Distal hereditary motor neuronopathies
Distal hereditary motor neuronopathies (distal HMN, dHMN), sometimes also called distal hereditary motor neuropathies, are a genetically and clinically heterogeneous group of motor neuron diseases that result from genetic mutations in various genes and are characterized by degeneration and loss of motor neuron cells in the anterior horn of the spinal cord and subsequent muscle atrophy.
Although they can hardly be distinguished from hereditary motor and sensory neuropathies on the clinical level, dHMNs are considered a separate class of disorders.
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:[1][2]
| Type | Common name Alternate names |
OMIM | Gene | Locus | Inheritance | Characteristics |
|---|---|---|---|---|---|---|
| HMN1 | Autosomal dominant juvenile distal spinal muscular atrophy | Template:OMIM2 | ? | 7q34–q36 | Autosomal dominant | Juvenile-onset |
| HMN2A | Autosomal dominant distal spinal muscular atrophy | Template:OMIM2 | HSPB8 | 12q24.23 | Autosomal dominant | Adult-onset. Allelic with Charcot–Marie–Tooth disease type 2F |
| HMN2B | Template:OMIM2 | HSPB1 | 7q11.23 | Autosomal dominant | Adult-onset | |
| HMN2C | Template:OMIM2 | HSPB3 | 5q11.2 | Autosomal dominant | ||
| HMN2D | Distal spinal muscular atrophy with calf predominance | Template:OMIM2 | FBXO38 | 5q32 | Autosomal dominant | Juvenile- or adult-onset, slowly progressive, affects both proximal and distal muscles, initially manifests with calf weakness which progresses to hands |
| HMN3 HMN4 |
Distal spinal muscular atrophy type 3 | Template:OMIM2 | ? | 11q13 | Autosomal recessive | HMN3 – benign form: early adult onset, slowly progressive, no diaphragmatic paralysis HMN4 – severe form: juvenile-onset with diaphragmatic paralysis |
| HMN5A | Distal spinal muscular atrophy type VA | Template:OMIM2 | GARS | 7p14.3 | Autosomal dominant | Upper limb predominance with spasticity of lower limbs Locus and phenotype overlapping with CMT-2D and SPG-17 |
| HMN5B | Distal spinal muscular atrophy type VB | Template:OMIM2 | REEP1 | 2p11.2 | Autosomal dominant | Locus and phenotype overlapping with SPG-31 |
| HMN6 | Distal spinal muscular atrophy type 1
Spinal muscular atrophy with respiratory distress type 1 |
Template:OMIM2 | IGHMBP2 | 11q13.3 | Autosomal recessive | Infant-onset, severe, with diaphragmatic failure |
| HMN7A | Spinal muscular atrophy with vocal cord paralysis
Harper–Young myopathy |
Template:OMIM2 | SLC5A7 | 2q12.3 | Autosomal dominant | Infant-onset with vocal cord paralysis |
| HMN7B | Template:OMIM2 | DCTN1 | 2p13.1 | Autosomal dominant | Adult-onset with vocal cord paralysis and facial weakness | |
| HMN-J | Distal spinal muscular atrophy type 2
Jerash type spinal muscular atrophy |
Template:OMIM2 | ? | 9p21.1–p12 | Autosomal recessive | Juvenile-onset with pyramidal features |
See also
- Motor neuron disease
- Hereditary motor and sensory neuropathies
- Spinal muscular atrophies
- Charcot–Marie–Tooth disease
- Hereditary spastic paraplegia
References
- ^ Irobi, J; De Jonghe, P; Timmerman, V (2004). "Molecular genetics of distal hereditary motor neuropathies". Human Molecular Genetics. 13 (suppl 2): R195 – R202. doi:10.1093/hmg/ddh226. PMID 15358725.
- ^ Scherer, SS (2006). "Finding the causes of inherited neuropathies". Archives of Neurology. 63 (6): 812. doi:10.1001/archneur.63.6.812. PMID 16769861.