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Association between centromeric deletions of the SMN gene and sporadic adult-onset lower motor neuron disease.

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Association between Centromeric Deletions
of the SMN Gene and Sporadic Adult-Onset
Lower Motor Neuron Disease
Bruno Moulard, MD, PhD,* FranGois Salachas, MD, PhD,? BtnCdicte Chassande, M D , t Valerie Briolotti,$
Vincent Meininger, MD, PhD,t Alain Malafosse, MD, PhD,§ and William Camu, MD, PhDS
The telomeric copy (r) of the survival motor neuron (SMN) gene is homozygously deleted in more than 90% of patients
with infantile motor neuron disease (MND). In the general population, no homozygous SMNt deletion has been found,
whereas 5% of centromeric SMN (SMNc) deletions can be observed. Although SMNt deletions appear causal for infantile
and at least some adult-onset spinal muscular atrophy (SMA) (type IV), the respective role of SMNdeIetions remains
unclear in adult-onset MNDs. We studied SMN gene in three different groups of patients with adult-onset MNDs. In
sporadic amyotrophic lateral sclerosis (ALS; n = 177) and familial ALS (n = 66), no SMNt deletion had been found, and
the frequency of SMNc deletions was not increased. Conversely, among the 14 patients with sporadic pure lower MND
(LMND), we found 2 patients with homozygous SMNt deletions (14%)and 5 patients with homozygous SMNc deletions
(36%).These data suggest that (1) SMNt deletions do not account for the major part, if any, of adult-onset LMND cases;
and (2) SMNc deletions act as a susceptibility factor for LMNDs in adults. The clinical and genetic heterogeneity of
LMND cases, including SMA type IV,are yet to be unexplained. Further studies on large groups of adult-onset LMND
patients are warranted to refine its nosology.
Moulard B, Salachas F, Chassande B, Briolotti V, Meininger V, Malafosse A, Carnu W.
Association between centromeric deletions of the SMN gene and sporadic adult-onset
lower motor neuron disease. Ann Neurol 1998;43:640-644
Childhood-onset proximal spinal muscular atrophy
(SMA) is the most common and severe infantile motor
neuron disease (MND). The disease is characterized by
a dramatic degeneration of spinal and bulbar motor
neurons.' SMA is inherited with an autosomal recessive
trait and recent studies point out the interest in the
survival motor neuron (SMN) gene on chromosome
5q13, which is deleted on both exons 7 and 8 in more
than 90% of the cases.223SMNis present in two copies
on chromosome 5q13, telomeric (SMNt) and centromeric (SMNc). Only homozygous SMNt deletions are
associated with SMA, and they are not found in the
general population. Homozygous SMNc deletions have
rarely been described in SMA, but are present in 2 to
5% of unaffected subjects.233However, little is known
about the incidence of those deletions in other MNDs,
namely, adult-onset MNDs. Amyotrophic lateral sclerosis (ALS) is the most frequent adult-onset MND,
leading to death in a few months or years after onset.*
In a manner similar to SMA, the disease affects spinal
and bulbar motor neurons, but the degeneration also
involves the corticospinal tract. ALS is mainly sporadic,
but familial cases with an autosomal dominant inheritance account for 10% of the cases.' In a subset of
families, several mutations in the copperhinc superoxide dismutase (SODI) gene on chromosome 21 have
been described.6 However, the cause of this disease remains unknown in the great majority of the cases. The
term adult-onset pure lower motor neuron disease
(LMND) defines a group of diseases characterized by
the degeneration of lower motor neurons, a distal and
asymmetrical onset, a rather disabling course, and the
absence of familial history. Those elements are helpful
for differentiating LMND from the rare adult-onset
SMA, namely, type IV.' The etiopathogenesis of adult
LMND is unknown, but owing to its severity, this disorder is often considered a possible ALS variant. We,
and many other authors,'-''
have described several
families where SMA and adult-onset MNDs coexisted,
suggesting that childhood- and adult-onset MNDs
From the *Laboratoire de Mtdecine Exptrimentale, Institut de Biologie, and $Service de Neurologie B, HBpital Gui de Chauliac and
Laboratoire de Physiopathologie Neuromusculaire, INSERM CJF
37-02, Institut de Biologie, Montpellier; and ?Service de Neurologie, Division Mazarin, Hbpital de la SalpCtri&re,Paris, France; and
§Division de Neuropsychiatrie, HBpital Belle-Idte, GenPve, Switzerland.
Received May 14, 1997, and in revised form Aug 28 and Dec 1.
Accepted for publication Dec 6, 1997.
Address correspondence to Dr Camu, Service de Neurologie B,
HBpital Gui de Chauliac, 34295 Montpellier Cedex 5 , France.
640 Copyright 0 1998 by the American Neurological Association
share a common genetic background (cases are reviewed by de Belleroche and associates5). We then
studied SMN polymorphisms in three different groups
of adult-onset MNDs, that is, sporadic ALS (SALS;
n = 177), familial ALS (FALS; n = 66), and LMND
(n = 14). Here, we show that homozygous SMNc deletions are present in 36% of the LMND cases, and
the frequency of those deletions in SALS and FALS is
comparable with that of the general population. Furthermore, although SMNt deletions are absent in our
SALS and FALS cases, we describe 2 LMND patients
with this deletion. These data suggest that (1) homozygous SMNt deletions do not comprise or explain the
occurrence of LMND in adults; and (2) the occurrence
of homozygous SMNc deletions may be a genetic risk
factor for adult-onset LMND.
Patients and Methods
Patients
FALS (n = 66) and SALS patients (n = 177) had probable
or definite ALS according to international criteria requiring
unequivocal upper and lower motor neuron signs in two or
three regions (eg, bulbar level, upper limbs, and/or lower
limbs), respectively.”,’2 The third group was composed of
14 subjects suffering from late adult-onset LMND, in whom
motor neuropathies with or without conduction blocks,
Kennedy’s disease (absence of abnormal CAG e~pansion),’~
lymphoma, and malignant plasma cell dyscrasia have been
excluded. For those patients, careful attention was given to
the criteria of entry in the study, to ensure that they did not
fulfill criteria for the rare form of adult-onset proximal spinal
muscular atrophy (SMA), the so-called type IV.’” In brief,
they all had an asymmetrical and distal onset of weakness,
with an unequivocal progression throughout the years and
no familial history of MND. For all the patients enrolled in
this study, classification has been done prospectively, and the
subjects have been followed longitudinally to ensure, after
years or at the time of death, that criteria for diagnosis were
still fulfilled.
The following clinical data were obtained for all subjects
(Table 1): (1) age at onset, defined as the time at which the
first symptoms of muscle weakness were noted by the patient; (2) duration of the disease, defined as the interval between onset and death, and expressed as the median survival
for each group, because a significant number of patients were
still alive; and (3) sex.
Analysis of SMN Polymorphisms
Homozygous deletions for SMNt and SMNc in exons 7 and
8 were studied as previously
In brief, both exons were first amplified by polymerase chain reaction (PCR),
using R1 11 and X7DRA as primers for exon 7 and 541C960
and 541C1120 for exon 8. Each product was then digested
at 37°C overnight, with 5 U DraI for exon 7 and 5 U DdeI
for exon 8.14 After digestion, the pattern was analyzed by gel
electrophoresis on 4% Nu Sieve GTG agarose (Biogel, Vista,
CA). Each abnormal pattern was further confirmed by
single-strand conformation polymorphism according to the
technique of Lefebvre and colleagues; slightly modified.
In brief, both exons were amplified by radioactive PCR
([a-33P]dCTP, Isotopchim, Ganogobie, France) with R1 11
and 541C770 for exon 7 and 541C960 and 541C1120 for
exon 8. The PCR product ran, at 4 W, on electrophoresis gel
(Hydrolink MDE, FMC Bioproducts, Rockland, ME) at
room temperature for 14 hours for exon 8 and 15 hours for
Table 1. Characteristics of the Patient5
Age at Onset
n
Sporadic ALS
Whole group
SMNt deletion
SMNc deletion
No deletion
(yr)
177
0
11 (6.2%)
166
Familial ALS
Whole group
SMNt deletion
SMNc deletion
No deletion
LMND
Whole group
SMNt deletion
SMNc deletion
No deletion
66
6 2 2 11
Duration
(mo)
28
Sex Ratio
(M@)
1.21 (97180)
-
-
-
63 k 9
6 2 & 11
29
28
1.2 (615)
1.21 (91175)
52 -+ 12
29
1.2
-
-
-
1 (1.5%)
65
61
52 t 12
48
29
M
14
2 (14%)
5“ (36%)
7
46-+ 15
28
40 ? 8
5 6 ? 13
36
140
25
36
0
(36130)
1.16 (35130)
1.80
1
1.50
2.5
(915)
(111)
(312)
(512)
Centromeric (c) and telomeric (t)survival motor neuron (SMN)gene deletions on exons 7 and 8 were determined on agarose gel after a specific
polymerase chain reaction amplification for each exon. The presence of SMN deletion was confirmed by single-strand conformation polymorphism. The percentages for each subgroup are given in reference to the n value for the whole group. The frequency of deletions was compared
between the groups by using
statistics.
xz
ap
< 0.001.
A L S = amyotrophic lateral sclerosis; LMND = lower motor neuron disease.
Moulard et al: SMN Deletions and Lower Motor Neuron Disease 641
exon 7. For most of the patients, SMN deletions were con-
firmed by Dr J. Melki (Hopital Necker, Paris, France).
StatisticaI Analysis
The frequency of SMN deletions between the groups was
compared by using x2 statistics with Yates’ correction when
needed, using Statgraphics, version 2.6, software.
Results
We determined SMN gene polymorphisms in 257 patients with adult-onset MND-66 FALS patients, 177
SALS, and 14 LMND. The characteristics of the ALS
groups corresponded to those of the literature, with an
earlier age of onset and the predominance of spinal onset in FALS compared with SALS.5 In LMND, onset
was slightly earlier than ALS and median survival was
higher.7
Homozygous deletions in the SMN gene were observed in 19 patients (Fig). SMNc deletions of both
exons 7 and 8 were found in only 1 FALS patient
(1.5%) and in 11 SALS patients (6.2%) (Table 2). The
type and frequency of homozygous SMN deletions in
A L S (sporadic and familial) did not differ from different groups in the literature (ie, normal individual^,^^'^
SMA parents,16 or other ALS patient^'^).
In the 14 subjects with LMND, seven homozygous
deletions (50%) were noted-five
centromeric in both
exons 7 and 8, one telomeric in exon 7, and one telomeric in both exons 7 and 8 (see Table 2). The com-
642
Annals of Neurology Vol 43
No 5
May 1998
parison of the frequencies of SMNc deletions between
the three MND groups was highly significant ( p <
0.001; see Table 1). One can consider that the 2 patients with SMNt deletion have in fact adult-onset
SMA such as other already described cases.2’3,18219
This
was also supported by their clinical profile, which was
different from that of the other LMND patients. Onset
of the disease was before 30 years, and evolution was
the slowest of their group, with a disease duration of
190 and 90 months, respectively, although the handicap was severe.
In SALS and FALS, age of onset, median survival,
and sex ratio did not significantly differ either with or
without SMN deletion. Of the 11 ALS patients with
SMN deletions, 5 were still alive after 14, 22, 31, 92,
and 92 months of disease, respectively. Their clinical
profile was undoubtedly that of ALS, with no atypical
clinical feature even if, in 2 cases, there was unusually
long-lasting ALS (92 months).
In the LMND group, when SMNc deletions are
present, the disease starts earlier (40 vs 56 years without SMNc deletion) and is more severe (25 vs 36
months), and the gender (M/F) ratio is lower (1.5 vs
2.5). This contrasts not only with LMND patients
without any SMN deletion but also with the 2 patients
with SMNt deletions (see Table 1). However, because
of the small number of patients in each subgroup, a
Table 2. Homozygous SMN Deletions
SMNt Deletion
No. of
No
Deletion
Exon 7
0
0
1
0
0
0
0
0
0
11
5
166
65
7
0
0
0
0
MD
2
0
11
2
MD
13
235
144
347
138
Exon 7
Exon 8
Exon 7
Sporadic ALS
Familial ALS
177
66
14
0
0
1
0
0
0
246
152
348
154
0
0
0
0
0
0
0
0
ALS”
+8
Exon 8
Patients
Patients and controls from the
literature
Normal individuals’
Normal individuals3
SMA parents”
+8
Exon 7
Subjects
LMND
SMNc Deletion
1
0
6
MD
1
1
SMNt = telomeric survival motor neuron ( S M N ) gene; SMNc = centromeric SMN; ALS = amyotrophic lateral sclerosis; LMND = lower
motor neuron disease; SMA = infantile spinal muscular atrophy; MD = missing data.
statistical analysis regarding these parameters was not
possible for the whole LMND group.
Discussion
In different groups of adult-onset MNDs (FALS,
SALS, and LMND), we have shown that homozygous
deletions in the centromeric part of the SMN gene are
significantly more frequent in LMND. In SMA, telomeric deletions of SMN exons 7 and 8 are closely associated with the disease, but only a few patients were
found to carry SMNc d e l e t i ~ n .Little
~
is known about
the role of the centromeric region of the SMN gene,
but the high frequency of SMNc deletions in adultonset LMND, and the difference in clinical profile of
those subjects in our study (earlier onset, more severe
evolution, and different gender ratio) compared with
those without SMNc deletion, suggest that this deletion
may be a genetic factor of susceptibility for developing
LMND.
The frequency of SMNc deletions in SALS in our
study is similar to that found in a recent study,” 6.4%
compared with 8.4% (see Table 2). However, if additional deletions were described in exons 7 and 8 alone
(3 cases, centromeric) in this last study, no specific data
were available from LMND patients because of the
small number of patients. The study by Jackson and
collaborator^'^ focused on the NdP gene. This gene,
as SMN, is associated with childhood-onset SMA but
to a much lesser extent.2o Homozygous N A P deletion
was found in 1 patient with typical ALS in the study
by Jackson and colleague^.'^ We also searched for
NMP deletions and found 1 ALS patient with a deletion (data not shown). The frequency of NAIP deletions in both studies corresponds to the estimated frequency in the general population. In SMA, the N A P
deletion usually coexists with the SMNt d e l e t i ~ n .Sub~
sequently, the absence of a concomitant SMN deletion
in 2 patients with ALS does not allow supposition that
the N A P deletion plays a role in the etiopathogenesis
of ALS.
In adult-onset SMA, SMNt deletions have been described but less frequently than in the childhood-onset
type.1s919Nevertheless, the strong association between
SMA and SMNt deletions, in the literature, led us to
consider that our 2 patients with both LMND and
SMNt deletions had in fact adult-onset SMA, even
without a family history. O n the other hand, the following are several reasons for arguing that LMND patients with SMNc deletions cannot be considered nosologically as having the same type of MND: (1) The
onset of the disease is distal and asymmetrical; (2) there
is a clear evolution of the disease throughout the years;
(3) there is no family history; (4) SMNc deletions have
not been associated with SMA in any previous study,
even in the less severe cases, namely, adult-onset SMA
type IV; and (5) in the LMND group, those patients
with SMNt deletions are consistently different from
those with SMNc deletions, with an earlier onset and
with a much less severe disease with long-lasting evolution. A recent report strengthens these points, showing that a father with distal SMA and his son with
proximal SMA (SMA type I) had no common abnormality on the SMN gene.2’
Not all the LMND patients had one or the other
SMN deletion. We cannot, however, rule out the possibility that other abnormalities of the SMN genes are
present in those patients, or in ALS. In support of this
hypothesis, mutations have been found in different
areas of the SMN gene for a more restricted number of
patient^.^^-^^ Different murations on the same gene
have already been shown to be responsible for different
phenotypes. In ALS, where more than 60 SOD1 mutations have been described, different point mutations
can lead to strikingly different phenotypes in which the
motor neuron degeneration remains the main clinical
feature although disease duration may vary from 1 to
Moulard et al: SMN Deletions and Lower Motor Neuron Disease
643
20 years.26 However, the nosology of LMND is much
less precise than that of ALS, and larger studies, necessarily multicentric, and focused on this type of
MND, are then warranted to confirm our data and
help to refine our understanding of this disease.
In summary, the study of the SMN gene on chromosome 5q13 in adult-onset MNDs showed that centromeric deletions were statistically more frequent in
LMND than in sporadic or familial ALS. The hypothesis that the telomeric part of the SMN gene has a major role on motor neuron metabolism is a consequence
of studies on childhood-onset SMA. The high frequency we found for centromeric deletions in adultonset LMND, a disease that is in several respects nosologically distinct from SMA, and the particular clinical
profile of those subjects, led us to hypothesize that
both parts of the SMNgene could be involved in motor neuron metabolism. SMNt would have a major influence leading to severe motor neuron degeneration
when abnormal, and SMMc would exert a less important role, such as that of a susceptibility factor, increasing the risk of having adult-onset lower motor neuron
degeneration.
The Association Franpise pour la Recherche sur la Sclkose Laterale
Amyotrophique and the Association FranCaise contre les Myopathies
provided financial support. This study was also supported by PHRC
and DRC AP-HP grants.
We gratefully acknowledge the contribution of Dr J. Melki for
checking our genetic data.
References
1. Emery AEH. The nosology of the spinal muscular atrophies.
J Med Genet 1971;8:481-495
2. Lefebvre S, Burglen L, Reboullet S, et al. Identification and
characterization of a spinal muscular atrophy-determining gene.
Cell 1995;80: 155-1 65
3. Rodrigues NR, Owen N, Talbot K, et al. Gene deletions in
spinal muscular atrophy. J Med Genet 1996;33:93-96
4. Rowland LP. Ten central themes in a decade of amyotrophic
lateral sclerosis research. In: Rowland LP, ed. Advances in neurology, vol 56: motor neuron disease. New York: Raven Press,
1991:3-23
5. de Belleroche J, Leigh PN, Clifford Rose F. Familial motor
neuron disease. In: Leigh PN, Swash M, eds. Motor neuron
disease: biology and management. London: Springer-Verlag,
1995:35-5 1
6. Rosen DR, Siddique T, Patterson D, et al. Mutations in CulZn
superoxide dismutase gene are associated with familial amyotrophic lateral sclerosis. Nature 1993;362:59-62
7. Swash M, Schwartz MS. Motor neuron disease: the clinical syndrome. In: Leigh PN, Swash M, eds. Motor neuron disease:
biology and management. London: Springer-Verlag, 1995:l-17
8. Shaw PJ, Ince PG, Goodship J, et al. Adult onset motor neuron
disease and infantile Werdnig-Hoffmann disease (spinal muscular atrophy type I) in the same family. Neurology 1992;42:
1477-1480
644 Annals of Neurology Vol 43
No 5
May 1998
9. Appelbaum JS, Roos RP, Salazar-Grueso EF, et al. Intrafamilial
heterogeneity in hereditary motor neuron disease. Neurology
1992;42: 1488-1492
10. Camu W, Billiard M. Coexistence of ALS and WerdnigHoffmann disease within a family. Muscle Nerve 1993;5:569570
11. Swash M, Leigh PN. Criteria for diagnosis of familial amyotrophic lateral sclerosis. Neuromusc Disord 1932;2:7-9
12. Brooks BR. El Escorial World Federation of Neurology criteria
for the diagnosis of amyotrophic lateral sclerosis. J Neurol Sci
1994;124(Suppl):96-107
13. La Spada AR, Wilson EM, Lubahn DB, et al. Androgen receptor gene mutations in X linked spinal and bulbar muscular atrophy. Nature 1991;352:77-79
14. Van der Steege G, Grootscholten PM, Van der vlies P, et al.
PCR-based rest to confirm clinical diagnosis of autosomal recessive spinal muscular atrophy. Lancet 1995;345:985-986
15. Rodrigues NR, Owen N, Talbot K, et al. Deletions in the survival motor neuron gene on 5q13 in autosomal recessive spinal
muscular atrophy. Hum Mol Genet 1995;4:631-634
16. Hahnen E, Forkert R, Marke C, et al. Molecular analysis of
candidate genes on chromosome 5q13 in autosomal recessive
spinal muscular atrophy: evidence of homozygous deletions of
the SMN gene in unaffected individuals. Hum Mol Genet
1995;4:1927-1933
17. Jackson M, Morrison KE, Al-Chabali A, et al. Analysis of chromosome 5q13 genes in amyotrophic lateral sclerosis: homozygous NAIP deletion in a sporadic case. Ann Neurol 1996;39:
796-800
18. Clermont 0, Burlet P, Lefebvre S, et al. SMN gene deletions in
adult-onset spinal muscular atrophy. Lancet 1995;346:17121713
19. Brahe C, Servidei S, Zappata S, et al. Genetic homogeneity
between childhood-onset and adult-onset autosomal recessive
spinal muscular atrophy. Lancet 1995;346:741-742
20. Roy N, Mahadevan MS, McLean M, et al. The gene for neuronal apoptosis inhibitory protein is partially deleted in individuals with spinal muscular atrophy. Cell 1995;80:167-178
21. Spranger S, Rudnik-Schoneborn S, Spranger M, et al. Proximal
and distal spinal muscular atrophy in one family: molecular genetic studies provide further evidence for the non-allelic origin
of both diseases. J Med Genet 1997;34:340-342
22. Bussaglia E, Clermont P, Tizzano E, et al. A frame-shift deletion in the survival motor neuron gene in Spanish spinal muscular atrophy patients. Nat Genet 1995;11:335-337
23. Brahe C, Clermont 0, Zappata S, et al. Frameshift mutation in
the survival motor neuron gene in a severe case of SMA type I.
Hum Mol Genet 1996;5:1971-1976
24. Parsons DW, McAndrew RE, Monani UR, et al. An 11 base
pair duplication in exon 6 in the SMN gene produces a type 1
spinal muscular atrophy (SMA) phenotype: further evidence for
SMN as the primary SMA-determining gene. Hum Mol Genet
1996;5: 1727-1732
25. Hahnen ET, Wirth B. Frequent DNA variant in exon 2a of the
survival motor neuron gene (SMN): a further possibility for distinguishing the two copies of the gene. Hum Genet 1996;98:
122-123
26. Fbdunovic A, Leigh PN, on behalf of the European Familial
ALS Group. Cu/Zn superoxide dismutase gene mutations in
amyotrophic lateral sclerosis: correlation between genotype and
clinical features. J Neurol Neurosurg Psychiatry 1996;61:565572
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