Charcot-Marie-Tooth type X1 disease (CMTX1) is an X-dominant peripheral neuropathy caused by mutations in the GJB1 gene. Molecular genetic analysis of the GJB1 gene is crucial for CMTX1 diagnosis and for genetic counselling. To date, molecular genetic analysis of the GJB1 gene revealed 264 mutations in the GJB1 gene. In spite of the rising number of GJB1 gene mutations, family history was documented in only a few CMTX1 cases. The aim of this study was a molecular genetic analysis of the GJB1 gene in 7 families, performed in 19 CMTX1-affected patients and 13 healthy family members. Moreover, we attempted to report evidence of effects of 6 amino-acid substitutions described in this study. To the best of our knowledge, the G110D, V152D and K167E mutations are novel substitutions, which have not been reported so far.