Association between a frequent allele of the gene encoding OATP1B1 and enhanced LDL-lowering response to fluvastatin therapy

INTRODUCTION

Marked lowering of low-density-lipoprotein cholesterol (LDL-C) levels (< or =50%) with intensive statin therapy is associated with major reduction in cardiovascular risk, but is limited by a potential increase in adverse effects, thereby justifying optimization of LDL-C reduction with minimal risk. The organic anion transporting polypeptide-1B1 encoded by the SLCO1B1 gene is implicated as a major transporter in cellular uptake of statins, and notably fluvastatin. We postulated that genetic variation in SLCO1B1 might affect statin bioavailability, and might therefore influence drug response and potential adverse effects.

MATERIALS & METHODS

Elderly hypercholesterolemic subjects (n = 724), whose plasma lipid profile was determined before and 2 months after fluvastatin extended-release treatment (80 mg/day, n = 420), or placebo (n = 304), were genotyped for the most frequent nonsynonymous polymorphisms (SNP) in the SLCO1B1 gene (c.388A>G, c.463C>A and c.521T>C).

RESULTS

Due to linkage disequilibrium, only four alleles (*1b, *5, *14 and *15) of SLCO1B1 were detected in addition to the wild-type allele (*1a). The c.463A genotype, which was systematically associated with the c.388G SNP corresponding to the *14 allele was significantly associated with percentage LDL-C reduction from baseline (p = 0.005) and with mean post-treatment LDL-C values (p = 0.0005). Subjects homozygous for the c.463C genotype (n = 294) exhibited significantly less LDL-C reduction and higher post-treatment LDL-C levels (-31.5%, 138 mg/dl) relative to heterozygous C/A patients (-36.2%, 126 mg/dl; n = 111), and to homozygous A/A subjects (-41%, 115 mg/dl; n = 15).

CONCLUSIONS

These results reveal that OATP1B1 is implicated in the pharmacological action and efficacy of fluvastatin. Indeed, the common *14 allele, which is distinguished by the presence of the c.463C>A polymorphism, was associated with enhanced lipid-lowering efficacy in this study.

Liver insulin-like growth factor 2 methylation in hepatitis C virus cirrhosis and further occurrence of hepatocellular carcinoma

AIM: To assess the predictive value of the insulin-like growth factor 2 (Igf2) methylation profile for the occurrence of Hepatocellular Carcinoma (HCC) in hepatitis C (HCV) cirrhosis.

METHODS: Patients with: (1) biopsy-proven compensated HCV cirrhosis; (2) available baseline frozen liver sample; (3) absence of detectable HCC; (4) regular screening for HCC; (5) informed consent for genetic analysis were studied. After DNA extraction from liver samples and bisulfite treatment, unbiased PCR and DHPLC analysis were performed for methylation analysis at the Igf2 locus. The predictive value of the Igf2 methylation profile for HCC was assessed by Kaplan-Meier and Cox methods.

RESULTS: Among 94 included patients, 20 developed an HCC during follow-up (6.9 ± 3.2 years). The methylation profile was hypomethylated, intermediate and hypermethylated in 13, 64 and 17 cases, respectively. In univariate analysis, two baseline parameters were associated with the occurrence of HCC: age (P = 0.01) and prothrombin (P = 0.04). The test of linear tendency between the three ordered levels of Igf2 methylation and probability of HCC occurrence was significant (Log Rank, P = 0.043; Breslow, P = 0.037; Tarone-Ware, P = 0.039).

CONCLUSION: These results suggest that hypome-thylation at the Igf2 locus in the liver could be predictive for HCC occurrence in HCV cirrhosis.

Liver iron, HFE gene mutations, and hepatocellular carcinoma occurrence in patients with cirrhosis

BACKGROUND & AIMS

The influence of HFE gene mutations and liver iron overload on hepatocellular carcinoma (HCC) occurrence in patients with cirrhosis is subjected to controversial results. The aim of this work was to clarify this influence in a large cohort of prospectively followed-up cirrhotic patients classified according to the cause of their liver disease.

METHODS

Three hundred one consecutive cirrhotic patients (162 alcoholics and 139 HCV-infected patients) were included at time of diagnosis of cirrhosis and followed-up. Liver iron overload on initial biopsy according to modified Deugnier's score and C282Y/H63D HFE gene mutations were assessed.

RESULTS

In patients with alcoholic cirrhosis (mean iron score, 2.0 +/- 3.0; mean time of follow-up, 66.1 +/- 45.1 months), 40 (24.6%) developed HCC. Thirteen (8.02%) were heterozygotes for C282Y HFE gene mutation and had higher hepatic iron scores (3.6 +/- 3.8 vs 1.9 +/- 2.8, respectively, P = .05). In univariate analysis, liver iron overload as a continuous variable (HR, 1.23 [1.13-1.34], P < .001) or in binary coding with an optimal threshold of iron score >/=2.0 (HR, 4.1 [2.1-7.3], P < .0001) and C282Y mutation carriage (HR, 2.7 [1.2-6.3], P = .01) were risk factors for HCC. In multivariate analysis, liver iron and C282Y mutation carriage remained independent risk factors for HCC. In patients with HCV-related cirrhosis (C282Y mutation carriage, 17 [12.23%]; mean liver iron score, 0.9 +/- 1.9; mean time of follow-up, 85.5 +/- 42.1 months; HCC, 63 [45.32%] patients), C282Y mutation carriage and liver iron were not associated with HCC occurrence.

CONCLUSIONS

Liver iron overload and C282Y mutation are associated with a higher risk of HCC in patients with alcoholic but not HCV-related cirrhosis.

Loss of parental-specific methylation at the IGF2 locus in human hepatocellular carcinoma

Significant production of the growth factor IGF2 has been reported in human hepatocellular carcinomas (HCCs). Disturbances associated with changes in methylation at this locus or affecting the 11p15.5 imprinting domain as a whole can be postulated in HCCs. In the present study, the methylation status of differentially methylated regions of the imprinted genes TSSC5, LIT1, and IGF2, which span the 11p15 domain, was analysed in 71 liver tissues from virus-associated and non-virus-associated HCCs compared with six normal liver tissues. Altered methylation of TSSC5 and LIT1 was observed in only 6% and 8% of HCCs, respectively, compared with 89% at the IGF2 locus, suggesting that these loci were not concomitantly dysregulated. These observations suggest that loss of parental-specific methylation at the IGF2 locus may be specifically associated with HCC, whether virus-associated or non-virus-associated, and arising in cirrhotic or non-cirrhotic livers.

MECP2 gene mutations in non-syndromic X-linked mental retardation: Phenotype-genotype correlation

Non-syndromic X-linked mental retardation (MRX) is a frequent cause of inherited mental retardation. It is a heterogeneous condition in which the first 12 genes discovered to date explain no more than 15% of the MRX situations ascertained by recurrence in multiplex families. In Rett syndrome (RTT), an X-linked dominant condition mostly sporadic and usually lethal in males, most affected females have been shown to be mutated in the Methyl-CpG binding protein 2 gene (MECP2) that maps at Xq28. Some mentally retarded males related to RTT females carry the same mutation. Several MRX families mapping to Xq28 were subsequently tested for MECP2 and a causative mutation was discovered in three families, suggesting that it could be one of the main genes involved in MRX. We report here the corresponding phenotypes in these three families of increasing severity. In family 1, an in-frame deletion DeltaP387-M466 was found in the 3' region. The patients had severe to mild non-progressive MR, with better motor skills than verbal abilities. In family 2, an Arg to Trp substitution (R167W) was found between the transcription repression domain (TRD) and the methyl binding domain (MBD). The patients had brisk reflexes and essential tremor with mild and non-progressive MR, poor motor co-ordination and written language difficulties. In the third family (MRX16), a Glu to Gly substitution (E137G) was found in the MBD. The patients had manifestations similar to those of family 2, but MR was mild to moderate, speech articulation was poor and some had verbal stereotypies. Regression of language skills was suspected in three patients. Phenotype-genotype correlation could thus be suspected and is discussed in these three families.

In vitro follicular growth affects oocyte imprinting establishment in mice

In vitro folliculogenesis of cryopreserved ovarian tissue could be an effective method for insuring fertility for patients who receive gonadotoxic treatment. Although several culture systems have been described for growing female gametes in vitro, the production of competent oocytes for further development remains a considerable challenge. The purpose of our study was to determine whether maternal primary imprinting progresses normally during mouse oocyte growth in vitro. We analysed the DNA methylation status of differentially methylated regions of the imprinted genes H19, Mest/Peg1 and Igf2R using fully grown germinal vesicle-stage oocytes (fg oocytes) produced by in vitro folliculogenesis from early preantral follicles. When compared to fg oocytes removal from control females, we observed after in vitro development, a loss of methylation at the Igf2R locus in six out of seven independent experiments and Mest/Peg1 locus (one out of seven), and a gain of methylation at the H19 locus (one out of seven). These results provide insight into the dysregulation of the process of primary imprinting during oocyte growth in vitro and highlight the need for effective new biomarkers to identify complete nuclear reprogramming competence after in vitro folliculogenesis.

DHPLC-based method for DNA methylation analysis of differential methylated regions from imprinted genes

The bisulfite genomic sequencing method is one of the most widely used techniques for methylation analysis in heterogeneous unbiased PCR, amplifying for both methylated and unmethylated alleles simultaneously. However, it requires labor-intensive and time-consuming cloning and sequencing steps. In the current study, we used a denaturing high-performance liquid chromatography (DHPLC) procedure in a complementary way with the bisulfite genomic sequencing to analyze the methylation of differentially methylated regions (DMRs) of imprinted genes. We showed reliable and reproducible results in distinguishing overall methylation profiles of DMRs regions of human SNRPN, H19, MEST/PEG1, LIT1, IGF2, TSSC5, WT1 antisense, and mouse H19, Mest/Peg1, Igf2R imprinted genes. These DHPLC profiles were in accordance with bisulfite genomic sequencing data and may serve as a type of "fingerprint," revealing the overall methylation status of DMRs associated with sample heterogeneity. We conclude that DHPLC analysis could be used to increase the throughput efficiency of methylation pattern analysis of imprinted genes after the bisulfite conversion of genomic DNA and unbiased PCR amplification.

Active caspase-8 translocates into the nucleus of apoptotic cells to inactivate poly(ADP-ribose) polymerase-2

Caspase-8 is the prototypic initiator of the death domain receptor pathway of apoptosis. Here, we report that caspase-8 not only triggers and amplifies the apoptotic process at cytoplasmic sites but can also act as an executioner at nuclear levels. In a murine model of acute ischemia, caspase-8 is relocated into the nucleus of apoptotic neurons, where it cleaves PARP-2, a member of the poly(ADP-ribose) polymerase family involved in DNA repair. As indicated by site-directed mutagenesis, PARP-2 cleavage occurs preferentially at the LQMD sequence mapped between the DNA binding and the catalytic domains of the protein. This is close to the cleavage sequence found in Bid, the cytoplasmic target of caspase-8. Activity assays confirm that cleavage of PARP-2 results in inactivation of its poly(ADP-ribosylation) property, proportional to the efficiency of the cleavage. Our findings add to the complexity of proteolytic caspase networks by demonstrating that caspase-8 is in turn an initiator, amplifier, and effector caspase.

ARX, a novel Prd-class-homeobox gene highly expressed in the telencephalon, is mutated in X-linked mental retardation

Investigation of a critical region for an X-linked mental retardation (XLMR) locus led us to identify a novel Aristaless related homeobox gene (ARX ). Inherited and de novo ARX mutations, including missense mutations and in frame duplications/insertions leading to expansions of polyalanine tracts in ARX, were found in nine familial and one sporadic case of MR. In contrast to other genes involved in XLMR, ARX expression is specific to the telencephalon and ventral thalamus. Notably there is an absence of expression in the cerebellum throughout development and also in adult. The absence of detectable brain malformations in patients suggests that ARX may have an essential role, in mature neurons, required for the development of cognitive abilities.

Five novel frameshift mutations in exon 3 and 4 of the MECP2 gene identified in Rett patients: Consequences for the molecular diagnosis strategy

Rett syndrome (RTT) is a severe progressive neurological disorder that affects almost exclusively females. The gene responsible for this disorder, MECP2, was recently identified by candidate gene strategy. Mutations were detected in 70-85% of RTT cases. We report here five novel frameshift mutations (named 345delC, 895del202, 989ins18del8, 996insAG and 1124del53) in exon 3 and 4 of the MECP2 gene. To avoid the missing of few small deletions in RTT patients using classical mutation screening approaches, we suggest that screening of the mutations in the MECP2 gene in RTT girls should include at least a large PCR to amplify exon 4 entirely.

MECP2 is highly mutated in X-linked mental retardation

Following the recent discovery that the methyl-CpG binding protein 2 (MECP2) gene located on Xq28 is involved in Rett syndrome (RTT), a wild spectrum of phenotypes, including mental handicap, has been shown to be associated with mutations in MECP2. These findings, with the compelling genetic evidence suggesting the presence in Xq28 of additional genes besides RabGDI1 and FMR2 involved in non-specific X-linked mental retardation (MRX), prompted us to investigate MECP2 in MRX families. Two novel mutations, not found in RTT, were identified. The first mutation, an E137G, was identified in the MRX16 family, and the second, R167W, was identified in a new mental retardation (MR) family shown to be linked to Xq28. In view of these data, we screened MECP2 in a cohort of 185 patients found negative for the expansions across the FRAXA CGG repeat and reported the identification of mutations in four sporadic cases of MR. One of the mutations, A140V, which we found in two patients, has been described previously, whereas the two others, P399L and R453Q, are novel mutations. In addition to the results demonstrating the involvement of MECP2 in MRX, this study shows that the frequency of mutations in MECP2 in the mentally retarded population screened for the fragile X syndrome is comparable to the frequency of the CGG expansions in FMR1. Therefore, implementation of systematic screening of MECP2 in MR patients should result in significant progress in the field of molecular diagnosis and genetic counseling of mental handicap.

Parental origin of de novo MECP2 mutations in Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder occurring almost exclusively in females as sporadic cases. Recently, DNA mutations in the MECP2 gene have been detected in approximately 70% of patients with RTT. To explain the sex-limited expression of RTT, it has been suggested that de novo X-linked mutations occur exclusively in male germ cells resulting therefore only in affected daughters. To test this hypothesis, we have analysed 19 families with RTT syndrome due to MECP2 molecular defects. In seven informative families we have found by DHPLC a nucleotide variant which could be used to differentiate between the maternal and the paternal allele. In each subject investigated from these families, we have amplified specifically each allele and sequenced allele-specific PCR products to identify the allele bearing the mutation as well as the parental origin of each X chromosome. This approach allowed us to determine the parental origin of de novo mutations in all informative families. In five cases, the de novo MECP2 mutations have a paternal origin and in the two other cases a maternal origin. In all transitions at CpG, the de novo mutation observed was of paternal origin. The high frequency of male germ-line transmission of the mutation (71% of RTT informative cases) is consistent with a predominant occurrence of the disease in females.

Missense mutation in PAK3, R67C, causes X-linked nonspecific mental retardation

X-linked mental retardation is a very common condition that affects approximately 1 in 600 males. Despite recent progress, in most cases the molecular defects underlying this disorder remain unknown. Recently, a study using the candidate gene approach demonstrated the presence of mutations in PAK3 (p21-activating kinase) associated with nonspecific mental retardation. PAK3 is a member of the larger family of PAK genes. PAK proteins have been implicated as critical downstream effectors that link Rho-GTPases to the actin cytoskeleton and to MAP kinase cascades, including the c-Jun amino-terminal kinase (JNK) and p38. We screened 12 MRX pedigrees that map to a large region overlying Xq21-q24. Mutation screening of the whole coding region of the PAK3 gene was performed by using a combination of denaturing gradient gel electrophoresis and direct sequencing. We have identified a novel missense mutation in exon 2 of PAK3 gene (R67C) in MRX47. This confirms the involvement of PAK3 in MRX following the report of a nonsense mutation recently reported in MRX30. In the MRX47 family, all affected males show moderate to severe mental retardation. No seizures, statural growth deficiency, or minor facial or other abnormal physical features were observed. This mutation R67C is located in a conserved polybasic domain (AA 66-68) of the protein that is predicted to play a major role in the GTPases binding and stimulation of Pak activity.

MECP2 mutations account for most cases of typical forms of Rett syndrome

Rett syndrome (RTT) is a severe progressive neurological disorder that affects almost exclusively females, with an estimated prevalence of approximately one in 10 000-15 000 female births. Most cases are sporadic, but several reports about familial recurrence support X-linked dominant inheritance with male lethality. The gene responsible for this disorder, MECP2, was recently identified by candidate gene strategy. Mutations were detected in <25% of RTT cases in this first report. To characterize the spectrum of mutations in the MECP2 gene in RTT patients, we selected 46 typical RTT patients and performed mutation screening by denaturing gradient gel electrophoresis combined with direct sequencing. We identified 30 mutations, accounting for 65% of RTT patients. They include 12 novel mutations (11 located in exon 3 and one in exon 2). Mutations, such as R270X and frameshift deletions in a (CCACC) (n) rich region, have been found with multiple recurrences. Most of the mutations were de novo, except in one family where the non-affected transmitter mother exhibited a bias of X inactivation. Although this study showed that MECP2 mutations account for most cases of typical forms of RTT (65%) and mutations in non-coding regions cannot be excluded for the remaining cases, an alternative hypothesis that takes into account the homogeneous phenotype and exclusive involvement of females, could be the implication in RTT of a putative second X-linked gene.