5 Arteriohepatic dysplasia (Alagille syndrome; Watson-Alagille syndrome)

5

Arteriohepatic dysplasia (Alagille syndrome; Watson-Alagille syndrome)

JOHN C. MACMILLAN MD, fwzp(Edin), FRACP Associate Professor, Department of Medicine, University of Queensland and Director, Queensland Clinical Genetics Service Royal Children k Hospital & District Health Services, Herston, Brisbane 4029, Australia

ROSS SHEPHERD MD, FRCP, FRACP Professor of Paediatrics & Child Health, University of Queensland and Director of Gastroenterology and Hepatology Royal Children S Hospital, Herston, Brisbane 4029, Australia

MANDY HERITAGE BSc Research Officer Queensland Institute qf Medical Research. Herston, Brisbane 4029, Australia

Alagille syndrome (AS) (arteriohepatic dysplasia, Alagille-Watson syndrome) is a multisystem disorder with hepatic, skeletal, eye, cardiac and renal manifestations. It results from mutation of the JAG1 gene, located on chromosome 20, which encodes a ligand for Notch receptor(s). The interactions of Notch receptors and their ligands are crucial in controlling cell fate decisions in a variety of developmental processes. AS varies in its severity, even in the same family, from asymptomatic gene carriers through to lethality due to inoperable cardiac or end-stage liver disease. However, advances in medical and surgical therapy have improved the prognosis at the severe end of the spectrum. It is hoped that the enhanced understanding of the biology of AS resulting from the cloning of the JAG1 gene will enable us to develop additional strategies for more effective treatments.

Key words: Alagille syndrome; Jagged; Notch; pathogenesis; management.

Alagille syndrome (AS) is characterized by a marked paucity of interlobular bile ducts and cholestasis, occurring in association with widely variable cardiovascular, facial, ocular, skeletal and neurodevelopmental features. It has been recognized as a distinctive disorder for more than 35 years (Alagille et al, 1969, 1975; Watson and Miller, 1973) and in 1997 the genetic basis for the disease was identified (Li et al, 1997a; Oda et al, 1997). This chapter discusses first these most recent developments in the hope that it will help the reader to understand better the pathological mechanisms BailliPre’s Clinical Gastroenterology - 275 Vol. 12, No. 2, June 1998 Copyright 0 1998, by Baillitre Tindall ISBN o-7020-2450-3 All rights of reproduction in any form reserved 0950-3528/98/020275+ 17 $12.00/00

276 J. C. MACMILLAN ET AL

behind the multisystem manifestations of Alagille syndrome. As is often the case, however, the identification of the underlying molecular genetic mutations has not yet had direct impact on patient care.

MOLECULAR GENETICS AND BIOLOGY

Alagille syndrome arises as a result of mutation of the human homologue (JAG]) of the rat Jagged1 gene (Li et al, 1997; Oda et al, 1997a). JAGI stretches over 36 kb of genomic DNA on chromosome 20~12, comprises 26 exons varying in size from 28 to 2284 bp and has a 5.9 kb mRNA. Intron sizes vary from 89 bp to 9 kb (Oda et al, 1997b).

The cDNA cloned by Oda et al (1997b) has three alternative poly- adenylation sites, and Northern blot analysis indicates high level expression in adult ovary, prostate, pancreas and heart with some of the lowest levels being found in liver, testes, thymus and kidney. Developmentally it is expressed at high levels between 16 and 32 weeks in fetal kidney, in lung between 18 and 22 weeks and in lower levels in liver (16-32 weeks) and brain (20-25 weeks) (Li et al, 1997).

The Jagged1 gene encodes a protein belonging to the family of Notch ligands. Notch and its homologues are regulatory receptors of the signalling pathway controlling cell fate decisions in a number of developmental processes. Notch regulates the ability of undifferentiated cells to differ- entiate in response to a number of ligands, including Delta and Serrate. These ligands were originally detected in Drosophila where there has been extensive work published outlining the effects of mutations in these genes in the development of eyes (Sawamoto and Okano, 1996), wings (Panin et al, 1997) and neural precursors (Seugnet et al, 1997). Whereas in Drosophila there is a single gene encoding Notch receptors, in vertebrates four genes have been identified. The four Notch receptors, Notch1 , Notch2, Notch3 and Notch4 all share a basic structure of 34-36 extracellular epi- dermal growth factor (EGF)-like repeats, three extracellular cysteine-rich Notch/Lin-12 repeats, a transmembrane anchor, an intracellular domain containing approximately seven ankyrin repeats and a PEST sequence (Reaume et al, 1992; Lieber et al, 1993). Mutations in Notch] in humans are associated with T-cell lymphoblastic leukemia (Ellisen et al, 1991). Notch2 and Notch3 are located at chromosome regions of neoplasia- associated translocation (Larsson et al, 1994) and mutations in Notch3 have also been found in CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) (Joutel et al, 1996). Notch4 expression is seen during embryogenesis in endothelial cells of blood vessels forming dorsal aorta, intersegmental vessels, cephalic vessels and heart (Shirayoshi et al, 1997).

The single Serrate/Jagged gene in Drosophila is represented by at least two genes in vertebrates, Jagged2 being expressed in the apical ectodermal ridge (indicating possible involvement in limb formation) and developing thymus (Shawber et al, 1996) and Jagged1 expressed in the heart and eye (especially the ciliary margins of the retina) (Bao and Cepko, 1997). The

ARTERIOHEPATIC DYSPLASIA 277

Notch ligands also contain conserved sequences: a conserved DSL domain (named after Delta, Serrate and Lag-2 ligands for C. Elegans Notch); a varying number of EGF-like repeats (16 in human Jagged]); a cysteine- rich Notch region (CR); and a transmembrane domain (Rebay et al, 1991). The EGF-like repeats, the DSL domain and the CR region are all highly important for ligand-receptor interactions.

Mutations reported to date in cases of Alagille syndrome include deletions (causing a frame shift), single and five-nucleotide insertions and a splice donor mutation (Li et al, 1997; Oda et al, 1997a). All of these mutations are located within the highly conserved regions of JAGl, in the DSL domain, within the EGF-like repeats or the CR region. As a result the mutations cause translational frameshifts which are expected to alter the protein’s structure and function significantly. For example, an AS patient may produce a truncated version of JAG1 that is missing the transmembrane domain, the CR region and some EGF-like repeats, which will effect the cell surface binding capabilities and the ligand-receptor interactions with the Notch receptors. It is also likely that a normal variant of the protein exists, lacking the transmembrane domain resulting from alternate splicing which skips exon 20 (Zimrin et al, 1996; Li et al, 1997).

The mechanism by which mutations in Jagged1 cause the abnormalities seen in AS is unknown but is likely to be related to haplo-insufficiency and a disturbance in the ratio of the ligand-to-Notch receptors. Haplo- insufficiency is likely in view of the documented chromosomal deletions of 2Op seen in rare cases of AS (see below) and is consistent with the Delta and Notch-deficient heterozygote mutant phenotypes of Drosophila (Lindsley and Zimm, 1992). There are other examples of human disease where gene dosage is critical to normal function; haplo-insufficiency for peripheral myelin protein 22 (PMP22) causes hereditary neuropathy with liability to pressure palsies, whereas overexpression due to functional trisomy causes hereditary motor and sensory neuropathy type Ia (Pate1 and Lupski, 1994).

It is not known at present whether Jagged1 acts as a ligand at all four Notch receptors identified to date and whether there is tissue/organ-specific interaction with particular receptors. It is known, however, that during angiogenesis, Jagged-Notch signalling is involved in fibroblast growth factor-induced endothelial cell migration, growth and differentiation (Zimrin et al, 1996), where Notch1 and Notch2 has been shown not to be involved. Also, it is known that Notch4 expression is endothelial cell- specific during development (specifically within the heart) (Uyttendaele et al, 1996); thus it can be hypothesized that Jagged1 interacts with Notch4 during the tubular formation that occurs within angiogenesis. It is known that a reduction in Jagged (induced using antisense therapy) is associated with a marked increase in invasion and tube formation in response to fibroblast growth factor of microvascular endothelial cell in culture (Zimrin et al, 1996). We also do not know the basis for the phenotypic variability of AS even within the same family (although the same can be said for practically every autosomal dominant disorder). Given the wide spectrum of expression of Notch and its ligands it is surprising that, in AS, we do not


see evidence of central or peripheral nervous system dysfunction (see below).

CYTOGENETICS

Prior to the cloning of the gene it was known that a number of cases of Alagille syndrome had chromosomal deletions. The case reported by Byrne et al (1986) with a 22~11.2 deletion had signs additional to those normally seen in AS, namely, jejunal stenosis, neonatal hypoglycaemia and hypo- calcaemia and multiple minor anomalies. Schnittger et al (1989) reviewed nine published cases of AS with chromosome 2Op deletions and reported an additional adult case, concluding that AS was a contiguous gene syndrome located between 2Op 12.1 and p 11.23. Anad et al (1990) reported a further five cases with interstitial deletions, including the first parent-child pair with AS and a deletion.

The subsequent failure by a number of groups (Desmaze et al, 1992; Deleuze et al, 1994; Rand et al, 1995) consistently to identify microdeletions by combined use of FISH (fluorescent in situ hybridization) and molecular analysis for allelic loss in 2Op did not confirm Schnittger’s contention that AS was a contiguous gene syndrome. Similarly, Krantz et al (1997) found cytogenetic abnormalities in only two of 56 (3.6%) AS cases and molecular deletions of 2Op in only three of 45 (6.7%, including the two cytogenetic deletions).

Rarely, families have been reported where an apparently balanced cytogenetic translocation has segregated with Alagille syndrome. In the family reported by Spinner et al (1994) the karyotype was 46XX(XY),t(2;20)(q21.3;p12). Other cytogenetic rearrangements reported include an interstitial deletion arising from segregation of a maternal ins(7;20)(q11.23;pll.23pl2.2 or ~12.2~13) in a patient with absent corpus callosum (Li et al, 1996) and a family with a duplication of 2Op11.21- ~11.23 (Moog et al, 1996).

CLINICAL GENETICS

Alagille syndrome is an autosomal dominant disease (Watson and Miller, 1973) with the majority of cases born to an affected parent. Overall, the proportion of new mutations is estimated to be 15%, although this rises to 45% where both parents are clinically normal (Dhome-Pollet et al, 1994). From a counselling point of view this means that the normal parents of an isolated affected child have a 55% chance of being a gene carrier (Dhome- Pollet et al, 1994). Elmslie et al (1995) estimated in their study that 50% of cases represented new dominant mutations. Dhome-Pollet et al (1994) reported 94% penetrance based on a segregation ratio of 0.47 where a single feature (excluding facies) was used to classify a family member as affected (see below for features). Early suggestions that clinical severity was greater in the offspring of affected mothers, as in myotonic dystrophy


(Shulman et al, 1984), have not been borne out (Dhome-Pollet et al, 1994; Elmslie et al, 1995) neither is there evidence of the anticipation seen in triplet repeat disorders (Elmslie et al, 1995). The variability in expression of the disease in families makes counselling difficult and often inaccurate, although one would hope that molecular identification of asymptomatic carriers will soon be feasible. At the time of writing it is too early to know what percentage of cases of Alagille syndrome have detectable mutations; there has certainly been no suggestion of genetic heterogeneity.

EPIDEMIOLOGY AND OUTCOME

The estimated incidence of Alagille syndrome in mixed Caucasian populations is 1 in 100 000 live births with no gender differences when ascertained on the basis of neonatal liver disease (Danks et al, 1977; Mueller et al, 1984). It accounts for approximately 5% of presentations of prolonged neonatal cholestasis. The outcome and natural history is variable, with a 74% lo-year survival in one study. Complex cardiovascular anomalies are a major cause of early mortality, and hepatic manifestations are a major cause of morbidity and late mortality, accounting for approximately 5% of all paediatric liver transplants. At one referral centre for liver disease (Hoffenberg et al, 1995), the predicted probability of reaching adulthood without transplantation was about 50%, and the probability of long-term survival, including those transplanted, was 87%.

Hepatic

Table 1. Features of symptomatic Alagille syndrome.

Frequency (%)

Jaundice 95 Hepatomegaly 95 PIWhlS 80 (26 months) Cirrhosis 14 (>12 years) Liver failure rare Hepatocellular carcinoma reported

Extrabepatic Vascular Murmur Peripheral pulm stenosis Pulm stenosis + other Tetralogy of Fallot Complex heart anomaly Cerebrovascular accidents

Facial Distinctive triangular facies Ocular Posterior embryotoxon

Iris mosaicism Glaucoma

Vertebral Butterfly vertebrae Interpedicular narrowing

Other Neurological disturbance Growth failure Vitamin deficiency (ADEK) Renal linidosis

95 50 50 20 10

5 75 70 50 Rare 50 50 Secondary to cholestasis


CLINICAL MANIFESTATIONS

The cardinal features of Alagille syndrome and their estimated frequency are listed in Table 1 and discussed by system. Subsequently, Alagille et al (1987) proposed that the clinical (phenotypic) diagnosis be based on the occurrence of cholestasis with histological paucity of interlobular bile ducts, plus two of four extrahepatic features (characteristic facies (Figure l), cardiac murmur, vertebral anomalies, posterior embryotoxon). In addition, a family history of related clinical features is positive in at least 20% of pedigrees.

The syndrome usually presents as prolonged neonatal cholestasis (conjugated hyperbilirubinaemia, pale stools, dark urine), in association with the variable extrahapatic syndromic features. In this age group, it must be distinguished from biliary atresia, neonatal hepatitis and metabolic liver

Figure l(A). A 5-year-old boy with Alagille syndrome. Note the broad forehead, triangular facies and mild hypertelorism.


diseases, usually by the finding of bile duct paucity on liver biopsy, and the presence of a patent but often hypoplastic extrahepatic biliary tree on scintigraphy or, if necessary, cholangiography. The cardiac lesions vary from a clinically insignificant peripheral pulmonary artery stenosis to life- threatening complex congenital anomalies (see below). Mostly, the jaundice abates by 6-12 months, at which time pruritus and failure to thrive supervene.

Older children with the syndrome may present with pruritus, with xanthomata and/or features of chronic liver disease. The pruritus often resolves during adolescence. Adults are commonly undiagnosed until a related index case is diagnosed, but may have a history of pruritus as a child. We and others (Hoffenberg et al, 1995) have observed a striking prevalence of cerebrovascular accidents in young adults with the syndrome, following earlier sporadic reports of death from intracranial haemorrhage (Alagille et al, 1987).

Figure l(B).


Hepatic features

While the majority have hepatic manifestations, there is great variability in hepatic disease related to age, severity and even within families. Neonatal jaundice is present in the majority, presenting as a prolonged conjugated hyperbilirubinaemia, pale stools and dark urine in the neonatal period. A bleeding tendency caused by vitamin K malabsorption is common in untreated patients in this age group. In about half of these, jaundice resolves by 6-12 months but may recur during intercurrent illnesses or with the occurrence of end-stage liver disease later in life. Mild jaundice and/or persisting elevations of serum alkaline phosphatase and y-glutamyl transferase may persist for many years, overshadowed by cholestasis, with elevated serum bile acids, manifest by the onset of pruritus after 6-12 months, and xanthomata and hypercholesterolaemia by l-3 years. The pruritus can be debilitating and intolerable, leading to lichenification and scarring of the skin. Firm hepatomegaly is present in virtually all symptomatic patients, and splenomegaly appears commonly by 1 O-l 2 years. Surprisingly, the severity of the cholestasis often abates in some patients after lo-12 years, possibly as the major bile ducts adapt to some biliary secretion. In a review of 45 patients (Perrault, 1981) 14% had developed ‘cirrhosis’ (see hepatic pathology below) by a mean age of 12 years. Hepatocellular carcinoma has been reported in Alagille syndrome with and without cirrhosis (Bekassy and Garwicz, 1992; Keeffe et al, 1993). Hepatic synthetic function is usually well preserved, but progression to hepatic failure, though rare, and severe liver-related morbidity, are recognized increas- ingly, as evidenced by the need for liver transplantation in some patients.

Hepatic pathology

Characteristically, the typical histological finding of interlobular bile duct paucity evolves over time, and because the portal tracts are so incon- spicuous, or sometimes in early life clouded by portal inflammation and giant cells, initial biopsies may be misinterpreted by the inexperienced observer. Histological cholestasis is also prominent early, tending to decrease with the age of the patient. Thus, longitudinal repeat biopsies are useful in assessing this condition. Paucity of ducts is defined as a ratio of duct to portal tracts of ~0.5, where at least five to 10 portal tracts are present in the biopsy (Kahn et al, 1989). Ultrastructural studies have demonstrated relatively normal bile canaliculi, retention of bile in hepato- cytes at the Golgi complex, and unusually large amounts of intercellular bile. How this relates to the duct paucity is unknown but abnormal bile secretion may theoretically result in duct loss (Valencia-Mayoral et al, 1984). In cases that have come to liver transplantation, Hashida and Yunis (1988) have described perisinusoidal (as opposed to portal) fibrosis, with an irregular distribution, most severe nearest the hilus and distinctively different from secondary biliary cirrhosis.

Longitudinal assessment by biopsy has also identified some unusual scenarios such as that reported by Fujisawa et al (1994) where a case of AS


(cholestasis, posterior embryotoxon, peripheral pulmonary artery stenosis) had a liver biopsy showing absence of interlobular bile ducts at age 1.5 years but normal interlobular bile ducts on re-biopsy at age 9.5 years. Although hepatic disease predominates in terms of clinical presentation, morbidity and long-term prognosis, its severity does not correlate with other manifestations.

Extrahepatic features (Table 1)

Cardiac and vascular

Congenital heart disease occurs in between 85 and 100% of series of AS reported to date (Alagille et al, 1987; Krantz et al, 1997). Vascular abnormalities are found mostly in the pulmonary vascular tree, commonly with isolated peripheral pulmonary stenoses of no clinical significance, resulting in murmurs on auscultation. However, pulmonary vascular hypoplasia, or severe pulmonary artery stenosis, often in association with other congenital heart anomalies, such as tetralogy, truncus arteriosus, septal defects, and/or systemic vascular abnormalities, may be major features of some cases (Alagille et al, 1987; Silberbach et al, 1994). Shefler et al (1997) have recently reported narrowing of the abdominal aorta in Alagille syndrome. There is also a reported risk of intracranial haemorrhage as mentioned above, particularly in young adults. Intracranial haemorrhage may be related to abnormalities in clotting secondary to chronic liver disease but may also occur with structural abnormalities in intracranial vessels. Of 20 index cases seen at our centre over 10 years, three have had a parent die of intracranial haemorrhage below the age of 25 years, and one index case is hemiplegic following a cerebrovascular accident. Vascular anomalies, including cerebral aneurysm, were responsible for some cases, but early atherosclerosis may have had a role. We are not aware of any published reports of histological abnormalities in intracranial vessels in AS, but given the known relationship between Jagged-Notch interactions and angiogenesis (Zimrin et al, 1996) it might be expected that the vascular manifestations would not be confined to the pulmonary and aortic tracts.

Facial appearance

The characteristic facies described initially by Alagille et al (1975) are useful in diagnosis (Figure l), and consist of a distinctive triangular face with a broad forehead, a saddle-shaped nose, widely spaced deep set eyes and a pointed chin.

Skeletal

One of the cardinal features of Alagille syndrome is butterfly vertebrae. This is reported in between 17 and 100% of cases studied (Riely et al, 1979; Dahms et al, 1982) with an overall frequency of about 70% (Krantz et al,


1997). Other findings include lack of normal increase in interpedicular distance in the lumbar spine, spina bifida occulta, pointed anterior process to C 1, fused and hemi-vertebrae, rib anomalies and short fingers (Riely et al, 1979; Rosenfield et al, 1980; Berman et al, 1981; Mueller et al, 1984). These vertebral anomalies are helpful diagnostically, but may not always be obvious in the neonatal period.

Eye Slit-lamp examination of the eyes is best to detect ocular defects (Brodsky and Cunniff, 1993). Posterior embryotoxon, although not entirely patho- gnomonic of Alagille syndrome, occurs in 90% of patients. This is characterized by a prominent Schwalbe’s line (a line of material in the anterior chamber at the junction of the cornea and the uveal trabecular meshwork of the iris). Although usually asymptomatic, such anterior chamber malformations can result in glaucoma (Potamitis and Fielder, 1993). In addition, an unusual mosaic pattern of iris stroma is present in many patients. Ocular problems secondary to chronic cholestasis such as night blindness, and retinal pigment may also occur. Nischal et al (1997) found ultrasound evidence of unilateral optic nerve drusen in 95% and bilateral disc drusen in 80% of AS children.

Renal Renal involvement in AS may comprise mild abnormalities in function (Riely et al, 1979; Rosenfield et al, 1980), changes associated with the hypercholesterolaemia of cholestasis such as mesangiolipidosis (Chung- Park et al, 1982; Alagille et al, 1987; Russo et al, 1987) and structural abnormalities (Martin et al, 1996). The structural abnormalities include cystic dysplastic kidneys (Martin et al, 1996), unilateral aplasia, micro- cystic tubular dilatation with interstitial fibrosis (Hymans et al, 1983; Tolia et al, 1987) and medullary cystic disease (Oestreich et al, 1983).

Other

Other reported manifestations, such as neurodevelopmental delay, malnutrition, growth failure, fat-soluble vitamin and essential fatty acid deficiency and lipid nephropathy, are probably secondary to the severe cholestasis and are, in the main, preventable with nutritional therapy. Mental retardation was a major feature in initial reports, but since the recognition of the important role of vitamin E in neurodevelopment following the discovery of a distinctive cholestasis-related degenerative disorder due to vitamin E deficiency (Sokol et al, 1985), and the institution of more aggressive nutritional therapy (Shepherd, 1994), this is observed less frequently.

Similar comments apply to the occurrence of bone disease, night blindness, and growth failure. Bucuvalas et al (1993), however, concluded that growth-retarded children with AS are insensitive to growth hormone as the


levels of insulin-like growth factor-I (IGF-I) did not rise on challenge with recombinant GH. They suggest that the IGF-I treatment may benefit AS children. Bone disease, with fractures, osteopoenia, and rickets has a complex aetiology in cholestasis, with protein deficiency (matrix) and calcium, phosphorous, vitamin D and magnesium metabolism (structure) all implicated.

MANAGEMENT

When the diagnosis is suspected by the clinical phenotype and liver histology, appropriate management rests on the following:

1. A comprehensive evaluation, documenting all possible manifestations, including liver biochemistry and biopsy, cardiovascular studies, slit- lamp ocular examination, spine X-ray, serum bile acids, cholesterol and triglycerides. Some of these studies, as well as the liver biopsy, may need repeating on follow-up due to age-related variations in findings.

2. A complete genetic evaluation, including family pedigree (with examination of family members), molecular genetic studies, cytogenetic studies, and appropriate genetic counselling.

3. An ongoing assessment and treatment of the (potentially preventable) effects of chronic cholestasis, particularly nutrition, growth, essential fatty acid and fat soluble vitamin status, and neurodevelopmental status.

4. Appropriate treatment of congenital and acquired defects, such as congenital heart abnormalities, pruritus, xanthomata and endstage liver disease.

Treatment is essentially supportive, directed at preventing the nutritional effects of cholestasis, managing the pruritus and hypercholesterolaemia, with appropriate management of organ-specific abnormalities such as congenital heart disease, and liver failure. The outcome is highly variable but is primarily related to the severity of the cardiac and/or hepatic manifestations with mortality attributable equally to each. Quality-of-life issues, particularly with respect to pruritus, the severity/progression of liver disease and the presence or absence of severe cardiac anomalies are important considerations in determining treatment by liver transplantation, cardiac transplantation or, rarely, both.

Nutritional therapy

The nutritional effects of chronic cholestasis in children include protein- energy malnutrition from anorexia, impaired protein synthesis and amino acid metabolism, altered energy metabolism, and malabsorption of energy, essential fatty acids, and fat soluble vitamins (Shepherd, 1994). In infants, the provision of adequate absorbable calories, protein and fat soluble vitamins is particularly important to achieve satisfactory growth and correction of vitamin A, D, E and K and mineral deficiencies. While


cholestasis persists there is a need for aggressive nutritional support (Shepherd, 1994).

Specialized hepatic formulae (rich in branched-chain amino acids, with medium- and long-chain triglycerides to enhance energy absorption, and adequate non-nitrogen calories) are available for infants, children and adults as either oral or enteral supplements (Generaid Plus, SHS Ltd; Aminoleban, Otsuka Pharmaceuticals). Controlled trials of nocturnal enteral administration have indicated nutritional benefits in malnourished children with chronic cholestasis (Chin et al, 1992).

Parenteral vitamin K should be considered for rapid correction of pro- thrombin abnormalities and thereafter oral supplementation (5-10 mg/day) is necessary. Supplements of vitamin E (water-soluble TPGS, 25 IU/kg/day, Liqui-E) are always advised to prevent the potentially serious neuroaxonal degeneration caused by chronic cholestasis-associated vitamin E deficiency (Sokol et al, 1993). Most patients require 600-3000IU/day of water- miscible vitamin A (Aquasol A), taking care to avoid toxicity, to maintain normal vitamin A levels (best measured by the molar ratio of retinol to retinol-binding protein). Serial monitoring of serum 25OH-D accom- panied by adequate sunlight exposure and a good intake of protein, calcium and phosphorous will minimize osteopaenia and rickets. Small doses of 25OH-D (5 mcg/kg/day) are useful in documented deficiency. Essential fatty acid deficiency is prevented by the provision of some long-chain triglycerides. and adding corn or safflower oil to foods.

Pruritus

Pruritus management for Alagille syndrome is generally one of therapeutic trial and no one agent seems universally helpful. In children, fingernail trims, long cotton nightwear and cotton mittens, skin and hand hygiene, emollients and night-time antihistamines as a sedative can minimize skin damage. Cool baths and fans can give temporary relief. Therapeutic trials of commonly used agents for pruritus due to cholestasis, such as cholestyramine (bile-acid binding resin), rifampicin (bile-acid uptake inhibitor), ursodeoxycholic acid (UDCA, a potent choleretic and hepatoprotective agent) and phenobarbital (microsomal induction) are worth- while. In Alagille syndrome, the last is disappointing, but cholestyramine, tifampicin and UDCA all seem helpful in approximately 50-80% of patients (Balistreri et al, 1992; Gillespie and Vickers, 1993; Gregorio et al, 1993). The use of cholestyramine is limited by unpalatability and its tendency to cause metabolic acidosis and malabsorption. However, with administration mixed with juice or as a candy bar (500 mg/kg/day), and avoidance of co-administration of vitamin supplements or food, and good compliance over time, this appears to give the best results. UDCA (lo-20 mg/kg/day) may prove to be the preferred therapy because of its safety and hepatoprotective effects, but the clinical response is variable, including some patients whose pruritus seems to be worsened by this agent. Other therapies for pruritus such as UVB light, carbamazepine and steroids have not been subject to systematic study. Unrelieved, intractable pruritus


may lead to consideration for biliary diversion, particularly when associated with xanthomata. This operation has anecdotally resulted in marked improvement in symptoms in some cases, although the mechanism for improvement is unclear and more systematic study is necessary. Finally, unrelieved, intractable pruritus, when associated with progressive liver disease, is cured by liver transplantation.

Hyperlipidaemia/xanthomata

Severe hyperlipidaemia in young adults with Alagille syndrome has been associated with early atherosclerosis and renal lipidosis causing renal failure, although much of the cholesterol is in lipoprotein X, which does not affect vascular endothelium (Gottrand et al, 1995). The disfiguring and functional effects of multiple xanthomata also may be underestimated. Both cholestyramine and UDCA may improve hypercholesterolaemia by as much as 50% (Balistreri et al, 1992). Cholesterol synthesis inhibitors (simvastatin) have no effect on bile acid metabolism and would appear to have little role in cholestasis-induced hyperlipidaemia. Cholesterol levels and xanthomata may decrease after biliary diversion and are completely corrected by liver transplantation, but the role of surgery for these problems alone is unclear, and other factors such as liver dysfunction, quality of life, and growth need to be taken into account.

Liver transplantation

Hepatic transplantation is a treatment consideration for progressive liver disease, inanition, or debilitating refractory pruritus, and if successful may transform the life of some patients with Alagille syndrome. The median age for transplantation in one series was 6.5 years (Hoffenberg et al, 1995). However, transplantation outcomes are below average (57% survival, Tsakis et al, 1993) possibly because of the greater risk due to the vascular and nutritional defects commonly associated with this syndrome. Careful pretransplant assessment and nutritional rehabilitation is warranted. Some severe cardiopulmonary defects such as inoperable pulmonary artery hypoplasia may preclude liver transplantation.

CONCLUSION

The recognition of Alagille syndrome has, over 35 years, led to an improved understanding and management of this often debilitating multisystem genetic disorder. As more patients reach adulthood, the importance of prevention of secondary manifestations and recognition of longer-term manifestations is emphasized. The recent cloning of the gene, and current research on the gene product, recognized as a Notch ligand, important in cell fate decisions in a number of developmental processes, gives improved insight into the biology of the condition and may ultimately enable us to develop appropriate specific therapies for Alagille syndrome.


Acknowledgements JCM & RS receive funds from the Royal Children’s Hospital Foundation, Herston, Brisbane for their research on AS. MH is in receipt of a Sasakawa Memorial Fund Ph.D. Scholarship. Research on nutritional aspects of childhood liver disease is supported by the Queensland Liver Transplant Service. We are grateful to the patients and families with Alagille syndrome and the Alagille Support Group of Australia for their support.

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5 Arteriohepatic dysplasia (Alagille syndrome; Watson-Alagille syndrome)