With radical developments in the field of medical science and technology, life expectancy has considerably increased among humans. Remedying and managing ailments may effectively increase the number of days in a person’s life but it does not guarantee a sustained state of good health throughout this extended lifespan. With this overall increase in life expectancy, degenerative diseases (diseases resulting from changes arising as a consequence of accumulation of damage from continuous and prolonged use of cells and tissues) are becoming more and more common. Degenerative diseases, along with its rather gradual onset and irreversible nature, are often contrasted to infectious diseases, which have a relatively sudden onset and in some cases can be effectively alleviated through medicinal or surgical procedures.
Neurodegenerative diseases, the type of degenerative diseases affecting the central nervous system (comprising of the brain and spinal cord) and the peripheral nervous system (comprising of neuronal cells outside of the brain and spinal cord) have gained prominence in scientific literature in the last century. Neurodegeneration can be defined as the gradual structural and functional loss of a neuron leading to a decline in its operational efficiency and eventually its death. Such changes lead to a quite heterogeneous assortment of disorders with an extremely variable array of underlying causes, which are further complicated by environmental factors and genetic predispositions of individuals. The general layout followed by almost all pathologies arising due to these progressive degenerations often involves deterioration of signal transduction in the nervous system.
Degenerative diseases of the nervous system can be loosely categorized based on the component of the nervous system it is affecting:
· Degenerative diseases of the central nervous system (CNS): Affects primarily the brain and the spinal cord. These types of degenerative diseases include dementia and its subtypes, amyotrophic lateral sclerosis (ALS), Huntington’s disease, Lewy body diseases, Parkinson’s disease, and Friedreich’s ataxia among others. With progression, all the diseases gradually show sub-cellular similarities with one another with respect to atrophy and dysfunction.
· Degenerative diseases of the peripheral nervous system (PNS): Also known as neurodegenerative diseases of the motor neurons (MND), these primarily disturb the neuronal structures excluding CNS components. In a motor neuron disease, the cells controlling the voluntary muscle control is selectively targeted. These diseases essentially affect either the upper motor neurons (UMN) as seen in primary lateral sclerosis (PLS), amyotrophic lateral sclerosis (ALS), hereditary spastic paraplegia (HSP), and pseudobulbar palsy or the lower motor neurons (LMN) as seen in progressive muscular atrophy (PMA), and progressive bulbar palsy (PBP).
The irreversible nature of neurodegenerative diseases leads towards an inevitable death as a result of the affliction. Although treatment can help relieve and manage the symptoms to a great extent, there is presently no cure or a way slow down the progression once neurodegeneration is set into motion.