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—in the United States—Lou Gehrig's disease (LGD), is a rare, terminal neurodegenerative disorder that results in the progressive loss of both upper and low ...
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, ...
s in various
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
s and are characterized by degeneration and loss of
motor neuron
A motor neuron (or motoneuron), also known as 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 o ...
cells in the
anterior horn of the spinal cord 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), malnutrition, poor nourishment, poor circulatory system, circulation, loss of hormone, ...
.
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.
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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—in the United States—Lou Gehrig's disease (LGD), is a rare, terminal neurodegenerative disorder that results in the progressive loss of both upper and low ...
*
Hereditary motor and sensory neuropathies
*
Spinal muscular atrophies
*
Charcot–Marie–Tooth disease
*
Hereditary spastic paraplegia
Hereditary spastic paraplegia (HSP) is a group of inherited diseases whose main feature is a progressive Gait abnormality, gait disorder. The disease presents with progressive stiffness (spasticity) and contraction in the lower limbs. HSP is als ...
References
{{Peripheral nervous system disease
Motor neuron diseases