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CMT1A Associated With The 17p11.2 Duplication: Differential Features And Correlation

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A duplication on chromosome 17p11.2 encompassing the gene coding for the peripheral myelin protein-22 (PMP22) is the most common genetic abnormality underlying Charcot-Marie-Tooth disease (CMT). We report clinical and electrophysiologic features of our series of CMT1A patients harboring the duplication. There were 92 patients from 53 families representing 42% of all CMT index cases (n = 125) and 64% of CMT1 probands (n = 83). In CMT1A patients, mean age at onset was 9.7 ± 11.4 and was significantly lower than in non-duplicated CMT1 cases (12.6 ± 9.7, p < 0.01) and CMT2 cases (21.5 ± 17, p < 0.001). Clinical severity was similar to that of CMT2 patients, but significantly milder than in non-duplicated CMT1 cases. Pes cavus, upper limb involvement, deep tendon reflexes abnormalities, and sensory loss were more frequent compared to CMT2. Electrophysiologic examination revealed motor and sensory conduction velocity (MCV, SCV) slowing below 32 m/s in upper limbs. MCV and SCV were significantly lower than in non-duplicated CMT1 patients. Amplitudes of upper limb compound muscle action potentials (CMAPs) and of upper and lower limb sensory action potentials (SAPs) were significantly lower than in CMT2, paralleling clinical differences. Clinical severity correlated with CMAP amplitudes and with disease duration. On the other hand, MCV slowing was not correlated with either severity or duration of the disease. We found a direct correlation between age at onset and upper limb MCV slowing. Conclusions: CMT1A is an early-onset but slowly progressive disorder, on average milder than other CMT1. Axonal loss rather than demyelination per se underlies disease progression.
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Document Type: Abstract

Affiliations: Istituto Nazionale Neurologico “C.Besta”, Milano.

Publication date: March 1, 2001

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