We will successively discuss biomarkers in blood, in cerebrospinal fluid, and biomarkers in imaging and neurophysiology. They are currently not used in current practice but are the main current topics of biomedical research in 2011.

1 / Why develop biomarkers?
The pathogenesis underlying amyotrophic lateral sclerosis (ALS) is not limited to the motor neurological system. We now know that patients may develop memory disorders  and behavioural changes related to frontal function  (Tsermentseli and al, 2011), extrapyramidal syndrome (hypertonia, akinesia or tremor) (Pradat and al, 2009) or pain. The hypothesis stating that ALS is restricted  to a selective impairment of the first and the second motor neuron should gradually be re-oriented in favor of the notion of "syndrome" (all clinical signs and symptoms that a patient is likely to develop for certain type of diseases) with different clinical expressions (called phenotypic): bulbar onset, limb onset limited for a long period to  upper limbs or pseudo polyneuropathy  form starting with lower limbs (mimicking an alteration of the legs nerves). The disease progression is also different from patient to another and the needs of patients must be anticipate accordingly.
The disease is in its most common form sporadic and therapeutic trials conducted on the only validated SOD1 murine model (SOD 1) remain insufficient, as they don’t reproduce the disease developed in humans (Bowling and al, 1993). Currently, the only therapeutic amending the duration of evolution is riluzole RILUTEK® which brings an increase in ife expectancy of 7% in the treated group compared to placebo, meaning an average of additional  3 months in life expectancy. Clinical trials assess the efficacy on the following criteria: the date of death from the onset of the disease, functional vital capacity (respiratory parameter), the score of clinical disability on a scale specific to ALS (score ALS - FRS). These criteria are questionable because very strict (death) or insufficiently sensitive (ALS - FRS). Patients are evaluated in a single group which does not consider the various forms of the disease limiting the interest of some results. The discovery of biomarkers would certainly help refine analysis.
 
2 / Definition
The Council for research development in Great Britain define a biomarker as "a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention".
There are :
-The "diagnostic" biomarkers that brings arguments for the diagnosis,
-The "phenotypic" biomarkers to distinguish the different clinical forms of disease,
-The “disease progression” biomarkers.
-The biomarkers to monitor a "therapeutic benefit”.
 
3 / Requirement for a perfect biomarker in ALS syndrome :
- Sensitive and specific for ALS syndrome, ideally detectable before the onset of severe clinical symptoms and/or at the pre-symptomatic stage for familial forms.
The specificity is in statistics and in epidemiology, the ability of a diagnostic test or examination to give negative results when the disease (or item) is not existing. The sensitivity demonstrates the probability to get a positive result only if the disease is there.
- Ability to differentiate different SLA clinical phenotypes.
- Able to describe in advance the evolution of major symptoms, including respiratory symptoms, in order to consider the earliest possible therapeutic interventions (non-invasive ventilation).
- Able to change quickly as a result of the administration of a therapeutic agent (shortening therapeutic trials, obtain a more relevant model than the murine’s one).
- Easy to use, easy to measure, reproducible, even in patients in advanced stage of the disease.

4 / Biomarkers in the blood or cerebrospinal : major publications

 

5/ Imaging Biomarkers:

6/ Neurophysiological Biomarkers:

A cortical hyperexcitability in Transcranial Magnetic stimulation by decrease in intra cortical inhibition interval is usually described in sporadic ALS (Ziemman and al,1997), this anomaly would be present at the early stage of the disease and in some healthy carriers of the SOD1 mutation (Bowling and al, 1993).
At a muscular level, the expression of Nogo A (protein associated with myelin, potential inhibitor of neuronal growth) on muscle biopsy would be an early positive predictive factor of evolution towards SLA with a sensitivity of 94% and a specificity of 91% (Pradat and al, 2007).

REFERENCES

A Tessitore, F Esposito and MR Monsurro et al., Subcortical motor plasticity in patients with sporadic ALS: an fMRI study, Brain Res Bull 69 (2006), pp. 489–494. Bowling AC, Schulz JB, Brown RH Jr, Beal MF.Superoxide dismutase activity, oxidative damage, and mitochondrial energy metabolism in familial and sporadic amyotrophic lateral sclerosis.J Neurochem. 1993 
J Brettschneider, A Petzold, SD Sussmuth, AC Ludolph and H Tumani, Axonal damage markers in cerebrospinal fluid are increased in ALS, Neurology 66 (2006), pp. 852–856 J Brettschneider, K Widl, D Schattauer, AC Ludolph and H Tumani, Cerebrospinal fluid erythropoietin (EPO) in amyotrophic lateral sclerosis, Neurosci Lett 416 (2007), pp. 257–260 S Cronin, MJ Greenway and S Ennis et al., Elevated serum angiogenin levels in ALS, Neurology67 (2006), pp. 1833–1836 Devos D, Moreau C, Lassalle P, Perez T, De Seze J, Brunaud-Danel V, Destée A, Tonnel AB, Just N.Low levels of the vascular endothelial growth factor in CSF from early ALS patients.Neurology. 2004 Jun 8;62(11):2127-9 CM Ellis, A Simmons and DK Jones et al., Diffusion tensor MRI assesses corticospinal tract damage in ALS, Neurology 53 (1999), pp. 1051–1058. S Hosback, O Hardiman and CM Nolan et al., Circulating insulin-like growth factors and related binding proteins are selectively altered in amyotrophic lateral sclerosis and multiple sclerosis,Growth Horm IGF Res 17 (2007), pp. 472–479 K Houi, T Kobayashi, S Kato, S Mochio and K Inoue, Increased plasma TGF-beta1 in patients with amyotrophic lateral sclerosis, Acta Neurol Scand 106 (2002), pp. 299–301 Just N, Moreau C, Lassalle P, Gosset P, Perez T, Brunaud-Danel V, Wallaert B, Destée A, Defebvre L, Tonnel AB, Devos D.High erythropoietin and low vascular endothelial growth factor levels in cerebrospinal fluid from hypoxemic ALS patients suggest an abnormal response to hypoxia. Neuromuscul Disord. 2007 Feb;17(2):169-73 T Matsuishi, S Nagamitsu and H Shoji et al., Increased cerebrospinal fluid levels of substance P in patients with amyotrophic lateral sclerosis. Short communication, J Neural Transm 106 (1999), pp. 943–948. Moreau C, Devos D, Brunaud-Danel V, Defebvre L, Perez T, Destée A, Tonnel AB, Lassalle P, Just N.Paradoxical response of VEGF expression to hypoxia in CSF of patients with ALS.J Neurol Neurosurg Psychiatry. 2006;77:255-7. Moreau C, Gosset P, Brunaud-Danel V, Lassalle P, Degonne B, Destee A, Defebvre L, Devos D. CSF profiles of angiogenic and inflammatory factors depend on the respiratory status of ALS patients  Amyotroph Lateral Scler. 2009;10:175-81. Moreau C, Devos D, Brunaud-Danel V, Defebvre L, Perez T, Destée A, Tonnel AB, Lassalle P, Just N Elevated IL-6 and TNF-alpha levels in patients with ALS: inflammation or hypoxia?. Neurology. 2005 Dec 27;65(12):1958-60 S Ono, T Imai and N Shimizu et al., Decreased plasma levels of fibronectin in amyotrophic lateral sclerosis, Acta Neurol Scand 101 (2000), pp. 391–394 S Ono, T Imai and M Tsumura et al., Increased serum hyaluronic acid in amyotrophic lateral sclerosis: relation to its skin content, Amyotroph Lateral Scler Other Motor Neuron Disord 1 (2000), pp. 213–218. S Ono, J Hu, N Shimizu, T Imai and H Nakagawa, Increased interleukin-6 of skin and serum in amyotrophic lateral sclerosis, J Neurol Sci 187 (2001), pp. 27–34 BM Patten, Y Harati, L Acosta, SS Jung and MT Felmus, Free amino acid levels in amyotrophic lateral sclerosis, Ann Neurol 3 (1978), pp. 305–309. EP Pioro, AW Majors, H Mitsumoto, DR Nelson and TC Ng, 1H-MRS evidence of neurodegeneration and excess glutamate+glutamine in ALS medulla, Neurology 53 (1999), pp. 71–79. PF Pradat, G Bruneteau and JL Gonzalez de Aguilar et al., Muscle Nogo-A expression is a prognostic marker in lower motor neuron syndromes, Ann Neurol 62 (2007), pp. 15–20. Pradat, P. F. & Dib, M. (2009). Biomarkers  in amyotrophic lateral sclerosis: facts and future horizons. Mol.Diag.Ther 13, 1-11.   Pradat PF, Bruneteau G, Munerati E, Salachas F, Le Forestier N, Lacomblez L, Lenglet T, Meininger V. Extrapyramidal stiffness in patients with amyotrophic lateral sclerosis.Mov Disord. 2009 Oct 30;24(14):2143-8 Rosengren, JE Karlsson, JO Karlsson, LI Persson and C Wikkelso, Patients with amyotrophic lateral sclerosis and other neurodegenerative diseases have increased levels of neurofilament protein in CSF, J Neurochem 67 (1996), pp. 2013–2018. G Siciliano, S Piazza and C Carlesi et al., Antioxidant capacity and protein oxidation in cerebrospinal fluid of amyotrophic lateral sclerosis, J Neurol 254 (2007), pp. 575–580 EP Simpson, YK Henry, JS Henkel, RG Smith and SH Appel, Increased lipid peroxidation in sera of ALS patients: a potential biomarker of disease burden, Neurology 62 (2004), pp. 1758–1765. Tsermentseli S, Leigh PN, Goldstein LH The anatomy of cognitive impairment in amyotrophic lateral sclerosis: More than frontal lobe dysfunction. Cortex. 2011 M Waragai, H Shinotoh, M Hayashi and T Hattori, High signal intensity on T1-weighted MRI of the anterolateral column of the spinal cord in amyotrophic lateral sclerosis, J Neurol Neurosurg Psychiatry 62 (1997), pp. 88–91 H Zetterberg, J Jacobsson, L Rosengren, K Blennow and PM Andersen, Cerebrospinal fluid neurofilament light levels in amyotrophic lateral sclerosis: impact of SOD1 genotype, Eur J Neurol14 (2007), pp. 1329–1333. U Ziemann, TMS and drugs, Clin Neurophysiol 115 (2004), pp. 1717–1729.