[Hereditary Polyneuropathies].

Area of Science:

• Neurology
• Genetics
• Neuroscience

Background:

• Hereditary neuropathies encompass various disorders, with Charcot-Marie-Tooth disease (CMT) being the most common.
• Clinical presentation, including pes cavus and motor deficits like foot drop, is typical but not specific for CMT.
• Over 80 genes are implicated in CMT, making clinical differentiation challenging.

Purpose of the Study:

• To highlight the diagnostic utility of neurography in differentiating hereditary neuropathies.
• To emphasize the role of median nerve conduction velocity in distinguishing CMT subtypes.
• To identify the genetic basis of the most prevalent CMT forms.

Main Methods:

• Clinical assessment for characteristic signs such as pes cavus and foot drop.
• Classical neurography to measure median nerve conduction velocity.
• Genetic analysis to identify mutations, duplications, or deletions in relevant genes, particularly PMP22.

Main Results:

• Median nerve conduction velocity thresholds (38 m/s) effectively differentiate between CMT type 1 and CMT type 2.
• CMT type 1A is frequently associated with PMP22 gene duplication.
• Hereditary neuropathy with liability to pressure palsy (HNPP) is linked to PMP22 gene deletion.

Conclusions:

• Neurography provides crucial objective data for classifying CMT subtypes, complementing clinical findings.
• PMP22 gene alterations (duplication and deletion) are key genetic drivers of the most common forms of CMT and HNPP.
• Understanding these genetic and electrophysiological distinctions is vital for accurate diagnosis and management of hereditary neuropathies.