Motor neuron disease can be viewed as an umbrella term describing a heterogeneous group of conditions, all of which are relentlessly progressive and ultimately fatal. The average life expectancy is 2 years, but with a broad range of months to decades. Biomarker research deepens disease understanding through exploration of pathophysiological mechanisms which, in turn, highlights targets for novel therapies. It also allows differentiation of the disease population into sub-groups, which serves two general purposes: (a) provides clinicians with information to better guide their patients in terms of disease progression, and (b) guides clinical trial design so that an intervention may be shown to be effective if population variation is controlled for. Biomarkers also have the potential to provide monitoring during clinical trials to ensure target engagement. This review highlights biomarkers that have emerged from the fields of systemic measurements including biochemistry (blood, cerebrospinal fluid, and urine analysis); imaging and electrophysiology, and gives examples of how a combinatorial approach may yield the best results. We emphasize the importance of systematic sample collection and analysis, and the need to correlate biomarker findings with detailed phenotype and genotype data.

P/Q-type calcium channels are known to form clusters at the presynaptic membrane where they mediate calcium influx, triggering vesicle fusion. We now report functional P/Q channel clusters in the axolemma of developing central axons that are also associated with sites of vesicle fusion. These channels were activated by axonal action potentials and the resulting calcium influx is well suited to mediate formation of a synaptic style SNARE complex involving SNAP-25, that we show to be located on the axolemma. Vesicular elements within axons were found to be the sole repository of vesicular glutamate in developing white matter. The axonal vesicular elements expressed the glutamate transporter V-ATPase, which is responsible for vesicular glutamate loading. The P/Q channel α 1A subunit was found to be present within the axolemma at early nodes of Ranvier and deleterious mutations of the α 1A subunit, or an associated α 2 δ-2 subunit, disrupted the localization of nodal proteins such as voltage-gated sodium channels, β IV spectrin and CASPR-1. This was associated with the presence of malformed nodes of Ranvier characterized by an accumulation of axoplasmic vesicles under the nodal membrane. The data are consistent with the presence of a vesicular signalling pathway between axons and glial cells that is essential for proper development of the node of Ranvier.

ObjectiveIschemic injury of axons is a feature of periventricular leukomalacia, a pathological correlate of cerebral palsy. Recent evidence suggests that axons are damaged before they receive the first layer of compact myelin. Here we examine the cellular mechanisms underlying ischemic‐type injury of premyelinated central axons.MethodsTwo‐thirds of axons in the postnatal day 10 (P10) rat optic nerve are small premyelinated axons (<0.4μm in diameter), and one‐third have undergone radial expansion in preparation for glial contact and the onset of myelination. Compound action potential recording and quantitative electron microscopy were used to examine the effect of modeled ischemia (oxygen‐glucose deprivation) upon these two axon populations. Glutamate receptor (GluR) expression was investigated using polymerase chain reaction (PCR) and immunostaining approaches at the confocal light and ultrastructural levels.ResultsOxygen‐glucose deprivation produced action potential failure and focal breakdown of the axolemma of small premyelinated axons at sites of contact with oligodendrocyte processes, which were also disrupted. The resulting axon loss was Ca2+‐dependent, Na+‐ and Cl−‐independent, and required activation of N‐methyl‐D‐aspartic acid (NMDA) and non‐NMDA GluRs. NMDA receptor expression was localized to oligodendrocyte processes at sites of contact with premyelinated axons, in addition to expression within compact myelin. No periaxonal NMDA receptor expression was observed on oligodendrocyte processes ensheathing large premyelinated axons and no protective effect of GluR block was observed in these axons.InterpretationNMDA receptor‐mediated injury to oligodendrocyte processes navigating along small premyelinated axons precedes damage to the underlying axon, a phenomena that is lost following radial expansion and subsequent oligodendrocyte ensheathment. Ann Neurol 2009;66:682–693

BackgroundMotor Unit Number Index (MUNIX) is a neurophysiological measure that provides an index of the number of lower motor neurons in a muscle. Its performance across centres in healthy subjects and patients with Amyotrophic Lateral Sclerosis (ALS) has been established, but inter-rater variability between multiple raters in one single subject has not been investigated.ObjectiveTo assess reliability in a set of 6 muscles in a single subject among 12 examiners (6 experienced with MUNIX, 6 less experienced) and to determine variables associated with variability of measurements.MethodsTwelve raters applied MUNIX in six different muscles (abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), tibialis anterior (TA), extensor dig. brevis (EDB), abductor hallucis (AH)) twice in one single volunteer on consecutive days. All raters visited at least one training course prior to measurements. Intra- and inter-rater variability as determined by the coefficient of variation (COV) between different raters and their levels of experience with MUNIX were compared.ResultsMean intra-rater COV of MUNIX was 14.0% (±6.4) ranging from 5.8 (APB) to 30.3% (EDB). Mean inter-rater COV was 18.1 (±5.4) ranging from 8.0 (BB) to 31.7 (AH). No significant differences of variability between experienced and less experienced raters were detected.ConclusionWe provide evidence that quality control for neurophysiological methods can be performed with similar standards as in laboratory medicine. Intra- and inter-rater variability of MUNIX is muscle-dependent and mainly below 20%. Experienced neurophysiologists can easily adopt MUNIX and adequate teaching ensures reliable utilization of this method.

In our study, home video facilities aided interpretation of ambulatory EEG recordings in approximately one third of patients. Technological advances and familiarity with portable recording devices will improve this figure and patients and their carers should be encouraged to use such facilities when available.