Full text of DOI:10.1359/jbmr.2002.17.6.1111

JOURNAL OF BONE AND MINERAL RESEARCH
Volume 17, Number 6, 2002
© 2002 American Society for Bone and Mineral Research
Localization of the Gene Causing Autosomal Dominant
Osteopetrosis Type I to Chromosome 11q12-13
ELS VAN HUL,1 JEPPE GRAM,2 JENS BOLLERSLEV,3 LIESBETH VAN WESENBEECK,1
DANNY MATHYSEN,1 POUL ERIK ANDERSEN,4 FILIP VANHOENACKER,5 and WIM VAN HUL1
ABSTRACT
The osteopetroses are a heterogeneous group of genetic conditions characterized by increased bone density due
to impaired bone resorption by osteoclasts. Within the autosomal dominant form of osteopetrosis, the
radiological type I (ADOI) is characterized by a generalized osteosclerosis, most pronounced at the cranial
vault. The patients are often asymptomatic but some suffer from pain and hearing loss. ADOI is the only type
of osteopetrosis not associated with an increased fracture rate. Linkage analysis in two families with ADOI
from Danish origin enabled us to assign the disease-causing gene to chromosome 11q12-13. A summated
maximum lod score of ؉6.54 was obtained with marker D11S1889 and key recombinants allowed delineation
of a candidate region of 6.6 cM between markers D11S1765 and D11S4113. Previously, genes causing other
conditions with abnormal bone density have been identified from this chromosomal region. The TCIRG1 gene
was shown to underly autosomal recessive osteopetrosis (ARO), and, recently, mutations in the LRP5 gene
were found both in the osteoporosis-pseudoglioma syndrome and the high bone mass trait. Because both genes
map within the candidate region for ADOI, it can not be excluded that ADOI is caused by mutations in either
the TCIRG1 or the LRP5 gene. (J Bone Miner Res 2002;17:1111–1117)
Key words: autosomal dominant osteopetrosis, chromosome 11, LRP5, TCIRG1
genes have been implicated in either induced or sponta-
neous osteopetrotic animal models,(4) in humans, cur-
rently, only three genes have been associated with osteo-
petrosis. The gene coding for carbonic anhydrase II has
been shown to cause a recessive form of osteopetrosis
that is associated with renal tubular acidosis and cerebral
calcification (MIM 259710).(5) Recently, the malignant
recessive form (MIM 259700), in most cases lethal at
early age, is proven to be caused by mutations in the
TCIRG1 gene in a subset of cases(6,7) and in a few
patients in the ClCN7 gene.(8,9)
INTRODUCTION
ONE IS a dynamic tissue that is remodeled constantly by
osteoblastic bone formation and bone resorption by
B
osteoclasts. Disturbance of the balance between these two
processes can result in a broad spectrum of pathological
conditions. One category of such conditions is the osteope-
troses grouped by a shared underlying pathogenic mecha-
nism, that is, impaired bone resorption.(1)
Different types of osteopetrosis are described both in
humans and in animals.(2,3) Despite the fact that several
The autosomal dominant form of osteopetrosis (ADO;
MIM 166600) is characterized by bone pain, back pain, and
All authors have no conflict of interest.
1Department of Medical Genetics, University of Antwerp, Belgium.
2Department of Medicine, Ribe County Hospital, Esbjerg, Denmark.
3Department of Endocrinology, Rikshospitalet, Oslo, Norway.
4Department of Radiology, Odense University Hospital, Denmark.
5Department of Radiology, University Hospital, Antwerp, Belgium.
1111

1112
VAN HUL ET AL.
FIG. 3. Radiograph of the pelvis (AP view). Sclerosis is seen of the
vertebral and pelvic bones, the sacrum, and proximal femora.
FIG. 1. X-ray from individual III9 (family A) at the age of 34 years.
Lateral radiograph of the skull shows uniform sclerosis of calvarium
and the skull base with an enlargement of the cranial vault. There is
obliteration of the frontal sinuses and mastoids.
FIG. 2. Plain radiograph of the lumbar spine (lateral view) from the
same individual as in Fig. 1. There is generalized increased radiopacity
of the vertebral bodies and the posterior elements of the spine because
of osteosclerosis.
FIG. 4. Plain radiograph of the right femur shows bone sclerosis with
narrowing of the medullary canal.

ADOI GENE ON CHROMOSOME 11q12-13
1113
FIG. 5. Pedigree of the Danish ADOI family A and associated chromosome 11q12-13 haplotypes. Men are represented by squares, women are
represented by circles. Blackened symbols represent affected individuals. The haplotypes segregating with the disease phenotype are indicated
with blackened bars. The haplotypes between brackets are deduced from results obtained in close relatives.
fractures sometimes associated with complications such as diagnosed by incidental radiography. Based on radiological
osteomyelitis and cranial nerve compression causing facial and clinical data, two subtypes (ADOI and ADOII) were
nerve palsy and vision and hearing problems.(10) However, recognized.(2,11) ADOII, the form originally described by
a high percentage of patients are asymptomatic and only Albers-Scho¨nberg,(12) is characterized radiologically by a

1114
VAN HUL ET AL.
FIG. 6. Pedigree of the Danish ADOI family B with associated chromosome 11q12-13 haplotypes.
sandwich-like appearance of the spine because of thicken- penetrance has been estimated between 60 and 80%.(13) No
ing of the end plates of the vertebral bodies (“Rugger-Jersey increased fracture rate is present in these patients.
spine”) and endobone structures. ADOI is characterized by
Because no gene or genetic localization for ADOI has
a generalized diffuse osteosclerosis, which is most pro- been reported, we performed a linkage study on two ex-
nounced at the cranial vault (Figs. 1–4). This type presents tended families of Danish origin both originating from the
as a fully penetrant disease, compared with type II where the county of Fyn in Denmark (Figs. 5 and 6). Blood samples

ADOI GENE ON CHROMOSOME 11q12-13
1115
TABLE 1. PAIRWISE LOD SCORES BETWEEN ADOI AND MARKERS FROM CHROMOSOME 11Q12-13
LOD score at ⌰ ϭ
Marker
Family
0
0.01
0.05
0.10
0.20
0.30
0.40
D11S1765
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
Ϫϱ
1.39
Ϫϱ
2.74
1.36
4.10
Ϫ0.02
Ϫ0.31
Ϫ0.33
2.86
0.07
2.93
4.74
1.68
6.42
3.16
0.46
3.62
0.80
Ϫ0.58
0.22
5.33
Ϫ1.78
3.55
3.14
1.24
4.38
Ϫ0.02
Ϫ0.26
Ϫ0.28
2.65
0.03
2.68
4.42
1.52
5.94
2.94
0.40
3.34
0.75
Ϫ0.44
0.31
4.97
Ϫ0.94
4.03
3.04
1.08
4.12
Ϫ0.02
Ϫ0.20
Ϫ0.22
2.38
0.00
2.38
3.99
1.32
5.31
2.65
0.33
2.98
0.69
Ϫ0.32
0.37
4.50
Ϫ0.56
3.94
2.47
0.75
3.22
Ϫ0.02
Ϫ0.10
Ϫ0.12
1.80
Ϫ0.04
1.76
3.07
0.90
3.97
2.01
0.22
2.23
0.55
Ϫ0.16
0.39
3.48
Ϫ0.22
3.26
1.67
0.42
2.09
Ϫ0.01
Ϫ0.05
Ϫ0.06
1.17
Ϫ0.03
1.14
2.03
0.47
2.50
1.28
0.13
1.41
0.41
Ϫ0.07
0.34
2.32
Ϫ0.08
2.24
0.73
0.13
0.86
D11S4205
D11S1883
D11S1889
D11S913
Ϫ0.02
Ϫ0.33
Ϫ0.35
2.92
0.08
3.00
4.82
1.72
6.54
3.21
0.48
3.69
0.81
Ϫ0.63
0.18
5.42
Ϫϱ
0.00
Ϫ0.01
Ϫ0.01
0.53
Ϫ0.01
0.52
0.86
0.12
0.98
0.52
0.06
0.58
0.23
Ϫ0.02
0.21
1.01
Ϫ0.02
0.99
D11S4178
D11S4113
Total
Ϫϱ
were taken from 25 individuals in family A and from 8
individuals in family B after obtaining informed consent.
Patients were diagnosed based on the presence of osteoscle-
rosis on X-rays and for some individuals bone mineral
density (BMD) measurements. The previously reported
family A(11) is updated in this study with the diagnosis of
ADOI in two more individuals. Individual III2 (II2 in pre-
vious study) was not radiologically examined before, but
radiological evidence for ADOI was now obtained. The
diagnosis of ADOI in one of his daughters already made
him an obligate carrier of the disease gene. Individual IV6
(III6 before) was very young at the time of the previous
study. X-rays taken now were still inconclusive because of
the young age of the girl. Therefore, bone mineral content
(BMC)/BMD measurements were performed. The proximal
femoral BMD value was ϩ3.6 SD above normal of the same
age (Z score) and clearly indicates this individual as being
affected. In comparison with a previous study, 4 extra
individuals at risk were studied. Three of these individuals,
a father and 2 daughters (III4, IV3, and IV4) clearly show
the radiological signs of ADOI. The 4th individual (IV7) is
a young boy at the age of 7 years. Because the X-rays taken
from him were not completely conclusive, BMC/BMD
measurements were performed. His age-adjusted BMD of
the spine was high but within the normal range (Z score,
ϩ1,8), making a definite conclusion impossible.
FIG. 7. Delineation of the candidate region for ADOI and relative
position of the TCIRG1 gene and the LRP5 gene. Idiogram of chro-
mosome 11 and position of the markers used are shown. Intermarker
distances in centimorgans were obtained from the Ge´ne´thon linkage
map.(14) In the right panel, the black bars indicate the delineated
candidate region for ADOI and the position of both genes that are
considered to be candidate genes for ADOI.
Family B has not been described before. This four-
generation pedigree (Fig. 6) also originates from the county
of Fyn, Denmark. They were all asymptomatic but otoneu-
rological examinations have shown mild entrapment of cra-
nial nerves. The radiological pictures of the patients are very
similar to those from patients of family A. Six patients were

1116
VAN HUL ET AL.
diagnosed in this family and 1 already deceased individual mal bone density are identified from this chromosomal
was reported to be affected. In total over the two families, region. More precisely, the TCIRG1 gene underlying the
20 patients are diagnosed or reported to be affected includ- malignant autosomal recessive form of osteopetrosis
ing 9 men and 11 women. No evidence is available for (ARO)(6,7) and the LRP5 gene causing both the
nonpenetrance.
osteoporosis-pseudoglioma syndrome (OPS), a recessive
To perform genetic linkage studies, DNA was isolated condition with juvenile-onset osteoporosis,(16,17) and a high
from fresh leukocytes using standard procedures. Markers bone mass (HBM) phenotype.(18) Both genes map close to
from the region of interest on chromosome 11 were selected each other within the region that could not be excluded for
from the Ge´ne´thon Genetic Linkage Map.(14) One oligonu- harboring the ADOI gene. D11S4178 is a marker flanking
cleotide from each pair of primers was labeled with T7 the LRP5 gene(18) but is not informative in the key recom-
polynucleotide kinase before polymerase chain reaction bination event in our family (Fig. 5). Therefore, we ana-
(PCR). Amplified products were separated by size on a 6% lyzed three other markers intragenic or close to LRP5
polyacrylamide gel and visualized by autoradiography. Two (D11S1917, D11S4087, and D11S1337) but none of these
point log of the odds (LOD) scores were calculated using was informative for the key recombination event (data not
MLINK version 5.1.(15) The disease frequency was set at shown). This implies that currently both the TCIRG1 gene
1/100,000 and an autosomal dominant mode of inheritance and the LRP5 gene can be considered candidate genes for
with 100% penetrance was assumed. Allele frequencies for ADOI. In the first case, this would be a second example of
the markers were set at 1/n with n being the number of an autosomal recessive osteopetrosis being allelic with a
alleles reported by Ge´ne´thon.(14)
dominant form after our recently reported evidence that
The chromosome 11q12-13 region is one of the priority mutations in the ClCN7 gene underlie ADOII.(9) Alterna-
regions analyzed in the two families because of the previous tively, ADOI could be caused by mutations in the LRP5
assignments of genes involved in bone-related diseases. As gene making it allelic to OPS and HBM. The radiological
shown in Table 1, results obtained in family A provide clear features of ADOI and HBM are strikingly similar but clin-
evidence for linkage between ADOI and this chromosomal ically HBM patients do not have any complaints and are
region. A maximum LOD score of ϩ5.42 was obtained with fully asymptomatic(19) whereas at least some ADOI patients
markers D11S4113 and D11S4136 and LOD scores above suffer from severe pain.(10) Whether a shared pathogenic
ϩ3 were obtained with five other markers. Analysis of the mechanism can underlie both conditions is at this point
smaller family B confirmed this linkage for marker difficult to conclude. ADOI is caused by an impaired bone
D11S4191 with a maximum LOD score above ϩ2.00. The resorption with a markedly reduced number and size of
maximum summated LOD score over the two families is osteoclasts(20) and no such data currently is available for the
ϩ6.54 for marker D11S1889 (Table 1).
HBM phenotype. Mutation analysis of both the TCIRG1
By haplotyping the markers on the pedigrees (Figs. 5 and gene and the LRP5 gene will reveal whether mutations in
6), cosegregation between this chromosomal region and the any of both are underlying ADOI or whether another, still
disease is visualized. Moreover, recombinants enable us to unidentified, gene might be involved.
delineate the candidate region. In family A, a recombination
event on the proximal side can be deduced for patient II1
and is transmitted to his descendants. The recombination
expands proximal of marker D11S1765 and marker
ACKNOWLEDGMENTS
This research was supported by a concerted-action grant
from the University of Antwerp (to W.V.H.) and a grant
(G.0404.00) from the “Fonds voor Wetenschappelijk onder-
zoek” (F.W.O. to W.V.H.) and an Interuniversity Attraction
Pole grant to W.V.H. Dr. Van Wesenbeeck and Dr. Mathy-
sen hold a predoctoral research position with the “Vlaams
instituut voor de bevordering van het wetenschappelijk-
technologisch onderzoek in de industrie.”
D11S4205 possibly is involved (Fig. 5). Another recombi-
nant on the proximal side only involving markers
D11S4102, D11S905, and D11S1763 can be seen in indi-
vidual III9 and her 3 children. On the distal side, individual
IV4 recombines for markers D11S1314 and D11S4207. In
family B, markers D11S4102 and D11S905 recombine in
individual III1 and on the distal side recombinants are seen
for all markers starting with D11S4113 in individuals III3
and III6 and their descendants. Lack of informativity makes
a
conclusion regarding the involvement or markers
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Address reprint requests to:
Wim Van Hul, Ph.D.
Department of Medical Genetics
University of Antwerp
Universiteitsplein 1
2610 Antwerp, Belgium
Olsen BR, Warman ML 1996 Osteoporosis-pseudoglioma syn- Received in original form September 21, 2001; in revised form
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