Crigler-Najjar syndrome: looking to the future does not make us forget the present.

Recently, the safety and efficacy of gene therapy were evaluated in patients with Crigler-Najjar syndrome (CNS). Although it is a promising curative option for CNS, many doubts still persist about its long-term efficacy and safety. Furthermore, there is a risk of overlooking several unresolved problems still present in current clinical practice. This letter is a call for action on crucial open issues that remain nowadays an unmet need in the management of CNS patients.

Gene Therapy in Patients with the Crigler-Najjar Syndrome.

BACKGROUND: Patients with the Crigler-Najjar syndrome lack the enzyme uridine diphosphoglucuronate glucuronosyltransferase 1A1 (UGT1A1), the absence of which leads to severe unconjugated hyperbilirubinemia that can cause irreversible neurologic injury and death. Prolonged, daily phototherapy partially controls the jaundice, but the only definitive cure is liver transplantation. METHODS: We report the results of the dose-escalation portion of a phase 1-2 study evaluating the safety and efficacy of a single intravenous infusion of an adeno-associated virus serotype 8 vector encoding UGT1A1 in patients with the Crigler-Najjar syndrome that was being treated with phototherapy. Five patients received a single infusion of the gene construct (GNT0003): two received 2×1012 vector genomes (vg) per kilogram of body weight, and three received 5×1012 vg per kilogram. The primary end points were measures of safety and efficacy; efficacy was defined as a serum bilirubin level of 300 µmol per liter or lower measured at 17 weeks, 1 week after discontinuation of phototherapy. RESULTS: No serious adverse events were reported. The most common adverse events were headache and alterations in liver-enzyme levels. Alanine aminotransferase increased to levels above the upper limit of the normal range in four patients, a finding potentially related to an immune response against the infused vector; these patients were treated with a course of glucocorticoids. By week 16, serum bilirubin levels in patients who received the lower dose of GNT0003 exceeded 300 µmol per liter. The patients who received the higher dose had bilirubin levels below 300 µmol per liter in the absence of phototherapy at the end of follow-up (mean [±SD] baseline bilirubin level, 351±56 µmol per liter; mean level at the final follow-up visit [week 78 in two patients and week 80 in the other], 149±33 µmol per liter). CONCLUSIONS: No serious adverse events were reported in patients treated with the gene-therapy vector GNT0003 in this small study. Patients who received the higher dose had a decrease in bilirubin levels and were not receiving phototherapy at least 78 weeks after vector administration. (Funded by Genethon and others; ClinicalTrials.gov number, NCT03466463.).

Gilbert or Crigler-Najjar syndrome? Neonatal severe unconjugated hyperbilirubinemia with P364L UGT1A1 homozygosity.

BACKGROUND: Several mutations of bilirubin uridine diphosphate-glucuronosyltransferase gene (UGT1A1) have been reported in patients with unconjugated hyperbilirubinemia. Few reports are available about the p.Pro364Leu mutation (P364L, c.1091C > T) in homozygous newborns. We describe the clinical, laboratory and therapeutic approach in two Chinese neonates with severe jaundice, homozygous for the P364L mutation. CASE PRESENTATION: Two Chinese breastfed female infants presented prolonged unconjugated hyperbilirubinemia at the age of 1 month. Total bilirubin was higher than 15 mg/dl (D < 1). An exhaustive etiological work-up to detect possible causes of hyperbilirubinemia (notably hemolytic ones) was negative. The promoter and coding regions of UGT1A1 were amplified by polymerase chain reaction (PCR) from genomic DNA isolated from leukocytes. Both patients resulted homozygous for a variant site within the coding region of the gene in the 4 exon, c.1091C > T, p.Pro364Leu. In front of the persistently high level of unconjugated bilirubin, phototherapy was performed without persistent results. A treatment with phenobarbital was then begun and bilirubin level progressively decreased, with a complete and persistent normalization. The therapy was stopped. CONCLUSION: UGT1A1 enzyme activity associated with the P364L mutation has been described as 35.6% of the wild-type enzyme activity. Photo-therapy and phenobarbital can be useful in front of persistently high level of unconjugated bilirubin. Our cases presented high bilirubin values, overlapping between Gilbert syndrome (GS) and Crigler-Najjar syndrome type II (CNS), but the complete normalization of bilirubin makes GS more likely. Homozygous P364L variant can be associated with severe neonatal unconjugated hyperbilirubinemia in Chinese infants, but jaundice can completely resolve in a few months, contrary to what happens in Crigler-Najjar syndrome type II.

Crigler-Najjar Syndrome Type 1: Pathophysiology, Natural History, and Therapeutic Frontier.

BACKGROUND AND AIMS: We describe the pathophysiology, treatment, and outcome of Crigler-Najjar type 1 syndrome (CN1) in 28 UGT1A1 c.222C>A homozygotes followed for 520 aggregate patient-years. APPROACH AND RESULTS: Unbound ("free") bilirubin (Bf ) was measured in patient sera to characterize the binding of unconjugated bilirubin (BT ) to albumin (A) and validate their molar concentration ratio (BT /A) as an index of neurological risk. Two custom phototherapy systems were constructed from affordable materials to provide high irradiance in the outpatient setting; light dose was titrated to keep BT /A at least 30% below intravascular BT binding capacity (i.e., BT /A = 1.0). Categorical clinical outcomes were ascertained by chart review, and a measure (Lf ) was used to quantify liver fibrosis. Unbound bilirubin had a nonlinear relationship to BT (R2  = 0.71) and BT /A (R2  = 0.76), and Bf as a percentage of BT correlated inversely to the bilirubin-albumin equilibrium association binding constant (R2  = 0.69), which varied 10-fold among individuals. In newborns with CN1, unconjugated bilirubin increased 4.3 ± 1.1 mg/dL per day. Four (14%) neonates developed kernicterus between days 14 and 45 postnatal days of life; peak BT  ≥ 30 mg/dL and BT /A ≥ 1.0 mol:mol were equally predictive of perinatal brain injury (sensitivity 100%, specificity 93.3%, positive predictive value 88.0%), and starting phototherapy after age 13 days increased this risk 3.5-fold. Consistent phototherapy with 33-103 µW/cm2 •nm for 9.2 ± 1.1 hours/day kept BT and BT /A within safe limits throughout childhood, but BT increased 0.46 mg/dL per year to reach dangerous concentrations by 18 years of age. Liver transplantation (n = 17) normalized BT and eliminated phototherapy dependence. Liver explants showed fibrosis ranging from mild to severe. CONCLUSION: Seven decades after its discovery, CN1 remains a morbid and potentially fatal disorder.

Disease burden of Crigler-Najjar syndrome: Systematic review and future perspectives.

BACKGROUND AND AIM: Crigler-Najjar syndrome (CNS) results from biallelic mutations of UGT1A1 causing partial or total loss of uridine 5'-diphosphate glucuronyltransferase activity leading to unconjugated hyperbilirubinemia and its attendant risk for irreversible neurological injury (kernicterus). CNS is exceedingly rare and has been only partially characterized through relatively small studies, each comprising between two and 57 patients. METHODS: A systematic literature review was conducted to consolidate data on the patient, caregiver, and societal burden of CNS. RESULTS: Twenty-eight articles on clinical aspects of CNS were identified, but no published data on its humanistic or economic burden were found. In patients with complete UGT1A1 deficiency (type 1 CNS [CNS-I]), unconjugated bilirubin levels increase 3-6 mg/dL/day during the newborn period and reach neurologically dangerous levels between 5 and 14 days of age. Phototherapy is the mainstay of treatment but poses significant challenges to patients and their families. Despite consistent phototherapy, patients with CNS-I have worsening hyperbilirubinemia with advancing age. Liver transplantation is the only definitive therapy for CNS-I and is increasingly associated with excellent long-term survival but also incurs high costs, medical and surgical morbidities, and risks of immunosuppression. CONCLUSIONS: Crigler-Najjar syndrome is associated with a substantial burden, even with existing standards of care. The development of novel disease-modifying therapies has the potential to reduce disease burden and improve the lives of CNS patients and their families.

Prevalence and Relevance of Pre-Existing Anti-Adeno-Associated Virus Immunity in the Context of Gene Therapy for Crigler-Najjar Syndrome.

Adeno-associated virus (AAV) vector-mediated gene therapy is currently evaluated as a potential treatment for Crigler-Najjar syndrome (CN) (NCT03466463). Pre-existing immunity to AAV is known to hinder gene transfer efficacy, restricting enrollment of seropositive subjects in ongoing clinical trials. We assessed the prevalence of anti-AAV serotype 8 (AAV8) neutralizing antibodies (NAbs) in subjects affected by CN and investigated the impact of low NAb titers (<1:5) on liver gene transfer efficacy in an in vivo passive immunization model. A total of 49 subjects with a confirmed molecular diagnosis of CN were included in an international multicenter study (NCT02302690). Pre-existing NAbs against AAV8 were detected in 30.6% (15/49) of screened patients and, in the majority of positive cases, cross-reactivity to AAV2 and AAV5 was detected. To investigate the impact of low NAbs on AAV vector-mediated liver transduction efficiency, adult wild-type C57BL/6 mice were passively immunized with pooled human donor-derived immunoglobulins to achieve titers of up to 1:3.16. After immunization, animals were injected with different AAV8 vector preparations. Hepatic vector gene copy number was unaffected by low anti-AAV8 NAb titers when column-purified AAV vector batches containing both full and empty capsids were used. In summary, although pre-existing anti-AAV8 immunity can be found in about a third of subjects affected by CN, low anti-AAV8 NAb titers are less likely to affect liver transduction efficiency when using AAV vector preparations manufactured to contain both full and empty capsids. These findings have implications for the design of liver gene transfer clinical trials and for the definition of inclusion criteria related to seropositivity of potential participants.

AAV8 Gene Therapy Rescues the Newborn Phenotype of a Mouse Model of Crigler-Najjar.

Adeno-associated viral (AAV) vectors can target the liver, making them an attractive platform for gene therapy approaches that require the correction of hepatocytes. Crigler-Najjar syndrome is an autosomal recessive disorder of bilirubin metabolism that occurs when the liver's uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) enzyme activity is partially or completely absent. This syndrome is characterized by elevated bilirubin levels in the blood. An AAV8 vector was developed expressing a codon-optimized human version of UGT1A1 from a liver-specific promoter. High doses of the vector rescued neonatal lethality in newborn UGT1 knockout (KO) mice, which serve as a model of Crigler-Najjar syndrome, and significantly increased survival from 5 to 270 days. Newborn UGT1 KO mice treated with AAV had serum total bilirubin levels that were 5.7 times higher than the levels seen in heterozygous and wild-type mice, likely due to dilution of vector genome copies (GC) in the liver resulting from a proliferation of hepatocytes during growth of the animal. The elevation in serum total bilirubin levels in adult UGT1 KO mice depended on the AAV8 vector dose. At doses <1011 GC/mouse, total bilirubin levels returned to those seen in phototherapy-rescued UGT1 KO mice. Mice injected with vector at 1011 or 3 × 1011 GC/mouse had sustained reduced total bilirubin levels throughout the duration of the study. When an AAV8 vector was re-administered in mice with elevated total bilirubin levels, serum total bilirubin levels decreased to wild-type levels (0.1-0.3 mg/dL) in mice that received a vector dose of 3 × 1012 GC/kg. Therefore, a low-level and likely transient decrease in serum total bilirubin during the first days of life is necessary for rescuing the lethal phenotype present in the neonatal UGT1 KO mouse. Furthermore, it was possible to ablate the elevated total bilirubin levels in adult mice by re-administering an AAV8 vector.

Crigler-Najjar Syndrome: Current Perspectives and the Application of Clinical Genetics.

BACKGROUND: Crigler-Najjar syndrome (CNS, OMIM: 218800) is the paradigm of an inborn error of metabolism and a rare genetic disease with an estimated incidence of 0.6-1.0 per million live births. Discrimination between CNS subtypes is usually done on the basis of the clinical criteria, such as response to phenobarbital treatment and other molecular and functional characteristics. METHODS: The identification of four novel pathogenic mutations and the analysis of residual activity of missense in UGT1A1 gene are useful for clinical diagnosis, and may reveal a new insight in enzyme activity, whereas the identification of pathogenic mutations will accelerate genetic counseling for newly identified CNS patients. RESULTS: Phototherapy, orthotropic liver transplantation, liver cell transplantation and gene therapy are treatment choices and candidates to fight back this syndrome. Due to the promising reports of gene therapy in small animal models, gene therapy approaches are expected to continue in preclinical research for developing safe and effective treatment of CNS. Gene transfer vectors using recombinant viruses, such as Adenovirus have been applied successfully in transferring UGT1A1 gene to the liver of Gunn rat model of CNS. CONCLUSION: In spite of remaining safety and efficiency issues, gene therapy promises to be a realistic treatment modality for CNS during the future decade.

[A 14-day-old boy with jaundice and apnoea]. / 14 dager gammel gutt med gulsott og apnéanfall.

We describe an infant who was readmitted from home at 14 days of age with jaundice and a history of apnoea and episodes of retrocollis/opisthotonos. He had been only mildly jaundiced on discharge from the maternity clinic at 2 days of age. The total serum bilirubin (TSB) on admission was 542 µmol/L, and the infant was treated intensively with triple phototherapy and exchange transfusion. In contrast to what is recommended in Norwegian national guidelines for management of neonatal jaundice, the parents had apparently neither received oral nor written information about jaundice and its follow-up at the time of discharge from maternity. They therefore contacted their child healthcare centre when they had questions about jaundice, though the national guidelines specifically state that follow-up for neonatal jaundice during the first 2 weeks of life is the responsibility of the birth hospital. Inappropriate advice resulted in delayed referral, and the child has been diagnosed with chronic kernicterus, probably the first such case in Norway since national guidelines were formalised in 2006. Genetic work-up disclosed compound heterozygosity for Crigler-Najjar syndrome type I, to the best of our knowledge the first instance of this disorder ever to have been diagnosed in Norway. The incidence of kernicterus is Norway is much lower than in other industrialised countries. This is most likely due to national guidelines for management of neonatal jaundice, which place the responsibility for management and follow-up of jaundice with the birth hospital during the crucial first 2 weeks of life. This case report reminds us that tragedies may occur when guidelines are disregarded.

Life-long correction of hyperbilirubinemia with a neonatal liver-specific AAV-mediated gene transfer in a lethal mouse model of Crigler-Najjar Syndrome.

Null mutations in the UGT1A1 gene result in Crigler-Najjar syndrome type I (CNSI), characterized by severe hyperbilirubinemia and constant risk of developing neurological damage. Phototherapy treatment lowers plasma bilirubin levels, but its efficacy is limited and liver transplantation is required. To find alternative therapies, we applied AAV liver-specific gene therapy to a lethal mouse model of CNSI. We demonstrated that a single neonatal hUGT1A1 gene transfer was successful and the therapeutic effect lasted up to 17 months postinjection. The therapeutic effect was mediated by the presence of transcriptionally active double-stranded episomes. We also compared the efficacy of two different gene therapy approaches: liver versus skeletal muscle transgene expression. We observed that 5-8% of normal liver expression and activity levels were sufficient to significantly reduce bilirubin levels and maintain lifelong low plasma bilirubin concentration (3.1±1.5 mg/dl). In contrast, skeletal muscle was not able to efficiently lower bilirubin (6.4±2.0 mg/dl), despite 20-30% of hUgt1a1 expression levels, compared with normal liver. We propose that this remarkable difference in gene therapy efficacy could be related to the absence of the Mrp2 and Mrp3 transporters of conjugated bilirubin in muscle. Taken together, our data support the concept that liver is the best organ for efficient and long-term CNSI gene therapy, and suggest that the use of extra-hepatic tissues should be coupled to the presence of bilirubin transporters.

[Crigler-Najjar syndrome. Report of one case with a long term follow up]. / Evolución prolongada en síndrome de Crigler-Najjar tipo I.

Crigler-Najjar Syndrome is an uncommon genetic disorder characterized by the elevation of unconjugated plasmatic bilirubin secondary to deficiency of the enzyme uridine diphosphate glucuronyltransferase (UDP-GT). We report a 19-years-old woman with the syndrome diagnosed during the neonatal period, when she developed a severe jaundice in the first 10 days of life, reaching unconjugated bilirubin levels of 29 mg/dl, with normal liver function tests. After transient response to phototherapy, the patient was referred to a tertiary medical center in which an extensive work up ruled out other etiologies and the diagnosis of type I Crigler-Najjar syndrome was established. Currently, the patient has a mild mental retardation. She is receiving homemade phototherapy 18 h per day with acceptable control of bilirubin levels. Many mutations have been associated with UDP-GT dysfunction resulting in a broad spectrum of the disease. When bilirubin rises above physiological limits, it permeates the hematoencephalic barrier, inducing bilirubin impregnation of basal ganglia with secondary neuronal damage and necrosis. The worst outcome, kernicterus, is characterized by mental retardation, central deafness, ophthalmoplegia, ataxia, athetosis, spasticity, seizures and death. First line therapy includes phototherapy, but definitive therapy is liver transplantation before the occurrence of neurological damage.

Evolución prolongada en síndrome de Crigler-Najjar tipo I / Crigler-Najjar syndrome. Report of one case with a long term follow up

Crigler-Najjar Syndrome is an uncommon genetic disorder characterized by the elevation of unconjugated plasmatic bilirubin secondary to deficiency of the enzyme uridine diphosphate glucuronyltransferase (UDP-GT). We report a 19-years-old woman with the syndrome diagnosed during the neonatal period, when she developed a severe jaundice in the first 10 days of life, reaching unconjugated bilirubin levels of 29 mg/dl, with normal liver function tests. After transient response to phototherapy, the patient was referred to a tertiary medical center in which an extensive work up ruled out other etiologies and the diagnosis of type I Crigler-Najjar syndrome was established. Currently, the patient has a mild mental retardation. She is receiving homemade phototherapy 18 h per day with acceptable control of bilirubin levels. Many mutations have been associated with UDP-GT dysfunction resulting in a broad spectrum of the disease. When bilirubin rises above physiological limits, it permeates the hematoencephalic barrier, inducing bilirubin impregnation of basal ganglia with secondary neuronal damage and necrosis. The worst outcome, kernicterus, is characterized by mental retardation, central deafness, ophthalmoplegia, ataxia, athetosis, spasticity, seizures and death. First line therapy includes phototherapy, but definitive therapy is liver transplantation before the occurrence of neurological damage.

Crigler-Najjar syndrome type I in a Turkish newborn caused by a novel mutation and Gilbert type genetic defect.

Crigler-Najjar syndrome (CNS), caused by deficiency of bilirubin uridine diphosphate glucuronosyltransferase (UGT) 1A1, is a rare and autosomal recessive inherited disorder characterized by severe unconjugated nonhemolytic hyperbilirubinemia since birth. We present a girl with CNS type I caused by a novel mutation and Gilbert type genetic defect. Gilbert's Syndrome (GS) and CNS type I both involve abnormalities in bilirubin conjugation secondary to deficiency of bilirubin UGT. The combined defects even in benign genetic forms were shown to cause more serious clinical disease. The patient has been treated with daily home-based phototherapy for more than nine months and considered as a candidate for liver transplantation.

[Crigler-Najjar type 1 in children]. / Crigler-Najjars sygdom type 1 hos børn.

Crigler-Najjar type 1 is a rare congenital disease caused by total lack of activity of bilirubin uridine diphosphate glucuronosyl transferase (UGT1A1) in the liver. The disease is characterised by a persistent severe unconjugated hyperbilirubinaemia. The primary treatment is phototherapy, with oral calcium phosphate as a possible supplementation. The effect of the treatment decreases by age, and if the phototherapy is insufficient the patient will need a liver transplantation. Hepatocyte transplantation has been tried with transient success. The risk of chronic bilirubin encephalopathy is considerable.

[Crigler-Najjar's syndrome is a rare cause of perinatal hyperbilirubinaemia]. / Crigler-Najjars syndrom er en sjælden årsag til perinatal hyperbilirubinæmi.

A seven-day-old, mature girl was hospitalized with serum unconjugated bilirubin 420 micromol/l. She was treated with phototherapy, which continued at home until the age of 14 years. Serum total bilirubin was then 250-300 micromol/l and she received a liver transplantation. At the age of 22 years she had no signs of chronic bilirubin encephalopathy. There was no activity of bilirubin UDP-glucuronosyl transferase in the liver, and a mutation was found in one of the coding exons in the gene. The girl suffered from Crigler-Najjar's syndrome type 1. In Denmark the incidence was about 2.7 × 10-6 in the period 1977-2010. The prevalence was about 0.5 × 10-6.

Beyond plasma bilirubin: the effects of phototherapy and albumin on brain bilirubin levels in Gunn rats.

BACKGROUND & AIMS: Severe unconjugated hyperbilirubinemia, as occurs in Crigler-Najjar disease and neonatal jaundice, carries the risk of neurotoxicity. This neurotoxicity is related to the increased passage of free bilirubin (UCB(free)), the fraction of bilirubin that is not bound to plasma proteins, into the brain. We hypothesized that albumin treatment would lower the UCB(free) fraction, and thus decrease bilirubin accumulation in the brain. METHODS: We treated chronic (e.g., as a model for Crigler-Najjar disease) and acute hemolytic (e.g., as a model for neonatal jaundice) moderate hyperbilirubinemic Gunn rats with phototherapy, human serum albumin (HSA) or phototherapy+HSA. RESULTS: In the chronic model, adjunct HSA increased the efficacy of phototherapy; it decreased plasma UCB(free) and brain bilirubin by 88% and 67%, respectively (p<0.001). In the acute model, adjunct HSA also increased the efficacy of phototherapy; it decreased plasma UCB(free) by 76% (p<0.001) and completely prevented the hemolysis-induced deposition of bilirubin in the brain. Phototherapy alone failed to prevent the deposition of bilirubin in the brain during acute hemolytic jaundice. CONCLUSIONS: We showed that adjunct HSA treatment decreases brain bilirubin levels in phototherapy-treated Gunn rats. We hypothesize that HSA decreases these levels by lowering UCB(free) in the plasma. Our results support the feasibility of adjunct albumin treatment in patients with Crigler-Najjar disease or neonatal jaundice.

Analysis of bilirubin UDP-glucuronosyltransferase gene mutations in an unusual Crigler-Najjar syndrome patient.

Crigler-Najjar (CN) syndrome is a rare autosomal recessive inherited disorder characterized by non-hemolytic, unconjugated hyperbilirubinemia. The levels of serum bilirubin and the response to phenobarbital treatment have been used to classify CN syndrome into two types: CN I and II. Mutations of the UGT1A1 gene have been found to be responsible for cases of CN syndrome. In the present study, the clinical features of a boy with an unusual type of CN syndrome were analysed. A DNA sample was obtained from the patient, and the promoter region, the exons and flanking intronic sequences of the UGT1A1 gene were analysed using the polymerase chain reaction and sequencing. The case was similar to CN type I in clinical features, but the therapeutic efficacy in the patient was superior to that typically observed in CN type II disease. Sequencing revealed compound heterozygous mutations, c.211G>A (p.G71R), c.1470C>T (p.D490D) and a normal homozygous A[TA]6TAA. No similar case has been reported worldwide and, considering the specific clinical features and therapeutic efficacy, a distinct type of CN was suspected. The phenotype of this unusual CN syndrome patient may be associated with the specific genotype.

Ezetimibe: A biomarker for efficacy of liver directed UGT1A1 gene therapy for inherited hyperbilirubinemia.

As recently demonstrated in patients with factor IX deficiency, adeno-associated virus (AAV)-mediated liver-directed therapy is a viable option for inherited metabolic liver disorders. Our aim is to treat Crigler-Najjar syndrome type I (CN I), an inherited severe unconjugated hyperbilirubinemia, as a rare recessive inherited disorder. Because the number of patients eligible for this approach is small, the efficacy can only be demonstrated by a beneficial effect on the pathophysiology in individual patients. Serum bilirubin levels in potential candidates have been monitored since birth, providing an indication of their pathophysiology. Adjuvant phototherapy to prevent brain damage reduces serum unconjugated bilirubin (UCB) levels in CN I patients to the level seen in the milder form of the disease, CN type II. This therapy increases the excretion of UCB, thereby complicating the use of UCB and conjugated bilirubin levels in serum as biomarkers for the gene therapy we try to develop. Therefore, a suitable biomarker that is not affected by phototherapy is currently needed. To this end, we have investigated whether estradiol, ethinylestradiol or ezetimibe could be used as markers for uridine 5'-di-phospho-glucuronosyltransferase isoform 1A1 (UGT1A1) activity restored by AAV gene therapy in Gunn rats, a relevant animal model for CN I. Of these compounds, ezetimibe appeared most suitable because its glucuronidation rate in untreated control Gunn rats is low. Subsequently, ezetimibe glucuronidation was studied in both untreated and AAV-treated Gunn rats and the results suggest that it may serve as a useful serum marker for restored hepatic UGT1A1 activity.

Mycophenolate mofetil impairs transduction of single-stranded adeno-associated viral vectors.

Adeno-associated virus (AAV) liver-directed gene therapy seems a feasible treatment for Crigler-Najjar syndrome type I, an inherited liver disorder characterized by severe unconjugated hyperbilirubinemia. Transient immunosuppression coupled with vector administration seems needed to overcome host immune responses that prevent long-term expression in patients. The immunosuppressive mycophenolate mofetil (MMF), which inhibits de novo synthesis of purines, is a promising candidate. To investigate the potential use of MMF in patients with Crigler-Najjar syndrome, we studied its effect on single-stranded AAV (ssAAV)-mediated correction of hyperbilirubinemia in the relevant preclinical model, the Gunn rat. Although MMF was well tolerated and effective it also impaired the efficacy of ssAAV. Subsequent in vitro studies showed that this effect is not specific for UGT1A deficiency. In fact, clinical relevant concentrations of mycophenolic acid (MPA), the active compound of MMF, also impair the transduction of HEK-293T cells by ssAAV. Because this effect was reversed by guanosine addition, it seems that intracellular levels of this nucleotide become limited, suggesting that MPA impairs second-strand DNA synthesis. This is corroborated by observations that MPA did not impair transduction of 293T cells by a self-complementary AAV (scAAV) vector and that MMF did not reduce the scAAV efficacy in the Gunn rat. In conclusion, MMF impairs ssAAV-mediated liver-directed gene therapy, which is relevant for the use of this immunosuppressive agent with single-stranded vectors. Furthermore, because this effect is due to impaired second-strand synthesis, the use of MMF with scAAV seems warranted.