Genetic risk factors for clozapine-induced neutropenia and agranulocytosis in a Dutch psychiatric population

Prescription of clozapine is complicated by the occurrence of clozapine-induced reduction of neutrophils. The aim of this study was to identify genetic risk factors in a population of 310 Dutch patients treated with clozapine, including 38 patients developing neutropenia and 31 patients developing agranulocytosis. NQO2 1541AA (NRH quinone oxidoreductase 2; protects cells against oxidative metabolites) was present at a higher frequency in agranulocytosis patients compared with control (23% versus 7%, P=0.03), as was ABCB1 (ABC-transporter-B1; drug efflux transporter) 3435TT (32% versus 20%, P=0.05). In patients developing neutropenia, ABCB1 3435TT and homozygosity for GSTT1^null (glutathione-S-transferase; conjugates reactive clozapine metabolites into glutathione) were more frequent compared with control (34% versus 20%, P=0.05 and 31% versus 14%, P=0.03), whereas GSTM1^null was less frequent in these patients (31% versus 52%, P=0.03). To investigate whether combinations of the identified genetic risk factors have a higher predictive value, should be confirmed in a larger case-control study.

Pharmacogenetics: from bench to byte--an update of guidelines

Currently, there are very few guidelines linking the results of pharmacogenetic tests to specific therapeutic recommendations. Therefore, the Royal Dutch Association for the Advancement of Pharmacy established the Pharmacogenetics Working Group with the objective of developing pharmacogenetics-based therapeutic (dose) recommendations. After systematic review of the literature, recommendations were developed for 53 drugs associated with genes coding for CYP2D6, CYP2C19, CYP2C9, thiopurine-S-methyltransferase (TPMT), dihydropyrimidine dehydrogenase (DPD), vitamin K epoxide reductase (VKORC1), uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), HLA-B44, HLA-B*5701, CYP3A5, and factor V Leiden (FVL).

D3 dopamine receptor mRNA expression in lymphocytes: a peripheral marker for schizophrenia?

BACKGROUND

Identification of schizophrenia, a common neuropsychiatric disorder, is based on clinical examination. An easily measurable peripheral marker, which may enable a more rapid and more accurate diagnosis, is not available. A possible candidate is the D3 dopamine receptor on lymphocytes.

OBJECTIVE

The D3 receptor is investigated for its clinical significance as a marker for diagnosing schizophrenia.

METHODS

From eight schizophrenic patients and eight controls lymphocyte RNA was isolated. A semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was carried out and the intensities of the specific D3 dopamine receptor bands of patients and controls were compared.

RESULTS

No difference could be seen between the intensities of the bands from patients and controls.

CONCLUSION

An aberrant D3 dopamine receptor mRNA expression in lymphocytes of schizophrenics could not be demonstrated. This might be caused by down-regulation of D3 receptor production by antipsychotic drug treatment. At present, the D3 receptor seems to have no diagnostic value in schizophrenia.

The effect of genetic polymorphism of cytochrome P450 CYP2C9 on phenytoin dose requirement

The cytochrome P450 enzyme CYP2C9 catalyses the metabolism of numerous therapeutic agents, including the anti-epileptic drug phenytoin. CYP2C9 is genetically polymorphic: two allelic variants are known, CYP2C9*2 and CYP2C9*3, differing from the wild-type CYP2C9*1 by a single point mutation. Both mutant alleles are associated with markedly impaired metabolic capacity for many CYP2C9 substrates compared to the wild-type, resulting in raised serum drug levels upon a given dose. Because this may be relevant in treatment with phenytoin, we studied the effect of CYP2C9 genotype on phenytoin dose requirement in a group of 60 epileptic patients on long-term phenytoin therapy. CYP2C9 genotyping was performed by polymerase chain reaction analysis, phenytoin serum concentrations were measured by high-performance liquid chromatography analysis and related to the maintenance doses. For patients carrying at least one mutant CYP2C9 allele (n = 17), the mean phenytoin dose required to achieve a therapeutic serum concentration was about 37% lower than the mean dose required by wild-type individuals (199 mg/day versus 314 mg/day; P < 0.01). A low maintenance dose (< 200 mg/day) sufficed for 47% of carriers, while 58% of normals required a high dose (> 300 mg/day) for an effective serum level. The results show that there is a strong association between CYP2C9 allelic variants and phenytoin dose requirement. Since phenytoin has a narrow therapeutic index and genotyping may be carried out rapidly and at low cost, dosage adjustment based on CYP2C9 genotype, especially at the induction of therapy, would be of value in order to lower the risk of concentration dependent drug intoxications in carriers.

[Maintenance dose requirement for phenytoin is lowered in genetically impaired drug metabolism independent of concommitant use of other antiepileptics]

OBJECTIVE

To investigate the effect of genetically determined impaired drug metabolism and of the use of comedication on phenytoin maintenance dose requirement.

DESIGN

Descriptive.

METHOD

In 60 patients on long-term phenytoin therapy the concentration of phenytoin in serum was measured and CYP2C9 genotyping was performed (mutant alleles of CYP2C9 are associated with impaired phenytoin metabolism). In addition, the use of other antiepileptics concurrently with phenytoin was reviewed: phenobarbital, carbamazepine and valproic acid. CYP2C9 genotype and comedication were connected to phenytoin daily dose requirement. The 60 patients were 38 men and 22 women, between 16 and 74 years of age, and all mentally disabled.

RESULTS

Genotyping revealed that of the 60 patients 38% (n = 23) carried at least one mutant CYP2C9 allele. Their mean dose of phenytoin was 199 mg dd, while the mean required maintenance dose in non-carriers (n = 37) was 287 mg dd (p < 0.01). When the use of comedication was taken into account, it appeared that the mean phenytoin daily doses in the different comedication groups did not differ significantly.

CONCLUSION

Patients with a genetically determined impaired phenytoin metabolism required on average a 30% lower dose than those with a normal metabolism, while the concomitant use of other antiepileptics appeared to have no effect on phenytoin dose requirement.

Cytochrome P450 enzyme system: genetic polymorphisms and impact on clinical pharmacology

The cytochrome P450 (CYP) enzyme system is involved in the metabolism and elimination of numerous widely used drugs. The capacity of this system varies from one person to another, leading to variable drug excretion rates and intersubject differences in the final serum drug concentrations. For this reason, therapeutic response and side-effects vary widely between patients treated with the same dose of drug. The intersubject variability in metabolic rate is largely determined by genetic factors. Some CYP enzymes, including CYP2D6 and CYP2C19, are genetically polymorphic. Several mutant alleles have been described, Environmental factors such as smoking, diet and co-administration of medications might also influence the CYP enzyme activity. By the use of genotyping or phenotyping methods every individual can be classified as either a poor, an intermediate, an extensive or an ultrarapid metabolizer. If this could be performed prior to drug therapy, the knowledge could be applied to drug selection and dose adjustment in order to reach therapeutic serum drug levels.

Evaluation of nonisotopic binding assays for measuring vitamin B12 and folate in serum

We report the evaluation of the microparticle enzyme immunoassay (MEIA) for estimating vitamin B12 and the ion capture (IC) assay for estimating folate in serum. The assays were performed with the Abbott IMx analyzer. Intra-assay coefficients of variation were from 3.4% to 8.0% for vitamin B12 and from 1.5% to 4.2% for folate, respectively. Interassay coefficients of variation ranged from 6.3% to 8.8% for vitamin B12 and from 3.9% to 11.3% for folate, respectively. Linearity was satisfactory, with an analytical recovery of 119 +/- 4% for vitamin B12 and 95 +/- 8% for folate. The detection limit was 56.2 pmol/l for vitamin B12 and 1.9 nmol/l for folate. Results of these assays correlated well with those from the cloned enzyme donor immunoassay (CEDIA), our current routine method: r = 0.97 for vitamin B12 (n = 47) and r = 0.97 for folate (n = 50). The MEIA and the IC assay were easy to perform with the IMx analyzer.

[Apolipoprotein E polymorphism and Alzheimer disease]

At present a reliable and specific diagnostic test of Alzheimer's disease is not available. Thus far, diagnosis is based on clinical criteria despite their occasional inadequacy. Post mortem search for neuropathological hallmarks can establish the diagnosis with certainty. In the present case control study we performed an apoE genotyping for 21 patients, divided into an Alzheimer-positive and an Alzheimer-negative group after neuropathological search. As described in the literature, the apoE-epsilon 4 allele was overrepresented in the Alzheimer-positive group, while in the Alzheimer-negative group the apoE-epsilon 3 allele dominated. The epsilon 4 allele of the apoE gene may be considered as a biological risk factor for the development of Alzheimer's disease. Especially in geriatric patients with cognitive impairment, apoE genotyping seems to be a supplementary tool for risk assessment.

Evaluation of the cloned enzyme donor immunoassay for measurement of phenytoin and phenobarbital in serum

We report the evaluation of the cloned enzyme donor immunoassay (CEDIA) for the estimation of phenytoin and phenobarbital in serum. The assays were performed with a Hitachi 911 analyzer. Intra-assay coefficients of variation were from 1.5 to 4.4% for phenytoin and 1.6 to 5.5% for phenobarbital. Interassay coefficients of variation ranged from 1.8 to 5.3% for phenytoin and 2.9 to 4.8% for phenobarbital. Linearity was satisfactory, with a recovery of 103% at 11 mg/L and 110% at 22 mg/L phenytoin and 93% at 14 mg/L and 101% at 40 mg/L for phenobarbital. The detection limit was 1.2 mg/L for phenytoin and 0.6 mg/L for phenobarbital. Results of this assay correlated well with those of a conventional high-performance liquid chromatography (HPLC) method; r = 0.99 for phenytoin (n = 47) and r = 0.98 for phenobarbital (n = 48). The CEDIA was easy to handle and especially suitable for short turn-around time application.

Nonisotopic Binding Assay for Measuring Vitamin B12 and Folate in Serum

We evaluated a nonisotopic method (CEDIA; cloned enzyme donor immunoassay) for estimating vitamin B12 and folate in serum. The assays were performed with a Cobas-Mira analyzer. Intra-assay CVs were from 3.7% to 11.0% for vitamin B12 and from 1.2% to 10.7% for folate. Interassay CVs ranged from 9.5% to 11.9% for vitamin B12 and from 6.1% to 18.5% for folate. Linearity was satisfactory, with analytical recovery of 94% at 8.7 and 25.4 nmol/L for folate and 280 and 554 pmol/L for vitamin B12. The detection limit was 3.6 nmol/L for folate and 12.3 pmol/L for vitamin B12. Results of this assay correlated well with those of a conventional radioassay: r = 0.98 for vitamin B12 (n = 51) and r = 0.97 for folate (n = 57). The CEDIA was easy to perform but appeared to be unreliable for use with samples from myeloma patients.

Nonisotopic binding assay for measuring vitamin B12 and folate in serum

We evaluated a nonisotopic method (CEDIA; cloned enzyme donor immunoassay) for estimating vitamin B12 and folate in serum. The assays were performed with a Cobas-Mira analyzer. Intra-assay CVs were from 3.7% to 11.0% for vitamin B12 and from 1.2% to 10.7% for folate. Interassay CVs ranged from 9.5% to 11.9% for vitamin B12 and from 6.1% to 18.5% for folate. Linearity was satisfactory, with analytical recovery of 94% at 8.7 and 25.4 nmol/L for folate and 280 and 554 pmol/L for vitamin B12. The detection limit was 3.6 nmol/L for folate and 12.3 pmol/L for vitamin B12. Results of this assay correlated well with those of a conventional radioassay: r = 0.98 for vitamin B12 (n = 51) and r = 0.97 for folate (n = 57). The CEDIA was easy to perform but appeared to be unreliable for use with samples from myeloma patients.

[A family with hereditary spherocytosis discovered after an infection with human parvovirus B19]

Hereditary spherocytosis was diagnosed in five of six children in one family after a human parvovirus B19 (B19-virus) infection. The diagnosis was made on the basis of severe anaemia, demonstrable haemolysis, decreased osmotic fragility and an increased number of spherocytes. Since in the serum of the patients an increased level of IgG and IgM antibodies against B19 virus was detectable two weeks after the crisis it was concluded that the B19-virus infection caused the severe anaemia.

Autoradiographic localization of dopamine D2 receptors in the rat brain using the new agonist [3H]N-0437

The selective dopamine D2 agonist [3H]N-0437 was used to label dopamine receptors in vitro in slide-mounted rat brain microtome sections. The characteristics of the binding of [3H]N-0437 to tissue section were similar to those observed previously in membrane preparations and indicated that this ligand labels sites with the properties of a dopamine D2 receptor. The regional distribution of these receptors was examined by autoradiography and quantified by computer-assisted microdensitometry. The highest densities of [3H]N-0437 sites were observed in the nucleus caudate-putamen, accumbens, olfactory tubercle, island of Calleja and the glomerular layer of the olfactory bulb. Lower densities of binding sites were seen in stratum griseum superficialis of the superior colliculus, substantia nigra pars compacta and area ventral tegmental, entorhinal cortex and in the molecular layer of the 9th and 10th lobules of the cerebellum. Very low densities were seen in the neocortex and hippocampal formation. The density of [3H]N-0437 binding sites in the rat striatum are higher than those observed with other dopamine D2 [3H]agonists and comparable to those seen with [3H]antagonists. [3H]N-0437 is a new useful tool for the anatomical localization of dopamine D2 receptors in brain.