Collecting a set of psoriasis family material through a patient organisation; clinical characterisation and presence of additional disorders.

Abstract

The aim of the present study was to describe the clinical characteristics of a population of psoriatics sampled from a patient organisation and not from hospitals or out-patient clinics. Furthermore, we wanted to compare siblings with and without psoriasis regarding the occurrence of other diseases.
At the end of 1991, we initiated a project which aimed to study genetic factors leading to psoriasis. Firstly, we sent questionnaires to all the members of the Swedish Psoriasis Association. We then examined 1,217 individuals (570 with psoriasis) from 310 families, in their homes in the southern part of Sweden. All the available family members were examined clinically and asked about the course of the skin disease and the occurrence of other diseases. The eight hundred members of the proband generation were divided into two groups, with or without psoriasis, and their clinical features were compared.
Most individuals in this study population had a mild form of psoriasis. The siblings with psoriasis had joint complaints significantly more frequently than their siblings without the skin disease and those with joint complaints had more widespread skin disease. Among the other studied concomitant diseases (iritis, heart or hypertension disease, endocrine disease, inflammatory bowel disease and neurological disease), we were not able to find any difference. Seventy-seven of 570 persons were found to be in remission (13.5%). Females had a mean onset 2.5 years earlier than males. We were not able to find any correlation between the extent of the skin disease and age at onset. Twice as many persons with joint complaints were found among those with psoriasis than among those without, 28% versus 13%. Almost half (48%) the psoriatics who also had joint complaints had psoriasis lesions on their nails. Endocrine disorders were found in 9% of those without any allele for Cw6, but only in 1% of those who had Cw6. In fact, none of 183 Cw6 carriers had diabetes, as compared to the population prevalence of 3-5% in Sweden.
With the exception of joint complaints, persons with psoriasis, collected from a patient organisation, did not have an increased frequency of (studied) co-existing diseases.

Full text

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BioMed Central
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BMC Dermatology
Open Access
Research article
Collecting a set of psoriasis family material through a patient
organisation; clinical characterisation and presence of additional
disorders
Annica Inerot*1, Charlotta Enerbäck1, Fredrik Enlund2, Tommy Martinsson2,
Lena Samuelsson2, Jan Wahlström2 and Gunnar Swanbeck1
Address: 1Department of Dermatology, Sahlgrenska University Hospital/Sahlgrenska, SE-413 45 Göteborg, Sweden and 2Department of Clinical
Genetics, Sahlgrenska University Hospital/Ostra, SE-416 85 Göteborg, Sweden
Email: Annica Inerot* - annica.inerot@derm.gu.se; Charlotta Enerbäck - charlotta.enerback@clingen.gu.se;
Fredrik Enlund - fredrik.enlund@llcr.med.gu.se; Tommy Martinsson - tommy.martinsson@clingen.gu.se;
Lena Samuelsson - lena.samuelsson@obgyn.gu.se; Jan Wahlström - jan.wahlstrom@obgyn.gu.se; Gunnar Swanbeck - g.swanbeck@telia.com
* Corresponding author
Abstract
Background: The aim of the present study was to describe the clinical characteristics of a population of
psoriatics sampled from a patient organisation and not from hospitals or out-patient clinics. Furthermore,
we wanted to compare siblings with and without psoriasis regarding the occurrence of other diseases.
Methods: At the end of 1991, we initiated a project which aimed to study genetic factors leading to
psoriasis. Firstly, we sent questionnaires to all the members of the Swedish Psoriasis Association. We then
examined 1,217 individuals (570 with psoriasis) from 310 families, in their homes in the southern part of
Sweden. All the available family members were examined clinically and asked about the course of the skin
disease and the occurrence of other diseases. The eight hundred members of the proband generation
were divided into two groups, with or without psoriasis, and their clinical features were compared.
Results: Most individuals in this study population had a mild form of psoriasis. The siblings with psoriasis
had joint complaints significantly more frequently than their siblings without the skin disease and those
with joint complaints had more widespread skin disease. Among the other studied concomitant diseases
(iritis, heart or hypertension disease, endocrine disease, inflammatory bowel disease and neurological
disease), we were not able to find any difference. Seventy-seven of 570 persons were found to be in
remission (13.5%). Females had a mean onset 2.5 years earlier than males. We were not able to find any
correlation between the extent of the skin disease and age at onset. Twice as many persons with joint
complaints were found among those with psoriasis than among those without, 28% versus 13%. Almost
half (48%) the psoriatics who also had joint complaints had psoriasis lesions on their nails. Endocrine
disorders were found in 9% of those without any allele for Cw6, but only in 1% of those who had Cw6. In
fact, none of 183 Cw6 carriers had diabetes, as compared to the population prevalence of 3–5% in Sweden.
Conclusion: With the exception of joint complaints, persons with psoriasis, collected from a patient
organisation, did not have an increased frequency of (studied) co-existing diseases.
Published: 14 October 2005
BMC Dermatology 2005, 5:10 doi:10.1186/1471-5945-5-10
Received: 03 February 2005
Accepted: 14 October 2005
This article is available from: http://www.biomedcentral.com/1471-5945/5/10
© 2005 Inerot et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Background
Psoriasis is a common, genetically determined inflamma-
tory, proliferative disease of the skin, in which the
immune system is involved in the pathogenesis. Among
individuals with psoriasis, a substantial number also have
some involvement of the joint system, but for other con-
comitant diseases the evidence of a connecting relation-
ship to psoriasis is not clear.
Examinations of persons with psoriasis in census studies
have been made by Lomholt and Hellgren [1,2]. Many
studies with examination descriptions come from hospi-
tals or out-patient clinics [2-6]. The recent study by Gud-
jonsson et al [7] describing clinical characteristics in 369
patients with familial psoriasis was also community
based. Questionnaire studies of psoriasis were introduced
by Farber et al. [8] and have been followed by many oth-
ers from different countries [9-12].
At the end of 1991, we initiated a project designed to elu-
cidate the genetic factors involved in the pathogenesis of
psoriasis [13]. We sent questionnaires to all the members
of the Swedish Psoriasis Association, of which it is esti-
mated that approximately 10% of all Swedish psoriatics
are members. Individuals from the families were exam-
ined and blood samples were collected. Based on this
patient sample, we have previously reported on the iden-
tification of a novel psoriasis susceptibility locus on 3q21
(PSORS5; MIM 604316) through a genome wide scan
[14]. Furthermore, we have created a locus-specific SNP
map and we have utilised it to narrow down the size of the
candidate region to < 250 kb [15]. A candidate gene,
SLC12A8, is currently under investigation. The aim of the
present study was to describe the clinical characteristics of
this population of psoriatics. In contrast to other studies,
they were sampled from a patient organisation and not
from hospitals or out-patient clinics and are therefore
more likely to reflect the true clinical distribution of the
disease. There have been reports suggesting a relationship
between psoriasis and an increased risk of cardiovascular
disease [16], as well as several lifestyle factors, such as
smoking, obesity and diabetes [5,17,18]. We therefore
wanted to compare siblings with and without psoriasis
regarding the occurrence of other diseases.
Methods
The members of the Swedish Psoriasis Association consti-
tute the study base. Approval was obtained from the local
Ethics Committee. One of us (AI) examined 1,217 indi-
viduals from 310 different families. An analysis of the
inheritance pattern from families of members of the
Swedish Psoriasis Association was the reason for selecting
families in which the inheritance could fit an autosomal
recessive trait. We therefore selected families in which the
parents did not have the skin disease (which is 64% of the
material) and in which there were (in addition to the
proband) one or more siblings with psoriasis. Persons liv-
ing outside the Göteborg area were visited in their homes,
or, if they preferred, we met them at a doctor's office in
their neighbourhood. Blood samples were drawn at the
same time. The majority of the examinations took place in
September to May 1991–1998, in the southern part of
Sweden up to a level about 150 km north of Stockholm.
In families with two or more siblings, the examination
rate for all family members was 93%. Some parents were
not alive and a few individuals did not wish to take part
in the study. Another reason for incomplete families was
members living in another part of the country. The size of
the families that were examined is shown in Table 1.
All individuals were inspected on the scalp, the face, the
elbow area, the umbilical and perianal areas, the knees,
hands and feet and also in other areas where they were
aware of having any skin changes. The distribution of pso-
Table 1: Examined persons in all 310 families
Size of sibshipFamilies *Proband generation
Parent generation
NN with psoN total
N with psoN total
1
2
3
4
5
6
7
8
9
78
99
70
32
17
73
154
140
77
49
19
13
78
198
210
128
85
36
28
6 36
11154
127
54
28
8
3
0
1
2
0
0
0
6
4
1
1
2
9
7
2
0
0
3
4
7
8
9
10
20
Total 310539800
31417
*All families are not complete. This is most obvious in the small families, where only half of the individuals were examined. These families were not
ideal for our genetic study, but still represent the study population in this clinic examination study.

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riasis was recorded if the person had any active psoriasis
at examination on the scalp, face, trunk, anogenital area,
arms, legs, hands, feet or nails, i.e. in nine different loca-
tions. The subjects were also asked about other medical
problems. In addition to spontaneous information, they
were asked especially about joint complaints (both
peripheral joints and back involvement), iritis, problems
with heart disease or hypertension, endocrine disease
(mainly diabetes or thyroid disorder), inflammatory
bowel disease or neurological disease. We felt it was not
possible to obtain reliable information about psychiatric
or malignant disorders when meeting several members of
the family at the same time in a home environment for a
relatively short time. Because of the age difference
between the two generations, we have chosen to compare
these diseases among the groups with and those without
psoriasis in the proband generation only.
In 312 of the 800 individuals in the proband generation,
we had information about the presence or absence of the
allele Cw6 at the HLA-C locus. In previous studies from
our group [19,20], psoriatics have been analysed for the
presence of the Cw6 allele using a PCR-based typing
method, as previously described.
Statistical analysis
The data were analysed using the chi-squared test with
Yate's correction (comparison of two different groups). A
p value of < 0.05 was considered significant. Some other
statistical method was used when appropriate; this is
mentioned in the text when applicable.
Clinical diagnosis
For the majority of the probands, a dermatologist had
already established the diagnosis. When the patient was
free of skin changes at the examination, the diagnosis was
based on the medical history, including the name of the
dermatologist who made the diagnosis. The diagnostic
criteria were the same as those used in clinical practice.
Sharply demarcated, infiltrated, red skin lesions with sil-
very white scaling were considered to be psoriasis. Iso-
lated nail lesions were not considered sufficient for the
diagnosis. If unclear, the diagnosis was not set. Pustular
psoriasis was not included, if the person did not also have
psoriasis vulgaris.
Results
Correctness of diagnosis
During the first year of examination, three probands
turned out not to have psoriasis, although they thought
they had it and had joined the patient organisation. They
and their family members have been excluded from the
study. Apart from these three, all the probands had been
given a correct diagnosis. We found 51 persons with pso-
riasis, where the proband had originally said that his or
her relatives did not have psoriasis; twenty-five were sib-
lings, 11 mothers and 15 fathers. The sex of one-third of
the probands giving these reports was male (17/51),
which is the same proportion as in the whole material
(111/310). Among the relatives, there were three persons
whose siblings were thought possibly to have psoriasis by
the probands, but this could not be verified at the exami-
nation. Three other siblings were reported by the
probands to have psoriasis vulgaris, but it turned out to be
psoriasis pustulosa. All the other relatives reported by the
probands as having psoriasis could be verified as having
the disease.
Age of onset and duration of psoriasis
In the proband generation, the ages at examination
ranged from 16 to 79 years, with a mean of 40.5 years. The
mean age for the 539 individuals with psoriasis was 40.2
years and the corresponding figure for the 261 persons
without psoriasis was 41.3 years. There was no significant
difference in age between men and women. Age of onset
varied from the first year of life to 51 years of age. Females
had a mean onset 2.5 years earlier than males (18.0 versus
20.5). The gender difference in age at onset was increased
to 4 years when analyzing only HLA-Cw6-positive indi-
viduals and no difference was found for the HLA-Cw6-
negative. The duration of psoriasis varied from not being
aware of the diagnosis up to the age of 67 years (a woman
aged 74, already examined in 1991), the mean duration
being 21.0 years.
Remission
In some instances, the person who was being studied did
not have enough changes in the skin at the time of exam-
ination for the dermatologist to be able to make the diag-
nosis at that time-point, even though information from
previous examinations (mostly by dermatologists) or pic-
tures from earlier outbreaks indicated psoriasis. In these
cases, the person was diagnosed as having psoriasis, but
that it was currently in remission. Seventy-seven of 570
persons were found to be in remission, (13.5%; 95% CI:
13.5+/-2.8%), 43 women and 34 men, average age 40.2.
Guttate psoriasis
Only 15 individuals (including two sibling pairs) sponta-
neously described a history of guttate psoriasis. One
woman had had three guttate outbreaks. The highest age
at the time of the outbreak was 40 years.
Twins
Eleven pairs of twins were examined, four monozygotic
and seven dizygotic. Two of the monozygotic pairs were
discordant with respect to psoriasis (ages: 51 and 57
years) and three of the dizygotic pairs were discordant in
the same respect (ages: 29, 43 and 49 years).

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Concomitant diseases
Joint complaints
If a person had or had had significant pain or aching local-
ised to one or several joints (including back pain), he/she
was classified as having "joint complaints", without trying
to make a specific diagnosis. In a few persons who denied
experiencing symptoms from joints, joint deformation
like that caused by joint inflammation was seen at exami-
nation and these persons were also classified as having
"joint complaints". There were more than twice as many
persons with joint complaints among those with psoriasis
than among those without, 28% versus 13%, and the dif-
ference was significant (p < 0.001). Among female psori-
atics, 33% had joint complaints, while 21% of the men
had joint complaints (p < 0.01). Nail changes were more
common among psoriatics with joint complaints.
Iritis
In this case, there were very small numbers, with no differ-
ence between the groups.
Heart or hypertension disease
Considering that the mean age of these groups is around
40, low values would be expected and this is also what we
found. There was no significant difference between the
groups.
Endocrine disease
Four per cent reported a history of endocrine disorders,
with no difference between those with and without pso-
riasis. Of the 32 persons with endocrine disorders, 19 had
diabetes mellitus, 13 thyroid dysfunction (one of them
had both disorders) and one had a disease of the parathy-
roid glands. The prevalence of diabetes mellitus among
those people with psoriasis was 2%, while among siblings
without psoriasis the corresponding figure was 4%. This is
not a statistically-significant difference.
Inflammatory bowel disease
Of all the people in the proband generation, 19 individu-
als (3.5%) claimed to have inflammatory bowel disease.
No difference was found between the two groups in the
proband generation.
Neurological disease
Around 3% reported a history of some neurological dis-
ease. There was no significant difference between the
groups in the proband generation.
Information about diseases above are summarised in
Table 2.
Alopecia areata and vitiligo
Alopecia areata at examination or in the medical history
was found in six persons, three of whom had psoriasis.
Vitiligo was found in nine persons; only one of them had
psoriasis.
Location and extent of psoriasis, gender differences
The overall impression was that most people had a mild
form of the skin disease. The examined probands (n =
302) had an average number of 4.4 different locations for
their skin disease (men 5.1, women 3.9). Comparing
these means produced a significant difference (p < 0.001)
(Table 3).
Men and women in the proband generation who were not
themselves members of the Psoriasis Association had a
lower average number of psoriasis locations, 2.8 and 2.3
respectively (NS). Persons with joint complaints had
more widespread skin disease than those without joint
complaints. This difference was highly significant (p <
0.001), comparing medians (5.0 and 3.0) (rank sum test).
We were not able to find any correlation between the
extent of the skin disease and age, even if we divided the
material into men and women.
Table 2: Concomitant diseases at examinations in the proband generation
Siblings with psoriasis = 539 Siblings without psoriasis = 261
N = 800 "Yes"% "No" MV"Yes"%"No" MV
Joint complaints
Iritis
Heart or hypertension disease
Endocrine disease
Inflammatory bowel disease
Neurological disease
149
8
36
20
13
20
27.7
1.5
6.7
3.7
2.4
3.7
389
530
499
516
523
516
1
1
4
3
3
3
35
3
21
12
6
4
13.4
1.1
10.4
5.9
3.0
2.0
226
258
181
190
196
198
0
0
59
59
59
59
Numbers under "Yes" and "No" refer to individuals. For details see text. MV = missing value.

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The most common finding was psoriasis on the arms and
legs. Less common locations were the feet and the face.
The anogenital area was affected in 24.3% of all the exam-
ined persons (Figure 1).
Men had psoriasis of the face more frequently than
women. This difference was significant (p < 0.01). Men
also had psoriasis more frequently on the scalp and in the
anogenital area. The p-value for this difference was 0.03
for both scalp and anogenital location. The rest of the
locations were distributed with no gender difference. To
look for heredity in psoriasis when it came to severity, we
compared 132 sibling pairs. We were not able to find any
correlation between siblings from the same family and the
Table 3: Severity of psoriasis, measured as number of locations affected at examination
MalesFemales
N sum of locationsNsum of locations
average/median average/median
302 members/probands
237 siblings/not members
All 539 with psoriasis
110
135
245
5.1/5
2.8/3
3.9/4
192
102
294
3.9/4
2.3/2
3.4/3
Male members of the psoriasis association have a more extended skin disease than females. Non members with psoriasis have fewer locations
affected.
Body distribution of psoriasis
Figure 1
Body distribution of psoriasis. Body distribution of psoriasis among the 570 individuals with the diagnosis. In addition to the
539 persons in the proband generation, 31 in the parent generation, who also had psoriasis, have been included.
Distribution of psoriasis
0
10
20
30
40
50
60
70
80
Arms Legs ScalpTrunk NailsHands AnogenitalFeetFace
Affected site
Relative frequency %

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severity of the skin disease, measured as the number of
locations with involvement. Nor were we able to find any
relationship between the extent of the disease and the
presence or absence of an allele for Cw6.
Location of psoriasis and the occurrence of concomitant disease
Almost half (48%) of those psoriatics who also had joint
complaints had psoriasis lesions on their nails, compared
with 31% in the group without joint complaints. The chi-
squared test showed that this was a highly significant dif-
ference (p < 0.001). A significant difference (p < 0.001)
was also seen if there was anogenital psoriasis. A statisti-
cally-significant difference was also found if there was
psoriasis on the trunk or the legs (p = 0.02). For the rest of
the locations, we were not able to find any significant dif-
ferences, after examining all the recorded locations and
concomitant diseases.
HLA-Cw6
For 312 of all 800 in the proband generation, we had
information about the presence or absence of the Cw6
allele at the HLA-C locus in the HLA region on chromo-
some 6 p. When examining other concomitant diseases,
we found a difference in the prevalence of endocrine dis-
ease. This group of disorders was found in 9% of those
without any allele for Cw6, but only in 1% of those who
had Cw6. This difference is highly significant (p = 0.002),
but it is based on very small numbers (11 of 119 without
Cw6 and two of 183 with Cw6). Both persons with Cw6
and endocrine disorders had thyroid disease and neither
had diabetes mellitus. Among the 436 for whom we had
no information about the Cw6 status, but information
about endocrine disease, the prevalence was 4%.
Discussion
The psoriasis family material examined in this study was
recruited from a well-informed patient organisation, i.e.
the Swedish Psoriasis Association, and not, as in most
other studies, from hospitals or out-patient clinics. These
individuals are more likely to be representative of most
persons with psoriasis than patients from hospitals. Fur-
thermore, this family study of psoriasis is the largest in
which all the individuals have been examined by one der-
matologist and no previous study has compared the
occurrence of concomitant diseases in siblings without
psoriasis. The distribution of psoriasis was about the same
as that reported by Lomholt [1,3] and Fleischer et al. [12]
and partly also like that reported by Hellgren [2] and Far-
ber and Nall [21]. The majority of the individuals had a
mild disease and an estimation of the PASI score for the
average psoriasis person in this study would probably not
exceed 4 (theoretical range 0–72). We have used a simple
method of recording any active psoriasis lesion in nine
different body regions, instead of using the PASI score
[22]. When it came to the extent of the skin disease, we
found a difference between men and women who were
members of the Swedish Psoriasis Association. However,
among the siblings, we were not able to find a significant
difference between men and women. As the siblings are
seldom members of the association, it is probable that
they are a better reflection of the country's population.
Lomholt [1] found no difference between men and
women when visiting people in their homes, but Molin
[3], who investigated 300 former in-patients with psoria-
sis, found that men had a more severe skin disease, when
it came to both the extent of lesions and the course.
Fleischer et al. [12], who used a self-administered psoria-
sis area severity index score, found a significant difference
between men and women, with men having a higher
score. In a questionnaire survey of the Psoriasis Society of
the Greater Helsinki area, Könönen et al. [9] also found
more severe and more frequent skin lesions in men. In a
study from Island based on 369 psoriatics, Cw6-positive
patients was found to have more extensive plaques and
overall disease severity [7]. However, we were not able to
find any correlation between the prevalence of Cw6 and
the extent of the skin disease, in agreement with previous
observations on 64 patients by Ikähemo et al. [23]. A pos-
sible reason why we did not find any difference in (dis-
ease) severity correlated to the age at onset or Cw6 may be
because the individuals with psoriasis were homogeneous
in that most of them had very mild disease.
The overall gender difference in age at onset was 2.5 years
in accordance with many other studies [3,21]. However,
this difference was increased in the Cw6-positive group (4
years) and was not found at all in the Cw6-negative group
in accordance with the observations of Gudjonsson et al
[7].
There are not many reports of periods of remission in pso-
riasis. We found that 13.5% (77/570) were free of disease
at examination. Lomholt [1] found 11% (28/252), Nevitt
and Hutchinson [24] 9% of 75 examined and, in a Danish
study of twins [25], 13 of 48 (26%) were free from skin
lesions at examination.
We felt it was not possible to obtain reliable information
about psychiatric or malignant disorders when meeting
several members of the family at the same time in a home
environment for a relatively short time. Some individuals
reported atopic dermatitis in the group both with and
without psoriasis, but we did not ask specific questions
about this diagnosis and we found this information unre-
liable for analysis.
Eleven pairs of twins among 800 siblings are in the range
of what can be expected. About half of them were con-
cordant with respect to psoriasis, among both
monozygotic and dizygotic pairs. This is too small a

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number to draw any conclusions about the heredity of
psoriasis.
It is difficult to compare the frequency of co-existing or
concomitant diseases with that in other studies, as the
study design varies a great deal. Probably the most impor-
tant factor that can result in very different figures is the
selection of the study population. The study by Lindegård
[26] reflected the population of psoriatics requiring hos-
pitalisation in the 1970s and this cannot be compared
with the main population of psoriatics at the present time.
In a small sample of 33 consecutive psoriatics in our own
investigation, only two had been hospitalised because of
their skin disease. It is our impression that this is also
reflected in the whole of our material.
The problem of defining a concomitant disease adds to
the selection problem when attempting to compare
different studies. This is illustrated by the many different
prevalence figures relating to joint complaints and/or
arthritis in connection with psoriasis [27,28]. We found
that 28% of psoriatics and 13% of their siblings without
the skin disease had joint complaints, including back
pain. In our study, women had significantly more joint
complaints than men, which has previously been shown
by Farber et al. [8]. We cannot rule out the possibility that
there might be individuals with rheumatoid arthritis in
our "joint complaints" group, especially among women.
The fact that joint complaints are more common if the
person has psoriatic nail lesions has been known for
many decades [29]. Previous investigations have also
shown a relationship between the occurrence of joint
complaints and the presence of psoriasis on the buttocks
and in the groin [11] and between a genital localisation of
psoriasis in men and arthritis [3]. Our observation that
there are more joint complaints if there are skin lesions in
the anogenital area lends further strength to these obser-
vations. We also found that there was an association
between the extent of psoriasis (number of locations) and
joint complaints, as previously observed by several inves-
tigators [3,9,12,30]. Lomholt [1] found only four persons
with psoriasis arthritis among 253 native Faroese with
psoriasis. He found no one with diabetes mellitus and
stated that, in his clinical practice, he also very seldom
found diabetes together with psoriasis. The average age of
his studied population was around 10 years less than that
of the proband generation in our investigation. We now
know that the presence of Cw6 is associated with the early
onset of psoriasis [19,20]. and we can therefore speculate
that many of the psoriatics in Lomholt's study could have
had an allele for Cw6. In our material, none of the persons
with a known presence of Cw6 had diabetes mellitus. If
Cw6 protects from diabetes mellitus, this could perhaps
be a reason why psoriasis vulgaris has stayed in the popu-
lation. However, it is of importance to add that Cw6
might not be the primary association in the HLA region. It
has not been made clear whether the association reflects
the fact that Cw6 is the true disease-causing allele or is due
to linkage disequilibrium with a nearby located gene. Like
Farber et al. in 1968 [8], we found a 2% prevalence of dia-
betes mellitus in the proband generation with psoriasis. In
a later report from the same author [8] comprising more
than 5,600 patients, a total of 3.5% of the psoriasis
patients reported having diabetes mellitus. The prevalence
of diabetes mellitus in the general population in Sweden
is reported to range from 3–5% [31,32]. In our study, thy-
roid disorders were found in 13 individuals (= 1.6%). By
way of comparison, a study in Malmö [33] found thyroid
disorders in 7.9% of a population aged around 45–50
years (men 1.5%, women 14.1%).
In the large hospital-based data register from Kiel, Hense-
ler & Christophers found more diabetes, heart failure and
obesity in psoriatics, compared with age-matched patients
with other skin diseases [5]. We were not able to verify this
in our study population. Our findings are in agreement
with what was found in the case of psoriasis out-patients
in a large register study from Sweden [16]. When it came
to hypertension and heart disease, we found a prevalence
of 6–10% in the proband generation (mean age: 40). In
the case of unspecified "heart disease", it is difficult to find
figures for comparison in previous studies among the gen-
eral population, but, in a study of about 7,000 middle-
aged men, Eriksson & Lindgärde [33] found that 5% were
receiving drug treatment for hypertension. Psoriasis in-
patients both in Finland (1973–1984) [17] and in Swe-
den (1964–1995) [16] had an increased mortality rate
compared with the general population. In Finland, analy-
ses of the causes of death revealed excess mortality related
to alcohol and smoking. In the parent generation, only
five persons (1.2%) reported having inflammatory bowel
disease, compared with 3.5% in the proband generation.
It is known [34] that this group of diseases has increased
in the population and the age at onset is often below 40
years, but the prevalence in the general population is
reported to be below 1% [34-36].
In conclusion, we have analysed a large set of family mate-
rial comprising psoriasis patients, healthy siblings and
their parents collected through a patient organisation. The
clinical features and the presence of other diseases were
recorded and compared. All the individuals in the study
were examined by the same dermatologist. It is likely that
this study design provides a better representation of pso-
riasis in general than when patients collected from hospi-
tal cohorts are used. The patient material characterised in
this study has been used for the identification of the
PSORS5 gene locus and it will be the subject of further
genetic and clinical study in the near future.

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Page 8 of 8
(page number not for citation purposes)
Competing interests
The author(s) declare that they have no competing
interests.
Authors' contributions
GS initiated the psoriasis genetic project and together with
JW and TM designed the study. CE performed the genetic
analysis. AI examined the persons in the families and
drafted the manuscript. All authors contributed and
approved the final manuscript
Acknowledgements
The psoriasis genetic project has been supported by the Swedish Psoriasis
Association, the Welander Foundation, the Swedish Medical Research
Council (project no. B96-19X-11246-02B) and Glaxo-Wellcome Research
Foundation and Development Ltd.
We thank Tommy Johnsson for statistical guidance.
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