• Users Online: 248
  • Home
  • Print this page
  • Email this page
Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 


 
 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 53  |  Issue : 4  |  Page : 238-243

Role of interleukin-6 in refractory epilepsy


1 Department of Neurology, Cairo University, Cairo, Egypt
2 Department of Neurology, Beni Suef University, Beni Suef, Egypt
3 Department of Clinical and Chemical Pathology, Beni Suef University, Beni Suef, Egypt

Date of Submission27-Nov-2016
Date of Acceptance14-Dec-2016
Date of Web Publication17-Mar-2017

Correspondence Address:
Amany H Ragab
Department of Neurology, Cairo University, 11728
Egypt
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-1083.202384

Rights and Permissions
  Abstract 

Background
There is increasing evidence of a complex relationship between epilepsy and the immune system.
Objective
The aim of this study was to ascertain the relationship between inflammatory cytokines, immune system dysregulation, and the pathogenesis of refractory epilepsy by determining the level of interleukin-6 (IL-6) in patients with refractory epilepsy and its relation to different factors.
Patients and methods
This study was conducted on 30 patients with refractory epilepsy and 10 healthy control participants. All patients were assessed using clinical evaluation, conventional digital electroencephalogram, brain MRI, routine laboratory tests, and IL-6 level in serum.
Results
Serum IL-6 level was significantly higher in patients with refractory epilepsy than in the control group.
Conclusion
There is a significant association between serum IL-6 level and refractory epilepsy.

Keywords: cytokines, inflammation, interleukin-6, refractory epilepsy


How to cite this article:
El-Fayoumy NM, El-Massry HA, Hegazy MM, Ragab AH, Mohamed RA, Abdel Alim SG. Role of interleukin-6 in refractory epilepsy. Egypt J Neurol Psychiatry Neurosurg 2016;53:238-43

How to cite this URL:
El-Fayoumy NM, El-Massry HA, Hegazy MM, Ragab AH, Mohamed RA, Abdel Alim SG. Role of interleukin-6 in refractory epilepsy. Egypt J Neurol Psychiatry Neurosurg [serial online] 2016 [cited 2017 Jun 26];53:238-43. Available from: http://www.ejnpn.eg.net/text.asp?2016/53/4/238/202384


  Introduction Top


More than 30% of all patients with epilepsy have uncontrolled seizures or medication adverse effects despite proper medical management [1],[2],[3].

Refractory epilepsy was defined as a condition in which at least two antiepileptic drugs have failed to control seizures [4]. It is claimed to be associated with increased risk of injury and subsequent mortality and psychological and cognitive dysfunction [5].

A complex relationship between epilepsy and the immune system is increasingly acknowledged, including abnormalities in expression of immune mediators and cells, which have been observed in patients with epilepsy and animal models [6]. This seems to play an important role in epileptogenesis [7].

Active inflammation has been detected in inflammatory epilepsies owing to Rasmussen’s encephalitis or limbic encephalitis and other causes of pharmacoresistant epilepsies [8],[9].

Interleukin-6 (IL-6) is a cytokine involved in B-cell differentiation into mature antibody-producing cells. Also, it is important in the regulation of immune cells, including T cells, and the regulation of hematopoietic progenitor cells, hepatocytes, the skeleton, the placenta, the cardiovascular system, and the nervous and endocrine systems [10],[11].

IL-6 has been shown to be involved in the pathogenesis of neuropsychiatric disorders. IL-6 levels have been reported to be elevated in epilepsy in both postictal and interictal states [12],[13],[14],[15].

Patients with family history of epilepsy had higher level of IL-6 compared with sporadic cases. In many animal models of epilepsy, acute seizures cause glial activation, increased cytokine production, and trigger a rapid inflammatory response in the involved brain areas [16],[17].

The aim of this work was to ascertain the relationship between inflammatory cytokines, immune system dysregulation, and the pathogenesis of refractory epilepsy by determining the level of IL-6 in patients with refractory epilepsy, and whether there is a possible relation between its level and different factors influencing the epileptic disorder.


  Patients and methods Top


Patients

This study is a case–control study conducted on 40 adult Egyptian participants during the period between September 2013 and February 2014. They were grouped as follows:

Group I included 30 patients with nonlesional epilepsy diagnosed according to the criteria of International League Against Epilepsy (ILAE, 2010) [18] and having intractable epilepsy according to the criteria of Arroy et al. [4], with at least two appropriate antiepileptic drugs having failed to control seizures, who were recruited from Neurology Clinics and Neurology Departments in Beni-Suef and Cairo University Hospitals.

Group II included 10 normal age-matched and sex-matched healthy volunteers.

Inclusion criteria

  1. Age younger than 18 years.
  2. Patients with nonlesional epilepsy, diagnosed by history taking from the patient and an eye witness according to the criteria of International League Against Epilepsy (ILAE, 2010) [18].
  3. Patients diagnosed as having intractable epilepsy according to the criteria of Arroy et al. [4] with at least two appropriate antiepileptic drugs having failed to control seizures, and the patients are compliant with anti epileptic drugs (AEDs).


Exclusion criteria

  1. Patients with lesional epilepsy (excluded by MRI brain).
  2. Patients with severe adverse drug reactions.
  3. Patients with poor compliance with AEDs.
  4. Patients with alcohol or drug abuse.
  5. Patients with severe mental or psychiatric illness.
  6. Patients with special epileptic syndrome, and patients receiving epileptogenic drugs.
  7. Patients with systemic illness (uncontrolled diabetes mellitus, hypertension, renal, liver, neoplastic, connective tissue disorders, morbid obesity, and anemia) to exclude causes that may lead to increased IL-6 serum levels.


Methods

All patients will be subjected to the following:

  1. Thorough history taking, including the symptoms felt by the patient, the signs observed by the eye witness during seizures, and classification of epileptic seizures according to the International League Against Epilepsy (ILAE, 2010) [18].
  2. Thorough medical examination including different systems assessment to exclude any associated medical illness.
  3. Thorough neurological assessment including the neurological assessment sheet currently used in the Neurology Department, Beni-Suef University Hospital.
  4. Electroencephalogram

    (EEG).EEG was done to verify the type of seizures using 10–20 electrode system by Eb Neuro (Arbizzano di Valpolicella (VR), Italy).
  5. Neuroimaging (MRI brain): (T1, T2, proton density, FLAIR, and with contrast if needed) to exclude structural lesions.
  6. Laboratory investigations:

    Complete blood count, fasting blood sugar, postprandial blood sugar, liver and kidney functions tests, serum calcium, serum potassium, serum sodium, erythrocyte sedimentation rate, thyroid functions, and immune profile as antinuclear antibody and antinucleocytoplasmic antibody, if needed.
  7. Serum level of IL-6 by enzyme-linked immunosorbent assay:

    For the control group, the following were conducted:
    1. Full history, neurological examination, and medical examination to exclude uncontrolled diabetes, hypertension, and any conditions that increase IL-6 level such as anemia, liver diseases, obesity, and autoimmune disorders.
    2. Routine laboratory examination, including complete blood count, blood sugar, kidney function test, liver function test, and serum electrolytes.
    3. Serum IL-6 level.


Methodology of serum interleukin-6 assay

Samples were collected at least 24 h away from an epileptic attack. In total, 3 ml of blood samples were withdrawn from peripheral veins by venipuncture in plain tubes, left at room temperature for 30 min, and then centrifuged at 3000 rpm for 10 min to separate the sera to analyze the level of IL-6 by enzyme-linked immunosorbent assay. Sera were stored at −20°C till the time of assay. The quantitative measurement of human IL-6 in serum, plasma, cell culture supernatants, and urine was done (Ani Biotech OyOrgenium Laboratories Business Unit, Vantaa, Finland). The standard curve was used to determine the amount of IL-6 in an unknown sample. The standard curve was generated by plotting the average OD (450 nm) obtained for each of the standard concentrations on the vertical (Y) axis versus the corresponding IL-6 concentration (pg/ml) on the horizontal (X) axis. The standard curve was constructed using graph paper.

The research received prior approval by the appropriate institutional review board, and an informed consent was obtained from each volunteer or patient.

Statistical analysis

Data were analyzed using the software Statistical Package for Social Science (SPSS, Armonk, New York, USA) version 19. Frequency distribution with its percentage and descriptive statistics with mean and SD were calculated. χ2-Test, t-test, and correlations were done whenever needed. P value less than 0.05 was considered significant.


  Results Top


Descriptive data

Demographic and clinical data of both groups were described in [Table 1] and [Figure 1],[Figure 2],[Figure 3].
Table 1 Demographic and clinical data of the two studied groups

Click here to view
Figure 1 Types of seizures among the patients group.

Click here to view
Figure 2 Types of auras in patients with focal epilepsy with secondary generalization.

Click here to view
Figure 3 Electroencephalographic (EEG) findings in the patients group.

Click here to view


Comparative results

  1. Comparison between IL-6 levels in patients and controls

    The mean value of IL-6 was higher in group I (n=30) (mean±SD=24.8±62.8) (range 0.3–249 pg/ml) than in group II (n=10) (mean±SD=1.11±0.49) (range 0.0–1.7 pg/ml), and the difference was statistically significant (P=0.024) ([Table 2]).
    Table 2 Level of interleukin-6 in both groups

    Click here to view
  2. Comparison between IL-6 level and sex of patients and controls

    In group I, the mean±SD of IL-6 in males was 15.7778±58.22695, whereas the mean±SD in females was 38.6750±69.35797, with no statistically significant difference (P=0.34).

    In group II, the mean value of IL-6 in males was 1.3000±0.27080, whereas the mean±SD in females was 0.6667±0.65064, with no statistically significant difference (P=0.051).
  3. Relation of IL-6 levels in patients with the type of seizure

    The mean value of IL-6 level in patients with generalized tonic clonic seizures (GTCs) was 26.3200±66.32653 (range 0.3–249 pg/ml), in patients with focal fits was 115.7500±161.57390 (range 1.5–230 pg/ml), and in patients with focal fits with secondary generalization was 9.3692±24.08092 (range 0.3–89.10 pg/ml); however, no statistically significant difference was found (P=0.08).
  4. Relation between IL-6 levels in patients and EEG results

    The mean value of IL-6 level is higher in patients with abnormal EEG (mean±SD=23.20±61.10) than the mean value of IL-6 level in patients with normal EEG (mean±SD=2.11±1.39); however, no statistically significant difference was found (P=0.34).
  5. Comparison between IL-6 level in patients with history of status epilepticus and patients with no history of status epilepticus

    The mean value of IL-6 in patients with history of status epilepticus was 9.63±11.58 and in patients with no history of status epilepticus was 26.64±66.01, with no statistically significant difference (P=0.66).
  6. Comparison between IL-6 level in patients with family history of epilepsy and patients with no family history of epilepsy

    The mean value of IL-6 in patients with family history of epilepsy was 1.10±0.76 and in patients with no family history of epilepsy was 28.60±66.84, with no statistically significant difference (P=0.42).
  7. Comparison between IL-6 levels in patients on double therapy and patients on triple therapy

    The mean value of IL-6 in patients on double therapy was 34.94±77.29 and in patients on triple therapy was 9.93±27.39, with no statistically significant difference (P=0.29)


Correlative results

There wasno statistically significant correlation between IL-6 level and age of patients (r=0.062 and P=0.745), age of onset of seizures (r=0.207 and P=0.273), duration of seizures (r=0.175 and P=0.356), frequency of seizures per month (r=0.002 and P=0.990), and duration of fits (r=0.234 and P=0.213).

There was no statistically significant correlation between IL-6 level and age of normal participants (r=0.301 and P=0.398).


  Discussion Top


The present study was designed to ascertain the relation between inflammatory cytokines, immune system dysregulation, and the pathogenesis of refractory epilepsy. The aim was to determine the level of IL-6 in patients with refractory epilepsy and search for possible relations between its level and different factors influencing the epileptic disorder.

The mean serum levels of IL-6 measured in our patients were found significantly higher compared with the control group (P=0.024). These results coincide with the results of many researchers who found that levels of IL-6 were higher in patients with refractory epilepsy compared with healthy controls [6],[12],[19],[20],[21],[22].

A previous study suggested that elevation in IL-6 is not fully explained by postictal increase but may reflect a chronic inflammatory system activation resulting from recurrent seizures, as IL-6 level was elevated in patients with frequently occurring seizures. This indicates that poorly controlled seizures may cause inflammatory system activation with potential neurotoxic effects. They also found that the levels of IL-6 were significantly elevated in patients with severe to profound intellectual disability but not in mild to moderate level disability. They also noted that the frequency of seizures is considerably higher in patient groups with most severe intellectual disability [21].

A study found that most of the patients with increased levels of IL-6 had frequent seizures, and the chronic overproduction of cytokines may be because of an active epileptic process in the brain, a finding that is not found in the present study, as there was no significant relationship between the frequency of seizures and IL-6 level. They suggested that chronic stimulation of IL-6 may lead to structural changes that may predispose to refractory seizures [20].

Two previous studies found slightly increased IL-6 levels in patients with chronic epilepsy when compared with healthy controls. They suggested that cytokine levels might be disturbed in chronic epileptic state during the interictal period. However, an effect resulting from recurring seizures cannot be excluded in explaining these slight differences between patient basal levels and healthy controls [6],[19].

It is postulated that only single seizures cause activation of cytokine cascade and associated inflammatory signals. In the case of recurrent seizures, these signals may result in structural changes in the nervous tissue with subsequent generation of drug refractory epilepsy [6].

A study found that the IL-6 level was significantly higher in patients with daily generalized motor seizures than in patients with intermittent seizures or the control group [22].

In the present study, the mean serum level of IL-6 was found to be higher in patients with focal epilepsy complex partial seizures (CPS) compared with those with generalized tonic clonic fits and focal fits with secondary generalization, but the difference was not statistically significant (P=0.08). These results agreed with the results of many publications [15],[21],[23].

In a study, the serum level of IL-6 was higher in patients with temporal lobe epilepsy (TLE) than patients with extra-TLE, but the difference was not statistically significant [21].

One study found no differences between different types of focal epilepsy and between focal and generalized epilepsies [15].

On the contrary, other studies found that the difference was statistically significant [14],[20],[24].

A study found that all patients with increased levels of IL-6 had TLE, which is known to be the most common epilepsy type refractory to drugs. Furthermore, concentrations of IL-6 were higher in patients with TLE compared with patients with extra-TLE [20]. This may be because medial temporal lobe structures have been shown to be extremely vulnerable during global ischemia and excessive excitatory activity [25],[26]. The abundance of projections from the medial temporal lobe to other areas in the brain (including the hypothalamus) may explain the activation of cytokine cascade specifically in TLE. An older finding of increased secretion of prolactin in TLE may support this hypothesis [27].

One study found that IL-6 level is increased in patients with TLE without hippocampal sclerosis, and this increase is not found in patients with hippocampal sclerosis. This may reflect neuroprotective effect of IL-6 against development of hippocampal sclerosis [14].

In the present study, the mean value of IL-6 level was higher in patients with abnormal EEG finding than the mean value of IL-6 level in patients with normal EEG finding; however, no statistically significant difference was found (P=0.34). Also, there was a higher level of IL-6 in patients with generalized epileptogenic dysfunction than patients with focal abnormality and patients with focal abnormality with secondary generalization; however, no statistically significant difference was found (P=0.15).

These results agreed with the results of many publications [14],[20],[21].

In the present study, there was no statistically significant association between clinical data (age, age at onset, sex, and number of antiepileptic drugs) and serum level of IL-6. These results agreed with many other studies [14],[20],[21].

In the present study, there was no statistically significant association between history of status epilepticus or duration of fit and serum level of IL-6.

On the contrary, a positive correlation between status epilepticus and IL-6 level was observed in one study [28].

Another study showed elevated IL-6 expression after pilocarpine-induced status epilepticus in the cells presumed to be glial and perivascular [29].

In the present study, there was no statistically significant association between family history of epilepsy and serum level of IL-6.

One study found significantly higher IL-6 level in patients with a family history of epilepsy [9].In the present study, there was no statistically significant association between duration of fit and serum level of IL-6. These results agreed with many other studies [14],[20],[21],[28].

Other studies found a statistically significant positive correlation between IL-6 level and seizure duration. Moreover, they found that there is a correlation between levels of IL-6 and the severity of seizures. It might be because seizures cause changes in cerebral tissue microenvironment causing the glial cell release of cytokines. So, increased cytokine levels have been found to be higher after more sever seizures (longer duration) [6],[19],[30].

The difference in the results between this study and other studies may be because of smaller sample size or owing to difference in immunological profile between Egyptians and other populations.

The activated glia and elevated cytokines contribute to seizure-related hippocampal pathology, such as neuronal death, reactive gliosis, and mossy fiber sprouting [29]. Accordingly, there may be a postulated role for anti-inflammatory therapy targeting activated astrocytes and microglia as a novel therapeutic strategy to prevent or limit epileptogenesis and cell injury associated with seizures in the vulnerable developing nervous system [9].

Acknowledgements

Ethical publication statement: The authors confirm that they have read the journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Sander JW. The epidemiology of epilepsy revisited. Curr Opin Neurol 2003; 16:165–170.  Back to cited text no. 1
    
2.
Sillanpää M, Schmidt D. Early seizure frequency and aetiology predict long-term medical outcome in childhood-onset epilepsy. Brain 2009; 132:989–998.  Back to cited text no. 2
    
3.
Kwan P, Arzimanoglou A, Berg AT, Brodie MJ, Allen Hauser W, Mathern G et al. Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia 2010; 51:1069–1077.  Back to cited text no. 3
    
4.
Arroy S, Brodie MJ, Avanzine G, Baumgartner C, Chiron C, Dulac O et al. Is refractory epilepsy preventable? Epilepsia 2002; 43:437–444.  Back to cited text no. 4
    
5.
Brodie MJ, Dichter MA. Antiepileptic drugs. N Engl J Med 1996; 334:168–175.  Back to cited text no. 5
    
6.
Lehtimaki K, Keranen T, Palmio J, Mäkinen R, Hurme M, Honkaniemi J et al. Increased plasma levels of cytokines after seizures in localization-related epilepsy. Acta Neurol Scand 2007; 116:226–230.  Back to cited text no. 6
    
7.
Vezzani A, Moneta D, Richichi C, Aliprandi M, Burrows SJ, Ravizza T et al. Functional role of inflammatory cytokines and anti-inflammatory molecules in seizures and epileptogenesis. Epilepsia 2002; 43:30–35.  Back to cited text no. 7
    
8.
Vezzani A, Granata T. Brain inflammation in epilepsy: experimental and clinical evidence. Epilepsia 2005; 46:1724–1743.  Back to cited text no. 8
    
9.
Choi J, Nordli DR, Alden TD, DiPatri A, Laux L, Kelley K et al. Cellular injury and neuroinflammation in children with chronic intractable epilepsy. J Neuroinflammation 2009; 6:38.  Back to cited text no. 9
    
10.
Hirano T, Taga T, Nakano N, Yasukawa K, Kashiwamura S, Shimizu K et al. Purification to homogeneity and characterization of human B-cell differentiation factor (BCDF or BSFp-2). Proc Natl Acad Sci USA 1985; 82:5490–5494.  Back to cited text no. 10
    
11.
Kishimoto T, Akira S, Narazaki M et al. Interleukin-6 family of cytokines and gp130. Blood 1995; 86:1243–1254.  Back to cited text no. 11
    
12.
Peltola J, Palmio J, Korhonen L, Suhonen J, Miettinen A, Hurme M et al. Interleukin-6 and interleukin-1 receptor antagonist in cerebrospinal fluid from patients with recent tonic-clonic seizures. Epilepsy Res 2000; 41:205–211.  Back to cited text no. 12
    
13.
Hulkkonen J, Koskikallio E, Rainesalo S, Keränen T, Hurme M, Peltola J. The balance of inhibitory and excitatory cytokines is differently regulated in vivo and in vitro among therapy resistant epilepsy patients. Epilepsy Res 2004; 59:199–205.  Back to cited text no. 13
    
14.
Bauer S, Cepok S, Todorova-Rudolph A, Nowak M, Köller M, Lorenz R et al. Etiology and site of temporal lobe epilepsy influence postictal cytokine release. Epilepsy Res 2009; 86:82–88.  Back to cited text no. 14
    
15.
Nowak M, Bauer S, Haag A, Cepok S, Todorova-Rudolph A, Tackenberet B et al. Interictal alterations of cytokines and leukocytes in patients with active epilepsy. Brain Behav Immun 2011; 25:423–428.  Back to cited text no. 15
    
16.
Turrin NP, Rivest S. Innate immune reaction in response to seizures: implications for the neuropathology associated with epilepsy. Neurobiol Dis 2004; 16:321–334  Back to cited text no. 16
    
17.
Borges K, Gearing M, McDermott DL, Smith AB, Almonte AG, Wainer BH et al. Neuronal and glial pathological changes during epileptogenesis in the mouse pilocarpine model. Exp Neurol 2003; 182:21–34.  Back to cited text no. 17
    
18.
Berg AT, Berkovic SF, Brodie MJ, Buchhalter J, Cross JH, Boas WvE et al. (2010) revised terminology and concepts for organization of seizures and epilepsies: Report of the ILAE Commission on Classification and Terminology, 2005–2009. Epilepsia 2010; 51:676–685.  Back to cited text no. 18
    
19.
Lehtimaki KA, Keränen T, Huhtala H, Hurme M, Ollikainen J, Honkaniemi J et al. Regulation of lIL-6 system in cerebrospinal fluid and serum compartments by seizures: the effect of seizure type and duration. J Neuroimmunol 2004; 152:121–125.  Back to cited text no. 19
    
20.
Liimatainen S, Fallah M, Kharazmi E, Peltola M, Peltola J. Interleukin-6 levels are increased in temporal lobe epilepsy but not in extra-temporal lobe epilepsy. J Neurol 2009; 256:796–802.  Back to cited text no. 20
    
21.
Lehtimaki KA, Liimatainenb S, Peltola J, Arvio M. The serum level of interleukin-6 in patients with intellectual disability and refractory epilepsy. Epilepsy Res 2011; 95:184–187.  Back to cited text no. 21
    
22.
Ishikawa N, Kobayashi Y, Fujii Y, Kobayashi M. Increased interleukin-6 and high-sensitivity C-reactive protein levels in pediatric epilepsy patients with frequent, refractory generalized motor seizures. Seizure 2014; 25:136–140.  Back to cited text no. 22
    
23.
Uludag IF, Bilgin S, Zorlu Y, Tuna G, Kirkali G. Interleukin-6, interleukin-1 beta and interleukin-1 receptor antagonist levels in epileptic seizures. Seizure 2013; 22:457–461.  Back to cited text no. 23
    
24.
Alapirtti T, Rinta S, Hulkkonen J, Mäkinen R, Keränen T, Peltola J. Interleukin-6, interleukin-1 receptor antagonist and interleukin-1 beta production in patients with focal epilepsy: a video-EEG study. J Neurol Sci 2009; 280:94–97.  Back to cited text no. 24
    
25.
Freund TF, Ylinen A, Miettinen R, Pitkänen A, Lahtinen H, Baimbridges KG et al. Pattern of neuronal death in the rat hippocampus after status epilepticus. Relationship to calcium binding protein content and ischemic vulnerability. Brain Res Bull 1992; 28:27–38.  Back to cited text no. 25
    
26.
Lim C, Alexander M, LaFleche G, Schnyer DM, Verfaellie M. The neurological and congnitive sequelae of cardiac arrest. Neurology 2004; 63:1774–1778.  Back to cited text no. 26
    
27.
Meierkord H, Shorvon S, Lightman S, Trimble M. Comparison of the effects of frontal and temporal lobe partial seizures on prolactin levels. Arch Neurol 1992; 49:225–230.  Back to cited text no. 27
    
28.
Sinha S, Patil S, Jayalekshmy V, Satishchandra P. Do cytokines have any role in epilepsy? Epilepsy Res 2008; 82:171–176.  Back to cited text no. 28
    
29.
Jankowsky JL, Patterson PH. The role of cytokines and growth factors in seizures and their sequelae. Prog Neurobiol 2001; 63:125–149.  Back to cited text no. 29
    
30.
Campbell I, Abraham C, Masliah E, Kemper P, Inglis JD, Oldstone M et al. Neurologic disease induced in transgenic mice by cerebral overexpression of interleukin-6. Proc Nalt Acad Sci USA 1993; 90:10061–10065.  Back to cited text no. 30
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

 
  In this article
Abstract
Introduction
Patients and methods
Results
Discussion
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed62    
    Printed0    
    Emailed0    
    PDF Downloaded14    
    Comments [Add]    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]