Dr Meera Narendran Motor neuron diseases are characterized by
selective degeneration of motor neurons, both upper and lower,
namely of the pyramidal fibers in cerebral cortex, of ventral
horn cells and of cranial motor nerve nuclei. In different cases
relative incidence of degeneration varies. In some the change is
maximal in the ventral horn cells, in others in the cranial
nerve nuclei, in others pyramidal fiber sclerosis is severe and
adds the appropriate clinical picture. Aeteology: – About 5 % of
cases are familial, showing autosomal dominant inheritance. In
many such families genetic defects lies on chromosome 21, the
enzyme involved being a superoxide dismutase (SOD1). For the
remaining 95 %, probable causes includes 1. Chronic Aluminium
toxicity 2. Slow virus infection 3. Auto immunity 5. Electrical
shock Another suggestive hypothesis is that glutamate which is a
primary excitatory neurotransmitter in the CNS, accumulates at
synapses and causes the neurons to die, probably through a
calcium dependent m