Brain Dopamine–Serotonin Vesicular Transport Disease and Its Treatment

Known disorders of biogenic amine neuromediators (dopamine, norepinephrine, epinephrine, and serotonin) involve defects in nine enzymes1-9 and one transporter.10 Affected persons present in early childhood with symptoms referable to the affected neurotransmitter, and the disorders are diagnosed by measurement of neurotransmitter breakdown products in the cerebrospinal fluid (CSF). A deficiency in dopamine results in movement disorder; deficient norepinephrine or epinephrine causes autonomic dysfunction; and serotonin deficiency leads to sleep and psychiatric disturbances.2,3,6
We describe members of a family with symptoms of deficiencies in dopamine (dystonia, parkinsonism, and oculogyric crises), serotonin (sleep and mood disturbance), and epinephrine and norepinephrine (diaphoresis, temperature instability, ptosis, and postural hypotension), with no demonstrable deficiency of neurotransmitters in the CSF. Genome investigation revealed a mutation in the gene encoding VMAT2 that compromises transport of biogenic amines into synaptic vesicles, resulting in impairment of their synaptic transmission without detectable reductions in their amounts.

 Brain Dopamine–Serotonin Vesicular Transport Disease and Its Treatment

Редкая генетическая аномалия как фактор риска развития шизофрении

Approximately 30 percent of people with a genetic disorder known as 22q11 deletion syndrome develop schizophrenia, making it one of the strongest risk factors for the disease.

 Rare genetic disorder points to molecules that may play role in schizophrenia

Генетические вариации эндоканнабиноидной системы и ответ на терапию циталопрамом

First line treatment of major depression is based on selective serotonin re-uptake inhibitors (SSRIs) that enhance serotonergic neurotransmission by blocking the serotonin transporter. However, clinical response is a complex phenomenon in which other systems such as the endocannabinoid system could be involved. Given the evidence for the role of the endocannabinoid system in the pathogenesis of depression as well as in the mediation of antidepressant drug effects, the aim of this study was to analyze genetic variability in the endocannabinoid system genes (CNR1, CNR2 and FAAH genes) and their role in clinical response (at week 4) and remission (at week 12) in SSRI (citalopram) treatment in a sample of 154 depressive outpatients, all of Spanish origin. All patients were treated with citalopram and followed over 12 weeks. Severity of depressive symptomatology was evaluated by means of the 21-item Hamilton Depression Rating Score (HDRS). No differences were found in any of the genotype distributions according to response or remission. The longitudinal study showed that (i) the CNR1 rs1049353-GG genotype conferred a better response to citalopram treatment in the subgroup of male patients and (ii) G allele carriers (CNR2 rs2501431) presented higher HDRS scores in the follow-up than AA homozygous allele carriers. Our results seem to suggest the involvement of CNR1 and CNR2 genes in clinical responses to citalopram treatment.

 Genetic variability in the endocannabinoid system and 12-week clinical response to citalopram treatment: the role of the CNR1, CNR2 and FAAH genes

Фолаты могут ослаблять негативную симптоматику у некоторых больных шизофренией

Folate supplementation appears to improve negative symptoms in schizophrenia patients, but only among those with a genetic variant of a folate-metabolizing enzyme, study results show.

It follows an earlier study by the same group showing that schizophrenia patients with low serum folate levels who were also homozygous for the 677C>T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene had severe negative symptoms.

Folate may improve negative symptoms in some schizophrenia patients

механизм работы СИОЗС

In a recent publication in Science, a team of researchers showed a possible mechanism of action for Fluoxetine. According to these scientists, it works through a completely new inhibitory pathway, which can also explain the lengthy and for patients often very frustrating waiting time before SSRIs work clinically. They found that in mice chronically fed with Fluoxetine, the expression of the gene that encodes the blueprint of SERT is reduced, which means less SERT is available to remove serotonin from the synapse. This is a surprising finding in itself, still, the mechanism how Fluoxetine down-regulates the SERT expression is even more surprising.

How Prozac works

Генотипы CYP450 и эффекты антипсихотиков

Metabolism of most antipsychotics depends on the CYP450 enzyme system, which is expressed predominantly in the liver (Table 1). CYP2D6 is one of these enzymes and may be responsible for metabolizing approximately 20% to 50% of all medications, including a number of antipsychotics.2 Genetic variations of CYP2D6 are common and the frequencies of these variants differ among racial groups.3

The half-life and other pharmacokinetic parameters of an antipsychotic metabolized by CYP2D6 may differ based on whether someone is a poor metabolizer (PM), intermediate metabolizer (IM), extensive metabolizer (EM), or ultrarapid metabolizer (UM).4 Regarding CYP2D6 metabolism among Whites, 3% to 5% are UMs, 70% to 80% are EMs, 10% to 17% are IMs, and 5% to 10% are PMs.5 By contrast, the percentage of PMs and UMs in the Asian population is low—about 1% for each phenotype; the IM phenotype is more common (65% to 70% in the Chinese population).5,6 The percentage of PMs in African Americans is roughly 2% to 6%.2

Cytochrome P450 (CYP) metabolism of commonly used antipsychotics*

Drug	CYP1A2	CYP2C9	CYP2C19	CYP2D6	CYP3A4/5
Aripiprazole				X	X
Asenapine	X			X	X
Chlorpromazine	X			X	X
Clozapine	X	X	X	X	X
Fluphenazine				X
Haloperidol	X			X	X
Iloperidone				X	X
Olanzapine	X			X
Paliperidone				X†	X†
Perphenazine	X	X	X	X	X
Quetiapine				X	X
Risperidone				X	X
Thioridazine			X	X
Ziprasidone	X				X
*Information obtained from the most recent prescribing information available from each drug’s manufacturer †According to paliperidone’s prescribing information, in vitro studies identify that CYP2D6 and CYP3A4 may be involved in paliperidone metabolism, but in vivo studies indicate that their role in eliminating paliperidone is minimal

Figure: Effects of CYP2D6 poor metabolizer status on the half-life of risperidone, aripiprazole, and iloperidone

EM: extensive metabolizer; PM: poor metabolizer
Source: References 7-9

It is not known if obtaining genotype information will provide better outcomes than a ‘trial and error’ approach

Should you order genetic testing to identify how patients metabolize antipsychotics?

Полиморфизм гена DRD2 и эффективность антипсихотической терапии

The DRD2 genetic variation is associated with clinical response to antipsychotic drug treatment. These data may provide proof-of-principle for pharmacogenetic studies in schizophrenia.

D2 Receptor Genetic Variation and Clinical Response to Antipsychotic Drug Treatment: A Meta-Analysis

Биология депрессии

The Biology of Depression: Guiding Treatment Selection

Нарушение клеточного цикла при шизофрении

Bahn and her colleagues are investigating disease markers in tissues such as skin, immune cells, and blood serum to find samples that give a real-time picture of the disease. Their studies of protein expression in fibroblasts (skin cells) on schizophrenia patients’ arms have identified systemic problems such as cell-cycle abnormalities (J. Proteome Res. 2010, 9, 521).

“It’s clear that schizophrenia has a very strong genetic component,” Bahn says. “Most genes are not used only in the brain. If there is an underlying abnormality at the genetic level that leads to pathology in the brain, the assumption can be made that there should also be dysregulation in the peripheral system. It may not lead to pathology, but it may reflect the pathology in the brain.”

A Systemic Look At Schizophrenia

The State of Pharmacogenetics Customizing Treatments

The State of Pharmacogenetics Customizing Treatments

A Prospective Cohort Study Investigating Factors Associated With Depression During Medical Internship

A Prospective Cohort Study Investigating Factors Associated With Depression During Medical Internship