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.

Another common system of classification groups many of DHMNs under the heading of spinal muscular atrophies.

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 OMIM Gene Locus Inheritance Common names and characteristics
DHMN1 182960 ? 7q34–q36 Autosomal dominant Autosomal dominant juvenile distal spinal muscular atrophy
Juvenile onset
DHMN2A 158590 HSPB8 12q24.23 Autosomal dominant Autosomal dominant distal spinal muscular atrophy
Adult onset. Allelic with Charcot–Marie–Tooth disease type 2F
DHMN2B 608634 HSPB1 7q11.23 Autosomal dominant Adult onset
DHMN2C 613376 HSPB3 5q11.2 Autosomal dominant
DHMN2D 615575 FBXO38 5q32 Autosomal dominant Distal spinal muscular atrophy with calf predominance
Juvenile or adult onset, slowly progressive, affects both proximal and distal muscles, initially manifests with calf weakness which progresses to hands
DHMN3
DHMN4		 607088 ? 11q13 Autosomal recessive Distal spinal muscular atrophy type 3
DHMN3 – benign form: early adult onset, slowly progressive, no diaphragmatic paralysis
DHMN4 – severe form: juvenile onset with diaphragmatic paralysis
DHMN5A 600794 GARS 7p14.3 Autosomal dominant Distal spinal muscular atrophy type VA
Upper limb predominance with spasticity of lower limbs
Locus and phenotype overlapping with CMT-2D and SPG-17
DHMN5B 614751 REEP1 2p11.2 Autosomal dominant Distal spinal muscular atrophy type VB
Locus and phenotype overlapping with SPG-31
DHMN6 604320 IGHMBP2 11q13.3 Autosomal recessive Distal spinal muscular atrophy type 1 (DSMA1); spinal muscular atrophy with respiratory distress type 1 (SMARD1)
Infant onset, severe, with diaphragmatic failure
DHMN7A 158580 SLC5A7 2q12.3 Autosomal dominant Spinal muscular atrophy with vocal cord paralysis; Harper–Young myopathy
Infant onset with vocal cord paralysis
DHMN7B 607641 DCTN1 2p13.1 Autosomal dominant Adult onset with vocal cord paralysis and facial weakness
DHMN8 600175 TRPV4 12q24.11 Autosomal dominant Congenital distal spinal muscular atrophy
Affects primarily distal muscles of lower limbs, non-progressive, rare
DHMNJ 605726 SIGMAR1 9p13.3 Autosomal recessive Distal spinal muscular atrophy type 2; Jerash type spinal muscular atrophy
Juvenile onset with pyramidal features

Note: Acronym HMN is also used interchangeably with DHMN.

See also

References
  1. 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.
  2. Scherer, SS (2006). "Finding the causes of inherited neuropathies". Archives of Neurology. 63 (6): 812–6. doi:10.1001/archneur.63.6.812. PMID 16769861.
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