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Anovel RAB7 mutation associated with ulcero-mutilating neuropathy.

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ed.14 These observations confirm that REM sleep and
dreaming, while linked, may depend on independent
generators.
In conclusion, our case demonstrates the existence of
total dream loss as a distinct neuropsychological dysfunction after deep bilateral occipital lobe damage, in
the absence of REM sleep changes.
Dr C. Gutbrod performed the neuropsychological testing. Dr K. O.
Lövblad performed the brain MRI. Drs P. Brugger, D. Weniger,
and B. Schuknecht made helpful comments.
References
1. Charcot M. Un cas de suppression brusque et isolée de la vision
mentale des signes et des objets (formes et couleurs). Progr Med
1883;2:568 –571.
2. Wilbrand H. Ein Fall von Seelenblindheit und Hemianopsie
mit Sectionsbefund. Dtsch Z Nervenheilkd 1887;2:361–387.
3. Grünstein AM. Die Erforschung der Träume als eine Methode
der topischen Diagnostik bei Grosshirnerkrankungen. Zeit ges
Neurol Psychiatr 1924;93:416 – 420.
4. Nielsen JM. Occipital lobes, dreams and psychosis. J Nervous
Ment Dis 1955;121:50 –52.
5. Murri L, Massetani R, Siciliano G, et al. Dream recall after
sleep interruption in brain-injured patients. Sleep 1985;8:
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7. Aserinski E, Kleitman N. Regularly occurring periods of eye
motility, and concomitants phenomena during sleep. Science
1953;118:273–274.
8. Hobson JA, Pace-Schott EF. The cognitive neuroscience of
sleep: neuronal systems, consciousness and learning. Nat Rev
Neurosci 2002;3:679 – 693.
9. Hobson JA. Sleep and dream suppression following a lateral
medullary infarct: a first-person account. Conscious Cogn
2002;11:377–390.
10. Lhermitte MJ. Syndrome de la calotte du pédoncule cérébral.
Les troubles psychosensoriels dans les lésions mésocéphaliques.
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11. Manford M, Andermann F. Complex visual hallucinations.
Clinical and neurobiological insights. Brain 1998;121:
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12. Takahashi N, Kawamura M. Pure topographical disorientationthe anatomical basis of landmark agnosia. Cortex 2002;38:
717–725.
13. Taylor SF, Liberzon I, Fig LM, et al. The effect of emotional
content on visual recognition memory: a PET activation study.
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14. Solms M. Dreaming and REM sleep are controlled by different
brain mechanisms. Behav Brain Sci 2000;23:843– 850.
A Novel RAB7 Mutation
Associated with UlceroMutilating Neuropathy
Henry Houlden, PhD, MRCP,1–3
Rosalind H. M. King, PhD, FRCPath,1 John R. Muddle,2
Thomas T. Warner, PhD, FRCP,1,2
Mary M. Reilly, MD, FRCP,3
Richard W. Orrell, MD, FRCP,1,2 and
Lionel Ginsberg, PhD, FRCP1,2
There are two known autosomal dominant genes for the
hereditary ulcero-mutilating neuropathies: SPTLC1 (hereditary sensory neuropathy type 1) and RAB7 (Charcot–
Marie–Tooth disease type 2B). We report a family with
autosomal dominant ulcero-mutilating neuropathy, developing in the teens and characterized by ulcers, amputations, sensory involvement in the feet but no motor features. Sequencing the RAB7 gene showed a novel
heterozygous A to C mutation, changing asparagine to
threonine at codon 161. The mutation is situated adjacent to a previously identified valine to methionine mutation at codon 162, implying a hotspot for mutations in
the highly conserved C terminus of RAB7.
Ann Neurol 2004;56:586 –590
The hereditary sensory neuropathies (HSNs) are a heterogeneous group of disorders characterized by prominent sensory loss, often with the development of skin
ulcers, arthropathy, osteomyelitis, and amputations.1
Similar features are seen in Charcot–Marie–Tooth disease type 2B (CMT2B), to the extent that some have
argued CMT2B would be better classified as a form of
HSN. Both HSN type 1 and CMT2B are autosomal
dominant conditions and their phenotypes overlap.
Age of onset in both disorders is typically in the teens,
sensory nerves are prominently affected, and there is a
high incidence of ulcero-mutilating complications. One
difference between HSN1 and CMT2B is said to be
the presence of positive sensory symptoms (paresthesias
From the 1University Department of Clinical Neurosciences, Royal
Free Campus, Royal Free and University College Medical School,
University College London; 2Department of Neurology, Royal Free
Hospital; and 3Center for Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, Queen Square, London,
United Kingdom.
Received Jun 14, 2004, and in revised form Jul 26. Accepted for
publication Jul 29, 2004.
Published online Sep 30, 2004, in Wiley InterScience
(www.interscience.wiley.com). DOI: 10.1002/ana.20281
Address correspondence to Dr Ginsberg, Department of Neurology,
Royal Free Hospital, Pond Street, London NW3 2QG, United
Kingdom. E-mail: lionel.ginsberg@royalfree.nhs.uk
586
© 2004 American Neurological Association
Published by Wiley-Liss, Inc., through Wiley Subscription Services
and lancinating or burning pain) in the former. More
marked distal motor involvement is said to favor a diagnosis of CMT2B. Unlike CMT2B, motor nerve conduction velocities in HSN1 families are occasionally
slowed, sometimes into the demyelinating range.2,3
Using linkage analysis, the gene for HSN1 was localized to chromosome 9q22.4 Mutations in the serine
palmitoyltransferase, long chain base subunit-1
(SPTLC1) gene were then identified as the cause.5,6 In
CMT2B, genetic linkage analysis identified a locus on
chromosome 3q13–q22.7–9 The small GTP-ase late
endosomal protein RAB7 was subsequently identified
as the disease gene.10 Two mutations have been described: a transition Val162Met mutation in exon 4
and a Leu129Phe mutation in exon 3.
RAB7 is one of more than 60 Ras-related GTP-ases.
These proteins regulate vesicle transport by the recruitment of specific effector proteins with a possible role
linking vesicles and target membranes to the cytoskeleton.11,12 RAB7 is involved in transport between late
endosomes and lysosomes. The mechanism of action of
RAB7 genetic mutations in the development of peripheral neuropathy is as yet unknown, although RAB proteins are known to be involved in neurite outgrowth.13
We report the clinical and pathological findings in a
further autosomal dominant ulcero-mutilating neuropathy family, with an Asn161Thr mutation in the RAB7
gene. This mutation is in a highly conserved region,
adjacent to the reported Val162Met mutation, suggesting a functionally important hotspot for RAB7 mutations. The mutation leads to a virtual absence of expression of a key RAB7 effector, RILP (Rab interacting
lysosomal protein), implying the pathogenetic mechanism for this neuropathy may be through this effector
pathway.
Materials and Methods
Nerve Biopsy
A sural nerve fascicular biopsy specimen was obtained from
the proband with informed consent and processed according
to our standard laboratory procedures.14 The procedure was
justified on routine diagnostic grounds, having taken place at
a time before molecular genetic testing for HSN1 and
CMT2B had become available, and after other affected family members had died. In addition to semithin sections for
light microscopy and morphometry, and ultrathin sections
for electron microscopy, frozen sections were stained immunocytochemically using a polyclonal antibody against RILP15
(gift from Dr C. Bucci).
Genetic Analysis
With informed consent, DNA was extracted from blood
samples obtained from affected and unaffected family members. The five exons and flanking intronic regions of the
RAB7 gene were amplified by polymerase chain reaction
(PCR) (primers available on request). PCR products were
purified (96-well plate; Millipore, Billerica, MA) and se-
quenced using the BigDye Terminator cycle sequencing kit.
Sequencing reactions were loaded on an ABI 3100 Genetic
Analyzer (Perkin Elmer Applied Biosystems, Foster City, CA).
Exons 5 and 6 of the SPTLC1 gene also were sequenced.5,6
Results
Clinical Details
The family reported here is an autosomal dominant,
three-generation, English pedigree with ulceromutilating neuropathy. The proband is a 56-year-old
man. At the age of 16 years, he developed a painful
ulcer on the left sole. This lesion never healed and he
had numerous operations on this foot. At the age of 47
years, he developed progressive right foot pain, with
swelling and deformity. There was also spontaneous
lancinating pain in the left foot. His mother had also
been affected, with scoliosis, ulcers, and operations on
her feet, including amputations. His maternal grandfather had a history of gangrene and leg amputation. His
brother and son were clinically normal.
On examination, the proband had gross deformity of
the right foot. The middle toe of his left foot had been
amputated. He had mild scoliosis. There was nystagmus to lateral gaze. In the limbs, there was no wasting.
Tone, power, and coordination were normal. The ankle jerks were absent. Plantar responses were downgoing. Vibration sensation was reduced to the costal margins. Joint position sense was abnormal at the toes.
Pin-prick sensation was impaired in the right foot and
later the left.
Blood tests were normal including syphilis serology.
Plain radiographs of the right foot showed a Charcot–
Lisfranc joint. Brain imaging showed cerebellar degeneration. Autonomic function tests were normal.
Nerve Conduction Studies
Motor nerve conduction studies in the proband were
normal in the upper limbs. In the lower limbs, distal
motor latency was prolonged in the common peroneal
nerve at 9.2 milliseconds, with a compound muscle action potential amplitude of 0.1mV. Sensory conduction velocities were normal throughout, but some sensory nerve action potentials were reduced in amplitude
(right median, 7␮V; left median, 5␮V; right ulnar,
3␮V; left ulnar, 3␮V; right radial, 23␮V; left sural,
7␮V). Thermal thresholds were abnormal at the right
thenar eminence (warming, 13°C; cooling, 2.5°C; difference, 15.5°C). At the lateral border of the right foot,
thresholds were also abnormal (warming, 13.4°C; cooling, 3.5°C; difference, 16.9°C). Large fiber nerve conduction studies were normal in the proband’s brother.
Nerve Biopsy
Sural nerve fascicular biopsy from the proband showed
moderately severe depletion of the myelinated fiber
population (Fig 1A). This was confirmed by mor-
Houlden et al: Neuropathy and RAB7 Mutation
587
Fig 1. Sural nerve biopsy from the proband. (A) Semithin resin section (thionin and acridine orange) showing loss of myelinated
fibers with prominent regenerative clusters (arrows). Bar ⫽ 50␮m. (B, C) Immunostaining against RILP in nerve biopsy from
proband and control, respectively. (brown) Horseradish peroxidase. Bar ⫽ 50␮m.
588
Annals of Neurology
Vol 56
No 4
October 2004
phometry: total myelinated fiber density was
3,301/mm2 compared with a value of 7,007/mm2 from
a normal control of the same age. The myelinated fiber
size distribution at first sight appeared relatively normal
because the loss of the normal small fiber population
was counterbalanced by the presence of many small regenerating fibers. There were very few remaining normal small fibers (see Fig 1A). No abnormal axonal or
Schwann cell inclusions were seen by light microscopy,
but electron microscopy showed some inclusions in
small unmyelinated axons suggesting active axonal loss.
This was confirmed by the presence of collections of
flattened sheets of Schwann cell processes. Some Remak bundles contained more axons than normal, also
suggesting regeneration. Immunostaining of the proband’s nerve biopsy specimen with polyclonal antibody
against RILP was markedly reduced compared with
control (see Fig 1B, C).15
Genetic Analysis
Sequencing the entire RAB7 gene in the proband
showed an A to C heterozygous mutation in exon 4
(Fig 2), causing an amino acid change from asparagine
to threonine at position 161. This change was absent
in the unaffected brother and in 200 chromosomes
from English controls on restriction enzyme digest
with the enzyme TaiI (Fermentas, Hanover, MD). No
other family individual was available for genetic analysis. Sequencing exons 5 and 6 of the SPTLC1 gene in
the proband was normal.
Discussion
The index case in this family showed an early-onset,
slowly progressive, ulcero-mutilating neuropathy with
amputations and no motor features. There was also evidence of central involvement with nystagmus and cerebellar atrophy on brain imaging. The neuropathy was
Fig 2. RAB7 exon 4. A to C heterozygous mutation. Amino
acid change is asparagine to threonine at position 161. Arrows
indicate mutation position.
Fig 3. Amino acid sequence of the RAB7 gene mutation region in a wide variety of species shows that this region is
highly conserved, underlining the functional importance of the
change. Mutations in the RAB7 gene in the family described
here (Asn161Thr) and reported by Verhoeven and colleagues
10
(Val162Met) are indicated in boldface and with arrows.
inherited in an autosomal dominant fashion over three
generations. Nerve conduction studies supported the
diagnosis of a sensory axonal neuropathy, although the
electrical features were mild. Sural nerve biopsy showed
appearances of a chronic active neuropathy causing axonal degeneration and prominent regeneration.
This family expands the phenotypic spectrum of
CMT2B. The findings in the proband suggest there
are few distinguishing features between CMT2B and
HSN1. Clinically, the presence of positive sensory features, the development of ulcers, and the need for amputations would indicate HSN1. The lack of motor
findings is more suggestive of HSN1 than CMT2B.
These anomalies, and the evidence for central nervous
system involvement, illustrate how establishing the genetic basis of a disease may expand the range of phenotypic manifestations. This phenomenon has been
recognized in the hereditary neuropathies since molecular genetic techniques became readily available.16
Pathologically, the proband’s sural nerve biopsy did
show features typical of CMT2, these being an axonopathy with marked regeneration, although previous
histological descriptions have largely been restricted to
CMT2A.16
The Asn161Thr mutation identified in this family is
only the third to be reported in the RAB7 gene. This
mutation is adjacent to the previously reported
Val162Met mutation, suggesting clustering at a potential hotspot for RAB7 mutations. Codons 161 and 162
are both highly conserved (Fig 3), implying functional
importance throughout evolution, and are located in
the C terminus region of RAB7. The other RAB7 mutation is located at codon 129, close to a conserved
guanine nucleotide binding domain.
RAB7 is a protein involved in vesicle transport between late endosomes and lysosomes and is thought to
act by the induction of a number of effectors.17 One of
the key effectors of RAB7 is RILP, which induces the
Houlden et al: Neuropathy and RAB7 Mutation
589
recruitment of dynein-dynactin motors to the late endosome/lysosome, thereby stimulating the transport of
these compartments toward the perinuclear region
along microtubules.15,18 The interaction of RAB proteins with effectors such as RILP may underlie the involvement of these proteins in neurite outgrowth.13
The significant reduction of RILP expression (Fig
1B, C) in the proband’s sural nerve biopsy suggests
that the mutation lies in an essential part of the gene,
crucial for RAB7 and RILP interaction. Alternatively,
the RAB7 mutation may cause a dominant negative effect with a reduction in RAB7 production and hence
RILP interaction. It seems less likely that mutant RAB7
causes the disease phenotype directly. If this were the
case, more widespread clinical abnormalities might be
expected, given the probable role of RAB7 in cellular
housekeeping. These putative mechanisms are probably
oversimplifications, however, because RAB7 may have
additional functions and intermolecular relationships.
Another RAB7 effector, RABring7, is thought to act in
tandem with RILP.19 A recent study has shown that
RAB7 may also be a proapoptotic protein.20
In conclusion, the ulcero-mutilating neuropathies are
a diverse group of disorders, both clinically and genetically. The family described here expands the range of
phenotypic manifestations of CMT2B and may give an
initial clue to the pathogenetic mechanism of RAB7
mutations.
We thank the family for their help with this project. We are also
grateful to Dr C. Bucci for the RILP antibodies, and to J. Workman for technical assistance. We thank the Wellcome Trust for help
with laboratory consumables. All DNA analyses were conducted in
the Neurogenetics Laboratory at the Institute of Neurology, Queen
Square, London, UK.
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October 2004
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small GTP-ase late endosomal protein RAB7 cause CharcotMarie-Tooth type 2B neuropathy. Am J Hum Genet 2003;72:
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17. Seachrist JL, Ferguson SS. Regulation of G protein-coupled receptor endocytosis and trafficking by Rab GTPases. Life Sci
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effector protein RILP controls lysosomal transport by inducing
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20. Edinger AL, Cinalli RM, Thompson CB. Rab7 prevents growth
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