From the Clinical Pharmacology Unit, University of Cambridge,
Addenbrooke's Hospital; and the MRC Biostatistics Unit (D.C.),
Cambridge, UK.
Tyrosine hydroxylase (TH) catalyzes the hydroxylation of
L-tyrosine to L-DOPA and is found in abundance in certain
neurons of the locus ceruleus, ventral tegmental area, and substantia
nigra, as well as the adrenal medulla and sympathetic
ganglia.3 A single copy gene encoding human TH
encompasses 13 primary exons spanning 8 kb and is located on chromosome
11p15, adjacent to Harvey ras 1 oncogene and insulin,
respectively.4 The TH gene consists of at least 4
splice variants, suggesting novel means of regulating CA levels
(although transgene experiments show conflicting results for its role
in the cardiovascular system5 6 ).
Crucially, this gene contains an informative (heterozygosity, 78%)
tetranucleotide (TCAT)9
microsatellite repeat marker located within intron
1,7 enabling investigators to study the TH locus.
Previous studies have used this short tandem repeat (STR) marker to
elucidate the role of TH in the etiology of
psychoses.8 We therefore have used this TH
polymorphism to determine whether this gene is one of the many now
considered to contribute, additively or epistatically, to the
pathogenesis of EH.
Using this marker polymorphism we were able to assess blood
pressure (BP) as (1) a quantitative trait in an association study using
a group of well-characterized hypertensive and control subjects, and
(2) a qualitative trait in an affected sibling pair (ASP) linkage study
using sibships from our local family practices. Furthermore, a recently
described common amino acid variant within exon 2 of the TH gene
causing a substitution of valine for methionine at codon
819 was typed in a recently recruited group of
young, mainly borderline, hypertensive patients (YHT) to determine
whether this potential functional variant was in linkage disequilibrium
(LD) with TH-STR. In any study of a candidate gene in EH, it is also
desirable to investigate an "intermediate phenotype" that
is likely to be more directly influenced by allelic variation in the
gene than BP itself. The most accessible intermediate phenotype
was plasma norepinephrine (NE), although it is well
recognized that there are many factors other than TH that contribute to
variation in plasma NE. We undertook a separate evaluation of this
intermediate phenotype in the YHT cohort in which NE and
epinephrine (EPI) had been estimated before any treatment over
the previous 2 years, and we investigated whether any relationship
existed between plasma CA levels and TH-STR or codon
81Val
Hypertensive Group: HT
Control Group: NT
Affected Sibling Group: ASP
Young Hypertensive Group: YHT
All subjects from our 4 groups (HT, NT, ASP, and YHT) were white. No
subject was in more than 1 group.
Laboratory
TH Codon 81 Genotype Analysis
Catecholamine Levels
Statistical Analysis
BP was assessed quantitatively using a multiple regression model in
both cohorts. TH genotype showed no significant relationship to
systolic or diastolic BP in either group
(quantitative trait analysis of BP using genotype 14
df, P>0.05; quantitative trait analysis
of BP for additive allele chromosomal effects 4 df,
P>0.05). However, when the 5 TH genotypes were
pooled into 3 groups (A, B, C, and DE recoded into group 1; D recoded
into group 2; and E recoded into group 3), there was a trend (NS) for
both systolic and diastolic BP to be lower in those
with the D allele in both NT and HT populations, when BP was
assessed quantitatively (exemplified in Figure 3
ASP Study
YHT Study
Our specialized hypertensive practice coupled with our local stable and
homogeneous population enabled us to undertake an
allelic-association and linkage study. These 2 methods allow BP to be
assessed both quantitatively and qualitatively using an internal,
informative microsatellite tetranucleotide repeat marker
within intron 1 of TH, our candidate gene. This is not the first
attempt to use microsatellite sequences rather than biallelic
polymorphisms in association studies.18 Our
population-based case-control study strongly suggested that the TH
locus is involved in the pathogenesis of EH (Tables 2
For a case-control study to demonstrate a 12% difference in allelic
frequency of a common polymorphism would require 250 affected
subjects with an equal number of controls to achieve a significant
difference at the 5% level, with 80% power.19
Thus, although this work was well powered, the accuracy in choosing the
unaffected control group in an association model is clearly crucial to
these types of study. From our large database of 30 000 locally
screened normotensive individuals, we randomly selected 206 NT subjects
who were well matched to our HT cohort. These individuals have been
followed up for 5 years. Commentators have rightly highlighted the main
failings of association studies, particularly regarding recruitment of
unaffected groups.20 All our subjects were
recruited from the same geographical area with a relatively healthy,
stable, and homogeneous population. This area has low
cardiovascular environmental risk factors, amplifying
any genetic contribution to hypertension.
Access to a group of young borderline hypertensives enabled us to show
from conditional haplotype probabilities that a recently identified
Val81Met common amino acid variant of potential functional
importance9 was in LD with TH-STR. This
particular YHT cohort was selected because pretreatment BP and CA
levels were available; because 60% to 70% of plasma CA variance is
known to be under genetic influence,21 22 we
investigated whether Val81Met or TH-STR could account for this
variance. Moreover, we hypothesized that a younger cohort with
hypertension, albeit borderline, would increase our chances of
detecting a genetic contribution to BP regulation. We were unable to
demonstrate any obvious relationship between either BP or plasma CA
levels and Val81Met, but a larger cohort of subjects is clearly needed
to exclude this amino acid variant in the control of either of these 2
variables.
Other investigators have shown that STR sequences could by themselves
be functionally active.23 Indeed, the D
allele was associated with lower BP (Figure 3
A linkage study was undertaken with ASPs from a separate cohort using
the TH marker. With 136 equivalent sibling pairs and a marker
(calculated in this study) with a heterozygosity of 74.5%, our
effective sample size was 67.2 sibling pairs (ie, the number of fully
informative sibpairs that would carry the same information), allowing
in this study a maximum logarithm of odds ratio (LOD) likelihood score
of 4.1, assuming a
Naturally, the results of this work apply best to the population
studied, but this study supports the role of the TH locus (or a nearby
gene) in the pathogenesis of EH.
Received December 30, 1997;
first decision January 22, 1998;
accepted June 2, 1998.
© 1998 American Heart Association, Inc.
Scientific Contributions
Positive Association of Tyrosine Hydroxylase Microsatellite Marker to Essential Hypertension
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
Abstract—Despite advances in the
understanding of monogenic hypertensive disorders, the genetic
contribution to essential hypertension has yet to be elucidated. The
position of tyrosine hydroxylase (TH) as the rate-limiting enzyme in
catecholamine biosynthesis renders it a candidate gene for
the etiology of hypertension. The TH gene contains an internal,
informative microsatellite marker (TCAT)9. We undertook (1)
an association study in a group of well-characterized hypertensive
subjects (HT) and control subjects (NT) and (2) an affected sibling
pair (ASP) study using sibships from our local family practices. Two
hundred twenty-seven hypertensive patients (pretreatment
systolic/diastolic blood pressure [BP] range,
139/94 to 237/133 mm Hg; age range [SD], 30 to 71 [8.5]
years) were age- and gender-matched with 206 control subjects (BP
range, 96/62 to 153/86 mm Hg; age range, 40 to 70 [7.6] years).
One hundred thirty-six affected sibling pairs were recruited for our
linkage study; 73 young borderline hypertensive subjects (YHT)
(pretreatment BP range, 123/76 to 197/107 mm Hg; age range, 20 to
51 [9.4] years) were also recruited in whom recent pretreatment
norepinephrine and epinephrine levels were
available. All subjects were white. The TH short tandem repeat (STR)
was amplified using specific polymerase chain reaction cycling
conditions in all subjects, and products were run on an ABI 373A
sequencer. TH alleles were assigned using Genescan and
Genotyper software. Five TH alleles were present and
designated A through E. Allele frequencies in the NT population (A,
B, C, D, and E: 0.24, 0.17, 0.13, 0.20, and 0.26, respectively) were
significantly different from the HT cohort (A, B, C, D, and E: 0.24,
0.19, 0.11, 0.11, and 0.35, respectively), P<0.0005
(Pearson's test 
2=19.94; 4 df). The E
allele appears overrepresented in the HT group, whereas
the D allele appears to be overrepresented in the NT
group. TH genotype frequencies were also significantly
different between cases and controls (P<0.001;
2=36.57; 14 df). Both groups were in
Hardy-Weinberg proportion. There was a trend (NS) for the D allele
to be associated with a lower BP when BP was analyzed as a
quantitative trait. ASP linkage data was analyzed using Splink,
a nonparametric program. Expected values for sharing 0, 1,
and 2 alleles (Z0, Z1, and Z2,
respectively) may be expected to be 25%, 50%, and 25%, respectively,
by chance (assuming identity by descent). These probabilities were
calculated by Splink as 34, 68, and 34, respectively, and compared with
observed values of 36.8, 67.9, and 31.3, respectively; thus, there was
no excess sharing of TH alleles among affected sibling pairs
(P=0.59; logarithm of odds ratio score, 0.0). TH
allele frequencies in our YHT group (A, B, C, D, and E: 0.24, 0.20,
0.12, 0.15, and 0.29, respectively) were similar to those of our NT
cohort (P>0.05). There was a trend for lower
pretreatment plasma norepinephrine levels with the D
allele in this YHT cohort. A common and potentially functional
variant at codon 81Val
Met within exon 2 of the TH gene
(which we show to be in linkage disequilibrium with TH-STR) was also
typed in our YHT but did not associate with catecholamine
levels and is therefore unlikely to account for our findings with D and
E TH-STR. In conclusion, the TH locus strongly associates with
essential hypertension in a case-control model using well-characterized
hypertensive and control groups. An ASP linkage model was negative,
presumably because of lack of power. This study suggests that the TH
gene, or a nearby gene, may be involved in the etiology of
essential hypertension.
Key Words: hypertension, essential • genetics • catecholamines • molecular biology • tyrosine hydroxylase • microsatellite marker
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
The role of catecholamines (CAs) in essential
hypertension (EH) was extensively investigated during the 1970s and
1980s. At that stage, few individual studies acknowledged in their
design and size the likelihood that EH is a polygenic condition in
which only a minority of patients might have elevated CA secretion.
Many methodological problems emerged, such as the interpretation of
plasma or urine CA levels as indices of sympathetic activity, the
relative roles of increased secretion versus reduced clearance, and
above all the need for careful matching of patients and control
subjects. Despite these difficulties a consensus emerged, especially
from the meta-analysis of plasma CA
studies1 and our own larger study of urine CA
during the Medical Research Council Hypertension
Trial,2 that CA secretion is increased in some
patients during the development of hypertension. In older patients with
EH, the role of increased CA secretion was less easy to establish,
possibly because it was superseded by the secondary changes of
remodeling. Even in the positive studies, the difficulty remained of
determining whether increased CA secretion was a primary or secondary
event. One of the attractions of the search for genetic abnormalities
in EH is that these abnormalities cannot be secondary to
hypertension. Met, which could be a functional
variant.
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Subjects
Ethical approval for this study was obtained from the local
ethics committee. All subjects were recruited from Cambridgeshire and
the East Anglia region in the UK.
Two hundred twenty-seven hypertensive patients (pretreatment
systolic/diastolic BP range, 139/94 to 237/133
mm Hg; age range [SD], 30 to 71 [8.5] years) were selected from a
population of 635 hypertensive subjects who form part of an ongoing,
long-term prospective study on the effects of antihypertensive agents.
In this long-term study, patients are randomized to 1 of the 4 main
groups of antihypertensive treatment. On recruitment, patients are
previously untreated and have either a pretreatment
diastolic BP reading >90 mm Hg or a pretreatment
systolic BP >160 mm Hg, each averaged over 3 consecutive
readings measured using a Datascope Accutorr 2A by the same observer
and sustained for 3 months. Heart rate (HR) and BP were measured in
triplicate at 5-minute intervals after subjects were supine for 15
minutes. Demographic data such as age, gender, cigarette smoking,
alcohol consumption, and body mass index (BMI) were recorded along
with serum cholesterol levels (Table 1
). Patients have been followed up for up
to 10 years.
View this table:
[in a new window]
Table 1. Demographic Data of NT and HT
Groups
Two hundred six control subjects (BP range, 96/62 to 153/86
mm Hg; age range [SD], 40 to 70 [7.6] years) were randomly
selected from our locally screened population of 30 000 healthy
subjects recruited from 43 general practices since 1990. An average of
3 BP readings were recorded using the same Datascope Accutorr 2A
machine in these general practices. Demographic details similar to
those of our HT group were documented (Table 1
). Subjects were excluded
if they had a previous diagnosis of cardiovascular
disease, hypertension, diabetes mellitus,
hypercholesterolemia, stroke, angina, or
myocardial infarction.
Hypertensive patients already receiving antihypertensive therapy
were identified by local general practitioners. These
probands were asked for details of siblings who were also receiving
treatment. These affected siblings were then contacted, and the general
practitioners for all members of each pedigree were asked
to confirm details of treatment and of pretreatment BP readings. In
total, 99 pedigrees (84 men; pretreatment BP range, 180/60 to 260/160
mm Hg; mean age [range/SD], 64.7 [37 to 83/10.3] years; BMI
[SD], 25.6 [6.0] kg/m2) were identified, one
third of which were larger than sibling pairs.
To determine whether Val81Met was in LD with the TH-STR and
whether there was any quantitative relationship between plasma CA and
this amino acid variant, 73 patients (40 men; pretreatment BP range,
123/76 to 197/107; mean age [range/SD], 37.7 [20 to 51/9.4] years),
for whom pretreatment free plasma CA levels were available, were
recruited from a separate BP treatment rotation study. Patients were
excluded if they were already receiving antihypertensive treatment;
were taking vasoactive drugs; or were pregnant, lactating, or females
of childbearing potential but not receiving adequate contraception.
TH Microsatellite Genotype Analysis
The TH-tetranucleotide microsatellite marker has an
expected allele length of 313 to 329 bp and a heterozygosity of
78%. A 5'TET-fluorescently labeled forward oligoprimer, which
appears green when excited by a laser from our ABI 373A sequencer, was
designed. The TET-labeled sense oligoprimer sequence was 5'-TCC AAA AAA
TCC AAG ATG GC-3'; the unlabeled antisense oligoprimer sequence was
5'-ACA GGG AAC ACA GAC TCC ATG-3'. DNA was extracted using a standard
phenol/chloroform extraction technique.10
Polymerase chain reactions (PCR) contained 100 ng genomic DNA, 26.6
pm/µL labeled forward and unlabeled reverse primer, 50 mmol/L
KCl, 10 mmol/L Tris HCl, pH 9.0, 0.1% Triton X-100, 0.2
mmol/L dNTPs, 1.0 mmol/L MgCl2, and 0.2 U
Taq polymerase (Promega Ltd). Reactions were scaled
to 12.5 µL PCR volumes. PCR products were denatured at 94°C for
2 minutes, followed by 28 cycles at 94°C for 1 minute and 24 seconds,
55°C for 1 minute, and 72°C for 45 seconds with a final extension
step of 72°C for 10 minutes, using a Biometra TRIO-Thermoblock. TH
microsatellite marker for our ASP linkage study was amplified using an
oil-free, 96-well Biometra UNO-Thermoblock with similar cycling
conditions as above, except the annealing temperature was reduced to
52°C, the extension time was increased to 1 minute, and the PCR cycle
was repeated 35 times. PCR products were loaded onto an ABI 373A
sequencer (Perkin Elmer), and data were analyzed using Genescan
and Genotyper software, allowing semiautomated assignment of
alleles by sibships. Of all samples, 7% to 8% were reamplified
and genotype was confirmed. All alleles were assigned by a
single observer.
Subjects from the YHT cohort were genotyped for the
amino acid variant Val81Met. The sense oligoprimer sequence was 5'-GGC
AGA GCC TCA TCG AGG AC-3', and the antisense oligoprimer sequence was
5'-AAA CAC CTT CAC AGC TCG GGA C-3'. Oligo primers were synthesized
using the ABI 391 (PCR-MATE, ABI). PCR conditions were similar to above
except that DynaZyme DNA polymerase (Flowgen) was used with a standard
buffer containing 1.5 mmol/L MgCl2.
Reactions were scaled to 25 µL volumes. PCR products were
denatured at 95°C for 2 minutes, followed by 40 cycles at 94°C for
1 minute, 63°C for 45 seconds, and 72°C for 2.5 minutes with a
final extension step of 72°C for 10 minutes. The 197-bp amplified
product was subsequently digested using NlaIII, which
recognizes the Met but not Val sequence. The 2 resultant products
(131 bp and 66 bp) were resolved using a 2% MetaPhor agarose gel
(Flowgen) stained with ethidium bromide (Figure 1).
View larger version (91K):
[in a new window]
Figure 1. Val81Met genotype analysis.
Lane 1, 197-bp homozygote; lane 2, 197-bp and 131- and 66-bp
heterozygote; lane 3, 197-bp homozygote; lane 4, 131- and 66-bp
homozygote; lane 5, control; and lane 6, 100-bp ladder. The 197-bp
amplified product was digested using NlaIII, which
recognizes the Met but not Val sequence. The 2 resultant products
(131 bp and 66 bp) were resolved using a 2% MetaPhor agarose gel
stained with ethidium bromide.
Plasma samples were collected from the YHT cohort from an
indwelling cannula after 15 minutes of supine rest. CAs (NE and EPI)
were assayed by alumina extraction11 followed by
high-performance liquid chromatography with
electrochemical detection using a model 510 pump, 460 EC detector
(Waters), and Spherisob ODS2, 150x4.6-mm column (Phase Separations).
The mobile-phase citrate/phosphate buffer contained 30 mmol/L
octanesulfonic acid, pH 6.0, and 10% vol/vol methanol, at a flow rate
of 1 mL/min.
Data were analyzed using SPSS for Windows, version
6.1.4, and SPlus, version 3.3. In our association study, BP was used as
the dependent variable in a multiple regression model in which age,
gender, BMI, cigarette smoking, alcohol, cholesterol level,
and TH genotype were predictors of outcome. Qualitative
variables (genotype and allele frequencies) were
analyzed using Pearson's 2 test.
Comparison of allele frequencies has greater power than comparison
of genotype frequencies because of fewer degrees of freedom,
and it is therefore more sensitive to gene-disease associations,
particularly when multiallelic microsatellite markers rather than
biallelic polymorphisms are used. In addition, TH genotypes
were analyzed using Lathrop's test,12
which assumes Hardy-Weinberg information from our control group. In all
analyses, P<0.05 was taken as statistically
significant. Linkage data from our ASP study was analyzed using
the nonparametric iterative program
Splink,13 designed locally at Cambridge. This
program negates the need to know control population allele
frequencies of markers by self-generating haplotype probabilities.
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
Association Study
Our NT and HT populations were well matched for a variety of
cardiovascular risk factors (Table 1). All subjects
were genotyped using the ABI 373A sequencer and Genescan and
Genotyper software. Five TH alleles were identified (Figure 2), which were designated A, B, C, D, and
E (relative sizes: 311, 315, 319, 323, and 327 bp, respectively). There
was a significant difference in TH genotype frequency between
the 2 groups using classic 2
(P<0.001; 2=36.57; 14
df) (Table 2) as well as
Lathrop's test (P<0.005; 2=31.10;
14 df). This difference was more pronounced using the more
powerful chromosome analysis 2 test
(P<0.0005; 2=19.94; 4
df) (Table 3). Allele D
was overrepresented in the NT cohort, while the E
allele was overrepresented in the HT group. Both groups
were in Hardy-Weinberg equilibrium.
View larger version (9K):
[in a new window]
Figure 2. Genotyping of TH tetranucleotide
alleles. Data generated by Genescan software is shown. The 2
highest peaks identify a heterozygote individual for the TH
tetranucleotide marker. The lower peaks are standard sizes
from a fluorescent 350-bp ladder.
View this table:
[in a new window]
Table 2. Genotype Frequencies in HT and NT
Populations
View this table:
[in a new window]
Table 3. TH Allele
Frequency by systolic BP against pooled
TH genotype in the HT cohort). There was no relationship
between TH genotype and HR in our hypertensive cohort (data not
shown).
View larger version (8K):
[in a new window]
Figure 3. Systolic BP (95% confidence interval) vs
pooled TH genotype in the HT cohort*. The figure shows the
trend for the D allele (2) to be associated with lower
systolic BP compared with the remainder TH alleles. *Where
1=A, B, and C alleles and DE genotype; 2=D allele; and
3=E allele.
We recruited 99 pedigrees (one third of which were larger than
sibling pairs), totaling 136 equivalent ASPs based on a conservative
estimate of K-1, where K is the number of affecteds (Table 4). Allele frequencies generated by
Splink (A, B, C, D, and E: 0.16, 0.22, 0.08, 0.15, and 0.39,
respectively) compared very favorably to those observed in our NT
population (P>0.05; 2=6.7; 4
df). Under Mendelian inheritance of each allele,
expected values for sharing 0, 1, and 2 alleles
(Z0, Z1, and
Z2, respectively) are expected to be 25%, 50%,
and 25%, respectively, by chance (assuming identity by descent). This
expected rate of allele sharing did not differ significantly from
the observed scores of 27%, 50%, and 23%, respectively (Table 5). Thus, there was no excess sharing of
TH alleles among affected sibling pairs (P<0.6).
View this table:
[in a new window]
Table 4. Number of Affected Sibling Pairs Used in Linkage
Study
View this table:
[in a new window]
Table 5. Identity by Descent (IBD) Assignments of Affected
Sibling Pairs
Seventy-three YHT were genotyped, and TH allele
frequencies (A, B, C, D, and E: 0.24, 0.20, 0.12, 0.15, and 0.29,
respectively) were similar to those in our NT population
(P>0.05; 2=2.2; 4 df).
The allele frequencies of the Val/Met molecular variant were
0.67/0.33, respectively. Conditional probabilities that the haplotype
carries the Val allele given the TH allele were A, B, C, D, and
E: 0.89, 0.17, 0.83, 0.27, and 0.97, respectively, suggesting that
codon Val81Met was in LD with the TH-STR (likelihood
2 test for LD 49.4; 8 df;
P<0.0001). Sixty-four subjects in our YHT cohort had
pretreatment plasma NE measured (mean±SD [range], 278.8±105.0 [73
to 556] ng/L), and 49 subjects had pretreatment EPI measured (mean±SD
[range], 43.5±29.9 [10 to 129] ng/L). There was a trend for
pretreatment plasma NE levels to be lower in those with the D
allele (Figure 4), although this did
not reach statistical significance. No relationship existed between
pretreatment plasma CA levels and Val81Met or plasma EPI and TH pooled
genotype (data not shown).
View larger version (9K):
[in a new window]
Figure 4. Plasma NE levels (95% confidence interval) vs
pooled TH genotype in the YHT cohort. The figure shows the
trend for the D allele (2) to be associated with lower plasma NE
levels compared with the remainder TH alleles. *Where 1=A, B, and C
alleles and DE genotype; 2=D allele; and 3=E
allele.
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
Gain of function mutations in Liddle's14 15
and glucocorticoid remediable aldosteronism16 and
loss of function in apparent mineralocorticoid
excess17 have shown how monogenic disorders can
cause hypertension. In most patients, however, the functional
consequences of the genetic mutations are likely to be much more
subtle, with some interacting to cause a higher or lower BP. Although
we and others are now engaged in whole genome screens in a systematic
attempt to find BP-responsible loci, it is unlikely that such studies
will have the resolving power to detect many of the mutations expected
in a common polygenic disease such as hypertension. There is therefore
a recognized need for association studies with initial candidate genes
chosen from known physiology, until more systematic genome-wide
association studies become feasible. and 3). Of
the 5 alleles identified, the D allele was
overrepresented in the NT cohort, while the E allele
was overrepresented in the HT group. Interestingly, the
effect of the 2 alleles is counterbalanced when they occur together
(Table 2). The availability of pretreatment BP measurements allowed us,
unusually, to investigate any quantitative effect with BP against TH
genotypes. There was a trend for lower BP in those with the D
allele in both NT and HT cohorts in a dominant model (Figure 3),
although this did not reach statistical significance. Conversely, there
was a dominant effect of the E allele causing a higher BP (Figure 3). The fact that the E allele did not result in even higher BP
illustrates the polygenic and complex nature of BP control. Indeed, it
is possible that the causes of EH will vary with age of onset, with EH
in those affected at a younger age due to fewer but more potent genes
compared with those with late-age onset, presumably resulting from a
greater gene-environment interaction. However, the age range of
subjects recruited for this study was not designed to test this
hypothesis. ), and this
allele, as would be predicted, also correlated with lower plasma NE
levels (Figure 4), although neither result reached statistical
significance. Plasma NE levels are difficult to measure reliably and
reproducibly, but their availability in a pretreated young hypertensive
cohort provided us with the ability to perform this useful
genotype-phenotype analysis. Study of a larger
group of hypertensives for whom pretreatment CA levels are available
may confirm or refute the suggestion that the NE levels are influenced
by TH-STR. 
s of 3.5.24 With this
number of ASPs, we were unable to demonstrate linkage, but an LOD score
of 0.0 (Table 5) does not exclude the TH locus. Thus, this study
illustrates the wide divergence in power, discussed recently by Risch
and Merikangas,25 between the association and
linkage approaches. To detect a small genetic contribution to EH onset
by the TH locus would require many thousands of ASPs, compared with the
relatively practical number required for an allelic-association model.
Moreover, although case-control studies cannot exclude the possibility
of unsuspected population stratification in 1 of the groups, they are
at present the only pragmatic type of association study in the
absence of the parental genotypes required for the family-based
alternatives.25 26
Acknowledgments
Dr Sharma is a British Heart Foundation Clinician Scientist. We
are grateful to Claire Dickerson and Chryssie Brown for help with
recruitment of our YHT group and sibling pairs, respectively, and
Jennie Fatibene for extracting DNA from the sibling blood samples. We
are indebted to our patients and local family practitioners.
Footnotes
Reprint requests to Dr P. Sharma, Addenbrooke's Hospital, Hills Rd, Cambridge CB2 2QQ, UK.
References
Top
Abstract
Introduction
Methods
Results
Discussion
References
This article has been cited by other articles:
 |
|
 |
|
  A L Markel, O E Redina, M A Gilinsky, G M Dymshits, E V Kalashnikova, Y. V Khvorostova, L A Fedoseeva, and G S Jacobson Neuroendocrine profiling in inherited stress-induced arterial hypertension rat strain with stress-sensitive arterial hypertension J. Endocrinol., December 1, 2007; 195(3): 439 - 450. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. C. Hunt Tyrosine Hydroxylase: Another Piece of the Genetics of Hypertension Puzzle Circulation, August 28, 2007; 116(9): 970 - 972. [Full Text] [PDF]
|
|
|
|
|
|
F. Rao, L. Zhang, J. Wessel, K. Zhang, G. Wen, B. P. Kennedy, B. K. Rana, M. Das, J. L. Rodriguez-Flores, D. W. Smith, et al. Tyrosine Hydroxylase, the Rate-Limiting Enzyme in Catecholamine Biosynthesis: Discovery of Common Human Genetic Variants Governing Transcription, Autonomic Activity, and Blood Pressure In Vivo Circulation, August 28, 2007; 116(9): 993 - 1006. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Rao, J. Wessel, G. Wen, L. Zhang, B. K. Rana, B. P. Kennedy, T. A. Greenwood, R. M. Salem, Y. Chen, S. Khandrika, et al. Renal Albumin Excretion: Twin Studies Identify Influences of Heredity, Environment, and Adrenergic Pathway Polymorphism Hypertension, May 1, 2007; 49(5): 1015 - 1031. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Zhang, F. Rao, J. Wessel, B. P. Kennedy, B. K. Rana, L. Taupenot, E. O. Lillie, M. Cockburn, N. J. Schork, M. G. Ziegler, et al. Functional allelic heterogeneity and pleiotropy of a repeat polymorphism in tyrosine hydroxylase: prediction of catecholamines and response to stress in twins Physiol Genomics, November 17, 2004; 19(3): 277 - 291. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. H. Gibbons, C. C. Liew, M. O. Goodarzi, J. I. Rotter, W. A. Hsueh, H. M. Siragy, R. Pratt, and V. J. Dzau Genetic Markers: Progress and Potential for Cardiovascular Disease Circulation, June 29, 2004; 109(25_suppl_1): IV-47 - IV-58. [Full Text] [PDF]
|
|
|
|
 |
|
 S. Rodriguez, T. R. Gaunt, S. D. O'Dell, X.-h. Chen, D. Gu, E. Hawe, G. J. Miller, S. E. Humphries, and I. N.M. Day Haplotypic analyses of the IGF2-INS-TH gene cluster in relation to cardiovascular risk traits Hum. Mol. Genet., April 1, 2004; 13(7): 715 - 725. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Hanaoka, Y. Droma, J. Hotta, Y. Matsuzawa, T. Kobayashi, K. Kubo, and M. Ota Polymorphisms of the Tyrosine Hydroxylase Gene in Subjects Susceptible to High-Altitude Pulmonary Edema Chest, January 1, 2003; 123(1): 54 - 58. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Albanese, N. F. Biguet, H. Kiefer, E. Bayard, J. Mallet, and R. Meloni Quantitative effects on gene silencing by allelic variation at a tetranucleotide microsatellite Hum. Mol. Genet., August 1, 2001; 10(17): 1785 - 1792. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. A. Papanikolaou and E. L. Sabban Ability of Egr1 to Activate Tyrosine Hydroxylase Transcription in PC12 Cells. CROSS-TALK WITH AP-1 FACTORS J. Biol. Chem., August 25, 2000; 275(35): 26683 - 26689. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||