents, referred to as ‘Byler’s syndrome’.
Clayton et al. originally reported the disease,1,2 with
other early reports describing the same or similar
In the past decades, patients presenting with neonatal
intrahepatic cholestasis were diagnosed with general
‘PFIC’ disease. Delineation between PFIC1, 2 and 3
was not possible until recent years, when the genetics of
the disease identified a number of putative genes. One
subset of patients, those with a high serum g-glutamyl-
transferase (g-GT) was determined genetically to be
PFIC3 patients. The remaining patients (PFIC1 and
PFIC2) still cannot be distinguished clinically without
genetic testing (Table 2).
Progressive familial intrahepatic cholestasis type 1
patients are most commonly newborns, with symptoms
of jaundice, pruritis, diarrhea and a failure to thrive in
the first several months. The disease is chronic and pro-
gressive, leading to cirrhosis and liver failure usually
within the first decade of life. The family history is often
negative but there are occasional reports of cholestatic
symptoms in parents. As the disease progresses, patients
develop hepatomegaly, malabsorption and splenome-
galy. Pancreatitis has also been reported. Hearing loss
has been reported.7 Biochemical tests of serum reveal
elevated 5¢-nucleotidase (5¢-NT), aspartate aminotrans-
ferase (AST), alkaline phosphatase (ALP), bile salts and
cholesterol. Progressive familial intrahepatic cholestasis
type 1 patients have low g-glutamyltransferase (g-GT).
Fat-soluble vitamin deficiencies (vitamin D, E, A and
K) are also common. Sweat chloride and sodium levels
can also be elevated.8–10 Not all patients have each
symptom and there is a broad variability in the time
course, recurrence and severity of symptoms. Progres-
sive familial intrahepatic cholestasis type 1 disease has
been described as having a spectrum of symptoms
because of this diversity of clinical features,11 and many
PFIC1 symptoms are also present in PFIC2 patients.
Morphologically, PFIC1 presents as canalicular
cholestasis with biliary plugs, lobular disarray, fibrosis
and cirrhosis as the disease progresses.12,13 Initially, his-
tology can be normal with a progression to signs of
cholestatic toxicity. Bile from PFIC1 patients has been
observed as being coarse and granular,13 and is com-
monly referred to as ‘Byler bile’.
Progressive familial intrahepatic cholestasis type 1 is an
autosomal recessive liver disease (Table 1). The first
genetic study linked the disease to region 18q21–q2214
and was further investigated until a specific gene was
determined.15,16 This gene was named according to the
disease, the familial intrahepatic cholestasis type 1 gene
(FIC1), but it has an official designation as ATP8B1. A
number of separate mutations were reported but the
Molecular mechanism of hereditary intrahepatic cholestasis
Bile acid secretion
PFIC, progressive familial intrahepatic cholestasis; BRIC, benign recurrent intrahepatic cholestasis.
†One BRIC patient was reported with mutations in ABCB1154 while other BRIC patients are not linked to the ATP8B1 loci.51,53
Clinical manifestations of PFIC1, 2, 3 and BRIC
DiseaseAge of onset CholestasisProgression to cirrhosis Serum g-GT levels
1 month-20 years
PFIC, progressive familial intrahepatic cholestasis; BRIC, benign recurrent intrahepatic cholestasis; g-GT, g-glutamyltrans-
Progressive familial intrahepatic cholestasis
mutations are found individually in patients. Patients
with a specific mutation (D554N) in FIC1 were
described with Greenland familial cholestasis.16 This
form of cholestasis fits within the spectrum of symptoms
for PFIC1 disease. Mutations in the FIC1 gene have also
been found in patients with benign recurrent intrahe-
patic cholestasis (BRIC). The FIC1 gene codes for a type
IV P-type ATPase. The type IV P-type ATPases function
as aminophospholipid flippases.17–23 How dysfunction of
this protein leads to cholestasis is unknown but is dis-
cussed in the section ‘Mechanism of disease’.
Liver transplant is the most effective form of treatment
for PFIC1 patients with progressive disease or estab-
lished cirrhosis, usually within the first decade.24,25 Bil-
iary diversion also exists as an effective treatment for
some PFIC1 patients, usually those without cirrhosis at
the time of surgery.26,27 Pharmacological treatment has
included supplements of fat-soluble vitamins, ursode-
oxycholic acid (UDCA) to promote bile flow,28
rifampin, phenobarbital and cholestyramine, which
reduces bile salt concentrations in serum and eases pru-
ritus. Extrahepatic symptoms do not resolve after liver
transplant (for example, diarrhea and short stature) and
liver steatosis develops in subsequent years.29 Ileal
bypass has also been investigated in a limited number of
patients but has not ensured good long-term results.26
Mechanism of disease
FIC1 is a member of the P-type ATPase family, which
includes well-studied proteins such as the calcium
pump and the sodium/potassium ATPase. FIC1
belongs to the type IV P-type ATPase subfamily, which
function as aminophospholipid translocases.17–23 This
function is unlike the typical P-type ATPases, which
pump metals or ions, rather, the function is a ‘flipping’
of specific phospholipids (phosphatidylserine and phos-
phatidylethanolamine) from the outer leaflet of the
membrane bilayer to the inner leaflet. This function is
found in most cellular membranes.
The site at which PFIC1 disease is caused was ini-
tially believed to be at the bile canaliculus due to the
basic observation that secretion of bile acids is very low
in the presence of high serum bile acids without hepa-
tocyte disruption (indicated by normal g-GT levels).
Theoretically, disruption of lipid asymmetry in the
canalicular membrane may decrease the function of res-
ident proteins, including the BSEP, resulting in intrac-
ellular accumulation of bile acid leading to cholestasis.
FIC1 was detected in the bile canalicular membrane
but was detected in greater abundance in the intestine18
and cholangiocytes.30 FIC1 and other homologs have
been detected by northern analysis in tissues through-
out the body.31 Due to the high expression levels of
FIC1 in the intestine, and the presence of diarrhea in
PFIC1 patients, the intestine was also implicated in the
etiology of the disease (Fig. 1). We have shown, using a
cell line-based study, that over-expression of FIC1 did
not effect the activity of the bile salt transporters, BSEP
or the intestinal apical sodium-dependent bile salt
transporter (ASBT).32 Therefore, systems to investigate
the loss of FIC1 function were developed.
A FIC1 (ATP8B1) mutant mouse has been created to
investigate PFIC1 disease.33 The ‘knock-in’ mouse
expresses a mutant FIC1 gene (ATP8B1G308V/G308V),
which has a mutation orthologous to that present in an
Amish group of PFIC1 patients. The mutation creates
an effective ‘knock-out’ mouse because FIC1 is unde-
tectable. The key observation in the mutant mice is
increased serum bile salts, particularly high after being
fed a bile salt-supplemented diet. Hepatic bile salt
secretion in the mutant mice is normal even after intra-
venous injection of hydrophilic bile salts or feeding of a
bile salt-supplemented diet. The authors detected an
increase in the bile salt pool in the mutant mice and
hepatic injury but no signs of cholestasis. The authors
also investigated the hepatic expression levels of genes
involved in bile salt homeostasis in the mutant mice. Of
note, the farnesoid X receptor (Fxr) was downregulated
twofold, the pregnane X receptor (Pxr) was upregulated
twofold but the expression of Bsep was not altered, con-
sistent with the phenotype of normal hepatic secretion.
In the ileum, the key genes involved in bile salt homeo-
stasis were unchanged in the mutant mouse, including
Fxr and Asbt levels. The mutant mouse clearly indicates
that loss of FIC1 disrupts bile salt homeostasis and
implicates the intestine, playing a clear role in this dis-
ruption. The differences between the FIC1 mutant mice
and human PFIC1 patients could be due to the differ-
ences in bile salt metabolism between the species.
Supporting a role for the intestine in the disease is the
observation that biliary diversion is a successful treat-
ment of PFIC1 patients who present for surgery prior to
established cirrhosis.26,27 Biliary diversion prevents
intestinal resorption of bile acids, reduces the intrahe-
patic bile acid pool and may prevent bile acid-induced
cholestasis. The clearance of bile at the jejunum leads to
the loss of cholestasis and the coarse granular bile
returns to the normal amorphous state. This indicates
that the canalicular membrane transporters can func-
tion normally, even with a mutation in FIC1.
Interestingly, patients who have had full liver trans-
plants do not re-develop cholestasis. If the defect in
humans was intestinal hyper-absorption of bile acid,
these patients should re-develop cholestasis. Therefore,
with this observation, the intestine is not the sole factor
in the etiology of the disease because the liver in PFIC1
patients also has some influence.
A study by Chen et al. assessed the loss of FIC1
expression in the intestine of PFIC1 patients.34 The
study demonstrated that FIC1 mRNA was absent in the
ileum of PFIC1 patients, and ASBT levels in these
patients were fourfold higher. Among other genes
assessed, the study showed that the farnesoid X recep-
tor (FXR) was reduced by 80%. These changes were
confirmed by antisense mediated knockdown of FIC1 in
a colon cancer cell line (Caco-2). The significance of
that study is that FIC1 (somehow) regulates FXR. With
FIC1 present, FXR expression is normal and regulates
the homoeostasis of bile acid uptake by downregulating
ASBT. Without FIC1, FXR expression is low, allowing
MJ Harris et al.
ASBT expression to increase and uptake of bile acid
from the gut to be enhanced. Furthermore, that study
investigated the relationship of FIC1, FXR and BSEP
by assessing the BSEP promoter activity in Caco-2 cells.
In FIC1 antisense-treated Caco-2 cells, the BSEP pro-
moter activity was diminished, whereas the ASBT pro-
moter was greatly enhanced, presumably via the loss of
FXR. This result can be superimposed to the situation
in the liver where the loss of FIC1 in PFIC1 patients
would result in diminished BSEP expression and thus
reduced bile salt secretion. Therefore, in PFIC1
patients, bile salt uptake from the ileum is enhanced
and bile salt secretion from the liver is diminished, a sit-
uation that explains the manifestation of cholestasis.
Other proteins that are relevant to bile salt metabolism
that are regulated by FXR and are implicated in the eti-
ology of PFIC1 disease include the hepatic basolateral
uptake transporter (sodium taurocholate cotransport-
ing polypeptide, NTCP) and cholesterol 7-a hydroxy-
lase (C7AH). Sodium taurocholate cotransporting
polypeptide would be downregulated in a cholestatic
liver (decreasing hepatic uptake of bile salt) but remains
normal or upregulated if FXR expression is reduced
through loss of FIC1. The bile salt pool increases
because FXR expression normally regulates C7AH. If
C7AH expression is not regulated, bile salt production
will continue in PFIC1 patients, thus raising the bile
salt pool. In patients who receive full liver transplant,
the increase in intestinal uptake presumably still
remains but the normal secretion from the newly trans-
planted liver prevents the development of cholestasis.
Therefore it is the combined intestinal and hepatic dys-
function via FXR alterations that lead to cholestasis.
In summary, the intestinal upregulation of ASBT and
the possible hepatic downregulation of BSEP, along
with an increase in the bile salt pool, would result in
cholestasis and is the proposed etiology of PFIC1 dis-
ease (Fig. 1). These effects are mediated by changes in
nisms leading to progressive
familial intrahepatic cholesta-
sis type 1 (PFIC1). Normal
FIC1 protein function involves
‘flipping’ of aminophospholip-
ids such as phosphatidylserine
(PS) from the outer mem-
brane leaflet to the cytoplas-
normal asymmetry of phos-
pholipids and normal bile
secretion via the bile salt
export pump (BSEP). When
FIC1 function is lost, as is the
case in PFIC1 patients, the
membrane would lose asym-
metry (yet to be shown exper-
imentally). In this situation,
because bile salt secretion is
develops. Concomitant with
the loss of canalicular bile
secretion is the increase in
cholestatic bile salt uptake and
an increase in the bile salt pool
across the intestinal wall. The
exact role that FIC1 plays in
this scenario is unknown,
although it is linked to a reduc-
tion in farnesoid X receptor
Progressive familial intrahepatic cholestasis
FXR expression due to the loss of FIC1. How FIC1
regulates FXR expression is yet to be determined.
Summerskill and Walshe, and Tygstrup first reported
BRIC, also known as recurrent familial intrahepatic
cholestasis (RFIC).35,36 The disease is rare and the num-
ber of cases reported worldwide is only in the hundreds.
Benign recurrent intrahepatic cholestasis patients
present with recurrent spontaneous bouts of pruritus
and jaundice (Table 2).35–41 Other symptoms can
include fatigue, loss of appetite, anorexia, peculiar
smell, dark urine, light stools and steatorrhea. These
bouts of sickness can last for weeks to months with
seemingly spontaneous recovery to normal. Serum
analysis reveals elevated bile acids (primary and second-
ary), elevated bilirubin and low g-GT levels. Bijleveld
et al. reported increased 3aOH-bile acids in urine,
which increase prior to presentation of itching or jaun-
dice and suggested that this is a predictive marker.38
Episodes of cholestasis are not age-related, because age
of onset is also variable with reported cases between the
ages of 1 year and 50 years. Tygstrup et al. reported a
number of patients with the same mutation but a broad
range of age of onset, severity and number of recur-
rences.39 This indicates a more complex system than
simple genetic/protein differences and may involve envi-
ronmental factors and possibly other genetic loci. Sup-
porting environmental triggers for the disease is the
study of two brothers who both had an attack of
cholestasis after gastroenteritis.38 One of these patients
also had upper respiratory tract infection and other
studies report influenza, otitis media, upper abdominal
pains, and skin eruptions in association with the bouts
of cholestasis.35,37,40,42–49 Brenard et al. reported cases of
BRIC with an emphasis on uncommon phenotypes
such as cases of BRIC without pruritus, cases with high
serum g-GT, a broad variation of increases in transam-
inases and alkaline phosphatase.41 Brenard et al. also
reported a normal frequency of gallstones compared to
controls but with earlier age of onset in BRIC patients.41
Van Ooteghem et al. reported four cases in which
BRIC was initially diagnosed, yet which later developed
into a syndrome more typical of PFIC1.50 The first
attack of cholestasis in these patients was between 6 and
15 months with progression to permanent cholestasis in
the second to fourth decade of life. Liver biopsies at a
late stage were characteristic of PFIC1 disease with
fibrosis. Mutations in ATP8B1 were found in two of
Liver biopsy is normal until a bout of illness, at which
point canalicular cholestasis is seen without fibrosis, cir-
rhosis and no extrahepatic bile duct obstruction. In a
follow-up study after 30 years, no signs of chronic liver
disease were observed.39 However, as mentioned above,
some BRIC patients may progress to chronic liver dis-
ease with fibrosis and porto-portal septa formation.50
Original chromosomal mapping for BRIC identified
chromosome 18q21,51,52 and the FIC1 gene (responsi-
ble for PFIC1) was identified as the gene for BRIC
(Table 1).15 The mutations include a point mutation
(I661T) and a three-amino-acid deletion 795–
7GNRdel. Another mutation resulting in skipping of
exon 4 has also been reported.50 Some BRIC patients
do not have linkage to 18q21, indicating genetic heter-
ogeneity for BRIC.51,53 One BRIC patient was reported
with two point mutations in ABCB11, the gene for the
BSEP,54 but it was not reported whether the 18q21
locus (FIC1) also had a mutation.
Treatment for BRIC has included corticosteroids, phe-
nobarbitol, cholestyramine, decreased fat diet,38
plasmapheresis41 and rifampin.55 Bijheleveld et al. pro-
posed that the increase in lithocholates in the serum
contributes to cholestasis (being cholestatic itself).38
Therefore treatment with cholestyramine and reduction
of intestinal bacteria may reduce these secondary bile
acids in serum. Brenard et al. describe a number of
treatments used in their patient cohort with varied suc-
cess.41 The treatments without success were phenobar-
bitol, UDCA and cholestyramine. Plasmapheresis was
also performed,41,56 with some improvement in pruritus
and biochemical results. These studies highlight the
ineffectiveness of current treatments and no treatment
has yet been reported for the management of cholestatic
episodes or prevention of recurrences.
Mechanism of disease
The mechanism for BRIC is as yet unknown. No studies
have shown functional reconstitution of FIC1 with
BRIC mutations, although the protein with a BRIC
mutation has been expressed and detected by western
blot analysis in a cell line.32 Bijleveld et al. showed that
during a bout of cholestasis, the increase in bile acids pre-
cedes the increase in bilirubin levels by approximately
2 weeks in this case, and bilirubin decreases after bile
acids.38 This indicates that bile acid-induced cholestasis
blocks canalicular function rather than a generic mal-
function of transporters at the canaliculus, which, if
genetic malfunction were the case, a concomitant
decrease would result in both bile acids and bilirubin.
The BRIC patients from the Faeroe Islands each had
the same mutation (I661T) but a broad range of age of
onset, severity of bout, and number of occurrences.39
This supports the idea that an environmental stimulus
MJ Harris et al.
and/or other genetic heterogeneity exists to trigger the
Based on the mechanism of PFIC1 disease as
described here, the BRIC mutations in the FIC1 gene
would cause aberrations in FXR expression and/or
function, leading to changes in bile salt homeostasis.
What is not explained by such a theory for BRIC is the
recurrent nature of the disease.
The advent of PFIC2 followed the delineation of clini-
cal, genetic and morphologic differences between
patients with familial intrahepatic cholestasis. Genetic
analysis was used to determine that locus heterogeneity
exists between PFIC patients with low g-GT. The gene
mutated in PFIC2 patients is ABCB11 coding for the
BSEP, an ATP binding cassette (ABC) transporter
found solely in the canalicular membrane of the liver.
The clinical symptoms of PFIC2 overlap with PFIC1
but with fewer extrahepatic abnormalities and fewer
recurrences, but generally more severe symptoms
(Table 2). Symptoms include pruritus, jaundice, and
failure to thrive. Biochemical tests show elevated 5¢-NT,
alanine aminotransferase (ALT), AST and serum bile
acid. The g-GT levels remain low.57 Hepatomegaly and
splenomegaly are common.
Bull et al. showed that there were morphological differ-
ences in livers between the traditional Byler kindred and
PFIC2 patients.13 The PFIC1 patients have the coarse
granular ‘Byler bile’ whereas PFIC2 patients have
amorphous bile with filamentous structures in the
ductules. The PFIC2 patients also have more hepato-
cellular disarray, neonatal (giant cell) hepatitis, chronic
inflammation, cirrhosis and inflammation and usually
present at an earlier age than PFIC1 patients.13,58 True
ductular proliferation is absent.
Molecular genetic techniques determined that non-
Byler families did not have any genetic linkage with chro-
mosome 18q21-q22.13,59,60 Homozygosity mapping and
a genome scan identified chromosome 2q24 as the
PFIC2 locus,61 with subsequent analysis identifying the
putative gene ABCB11, coding for the BSEP (Table 1).62
Ten mutations scattered throughout the coding region of
the gene have been reported so far in different patients.
The mutations are found individually in patients.
The treatment for PFIC2 is difficult to assess because of
the failure to differentiate PFIC1 and PFIC2 patients in
earlier studies. The most effective treatment is liver
transplant or biliary diversion.25,63 Ursodeoxycholic acid
has been used and should be considered initially for
symptomatic treatment but is effective only in a small
proportion of patients (approx. 10%).28,63
Mechanism of disease
Like most ABC transporters, BSEP is an ATP-depen-
dent export pump. The BSEP was shown to transport a
range of bile salts using expression of recombinant
mouse, rat or human protein.64–67 A BSEP knock-out
mouse was also created that had a clear decrease in bile
salt secretion with cholate secretion decreased to 6%
compared to wild-type mice.68 These experimental data
suggest that BSEP is the major bile salt carrier in the
canalicular membrane (Fig. 2). The etiology of PFIC2
disease was initially analyzed by investigating expression
of BSEP in liver samples and correlating this with the
mutations in ABCB11.58 That study demonstrated that
in most cases where BSEP protein was undetectable in
liver sections, mutations in ABCB11 were detected.
Mutations in recombinant BSEP and subsequent
expression in either insect cells69 or in a cell line70 dem-
onstrated reduction or abolition of bile salt transport by
BSEP with PFIC2 mutations. Studies of membrane
localization show that trafficking of BSEP is also altered
with some PFIC2 mutations.69–71 Further delineation of
the different mutations and correlation with BSEP
expression in liver sections may lead to different treat-
ment strategies for PFIC2 patients.
Progressive familial intrahepatic cholestasis type 3 is
clinically similar to PFIC1 and 2, with onset of chole-
static liver disease early in life. The characteristic differ-
ence between PFIC1/2 patients and PFIC3 patients is
an elevated g-GT in serum of PFIC3 patients. Jac-
quemin et al. studied 31 PFIC3 patients and reported
an extensive review of the clinical, morphological, and
genetic variation of the disease.72
Features include jaundice, pruritus, and discolored
stools. Gastrointestinal bleeding has been seen in later
onset (young adults) patients secondary to portal hyper-
tension and cirrhosis.72 Age of onset can be broad, from
1 month to 20.5 years, but rarely neonatal (Table 2).
Hepatomegaly and splenomegaly are common. Other
markers consistent with cholestasis in PFIC3 patients
are increased serum g-GT, ALT, ALP, conjugated
Progressive familial intrahepatic cholestasis
bilirubin and bile acids. Cholesterol levels are normal.
Biliary bile acid levels remain normal in the early stages
whereas biliary phospholipids are substantially reduced
(1–10%).72 Family history may reveal a similar disease
in siblings and also intrahepatic cholestasis of preg-
nancy (ICP) in some mothers of PFIC3 patients72 (see
the following section ‘Genetics’).
The liver histology shows bile ductular proliferation and
inflammatory infiltrate in the early stages of the disease.
Portal and peri-portal fibrosis, cirrhosis and cholestasis
are also seen especially in the later stages.73
PFIC3 is an autosomal recessive disorder. The gene
causing PFIC3 is ABCB4 on chromosome 7q21
(Table 1).73,74 ABCB4 codes for MDR3, which is an
ABC transporter protein. Patients have been found with
point mutations, premature stop codons and/or mRNA
instability. Immunohistochemistry demonstrated a loss
of MDR3 protein at the canalicular membrane in most
cases where mutations causing truncations occur in the
gene, and the presence of protein (normal or weak
staining) when a missense mutation occurs in the
gene.72 These observations are important for treatment.
Patients with missense mutations are also likely to have
onset of the disease later and a slower progresion com-
parative to patients with mutations causing truncations.
A link between PFIC3 and ICP has been established
through mutations in MDR3.75,76 Women, heterozygous
for a mutation in MDR3, have a predisposition to ICP,
with non-genetic factors also contributing to presenta-
tion of cholestasis.
Ursodeoxycholic acid is used with some success (in
approx. 30% of cases) as an initial therapy.28 Ursode-
oxycholic acid is a less toxic, more hydrophilic bile acid
and is therefore less damaging to biliary epithelia and
cholangiocytes. A mouse model of the human PFIC3
disease (mdr2 knock-out mice, see the following section
‘Mechanism of disease’) was created and feeding
UDCA to mdr2 knock-out mice replaced the endoge-
nous bile salt pool to UDCA.77 Such a shift in biliary
bile salt composition to the more hydrophilic bile acid
could also occur in PFIC3 patients treated with UDCA.
However, the use of UDCA is likely to work only in
patients with a MDR3 missense mutation (i.e. residual
protein/activity may be present) whereas patients who
do not respond are likely to have no MDR3 expres-
sion.72 Patients who do not respond to UDCA treat-
ment should be considered for liver transplantation.
Liver transplantation is the primary treatment.
Exciting research by deVree et al., using transplanta-
tion of normal or transgenic hepatocytes into the liver of
mdr2 knock-out mice, resulted in correction of the liver
disease.78 Further advancement of such technology
could see a similar technique used in PFIC3 patients in
Mechanism of disease
The function of MDR3 was determined by a knock-out
mouse model in which the mouse homolog of the
mediates adenosine triphosphate (ATP)-dependent bile salt secretion in the normal state. Once secreted across the canalicular
membrane of the hepatocyte, bile salts form mixed micelles with phosphatidylcholine, a phospholipid secreted by the multidrug
resistance protein 3 (MDR3) transporter. Micelles abrogate the detergent effects of bile salts. In PFIC2 patients, BSEP does not
function, either secondary to the absence of BSEP protein or expression of a dysfunctional transporter. The consequence is the
build up of bile salts within the hepatocyte, which manifests as clinical cholestasis and leads to liver failure.
Mechanism of progressive familial intrahepatic cholestasis type 2 (PFIC2) disease. The bile salt export pump (BSEP)
MJ Harris et al.
human MDR3 gene (mdr2) was disrupted.79 The knock-
out mice had low biliary phospholipids, normal bile
acid secretion, progressive liver disease, and histology
consistent with PFIC3 patients. The main difference in
cellular physiology between normal mice and the mdr2
knock-out mice is the lack of phospholipid translocation
into bile. Therefore, it can be concluded that the func-
tion of MDR2 is a phosphatidylcholine translocase. The
purpose of phospholipids in bile is to form micelles with
bile acid and to prevent crystallization of cholesterol.
Without the formation of micelles with bile acids, the
deleterious detergent effect of bile acids on the biliary
epithelium and cholangiocytes is not prevented.
Because bile acid secretion is maintained in PFIC3
patients, the condition is not true ‘cholestasis’ (Fig. 3).
It is the secondary effect of biliary secretion of bile acids
without phospholipids that leads to the presentation of
cholestatic markers in serum, particularly g-GT, an
increase in which is characteristic of hepatocellular dis-
‘Take home’ messages
(1) PFIC1, 2 and 3 are three diseases that share clinical
(2) There is no definitive clinical differentiation
between PFIC1 and PFIC2.
(3) BRIC presents with similar symptoms but is dis-
tinct due to its relapsing nature.
(4) Clinical differentiation for PFIC3 is limited to
(5) Treatment for PFIC1, 2 and 3 is limited to sur-
gery and liver transplantation.
(6) Treatment for BRIC is limited to reduction of
unrelenting pruritus during cholestasis.
(7) The mechanisms of disease for PFIC2 and PFIC3
are relatively well understood.
(8) The mechanisms of disease for PFIC1 are starting
to be unravelled but the mechanism for the recurrent
nature of BRIC remains elusive.
(9) How different mutations in the same gene lead to
either PFIC1 or BRIC is unknown.
(10) Some PFIC patients have no linkage to the three
known genetic loci, suggesting that other genes are
implicated in these diseases.
(11) With the recent advances in understanding of the
mechanism of PFIC diseases, it may be possible to tai-
lor new treatment regimens.
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