Fig. 1

A Pedigree of the present family. The proband is indicated (arrow). Individuals evaluated both clinically and genetically in this study are denoted by asterisks. B Serial photographs of the proband taken at age 29. The proband presented hand deformities characterized by curvature of the fingers. There was mild atrophy of the distal muscles of the hands, particularly of the thenar eminence. C Appearance of the legs of the proband. There was mild quadriceps wasting and simultaneous mild calf hypertrophy. D Fat-saturated MRI of the lower legs in the coronal plane and T2-weighted image in the axial plane of the lower third of the calves of the proband. High-intensity regions manifesting as neurogenic changes can be easily observed in the bilateral triceps surae muscles, with proximal dominant hypertrophy in the coronal plane (white arrowhead). There was moderate fatty atrophy involving bilateral tibialis anterior muscles in the axial plane (blue arrowhead), which predominated on the right side. Conversely, there was very slight hypertrophy in the posterior compartment muscles (yellow arrowhead), including the soleus, gastrocnemius, and tibialis posterior. R and L indicate right and left. E Electrophysiologic findings in the proband recorded from the left extensor digitorum communis. The insertion activity of needle electromyography at rest shows myotonic discharges (timebase set to 40 ms/division). F Appearance of the legs of the proband’s father at age 57. Pes cavus is pronounced. Mild proximal hypertrophy and distal atrophy of bilateral lower leg muscles were observed