Yeah, they believe that stuff. Look, if the regular medical community can't
help you, where are you supposed to go? I had that experience myself. The
"best" doc in ATL told me he couldn't help me. You bet I visited every
available recourse..

There is a condition where the heart rate rises due to inactivity called
deconditioning. You are supposed to be able to overcome that with 3 months
of cardiovascular training, but I know several people with asthma who
continue to report high heart rates even after the appropriate exercise. I
am watching that myself since it effects me.

Also read
http://www.mc.vanderbilt.edu/gcrc/adc/
Many of the heart/sob conditions the BE* people claim to fix are being
investigated by Vanderbilt. Look at the National Dysautonomia Research
Foundation papers.The definitive article which appeared 4 years ago
regarding vasovagal issues, suggested that these cases genetic in origin.
And I do have a couple of kids with this problem. It does not suggest that
the problem is OVERBREATHING. Another conflict between the CAM and the
regular medical community. That means of course that someone in the medical
community failed to understand the CAM. Well, read for yourself.

Expert Reviews in Molecular Medicine: http://www-ermm.cbcu.cam.ac.uk
Accession information: (01)00387-8h.htm (shortcode: txt001drn); 19 November
2001
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Genetic or acquired deficits in the norepinephrine transporter: current
understanding of clinical implications
Tahir Tellioglu and David Robertson

The norepinephrine transporter (NET) has a major role in terminating the
neurochemical signal established by the neurotransmitter norepinephrine (NE)
in the synaptic cleft. The NET is also the initial site of action for
therapeutic antidepressants, and drugs such as cocaine and amphetamines.
Polymorphisms in the NET gene have been identified, and associations with
several disorders such as depression have been proposed but not established.
However, evidence of a direct association between a genetic mutation of the
NET and an autonomic clinical syndrome has recently emerged. A patient and
her identical twin were evaluated for typical symptoms of orthostatic
intolerance (OI), a disorder mainly characterised by elevated heart rate on
standing, and both were found to have clinical and laboratory signs of
abnormal uptake of NE. Sequence analysis of the patients? NET gene
identified a mutation that resulted in more than 98% loss of function as
compared with the wild-type gene. This article reconsiders the important
role of the NET protein in the regulation of the nervous and cardiovascular
systems, reviews the literature for its polymorphisms and their suggested
clinical manifestations, and finally focuses on the effects of its defect on
the pathophysiology of OI, the only confirmed direct association between a
genetic mutation of the NET and a clinical syndrome.

Expert Reviews in Molecular Medicine ? Cambridge University Press ISSN
1462-3994

Author contact details

Catecholamines, a term for the hormones epinephrine (E, adrenaline),
norepinephrine (NE, noradrenaline) and dopamine, function as
neurotransmitters within the central nervous system (CNS) (Ref. 1). They are
involved in readying the body for the fight-or-flight response (also known
as the alarm reaction). Upon NE and E release, the heart beats stronger and
faster, blood pressure rises, more blood flows to the brain and muscles, the
liver releases stores of energy as a sugar the body can readily use
(glucose), the rate of breathing increases and airways widen, and digestive
activity slows. These reactions direct more oxygen and fuel to the organs
most active in responding to stress ? mainly the brain, heart and skeletal
muscles.

Catecholamines are synthesised from the amino acid tyrosine, which is
sequentially hydroxylated to form dihydroxyphenylalanine (dopa),
decarboxylated to form dopamine, and hydroxylated to form NE (see Fig. 1;
fig001drn). NE, the neurotransmitter of postganglionic sympathetic nerve
endings, exerts its effects locally, in the immediate vicinity of its
release. E, the circulating hormone of the adrenal medulla, influences
processes throughout the body. The release of NE at the sympathetic nerve
ending is triggered by depolarisation of the axonal membrane by an action
potential. NE release is presumed to occur by exocytosis. The biological
effects of catecholamines are terminated rapidly by uptake into the
sympathetic nerve endings, by conversion to inactive metabolites, and by
renal excretion. (For a comprehensive review of catecholamines, see Ref. 1.)

The concentration of catecholamines in the sympathoadrenal system remains
relatively constant despite marked changes in the level of sympathetic
activity. This steady state is the result of a careful balance among
catecholamine biosynthesis, storage, release, re-uptake and metabolism.
Genetic or acquired deficits could affect any of these steps and cause
alterations in the concentration of catecholamines, which has been suggested
to contribute to the development of some psychiatric and cardiovascular
disorders. Indeed, a recent study has linked a specific genetic defect in
the norepinephrine transporter (NET) protein with the disorder orthostatic
intolerance (OI). We discuss the implication of this finding towards the end
of this review article.

Norepinephrine
The neurochemical messenger NE plays an important role in human physiology
(Ref. 1). In the CNS, NE is involved in mood regulation, sleep regulation,
expression of behaviour, and the general degree of alertness and arousal. NE
also exerts central control over the endocrine and autonomic nervous system.
Outside the CNS and adrenal glands, NE is located in the sympathetic nerve
endings, and the NE content of a particular tissue reflects the extent of
its sympathetic innervation. Basal plasma NE concentrations are usually in
the range of 100 pg/ml to 350 pg/ml, are similar in men and women, and tend
to increase with age (Refs 2, 3). Basal NE levels vary throughout the day,
with the lowest levels occurring during the night, even in subjects who
remain continuously supine (Ref. 4). More than half of any interindividual
variation in plasma NE appears to be caused by undefined genetic factors
(Ref. 5).

The norepinephrine transporter
Re-uptake of NE by the NET protein (also known as uptake 1) is the primary
mechanism by which the biological effects of NE in the synapse are
terminated. This axonal event is an energy-requiring, saturable, sodium- and
chloride-dependent process (Ref. 6) (see Fig. 1; fig001drn). Approximately
70?90% of the NE released into many synapses is cleared by this mechanism,
and the remaining 10?30% spills over into the circulation or extraneuronal
tissue (uptake 2) (Ref. 7). The inactivation process through NET is
extremely important to prevent excessive increase of the NE concentration in
the synaptic cleft, and to limit its actions. NE re-uptake is relatively
more noticeable in heavily innervated tissues, such as heart. Interestingly,
the noradrenergic synaptic clefts in the heart are approximately three times
as narrow as the synaptic distances in the vasculature (Ref. 8), and
extraneuronal uptake (uptake 2) of the NE plays only a minor role in the
heart (Ref. 9). Therefore, the removal of NE from the synapses in the heart
is far more dependent on the activity of the NET than is NE removal from
synapses in the vascular beds (Ref. 10); thus, any impairment of NET would
markedly increase the NE concentration in the synaptic clefts of the cardiac
muscle.
Re-uptake of NE is competitive with a variety of naturally occurring amines
and drugs. Drugs of abuse such as amphetamine and cocaine, and
antidepressants (e.g. desipramine, imipramine, venlafaxine, mirtazapine,
reboxetine, bupropion), block the transport of NE, and result in an
elevation of the synaptic concentrations of NE and potentiation of the
activation of postsynaptic receptors (Refs 11, 12). Recent evidence has
shown that treatments with drugs that alter noradrenergic transmission can
cause an up- or downregulation of the NET (Ref. 13), which causes changes in
the sensitivity to endogenous catecholamines (Ref. 14). This phenomenon
contributes to the mechanism of action of some of these agents.

Knowledge of the gene structure of the antidepressant-sensitive NET
facilitates investigation of its potential role in psychiatric and/or other
disorders, and might aid structure-based drug design for the treatment of
human depression. Therefore, the transport protein responsible for neuronal
uptake of NE has been extensively investigated in the past decade. NET was
isolated by expression cloning in 1991, and the gene was found to be located
on human chromosome 16q 12.2 (Refs 15, 16). The NET gene is encoded by 14
exons, which span 45 kb from the start to the stop codon (Ref. 17). The
nucleotide and deduced amino acid sequence of the transporter predict a
protein of 617 amino acids, containing 12 membrane-spanning domains (Ref.
18) (see Fig. 2; fig002drn). The organisation of the protein is highly
homologous to that of other neurotransmitter transporters including those
transporting dopamine, epinephrine, serotonin and gamma-aminobutyric acid
(GABA), which are members of a family of sodium- and chloride-dependent
transport proteins in the plasma membranes of neurons and glial cells (Refs
17, 19).

NET polymorphisms
Genetic variations have been reported in the gene encoding the NET protein.
The complete coding region of the NET gene has begun to be screened for
genetic variants by single-stranded conformational polymorphism analysis,
and 13 DNA sequence variants have so far been identified (Ref. 20).
Similarly, an association between an exonic silent NET polymorphism (G1287A)
and the concentrations of monoamine metabolites in lumbar cerebrospinal
fluid (CSF) has been reported in healthy volunteers (Ref. 21). Efforts to
prove potential associations between genetic variances in the NET protein
and several psychiatric and cardiovascular disorders have not yet confirmed
the functional significance of the NET polymorphisms investigated.

NE dysregulation in psychiatric disorders
Alterations in the concentration of NE in the CNS have been hypothesised to
cause, or contribute to, the development of psychiatric illnesses such as
major depression. Many studies have reported altered levels of NE and its
metabolites normetanephrine (NMN) and dihydroxyphenylglycol (DHPG) in the
CSF, plasma and urine of depressed patients as compared with normal controls
(Refs 22, 23, 24). These variances could reflect different underlying
phenotypes of depressive disorders with varying effects on NE activity. The
melancholic subtype of depression [with positive vegetative features,
agitation, and increased hypothalamic?pituitary?adrenal (HPA) axis activity]
is most often associated with increased NE (Ref. 25). Alternatively,
so-called atypical depression is associated with decreased NE and HPA axis
hypoactivation (Ref. 25). In one study, urinary NE and its metabolites were
found to be significantly higher in unipolar and bipolar depressed patients
than in healthy volunteers, suggesting that unmedicated unipolar and bipolar
depressed patients have a hyperresponsive noradrenergic system (Ref. 26).
Increased NE activity has also been observed as a contributor to the
borderline personality disorder traits of impulsive aggression and affective
instability, high levels of risk taking, irritability, and verbal aggression
(Refs 27, 28).

Furthermore, abnormal regulation or expression of the human NET has been
reported in major depression (Ref. 29). In postmortem human brain, the
binding of [3H]nisoxetine to NET was measured autoradiographically, and high
levels of NET were identified mainly in dorsal raphe nuclei and in the locus
coeruleus (LC) (Ref. 30). However, in subjects diagnosed with major
depression, NET was decreased in the LC without significant differences in
the number of noradrenergic cells in brain tissues collected postmortem
(Ref. 29). Low levels of NET in the LC in major depression might reflect a
compensatory downregulation of this transporter protein in response to an
insufficient availability of its substrate (NE) at the synapse. These
studies suggest that abnormalities that can cause impaired noradrenergic
transmission could contribute to the pathophysiology of certain psychiatric
disorders.

NET polymorphisms in psychiatric disorders
Mutations in the gene encoding the NET (Table 1; tab001drn) have been
considered as a potential basis for some psychiatric illnesses. Thirteen NET
DNA sequence variants have been identified in patients suffering from
schizophrenia or bipolar affective disorder (Ref. 20). However, subsequent
case?control studies did not reveal any significant association between the
variances and those diseases (Ref. 20). In another study, 105 patients with
major depression, and 74 unrelated, matched controls, were analysed for a
silent G1287A polymorphism in exon 9 of the NET gene, but no significant
differences in genotype or allele frequencies were found between controls
and patients (Ref. 31). Hadley et al. genotyped six multigenerational
pedigrees containing multiple cases of manic depression with a DNA
polymorphism for the NET gene (Ref. 32). Using both parametric and
nonparametric methods, the authors found no evidence of linkage between
manic depression and the NET gene.

It has been suggested that polymorphisms of monoamine transporter genes
might contribute to personality factors. A recent study investigated the
association between temperamental personality dimensions (novelty seeking,
reward dependence, persistence and harm avoidance), measured with the
Temperament and Character Inventory (TCI), and polymorphism of the NET in
127 healthy Polish volunteers (Ref. 33). The NET gene polymorphisms showed
no significant association with any of the temperamental TCI subdimensions.

Dysregulation of NE has also been hypothesised to be involved in the
pathophysiology of Tourette syndrome (TS), an inherited, complex
neuropsychiatric disorder characterised by motor and vocal tics. Although
the predominance of evidence supports a critical role for dopamine
involvement, a central NE hyperactivity was suggested by the therapeutic
effects of the alpha2 adrenergic receptor agonist clonidine (Ref. 34).
Furthermore, antidepressant treatments that increase the NE content in CNS
have been shown to worsen the symptoms of TS (Ref. 35), consistent with a
genetic association of the NET gene with TS. Nonetheless, allele frequency
and genotype distribution of 12 DNA sequence polymorphisms showed no
differences between TS patients and controls (Ref. 36).

In summary, although alterations in the concentration of NE in the CNS have
been reported with major psychiatric disorders, there is currently no
evidence that NET dysfunction or abnormal gene sequence contributes to any
psychiatric illness.

NET downregulation in congestive heart failure
Patients with congestive heart failure (CHF) have increased sympathetic
nerve activity, as well as increased plasma and urinary levels of NE
concomitant with the severity of the ventricular dysfunction (Refs 37, 38,
39). Impairment of NE re-uptake by the NET has been shown in CHF (Refs 9,
40, 41). Although the exact mechanism involved in the NET impairment in CHF
is unclear, a significant reduction in the NET binding sites without a
decrease in NET gene expression and without a loss of noradrenergic nerve
terminals has been reported in an animal model of CHF (Ref. 42). In a recent
study, cardiac NET density has been found to be inversely correlated with
beta-adrenergic receptor kinase 1 (beta ARK1), a G-protein-coupled receptor
kinase that phosphorylates and desensitises beta-adrenergic receptors (Ref.
43). Inhibition of beta ARK1 activity or expression significantly enhances
cardiac function and potentiates beta-adrenergic receptor signalling in
failing cardiomyocytes (Ref. 44). This finding promises novel strategies in
the therapy of CHF.

NET gene mutation in OI
OI is a disorder of the autonomic nervous system and is characterised by a
variety of symptoms including increased heart rate (>100 beats/min),
weakness, fatigue, lightheadedness, nausea, excessive sweating, altered
mentation, and fainting, and these symptoms generally occur immediately
after assuming a standing position (Ref. 45). It has been estimated that
approximately 500 000 Americans suffer from some form of this disorder (Ref.
45). Patients often have high plasma NE concentrations (at least 600 pg/ml)
in relation to sympathetic outflow on standing, suggesting that the disorder
is a hyperadrenergic condition (Refs 46, 47). The pathophysiology of OI has
been associated with autonomic or neuroendocrine dysregulation, but, until
recently, its causes remained largely unknown, and were suggested to include
a variety of genetic and environmental factors. In particular, it was not
known whether the high levels of plasma NE in OI patients were a consequence
of increased release from neurons or decreased removal by NET.

The discovery of an OI patient who shared the disorder with her identical
twin sister prompted the search for a genetic basis (Ref. 3). Upon standing,
the twin sisters had very high plasma NE levels with relatively decreased
plasma DHPG, and a decreased NE clearance, indicating that much of the
increase in plasma NE resulted from an impaired removal of NE from the
synapse by NET.

The presence of similar biochemical and clinical findings in the twins
suggested a genetic origin. Direct sequence analysis of the patients? NET
gene (SLC6A2) on chromosome 16q (16) revealed two novel polymorphisms [a
silent (C154A) and a missense (G237C) mutation] (Ref. 3). The missense
mutation resulted in the replacement of an alanine residue with a proline
residue (Ala457Pro) in a highly conserved transmembrane region of the
transporter (see Fig. 2; fig002drn). Functional analysis of the patient?s
defective NET demonstrated that it had only 2% of the activity of the
transporter encoded by the wild-type gene in in vitro studies. Because the
substitution of proline disrupts the alpha-helical secondary structures that
are supported by alanine residues, this mutation might disrupt the transport
of NE.

The genetic defect in the NET protein, which results in decreased NET
activity, could explain cardiovascular and endocrine abnormalities such as
postural tachycardia and high plasma concentrations of NE in some patients
with OI. However, the G237C mutation was not detected in 40 other patients
with OI, and in 200 unrelated people including normal subjects and patients
with hypertension (Ref. 3). Thus, other genetic or environmental factors
must have contributed to the phenotype in patients with the specific gene
defect. Overall, the identification of NET deficiency provides a
pathophysiological focus that could potentially bring together the cardiac,
autonomic and CNS manifestations of OI.

Autoimmune mechanisms in NET impairment
The NET protein could be a possible target of an autoimmune reaction. Nearly
half of OI patients have had a recent viral illness such as the common cold,
before the onset of their symptoms (Refs 45, 48), suggesting that a
virus-triggered autoimmune reaction could be related to the pathophysiology
of OI. Although specific antibodies for nicotinic acetylcholine receptors
have been identified in the OI patients (Ref. 49), antibodies selective for
the NET have not yet been detected.

In a recent paper, we discussed a patient who had been suffering from Behcet
?s disease (a multisystem disorder presenting with vasculitis and
circulating autoantibodies) and had recently developed the autonomic
disorder OI (Ref. 50). The pathophysiology of OI and Behcet?s disease are
not well understood, but a common theory for each is a previous viral
infection. Higher serum antibodies against viruses including herpes simplex,
hepatitis C and parvovirus B19 are found in patients with Behcet?s disease,
suggesting a possible trigger role involving cross-reactive autoimmune
responses (Refs 51, 52).

Clinical implications and future directions
The steady-state regulation of the noradrenergic system is the result of an
intact NET. This system can be affected by several medications, by
haemodynamic changes (up- or downregulation), or by genetic defects in its
protein structure, and might contribute to the pathophysiology of major
disorders.

A decrease in transporter activity results in decreased removal of NE from
the synapses, but the specific symptoms of the diseases occur with some
anatomical features: the noradrenergic clefts in heart are approximately
three times narrower than the synaptic clefts in the vasculature (Ref. 8),
making NE removal in the heart more dependent on the activity of the NET
(Ref. 53). This phenomenon might explain the disproportionately greater
effect on heart rate than on blood pressure observed in patients with OI.

The genetic deficiency in the NET protein associated with OI is the first
functional mutation in human NET to be discovered, and suggests that there
might be other mutations that can affect NE regulation and contribute to the
pathophysiology of other diseases related to NE dysregulation. This might
also be the case for serotonin and dopamine transporters. Intensive research
has been going on, but no mutations have been detected yet.

This discovery of the association of NET mutation and OI should lead to
investigation of NET?s potential role in psychiatric, cardiovascular and/or
any other disorders. Although there is currently no evidence that abnormal
NET dysfunction contributes to any psychiatric illness, alterations in the
concentration of NE in the CNS suggest that NE dysregulation might cause, or
contribute to, the development of psychiatric illnesses.

Our new knowledge about the functional mutation of NET might aid
structure-based drug design for the treatment of human disease. Careful
psychiatric and neurological assessment of patients in whom NET functional
mutations are encountered should ultimately elucidate the role of this gene
product in CNS disorders.

Acknowledgements and funding
The authors thank John A. Phillips III, MD (Division of Genetics, Vanderbilt
University Medical Center, Nashville, TN, USA) and Richard Shelton, MD
(Department of Psychiatry, Vanderbilt University Medical Center, Nashville,
TN, USA) for reviewing the manuscript.

but

Well, I am 31 years old. I was diagnosed with asthma when I was 17.
Thinming back, I did have some symptoms when I was younger, but not
enough to speak up about it.

And I believe I have hyperventilated only once, about 5 years ago,
after I inhaled acid reflux the first time. I was having an asthma
attack, my throat and lungs were on fire, and my vocal cords were not
cooperating. It was over half an hour before I could speak. I was
pretty freaked out.

Most of my breathing is quite normal. Not shallow or fast. So, I don't
see how I could possibly be hyperventilating. Yet supposedly, this is
the cause of my wrist hurting? Yah, right.More likely, it is caused by
the activities preceding the pain.

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