GDAP1 and Charcot-Marie-Tooth disease type 2: Three families with CMT2 carried simultaneous heterozygous variants in MFN2 and GDAP1, among which F2 possessed variants c.613_622delGTCACCACAG (p.V205Sfs*26) in MFN2 and c.713G>T (p.W238L) in GDAP1, F3 harbored variants c.839G>A (p.R280H) in MFN2 and c.3G>T (p.M1)?