Sensory axonopathy in hereditary distal spinal muscular atrophy

Pes cavus and hereditary neuropathies: when a relationship should be suspected

The hereditary peripheral neuropathies are a clinically and genetically heterogeneous group of diseases of the peripheral nervous system. Foot deformities, including the common pes cavus, but also hammer toes and twisting of the ankle, are frequently present in patients with hereditary peripheral neuropathy, and often represent one of the first signs of the disease. Pes cavus in hereditary peripheral neuropathies is caused by imbalance between the intrinsic muscles of the foot and the muscles of the leg. Accurate clinical evaluation in patients with pes cavus is necessary to exclude or confirm the presence of peripheral neuropathy. Hereditary peripheral neuropathies should be suspected in those cases with bilateral foot deformities, in the presence of family history for pes cavus and/or gait impairment, and in the presence of neurological symptoms or signs, such as distal muscle hypotrophy of limbs. Herein, we review the hereditary peripheral neuropathies in which pes cavus plays a key role as a "spy sign," discussing the clinical and molecular features of these disorders to highlight the importance of pes cavus as a helpful clinical sign in these rare diseases.

Unraveling the genetics of distal hereditary motor neuronopathies

The hereditary motor neuronopathies (HMN [MIM 158590]) are a heterogeneous group of disorders characterized by an exclusive involvement of the motor part of the peripheral nervous system. They are usually subdivided in proximal HMN, i.e., the classical spinal muscular atrophy syndromes and distal hereditary motor neuronopathies (distal HMN) that clinically resemble Charcot-Marie-Tooth syndromes. In this review, we concentrate on distal HMN. The distal HMN are clinically and genetically heterogeneous and were initially subdivided in seven subtypes according to mode of inheritance, age at onset, and clinical evolution. Recent studies have shown that these subtypes are still heterogeneous at the molecular genetic level and novel clinical and genetic entities have been delineated. Since the introduction of positional cloning, 13 chromosomal loci and seven disease-associated genes have been identified for autosomal-dominant, autosomal-recessive, and X-linked recessive distal HMN. Most of the genes involved encode protein with housekeeping functions, such as RNA processing, translation synthesis, stress response, apoptosis, and others code for proteins involved in retrograde survival. Motor neurons of the anterior horn of the spinal cord seems to be vulnerable to defects in these housekeeping proteins, likely because their large axons have higher metabolic requirements for maintenance, transport over long distances and precise connectivity. Understanding the molecular pathomechanisms for mutations in these genes that are ubiquitous expressed will help unravel the neuronal mechanisms that underlie motor neuropathies leading to denervation of distal limb muscles, and might generate new insights for future therapeutic strategies.

Hereditary motor neuropathies and motor neuron diseases: which is which

When Charcot first defined amyotrophic lateral sclerosis (ALS) he used the clinical and neuropathological pattern of vulnerability as a guideline. Similarly other motor neuron diseases such as the spinal muscular atrophies (SMA) and the motor neuropathies (MN) were grouped following clinical criteria. However, ever since the etiology of these diseases has started to be disclosed by genetics, we have learnt that the limits of the syndromes are not as well defined as our forefathers thought. A mutation leading to ALS can also be associated with the clinical picture of spinal muscular atrophy; even more unexpected is the overlap of the so-called motor neuropathies with the clinical syndrome of slowly progressive ALS or that primary lateral sclerosis (PLS) can be caused by the same gene as that responsible for some cases of ALS. In this review we summarise recent work showing that there is a considerable overlap between CMT, MN, SMA, ALS and PLS. Insights into these phenotypes should lead to study of the variants of motor neuron disease and possibly to a reclassification. This comprehensive review should help to improve understanding of the pathogenesis of motor neuron degeneration and finally may aid the research for urgently needed new treatment strategies, perhaps with validity for the entire group of motor neuron diseases.