From the Departments of Cardiological Sciences (A.S.C., E.W.A.N., R.K.M.,
W.J.M.), Dermatology (S.C.), Pathology (M.I.O.), and Medical Genetics
(V.A.M.), St George's Hospital Medical School, London, UK; Yannis
Protonotarios Medical Center, Hora Naxos, Naxos, Greece (N.P., A.T.); and
Genetics Team, Section of Epidemiology, Institute of Cancer Research, Royal
Marsden Hospital, Sutton, Surrey, UK (R.S.H.).
Correspondence to Dr A.S. Coonar, Department of Cardiological Sciences, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK. E-mail a.coonar{at}sghms.ac.uk
Methods and ResultsWe evaluated the population of Naxos, Greece,
to identify probands, which was followed by family screening.
Twenty-one affected persons from 9 families of 150 persons were
identified. Linkage analysis was performed with microsatellite
markers. The disease locus mapped to 17q21. A peak 2-point LOD score of
3.62 at
ConclusionsHair and skin abnormalities were found to be reliable
markers of subsequent heart disease. This suggests the presence of a
single mutant gene with novel cardiac, skin, and hair function or two
or more tightly linked disease genes. Recessive inheritance of Naxos
disease and a founder effect were demonstrated. Identification of a
fully informative genetic marker linked to the disease and uncommon in
the background population may be of use as a test to identify disease
gene carriers.
In ARVC, the main clinical problems are arrhythmia, heart
failure, and sudden death.6 Risk factors for
sudden death are relatively poorly delineated. However, ARVC appears to
be relatively common in young persons, and particularly so in athletes.
In athletes who died suddenly, between 3% and
Epidemiological data are limited, but there is evidence to support
geographical clustering, for example in northern
Italy,8 and this may suggest areas of high
prevalence. In addition to sporadic cases, familial disease has
frequently been observed.10 13 14 15 16 17 18 In such
families, mendelian inheritance has been reported. Usually the pattern
of inheritance has been autosomal dominant, with various degrees of
clinical expression. Observation of familial disease led to the
hypothesis that a genetic abnormality may underlie cases of ARVC, and
recently three gene loci were reported in families with autosomal
dominant forms of the disease: 14q2324
(ARVD1),19 1q42 (ARVD2),20
and 14q1222 (ARVD3).21 As yet, no
disease-causing genes have been identified.
While investigating people affected by ARVC, we became
particularly interested in a variant form recently named Naxos
disease.22 This disease is characterized by
typical cardiac features of ARVC, which are accompanied by diffuse
NEPPK and WH, and has been reported only in people from the Greek
island of Naxos. We hypothesized that the disease had a genetic basis
and might have been introduced to the island from a single common
ancestor. If so, this disease potentially represented a
powerful model that could be of value to the determination of a
molecular basis for ARVC, and therefore we examined the question, Is
Naxos disease genetically determined? Further characterization of the
molecular basis of Naxos disease may suggest a paradigm that could be
useful to the determination of other forms of ARVC.
The PPKs are a genetically heterogeneous group of
diseases.23 Diffuse NEPPK, similar to that seen
in Naxos disease, is due to mutations in the type II keratin, keratin 1
(MIM *139350.4), which maps to 12q1113.24 25 In
contrast, focal NEPPK, dissimilar to that seen in Naxos disease, is due
to mutations in the type I keratin, keratin 16 mapping to 17q21 (MIM
*148067).26 27 Striated NEPPK (MIM 148700) maps
to 18q12 in proximity to a desmosomal gene
group,28 although as yet the specific mutation is
unknown. WH (MIM *194300) is tightly curled hair occurring in
non-Africans and is similar to that commonly seen in persons of African
origin, in whom it is a normal trait. It has been observed as an
isolated feature29 and as part of a disease
syndrome.30 Autosomal dominant with male-to-male
transmission, recessive, and sporadic forms have been described in
non-African pedigrees. The molecular basis of WH is unknown.
In this study, we report our investigation of the molecular genetics of
Naxos disease.
Clinical Evaluation
Genetic Evaluation
Thirty-eight of 150 family members and all 50 control subjects were
available for additional molecular genetic analysis. Of the 21
affected people originally identified, there were 18 survivors (1 more
died subsequently). Fourteen of them, along with 24 of their unaffected
relatives, were available, including at least 1 affected person from
each of the 9 families. In 3 of the 9 families, only the proband was
available. DNA was extracted from peripheral blood
leukocytes by standard methods. Subjects were genotyped by use
of microsatellite markers by polymerase chain reaction, followed by
electrophoresis in denaturing polyacrylamide gels and
visualization by autoradiography, or the LICOR DNA
sequencer 4000L system. Polymerase chain reaction amplification was
performed in a
Pedigree Analysis
Linkage Analysis
Two-point linkage analysis between markers D17S1294, D17S1293,
D17S800, KRT9, THRA1, D17S1299, and D17S809 gave evidence for linkage
of Naxos disease to 17q. The results of 2-point analyses for
each of these markers analyzed are shown in Table 1
The exclusion of linkage to reported ARVC loci and the identification
of a novel locus for Naxos disease implies a different, although still
possibly related molecular basis between the diseases. Given the
historical links with other Mediterranean peoples, it had been
suggested that ARVC on Naxos and that seen in Italy had a common
molecular basis. The previous mapping studies had all included families
from Italy. In the study that identified the ARVD1 locus at 14q2324,
a large multigenerational Italian family had been investigated, and
linkage to 17q21 had been excluded19; this
represents additional support for a distinct molecular basis
between this variant of ARVC and Naxos disease. Further evaluation of
other populations and families affected by ARVC for linkage to 17q21
could be of value in two ways. First, if linkage is identified in a
given family, such an observation may assist in assigning disease
status to additional family members of clinically undetermined
phenotype. Second, if other ARVC families do demonstrate
linkage to 17q21, the region in which there is a common or overlapping
conserved haplotype between the Naxos disease families and the ARVC
families may be significantly narrower. This would benefit
identification of an etiological gene by localizing it to a smaller
interval.
To explain the broad features of the phenotype, it is necessary
to consider two models: first, that the disorder may arise as a result
of mutation in a single gene that plays a critical role in more than
one biological pathway. Alternatively, mutation affecting two or more
tightly linked genes may produce the disease phenotype. There
is precedent for both of these models.45 46 47 This
region of 17q21 is gene rich and has been well explored as a
consequence of its proximity to BRCA1 (breast cancer gene
type 1). The disease haplotype is in proximity to a number of candidate
genes. In addition to at least 10 genes of the type 1 keratin
group,23 there are genes involved in
morphogenesis48 and the maintenance of
sarcolemmal integrity.49 Detailed high-resolution
physical map data have not been published. However, consensus map data
suggest that the type 1 keratin group may be organized into at least
two clusters. KRT9 is located in greater proximity to
KRT14, KRT16, and KRT17, whereas
KRT10, KRT13, and KRT15 have been
identified as being located on a different pulsed-field gel
electrophoresis fragment that is telomeric to
KRT9.50 Putative candidates that have
been excluded are NF1 (neurofibromatosis type 1
gene),51 ADL (adhalin
gene),52 and the Hox2 cluster
(homeobox genes).48 The Naxos disease haplotype
is telomeric to NF1 and centromeric to ADL and
the Hox2 cluster. Other disease candidates at this locus
include Tbx genes,53 54 55 as well as
members of the type 1 keratin cluster. Recently, mutations in the
Tbx5 gene, which maps to 12q24.1, were identified as the
cause of Holt-Oram syndrome, a disease characterized by cardiac and
upper limb abnormalities.56 57 Tbx
genes are thought to act as transcription factors modulating mesodermal
growth. It is of interest that the 12q12 region has homology with
17q21 and possibly arose because of duplication events at an earlier
evolutionary stage. In humans and at syntenic sites in other mammals,
there are groups of keratin genes, homeobox genes, and Tbx
genes at both loci.
Keratins are part of the intermediate filament family and, like other
members of this structurally and functionally related group, are known
to have a role in cell stability. Eight mutations have been identified
in keratin 9.43 58 59 60 61 62 All were exonic and
involved the conserved coil 1A of the rod domain, important in
heterodimerization and keratin stability. In all those cases, the
clinical pattern was of an epidermolytic PPK, different from the
diffuse NEPPK of Naxos disease. This does not exclude keratin 9, and
mutation analysis of this gene will be an important part of the
search for the etiological mutation. The keratin 9 intragenic marker
linked to Naxos disease is a short sequence repeat of the form
(TG)n and lies within intron 4. The effect on
gene function produced by this recessively inherited intronic sequence
variation cannot be reliably predicted. Therefore, because of this and
because keratin 9 is thought to be expressed in mature palmoplantar
epidermis but not in the heart,63 64 we are
extending our evaluation. This will include assessment of neighboring
genes as well as an investigation of intermediate filament gene
expression in the heart.
Support for the paradigm of an intermediate filament abnormality per
se, or an intermediate filamentrelated gene abnormality, stems from
the recent identification of mutation in the gene for plectin as the
cause of an autosomal recessive muscular dystrophy accompanied by
epidermolysis bullosa simplex.45 Plectin is
involved in intermediate filament attachment to the cell membrane in
both epithelial and muscle cells. In skin, plectin deficiency leads to
a failure of keratin filaments to attach to the plasma membrane via
hemidesmosomes, whereas in muscle there is abnormal localization of the
muscle intermediate filament desmin. The net result is cellular
fragility producing skin and muscle disease.65 It
is of interest that in this syndrome, as in Naxos disease, skin disease
clinically precedes the muscular abnormalities.
In ancient times, Naxos was the predominant island of the Aegean, its
wealth enabling it to export marble to mainland Greece for the
construction of temples and to supply large numbers of troops. Later it
saw a relative decline and in 1204 CE was annexed by
Venice. For this and other complex cultural reasons, a strong tradition
developed and remains for Naxians to have children only with other
Naxians, although not with close relatives. The people of Naxos screen
their children and know from their folklore that if they are born with
the hair and skin stigmata, they may die young. Identification of
linkage to 17q21 and a haplotype for Naxos disease offers a test to
identify risk status for the people of Naxos. In this study, the
genotype 11 for the KRT9 marker was observed only in clinically
affected persons, and this implies that the KRT9 marker 1 allele is
in strong linkage disequilibrium with the disease gene or genes. In
turn, this suggests that the heterozygous state 1/z (where z is any
other allele) for the KRT9 marker identifies the carrier state
among the Naxos population. With appropriate counseling and fully
informed consent, it will be possible to advise Naxians of the relative
risk to their offspring of Naxos disease.
Subsequent identification of the genetic abnormality in Naxos disease
may suggest related genes as candidates for other forms of ARVC. This
may also benefit our understanding of clinically overlapping syndromes,
which include right bundle-branch block/persistent ST-segment
elevation/sudden death syndrome,66 Uhl's
anomaly,67 and ARVC plus mitral valve prolapse
syndrome,68 and diseases that have both cardiac
and ectodermal abnormalities, such as Noonan
syndrome,69 cardiofaciocutaneous
syndrome,70 and LEOPARD
syndrome.71 In broader terms, an understanding of
the molecular basis of ARVC may benefit our understanding of the
biology of myocyte regulation, arrhythmogenesis, and heart failure.
Received October 29, 1997;
revision received January 20, 1998;
accepted January 23, 1998.
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© 1998 American Heart Association, Inc.
Clinical Investigation and Reports
Gene for Arrhythmogenic Right Ventricular Cardiomyopathy With Diffuse Nonepidermolytic Palmoplantar Keratoderma and Woolly Hair (Naxos Disease) Maps to 17q21
![]()
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
BackgroundArrhythmogenic right
ventricular cardiomyopathy (ARVC) is a
heart muscle disease of unknown etiology that causes
arrhythmias, heart failure, and sudden death. Diagnosis can be
difficult, and this hampers investigation of its molecular basis. Forms
of ARVC in which gene penetrance and disease expression are greater
should facilitate genetic study. We undertook a clinical and genetic
investigation of Naxos disease, originally described by Protonotarios
in 1986. This disease constitutes the triad of ARVC, diffuse
nonepidermolytic palmoplantar keratoderma, and woolly hair.
=0.0 was found with a marker within intron 4 of the keratin
9 gene, a member of the type I (acidic) keratin family. A preserved
homozygous disease haplotype was identified. Haplotype analysis
delimited the disease interval.
Key Words: genes cardiomyopathy Naxos disease
![]()
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
Arrhythmogenic right
ventricular cardiomyopathy is a heart
muscle disease pathologically characterized by the fibrofatty
replacement of myocytes and extracellular
matrix.1 2 3 The right ventricle is most
frequently involved, but left-sided cardiac disease also
occurs.4 The definitive diagnosis of ARVC
requires the demonstration of fibrofatty replacement of the
myocardium, which in life is usually not possible and
furthermore may represent only advanced disease. Therefore,
diagnostic criteria have been proposed by a combined
ESC/ISFC task force.5
30% were reported to
have had ARVC.7 8 9 The disease may have both a
variable presentation and a variable clinical
course, even within a single family,10 and in
many cases appears to be progressive.11 12 There
is also a higher than expected rate of structural, functional, and ECG
abnormalities in family members of persons with ARVC, and this may
represent early disease.10 13 14 15 16 This
clinical variation can make accurate diagnosis difficult, and because
the correct determination of disease status is vital to accurate gene
mapping and to subsequent gene identification, such
diagnostic uncertainty may be significantly
confounding.
![]()
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Subjects
The island of Naxos has
20 000 inhabitants made up of
200
apparently unrelated families, and we successfully screened all the
families to recruit subjects for this study. This was possible because
the only cardiologist on the island (N.P.) is a native of Naxos and
knows all these families personally. To identify index cases, screening
was particularly extensive in families with a history of cardiac, skin,
or hair abnormalities. After identification of an index case,
ascertainment was extended by use of public, medical, and church
records, and all available family members were invited for study.
Nine affected families were identified, from which 150 subjects were
recruited for this study. Fifty apparently unrelated control subjects
were randomly selected from 50 different unaffected Naxos families. All
study and control subjects participated after informed consent had been
obtained, and all subjects have been offered follow-up and
counseling.
Noninvasive cardiac assessment was performed on all subjects.
This included full clinical history and examination, resting 12-lead
ECG, ambulatory 24-hour ECG, and two-dimensional
transthoracic echocardiography. The
cardiac diagnosis was based on ESC/ISFC
guidelines.5 For the purposes of this
investigation, no person underwent invasive evaluation beyond venous
blood sampling. If clinical management reasons so indicated,
coronary angiography,
electrophysiological study, and
endomyocardial biopsy were performed. The cardiac
diagnosis was confirmed by pathological examination of tissue after
surgery or endomyocardial biopsy in a subset of
patients (n=3). Skin biopsy was performed in a subset of patients
(n=3). Control parameters were established by noninvasive
assessment of a group of 50 unrelated, healthy Naxians.
Pedigree analysis suggested autosomal recessive
inheritance. Developing the earlier hypothesis of a founder effect, we
hypothesized that a common ancestor had introduced a single copy of the
disease gene to the genetically isolated population of Naxos, and then
as a result of inbreeding, homozygous individuals arose with the
phenotype of Naxos disease. This allowed the efficient and
statistically powerful strategy of homozygosity mapping to be used to
examine loci based on a candidate gene
approach.31
-32P or infrared dyelabeled
reaction with 30 cycles at 94°C for 30 seconds, annealing for 60
seconds, and extension at 72°C for 60 seconds.
Oligonucleotides were supplied from Research Genetics
or derived from markers linked to the candidate genes. D17S1294,
D17S1293, D17S800, D17S1299, and D17S809 are positioned according to
data from the Cooperative Human Linkage Center
(CHLC).32 The other markers are ordered within
this region according to additional consensus information from the
Location Database (LDB),33 Genome Database
(GDB),34 and other high-resolution map data of
this region.35 Linkage analysis was
performed with the C version of the LINKAGE package,
FASTLINK,36 37 and the utility programs Makeped,
LCP, LRP, and UNKNOWN, from LINKAGE 5.1.38
Population allele frequencies were derived from the 50 Naxian
control subjects and not from published data from other populations
that may not have been representative.
![]()
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
Clinical Features
In every affected person, all three components of the Naxos
disease phenotype were observed together. There were no cases
in which only a solitary feature or two of the three features occurred.
In all affected persons, WH was present from birth and persisted
throughout life (Fig 1A
). Palmoplantar
erythema was present at or developed shortly after birth and
progressed to a diffuse NEPPK (Fig 1B
, 1C
, and 1D
). The cardiac
abnormality (Fig 2
) was not clinically
manifest until the patient was
15 years of age, and onset was
usually with palpitation or syncope. Three patients died during
follow-up: 2 suffered sudden death (Fig 3
, marked as *SD), and the other
developed progressive cardiac failure (Fig 3
, marked as *HF). There
were also 4 additional recently deceased persons who were known to have
had WH and PPK. In 3 of the 4, data from their medical records
supported a diagnosis of ARVC (Fig 3
, marked as ND). In the other
deceased person (Fig 3
, marked as ?ND), no additional cardiac data were
available.

View larger version (98K):
[in a new window]
Figure 1. A, WH as a feature of Naxos disease. Posterior
view showing tight curly hair in person with Naxos disease (non-African
ancestry). B and C, Palmar and plantar keratoderma in Naxos disease.
Note clear demarcation at border with dorsal skin. D, Histopathological
preparation of palmar skin biopsy. Severe hyperkeratosis without
epidermolysis.

View larger version (164K):
[in a new window]
Figure 2. Two-dimensional echocardiogram of heart showing
typical features of ARVC: right ventricular (RV) dilatation
and multiple saccular aneurysmal segments (arrows). There is
also right atrial (RA) dilatation. In contrast, left ventricle (LV) and
left atrium (LA) are normal. Accompanying ECG shows abnormal T-wave
inversion in leads V2 through V4,
consistent with abnormal repolarization affecting RV. Epsilon
waves are also observed.


View larger version (35K):
[in a new window]
Figure 3. Pedigrees of families affected by Naxos disease.
Haplotypes of family members available for molecular analysis
reveal a conserved disease haplotype (KRT9-THRA1-D17S1299) inherited in
autosomal recessive fashion, suggesting that these families are all
ancestrally related and that Naxos disease is the consequence of a
founder effect. *SD indicates sudden death during follow-up; *HF,
progressive cardiac failure leading to death during follow-up; ND, 3 of
the 4 persons who died suddenly reported to have PPK and WH with data
from medical records supporting a diagnosis of ARVC; and ?ND, 1 of
4 persons who died suddenly reported to have PPK and WH and no
additional medical data available.
We identified 9 affected families (Fig 3
). These families were
derived from 11 apparently unrelated Naxian families. Family trees
could be constructed for up to 7 generations back from the most recent,
and no other relationships could be identified between the kindreds to
this level. One hundred fifty living family members were recruited into
the study, from whom 21 living affected persons were identified (9
female, 12 male; age, 7 to 74 years, with a mean of 38 years at first
evaluation; age, 18 to 76 years, with a mean of 50 years at last
review). Pedigree inspection suggested autosomal recessive inheritance
of Naxos disease.
Thirty-eight family members comprising 14 people with Naxos
disease and 24 of their unaffected relatives were available for
molecular genetic analysis. At least 1 affected person was
available from each of the 9 families. In 3 of the 9 families, only the
proband was available for molecular analysis. By linkage
analysis, the following loci were excluded: the three loci for
autosomal dominant ARVC1921; two loci on
chromosome 1 implicated in dilated
cardiomyopathy39,40; also on
chromosome 1, the epidermal differentiation
complex41; the dystrophia myotonica protein
kinase CTGn repeat locus on
19q1342; the type II keratin cluster on
12q26,27; and the locus on 18q implicated in
striated NEPPK.28
. The peak 2-point LOD score was 3.62 at
=0.0 with the fully informative marker KRT9,43
giving evidence for linkage of Naxos disease to 17q21. The KRT9
allele 1, which cosegregated exclusively with the disease, had an
observed allele frequency of only 6.9% in the control group, and
this frequency was used for linkage analysis. The frequency of
this allele in the Naxos control population was similar to that
previously reported in another control group
(6%).43 The homozygous 11 genotype for
KRT9 was seen only in affected persons and not in their healthy family
members or in control subjects (Table 2
and Fig 3
). Haplotype analysis localizes the Naxos disease gene
to a region of
7 cM on 17q21 flanked by the markers D17S800 and
D17S80932 33 (Table 2
). A haplotype unique to all
the affected individuals is observed with 3 markers and comprises only
homozygous genotypes. The disease haplotype is given by the
markers KRT9-THRA1-D17S1299. Of the 14 affected persons, 3 (E11, I13,
and K17) did not have other family members available for molecular
analysis and therefore do not contribute to the LOD score,
suggesting that this estimate of linkage is likely to be
conservative.
View this table:
[in a new window]
Table 1. Two-Point LOD Scores Between Chromosome 17q Markers
and Naxos Disease
View this table:
[in a new window]
Table 2. Haplotypes of Persons With Naxos Disease
![]()
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
A challenge to the evaluation of people and families with ARVC is
the accurate identification of disease status. This reflects the
variable clinical expression of ARVC as well as the limitations
inherent to current methods of cardiac assessment. Clinical evaluation
of families from the island of Naxos, Greece, identified a syndrome in
which WH and PPK are predictive of the development of
ARVC.22 In contrast to many cases of ARVC,
this represented a disease variant in which
diagnostic status could be more confidently assigned. This
model is made more robust because in an isolated community, both
clinical and genetic heterogeneity are often reduced,
making disease phenocopies less likely.44 The
mode of inheritance appeared to be autosomal recessive. Linkage
analysis mapped the disease locus to 17q21, strongly supporting
a genetic basis for this disease. A homozygously inherited disease
haplotype that is common to all the affected individuals was
identified, which supports an autosomal recessive mode of inheritance
as well as a founder effect. This haplotype delimits the region of the
disease gene to
7 cM. Identification of a fully informative
molecular marker linked to the disease, infrequent in the background
population, and not seen in a homozygous form in healthy relatives or
control subjects could be used as a genetic test to identify risk
status among Naxians. This investigation also identifies a locus for
WH.
![]()
Selected Abbreviations and Acronyms
ARVC
=
arrhythmogenic right ventricular
cardiomyopathy
cM
=
centimorgan
ESC/ISFC
=
European Society of Cardiology/International Society
and Federation of Cardiology
LOD
=
logarithm of the odds
NEPPK
=
nonepidermolytic palmoplantar keratoderma
PPK
=
palmoplantar keratoderma
WH
=
woolly hair
![]()
Acknowledgments
We thank all Naxos disease families and the people of
Naxos. Dr Coonar is the recipient of a British Heart Foundation Junior
Research Fellowship and University of London research grant. Drs
Needham, Mattu, and McKenna as well as the laboratory facility are
funded by St George's Hospital Medical School. (University of London),
the Youde Foundation, and the British Heart Foundation. We would also
like to thank Dr Aris Anastasakis, Dr Evi Karvouni, and Dr Dimitris
Richter for facilitating clinical screening in Greece and Marietta
Bardanis in Naxos for follow-up genetic counseling. This work is
dedicated to the memory of Antonis P. Protonotarios.
![]()
References
Top
Abstract
Introduction
Methods
Results
Discussion
References
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Reentrant Arrhythmias. Lancaster: MTP
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