Orphan Peripheral Neuropathies

Abstract

Objectives: Generally, neuropathies of peripheral nerves are a frequent condition (prevalence 2-3%) and most frequently due to alcoholism, diabetes, renal insufficiency, malignancy, toxins, or drugs. However, the vast majority of neuropathies has orphan status. This review focuses on the etiology, frequency, diagnosis, and treatment of orphan neuropathies.

Methods: Literature reviewResults:Rareness of diseases is not uniformly defined but in the US an orphan disease is diagnosed if the prevalence is <1:200000, in Europe if <5:10000. Most acquired and hereditary neuropathies are orphan diseases. Often the causative variant has been reported only in a single patient or family, particularly the ones that are newly detected (e.g. SEPT9, SORD). Among the complex neuropathies (hereditary multisystem disorders with concomitant neuropathies) orphan forms have been reported among mitochondrial disorders (e.g. NARP, MNGIE, SANDO), spinocerebellar ataxias (e.g. TMEM240), hereditary spastic paraplegias (e.g UBAP1), lysosomal storage disease (e.g. Schindler disease), peroxisomal disorders, porphyrias, and other types (e.g. giant axonal neuropathy, Tangier disease). Orphan acquired neuropathies include the metabolic neuropathies (e.g. vitamin-B1, folic acid), toxic neuropathies (e.g. copper, lithium, lead, arsenic, thallium, mercury), infectious neuropathies, immune-mediated (e.g. Bruns-Garland syndrome), and neoplastic/paraneoplastic neuropathies.

Conclusions: Though orphan neuropathies are rare per definition they constitute the majority of neuropathies and should be considered as some of them are easy to identify and potentially treatable, as clarification of the underlying cause may contribute to the knowledge about etiology and pathophysiology of these conditions, and as the true prevalence may become obvious only if all ever diagnosed cases are reported.

Keywords: Neuropathy; hereditary; motor; nerve conduction velocity; orphan diseases; peripheral nerves; sensory.

Fig. 1

Classification of orphan peripheral neuropathies according to various criteria.

Fig. 2

Proposed diagnostic work-up for orphan peripheral neuropathies. Orange: demyelinating, blue: axonal, green: mixed. CTD: connective tissue diseases, SSN: subacute sensory neuropathy, MIDs: mitochondrial disorders, HSPs: hereditary spastic paraplegias, SCAs: spinocerebellar ataxias, LSDs: lysosomal storage diseases, TTR: transthyretin-related neuropathy, *: Treatable.