摘要:

Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurines such as mercaptopurine and thioguanine. TPMT activity exhibits genetic polymorphism, with about 1 in 300 inheriting TPMT-deficiency as an autosomal recessive trait. If treated with standard dosages of thiopurines, TPMT-deficient patients accumulate excessive thioguanine nucleotides (TGN) in hematopoietic tissues, leading to severe hematopoietic toxicity that can be fatal. However, TPMT-deficient patients can be successfully treated with a 10-15-fold lower dosage of these medications. The human gene encoding polymorphic TPMT has been cloned and characterized, and two mutant alleles have recently been isolated from TPMT-deficient and heterozygous patients (TPMT*2, TPMT*3), permitting development of PCR-based methods to identify TPMT-deficient and heterozygous patients prior to therapy. TPMT*3 is the predominant mutant allele in American whites, accounting for about 75% of mutations in this population. Ongoing studies aim to better define the influence of TPMT activity on thiopurine efficacy, to identify additional mutant alleles and determine their frequency in different ethnic groups, to elucidate the mechanism(s) for loss of function of mutant proteins, to identify potential endogenous substrates and to define the molecular mechanisms of TPMT regulation. Together, these advances hold the promise of improving the safety and efficacy of thiopurine therapy.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We investigated the involvement of CYP1A2 in the pharmacokinetics and metabolism of caffeine using mice lacking its expression (CYP1A2-/-). The half-life of caffeine elimination from blood was seven times longer in the CYP1A2 -/- than wild-type mice. The clearance was concomitantly eight times slower. No parameter that could affect the pharmacokinetics differed between CYP1A2 -/- and wild-type mice such as creatinine for kidney function; alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and bilirubin for liver function; or albumin for protein binding. Other P450s CYP2A, 2B, 2C, 2E1, and 3A were also unchanged in the knockout animals. Caffeine 3-demethylated metabolites thought previously to be characteristic of CYP1A2 (especially 1 -methylxanthine and 1-methylurate) were also found in the urines of the CYP1A2 -/- animals, although at 40% of the level found in wild-type mice. These data indicate that the clearance of caffeine in wild-type mice is primarily determined by CYP1A2.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

In order to investigate the prevalence of the Taq I A1allele of the dopamine receptor gene (DRD2) in obesity with and without comorbid substance use disorder, a total of 40 patients, from an outpatient neuropsychiatric clinic in Princeton, New Jersey, were genotyped for presence or absence of the Taq IDRD2A1allele. The primary inclusion criterion for 40 obese subjects was a body mass index (BMI) equal to or over 25 (uncharacterized); 11 obese subjects had severe substance use disorder; 20 controls had a BMI below 25; and, 33 substance use disorder (less severe) patients had a BMI below 25. The data were statistically compared with three different sets of controls divided into three separate groups (Group I, n=20; Group II, n=286; Group III, n=714). They differed according to screening criteria (drug, alcohol, nicotine abuse/dependence, BMI below 25 and other related behaviours including parental history of alcoholism or drug abuse and DSM IV, Axis I and Axis II diagnoses). Groups II and III were population controls derived from the literature. The prevalence of the Taq I A1D2dopamine receptor (DRD2) alleles was determined in 40 Caucasian obese females and males. In this sample with a mean BMI of 32.35 ± 1.02, the A1allele of the DRD2gene was present in 52.5% of these obese subjects. Furthermore, we found that in the 23 obese subjects possessing comorbid substance use disorder, the prevalence of the DRD2A1allele significantly increased compared to the 17 obese subjects without comorbid substance use disorder. The DRD2A1allele was present in 73.9% of the obese subjects with comorbid substance use disorder compared to 23.5% in obese subjects without comorbid substance use disorder. Moreover, when we assessed severity of substance usage (alcoholism, cocaine dependence, etc.) increasing severity of drug use increased the prevalence of the Taq IDRD2A1allele; where 66.67% (8/12) of less severe probands possessed the A1allele compared to 82% (9/11) of the most severe cases. Linear trend analyses showed that increasing use of drugs was positively and significantly associated with A1allelic classification (p<0.00001). These preliminary data suggest that the presence of the DRD2A} allele confirms increased risk not only for obesity, but also for other related addictive behaviours (previously referred to as the Reward Deficiency Syndrome) and that a BMI over 25 by itself (without characterization of macroselection or comorbid substance use disorders) is not a sufficient criterion for association with the DRD2A1allele

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Defects in serotonin metabolism, and abnormalities in both blood serotonin and tryptophan levels, have been reported in many psychiatric disorders. Tryptophan 2,3-dioxygenase (TDO2) is the rate limiting enzyme for the breakdown of tryptophan to JV-formyl kenurenine. Functional variants of this gene could account for the observed simultaneous increases or decreases of both serotonin and tryptophan in various disorders. We have identified four different polymorphisms of the human TDO2 gene. Association studies show a significant association of one or more of these polymorphisms and Tourette syndrome (TS), attention deficit hyperactivity disorder (ADHD) and drug dependence. The intron 6G-Tvariant was significantly associated with platelet serotonin levels. Only the association with TS was significant with a Bonferroni correction (p=0.005). Our purpose here is not to claim these associations are proven, but rather to report preliminary results and show that easily testable polymorphisms are available. We hope to encourage additional research into the potential role the TDO2 gene in these and other psychiatric disorde.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The majority of humans deficient in the cytochrome P450 CYP2D6 enzyme, so-called poor metabolizers (PMs), can now be identified by genotyping for several different PM-associated mutations. However, additional null alleles remain to be identified as demonstrated by subjects with the PM phenotype in the absence of a corresponding genotype. The rare 11 kb band on Xba I RFLP analysis, which is distinct from the 13 kb CYP2D6D (CYP2D6*5) allele, has been proposed to constitute such a unique non-functional allele. Here we demonstrate that the 11 kb band represents at least two different nine exon CYP2D7P/CYP2D6 hybrids generated by large deletions in the CYP2D gene cluster due to unequal cross-over or looping- out mechanisms. The total allele frequency was approximately 0.001-0.01 in European and North American Caucasians. The most common variant (CYP2D6*16) had breakpoints lying between the end of exon 7 and the start of exon 9 of the respective genes. The 'CFP2D7-like' part of the gene was most homologous to the previously described CYP2D7AP and CYP2D7(44/11.5) sequences. The other chimeric allele consisted of exon 1 of CYP2D7 and exons 2-9 from CYP2D6, and may be similar to a hybrid gene termed CYP2D6*13 recently described in a French individual. Two different routine PCR assays were developed for rapid and sensitive detection of these alleles, namely amplification of a 8 kb fragment from both CYP2D6*13 and CYP2D6*16, together with a CYP2D6*16-specific method which gave a 1.4 kb PCR product. The 8 kb assay for the CYP2D6*13 and CYP2D6*16 alleles also produced a 9.5 kb fragment in samples positive for the 13 kb CYP2D6*5 allele. Therefore, it is now possible to screen for the large CYP2D gene deletions by a single long PCR method.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The CYP2C19-associated oxidation polymorphism of mephenytoin was investigated in an Inuit population living in the high Arctic of Canada. Results were obtained for 152 subjects, of whom 90 were unrelated to first degree relatives. Phenotyping was based on the capillary gas chromatographic determination of the S/R enantiomeric ratio in overnight urine collected after a dose of 100 mg (K,S)-mephenytoin. The phenotype was confirmed by determining the S/R enantiomeric ratio after acid treatment of urine samples, and for some subjects, by determining urinary recovery of 4'-hydroxymephenytoin using capillary electrophoresis analysis. DNA was analysed for the ml and m2 mutations of CYP2C19. Three of 152 subjects (2.0%; 95% confidence limits: 0.0-4.2%) were phenotypically classified as poor metabolizers (PMs). Genotype analysis characterized three individuals as homozygous, and 28 individuals as heterozygous for the ml mutation, the remaining individuals being homozygous for the wild-type allele. The genotype of the three PMs was concordant with that of the phenotype. DNA fingerprinting confirmed that these three individuals were genetically unrelated. The allele frequency of the CYP2C19mI mutation, determined in unrelated subjects, was 0.12 (95% confidence limits: 0.07-0.17). CYP2C19m2 was not detected in this population. Thus, the Canadian Inuit resemble Caucasian rather than Asian populations in both the incidence of PM phenotype and the molecular basis of the polymorphism.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Tolbutamide undergoes hydroxylation in humans via a cytochrome P450-mediated pathway. The primary P450 isozyme responsible for this metabolism is thought to be CYP2C9. Population studies have indicated the existence of slow metabolizers of tolbutamide (~1 in 500) suggesting a rare polymorphism associated with 2C9. Several allelic variants of 2C9 have been identified; however, the effect of these allelic variations on metabolism in vivo is not established. In the present study, the coding regions, intron-exon junctions, and upstream region of CYP2C9 were amplified by PCR and sequenced in two slow metabolizers. One individual was homozygous for Leu359/Leu359and the other individual was heterozygous for Arg/Cys144and for Ile359/Leu359. No other genetic variations in 2C9 were detected in these individuals. PCR-RFLP tests showed that Arg144Tyr358Ile359Gly417is the principle CYP2C9 allele. Frequencies of the rarer Leu359and Cys144alleles were 0.06 and 0.08, respectively, in a Caucasian-American population and 0.005 and 0.01 respectively in African-Americans. The frequency of the Leu359allele was 0.026 in Chinese-Taiwanese, but the Cys144allele was not detected in this population. Studies in a recombinant yeast expression system showed that the Leu359variant had the highest Km and the lowest Vmac for hydroxylation of tolbutamide of all the CYP2C9 allelic variants. This allelic variant also had the highest Km for the 7-hydroxylation of S-warfarin. The present data suggest that the incidence of the Leu359allelic variant of CFP2C9 may account for the occurrence of poor metabolizers of tolbutamide.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The debrisoquine hydroxylase (CYP2D6), which metabolizes more than 30 different drugs, is highly polymorphic. In subjects having either very low or very high enzyme activity, drug therapy at recommended doses using CYP2D6 substrates may lead to either increased risk of side effects or therapeutic failure. We here describe PCR-based methods for detection of alleles having either duplicated, multiduplicated or deleted active CYP2D6 genes. As a control reaction, the entire coding region of the CYP2D6 gene is amplified. In conjunction with analysis of common mutations using this product as a template, the methods described can be used for genotyping of individuals being either poor, intermediate rapid, normal or ultrarapid metabolizers and provides an efficient tool for individualization of drug therapy.

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0960-314X    

出版商:OVID    

年代:1996

数据来源: OVID