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The status of HMSN type III
A A Gabreëls-Festen1, F J Gabreëls, F G Jennekens
1Institute of Neurology, University Hospital Nijmegen, The Netherlands.
Abstract:
The indistinctness of the HMSN type III concept of Dyck (1975) prompted us to evaluate the diagnostic criteria. Based on a literature review and the observations in five of our own cases, restricted criteria are formulated. We conclude that at present the diagnosis of AR HMSN type III can be applied reasonably to the condition of "congenital hypomyelination", which shows a congenital or early childhood onset, extremely slow motor nerve conduction velocities of less than 6-7 m s-1 in upper limbs, and in nerve biopsy only fibres with no or hardly any myelin and "onion bulbs" of basal lamina. Amyelination might be the most severe or earliest expression of congenital hypomyelination. The existence of an inherited type III with mainly classical onion bulbs is uncertain, as only sporadic cases have been described.
Insights
Diagnostic criteria for Hereditary Motor and Sensory Neuropathy type III (HMSN III) were refined. Current evidence suggests AR HMSN III aligns with congenital hypomyelination, characterized by early onset and severe nerve conduction deficits.
Area of Science:
- Neurology
- Genetics
- Pathology
Background:
- The diagnostic criteria for Hereditary Motor and Sensory Neuropathy type III (HMSN III), as initially proposed by Dyck (1975), lacked distinctness.
- This ambiguity necessitated a re-evaluation of the diagnostic framework for HMSN III.
Purpose of the Study:
- To evaluate and refine the diagnostic criteria for HMSN III.
- To establish clearer guidelines for diagnosing this neurological condition.
Main Methods:
- A comprehensive literature review was conducted.
- Clinical observations from five patient cases were analyzed.
Main Results:
- Restricted diagnostic criteria for HMSN III have been formulated.
- The condition "congenital hypomyelination" fits the current criteria for Autosomal Recessive HMSN type III (AR HMSN III).
- Key features include congenital/early childhood onset, extremely slow motor nerve conduction velocities (<6-7 m/s in upper limbs), and nerve biopsy findings of minimal myelin and basal lamina "onion bulbs".
Conclusions:
- Amyelination may represent the most severe or earliest form of congenital hypomyelination.
- The existence of an inherited HMSN III primarily characterized by classical onion bulbs remains uncertain due to the scarcity of described cases, with only sporadic instances reported.