Distal hereditary motor neuronopathies (distal HMN, dHMN), sometimes also called distal hereditary motor neuropathies, are a genetically and clinically heterogeneous group of
motor neuron disease
Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...
s that result from genetic
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...
s in various
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s and are characterized by degeneration and loss of
motor neuron
A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly ...
cells in the
anterior horn of the spinal cord
The anterior grey column (also called the anterior cornu, anterior horn of spinal cord, motor horn or ventral horn) is the front column of grey matter in the spinal cord. It is one of the three grey columns. The anterior grey column contains motor ...
and subsequent muscle
atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply ...
.
Although they can hardly be distinguished from
hereditary motor and sensory neuropathies on the clinical level, dHMNs are considered a separate class of disorders.
Another common system of classification groups many of DHMNs under the heading of
spinal muscular atrophies
Spinal muscular atrophies (SMAs) are a genetically and clinically heterogeneous group of rare debilitating disorders characterised by the degeneration of lower motor neurons (neuronal cells situated in the anterior horn of the spinal cord) and s ...
.
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Classification
In 1993, A. E. Hardnig proposed to classify hereditary motor neuropathies into seven groups based on age at onset, mode of inheritance, and presence of additional features. This initial classification has since been widely adopted and expanded and currently looks as follows:
Note: Acronym ''HMN'' is also used interchangeably with ''DHMN''.
See also
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Motor neuron disease
Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...
*
Hereditary motor and sensory neuropathies
*
Spinal muscular atrophies
Spinal muscular atrophies (SMAs) are a genetically and clinically heterogeneous group of rare debilitating disorders characterised by the degeneration of lower motor neurons (neuronal cells situated in the anterior horn of the spinal cord) and s ...
*
Charcot–Marie–Tooth disease
Charcot–Marie–Tooth disease (CMT) is a hereditary motor and sensory neuropathy of the peripheral nervous system characterized by progressive loss of muscle tissue and touch sensation across various parts of the body. This disease is the most ...
*
Hereditary spastic paraplegia
Hereditary spastic paraplegia (HSP) is a group of inherited diseases whose main feature is a progressive gait disorder. The disease presents with progressive stiffness (spasticity) and contraction in the lower limbs. HSP is also known as hereditar ...
References
{{CNS diseases of the nervous system
Motor neuron diseases