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Werner Syndrome
Marc Ialenti and Rushi Parikh
Werner Syndrome (WS) is an autosomal recessive disease that leads to the
premature manifestation of clinical symptoms associated with normal aging. Clinical
symptoms include: short stature, graying/loss of hair, osteoporosis, cataracts,
atherosclerosis, type II diabetes, hypogonadism, skin ulcers, reduced fertility, and high
incidence of malignant neoplasms. They appear in one’s 20’s and 30’s, and myocardial
infarction is the chief cause of death at approximately 48 of age. Individuals with WS
display significant genomic instability in the form of DNA repair and replication defects,
problems involving transcription and telomere maintenance, chromosomal
rearrangements, attenuated apoptosis, and recombinational defects. The Werner protein
(WRN) is involved in many crucial DNA metabolic pathways, particularly DNA repair
processes, and so it serves as a key link between faulty DNA repair and the mechanisms
of aging and cancer (1).
WRN Biochemistry and Genetics
WRN is a member of the RecQ family of DNA helicases and possesses ATPdependent 3’-5’ helicase and 3’-5’ exonuclease activity. The N-terminal region of WRN
has exonuclease domains, the central region contains the RecQ helicase domains, and the
C-terminal region possesses the nuclear localization signal (NLS) that controls the
nuclear targeting of WRN. The preferred substrates of WRN helicase include DNA
structures such as Holliday junctions, tetraplex DNA, forked duplexes, and mismatch
“bubble” duplexes, as well as DNA-RNA heteroduplexes. WRN exonuclease targets
DNA duplexes containing mismatch “bubbles”, a Holliday junction, or forks (2). The
NLS directs WRN to localize at nucleoli (transcription centers), replication forks (DNA
replication structures), DNA foci (DNA repair sites), and AA-PML bodies (telomere
metabolism sites) (1).
35 WRN mutations have been identified to date with each resulting in absent or
truncated protein products; it should be noted that WS is the only phenotype derived from
WRN mutations. Mutations types include: insertions, deletions, and splicing
donor/acceptor site mutations that result in frame shifts (no protein product), and
premature stop codons that result in truncated proteins. These mutations predominantly
occur in large introns and regulatory regions (2). The most prevalent mutation is 1336
C>T that accounts for nearly 25% of WS cases. The IVS 25-1G>C founder effect
mutation accounts for 60% of WS cases amongst the Japanese population (3). All WRN
mutations are characterized by the absence of the C-terminal region, and so the resulting
loss of NLS and improper transport of WRN to specific nuclear regions seems key for
WS pathogenesis (1).
WRN Molecular Biology
WRN is a critical participant in several DNA metabolic pathways—DNA repair,
replication, and recombination as well as transcription. WRN not only unwinds/digests
abnormal DNA structures during DNA metabolism, but it also helps regulate DNA repair
and recombination through unwinding/digestion of intermediate DNA structures.
Consequently, WRN clearly plays a key role in maintaining genomic integrity (1).
WRN’s role in DNA replication is supported by the fact that individuals with WS
have cells that undergo premature replicative senescence, exhibit longer S-phase, and
show a reduction of replication initiation sites in comparison to cells of normal
individuals (4). Recent studies have elucidated WRN’s interaction with DNA replication
components DNA polymerase δ, Replication Protein A, and FEN-1, which is involved in
the processing of Okazaki fragments during lagging strand synthesis (1).
The integral role WRN plays in DNA repair is supported by WS cells having nonhomologous chromosomal rearrangements that are consistent with defective DNA repair
mechanisms such as base excision repair and homologous recombinational repair (1).
For instance, recent studies have shown WRN’s key association with the Ku heterodimer
and DNA-dependent protein kinase, two major components involved in repairing double
strand DNA breaks (5). WRN’s role in DNA damage response pathways (DNA repair) is
further supported by its interaction with p53, a tumor suppressor protein that is critical for
apoptosis, cell cycle arrest, and senescence. Recent studies indicate that the
overexpression of WRN causes a increase in p53-dependent transcriptional activity and
that p53-mediated apoptosis is attenuated by WS cells (6).
As stated earlier, WRN is also involved in telomere metabolism. Telomere
dysfunction and shortening leads to replicative senescence and genomic instability.
Recent studies report that the expression of exogenous telomerase (telomere extender) in
WS fibroblast lengthens the cellular life span. These findings suggest that premature
senescence in WS cells is associated with telomeres, and more specifically, that WRN
mutations lead to accelerated telomere shortening and disruption of telomere structure
that the protective effects of telomerase may counteract against (7).
Future WRN Considerations
There are still many key features of WS that have yet to been explained. A better
understanding of the regulation of WRN cellular localization is crucial for elucidating its
cellular roles. Alterations such as post-translational modifications and specific protein
interactions may prove pivotal in the nuclear targeting of WRN. Additionally, how does
the lack of WRN helicase and exonuclease activities as well as the absence of WRN
protein interactions lead to the premature aging symptoms that define WS? Tackling
these and other issues regarding WS will lead to a better understanding of the aging
process and cancer predisposition (1).
WS Clinical Presentation and Diagnostic Testing
The age of onset of many of the symptoms caused by a WRN mutation is
approximately 10 – 20 years of age. Various methods of diagnosis have been established
based on the diseases’ cardinal and secondary signs and symptoms. Since this disease is
extremely rare, it is important to follow the established standards for diagnosis of WS.
Two diagnostic criteria have been established in order to standardize diagnosis based on
phenotype presentation.
The International Registry of Werner Syndrome has developed a list of cardinal
and secondary symptoms that may be used to diagnose WS. The cardinal signs and
symptoms, based on an onset after ten years of age, include bilateral cataracts,
characteristic skin, “bird like” faces (i.e. a pinched nasal bridge and loss of subcutaneous
tissue), short stature, premature graying and/or thinning of scalp hair, consanguinity, and
positive 24-hour urinary hyaluronic acid test (8). The secondary symptoms that have
been described are type 2 diabetes mellitus, hypogonadism, osteoporosis, evidence of
ostoesclerosis of the distal phalanges or toes, soft tissue calcificiation, atherosclerosis,
neoplasms, flat feet, and abnormally high pitched voice (8,9). A definite diagnosis is
defined as one in which all of the cardinal symptoms plus two secondary are identified.
A probable diagnosis is one in which three cardinal signs plus two secondary are
identified. Finally, a possible diagnosis is one in which either cataracts or dermatologic
alterations and any four of the secondary symptoms are identified.
A second method of diagnosing WS was established in 1997. This proposed
method is defined as one in which four of the five following symptoms are identified:
consanguinity, characteristic facial appearance, premature senescence, scleroderma-like
skin changes, and endocrine-metabolic disorders (10). Despite the fact that these
phenotype based standards have been set, it is important to use diagnostic and genetic
testing in order to diagnose WS.
One of the most reliant and widely used diagnostic tests for WS is a test for
hyperhyaluronic aciduria. WS patients show significantly higher levels of hyaluronic
acid in serum and urine than same aged controlled levels. The serum and urine hyaluronic
acid levels of WS patients are almost equal to those of normal controls over 80 years old
(12). Although this diagnostic test is normally helpful in determining the diagnosis of
WS, WS patients normally require genetic analysis to confirm the diagnosis.
WS Genetic Testing
Since the WRN gene is the only known gene to be associated with Werner
syndrome, defining the parameters for genetic testing is well determined. A genetic
sequence analysis of the WRN coding region detects mutations in both alleles for
approximately 90% of all individuals affected by WS (10). A false negative may be
determined if the genetic mutation is located in the intron, which is normally not
sequenced for genetic mutation. If a mutation is identified, a Western Blot is performed
in order to determine the amount of protein (leucocytes) production that is affected by the
mutation.
Patient Counseling and Family Planning
Following the diagnosis of WS, a physician must counsel his or her patient in
regards to the management of the disorder and family planning. At the time of initial
diagnosis, the physician should suggest that the patient undergo further medical testing in
order to determine the extent of significant findings and possible treatments. Type 2
diabetes mellitus is favorably controlled in many patients who are diagnosed with WS
(11). Surgical treatment is used to treat ocular cataracts in patients with WS. Most other
malignancies are treated with standard treatments.
The large amount of secondary complications that are caused by WS must also be
considered during patient counseling. Patients should be directed to continue
surveillance of the various complications that may be caused by WS (2). The patient
should be advised to maintain a healthy lifestyle in order to decrease the risk of
developing atherosclerosis at a young age (2).
Depending on the age of the patient, a discussion of the possibility of family
planning may be necessary. Many patients diagnosed with WS will experience a decline
in fertility soon after sexual maturity. Testicular atrophy and loss of primordial follicles
have been hypothesized as reasons why fertility declines following sexual maturity(2).
This high rate of infertility may cause patients to feel depressed or isolated.
Those patients who are determined to be fertile may request additional genetic
planning in order to determine risks involved with offspring. One of the most important
features of the WRN mutation is its high concentration among the Japanese population.
In Japan, the frequency of heterozygosity is between 1/20,000 – 1/40,000 (3). Compared
to the US population, which is predicted to be approximately 1/200,000, the Japanese
have a much greater risk of carrying a mutant allele. Worldwide, 1200 patients were
reported from 1904 to 1996, and 845 of these patients were from Japan (3).
The WRN mutation is inherited in an autosomal recessive manner. The rarity of
this allele in the United States population makes the risk of a carrier’s child developing
this disease to be extremely low. This risk, however, is greatly increased if the couple is
in a consanguineous relationship. The high allele frequency within the Japanese
population must also be taken into consideration when family planning is being
discussed. Finally, since no prenatal testing for WS is available, parental genetic testing
should be recommended for those who are planning a family.
One of the most difficult aspects of WS for many patients is dealing with the
emotional and psychological aspects of knowing that the age of mortality for this disease
is approximately 45 years of age. Mortality is most commonly due to atherosclerotic
heart failure or malignant tumor development (2). Discussion of these issues with WS
some patients may develop during the treatment process. It is important that the
physician remembers these facts during his or her counseling of the patient.
Despite the fact that WS is a rare genetic disorder, it may manifest as a physically,
emotionally, and psychologically damaging disorder. Population genetics serves as a
valuable resource when determining a patient’s risk of developing WS. Following an
appropriate clinical workup, a diagnosis of WS may be established. The physician must
recognize the various complications that are associated with this disorder, and must be
prepared to treat each or refer the patient to someone who can treat them.
References
1. Opresko, P. L., Cheng, W., Kobbe, ,C., Harrigan, J.A., and Bohr, V.A. (2003)
Werner syndrome and the function of the Werner protein; what they can teach us
about the molecular aging process. Carcinogenesis, Vol. 24, No. 5, 791-802
2. Hanson, N., Martin, G.M., Oshima, J. (2005) Werner Syndrome. Gene Review
3. Satoh M, Imai M, Sugimoto M, Goto M, Furuichi Y (1999) Prevalence of
Werner's syndrome heterozygotes in Japan. Lancet 353:1766
4. Salk,D., Bryant,E., Hoehn,H., Johnston,P. and Martin,G.M. (1985) Growth
characteristics of Werner syndrome cells in vitro. Adv. Exp. Med. Biol., 190, 305–
311.
5. Cooper,M.P., Machwe,A., Orren,D.K., Brosh,R.M., Ramsden,D. and Bohr,V.A.
(2000) Ku complex interacts with and stimulates the Werner protein. Genes Dev.,
14, 907–912.
6. Blander,G., Kipnis,J., Leal,J.F., Yu,C.E., Schellenberg,G.D. and Oren,M. (1999)
Physical and functional interaction between p53 and the Werner's syndrome
protein. J. Biol. Chem., 274, 29463–29469.
7. Wyllie,F.S., Jones,C.J., Skinner,J.W., Haughton,M.F., Wallis,C., WynfordThomas,D., Faragher,R.G. and Kipling,D. (2000) Telomerase prevents the
accelerated cell ageing of Werner syndrome fibroblasts. Nature Genet., 24, 16–
17.
8. Nakura J, Wijsman EM, Miki T, Kamino K, Yu CE, Oshima J, Fukuchi K, Weber
JL, Piussan C, Melaragno MI, et al. (1994) Homozygosity mapping of the Werner
syndrome locus (WRN). Genomics 23:600-8
9. Tsunoda K, Takanosawa M, Kurikawa Y, Nosaka K, Niimi S (2000) Hoarse voice
resulting from premature ageing in Werner's syndrome. J Laryngol Otol 114:61-3
10. Goto M (1997) Hierarchical deterioration of body systems in Werner's syndrome:
Implications for normal ageing. [Clinical review of Japanese Werner syndrome
cases] Mech Ageing Devel 98:239-254
11. Yokote K, Honjo S, Kobayashi K, Fujimoto M, Kawamura H, Mori S, Saito Y
(2004) Metabolic improvement and abdominal fat redistribution in Werner
syndrome by pioglitazone. J Am Geriatr Soc 52:1582-3
12. Tanabe M and Goto M (2001) Elevation of serum hyaluronan level in Werner's
syndrome. Gerontology 47:77-81