Mutations of the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) cause autosomal recessive Charcot-Marie-Tooth disease type 4A. We report four additional families with recessive mutations (487C-->T, Q163X; 359G-->A, R120Q) of GDAP1; Q163X occurred in three unrelated Hispanic families that had the same haplotype suggesting a Spanish founder mutation. Both the Q163X and the R120Q mutation cause demyelination and axonal loss. The patients had symptoms within the first two years of life and involvement of cranial, sensory, and enteric nerves. Neuropathology showed loss of large myelinated fibers, onion bulb formations and focal folding of the outer myelin lamina.