[Molecular diagnosis of axonal forms of Charcot-Marie-Tooth disease]

Charcot-Marie-Tooth (CMT) disease is the most common cause of inherited peripheral neuropathies with a frequency estimated at 1/2500. Electroneuromyographic examination distinguishes a myelinic form (CMT1) and an axonal form of the disease (CMT2). Significant genetic heterogeneity is found in CMT, with 15 genes or loci for CMT2. To date, a molecular diagnosis has not been established for most CMT2 patients and the distribution of identified mutations is wide spreading over nearly all genes. Simple guidelines for daily practice are difficult to establish from compilation of mutation reports or consultation of databases; little simplification can be expected from future findings. We present our results of molecular diagnosis for 251 CMT2 index cases characterized by their mode of inheritance (217 dominant and 34 recessive cases), and a motor conduction velocity in median nerve equal to or above to 38m/s. For each case, at least one of the genes known to date for CMT2 (MFN2, RAB7, GARS, NF-L, HSPB1, GDAP1, MPZ, HSPB8, GJB1, DNM2, YARS, LMNA, and MED25) was studied. Around 22% of diagnoses were established and efficiency was comparable for dominant or recessive cases. For dominant cases, the first objective was to search for mutations of proteins connexin32, mitofusin2 and P0. For recessive cases, GDAP1 provided the key to molecular diagnosis; lamin A/C mutations were only found for patients with an ethnic background from North Africa. Heat shock proteins HSPB1 and HSPB8 were implicated in a significant proportion of "spinal" (or pure motor) CMT2. NF-L or RAB7 mutations were rare. We did not identify any deleterious mutations in GARS, DNM2, YARS orMED2. We propose a simple decision tree for molecular diagnosis of CMT2.