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A genetic linkage study performed on a large family with autosomal dominant Charcot-Marie-Tooth neuropathy (HMSN type I) showed affected family members to have slow motor nerve conduction velocities, hypoactive tendon reflexes, and distal muscle weakness and atrophy. Results excluded close linkage of the neuropathy in this family to the Duffy blood group locus on chromosome 1. Previous studies in other families have shown positive linkage of HMSN type I to the Duffy locus. The present results provide support for the concept of genetic heterogeneity in HMSN type I. Comparison of this new family with the previous families showing linkage to Duffy reveals that the hereditary neuropathy not linked to the Duffy locus may have less severe slowing of motor nerve conduction velocities and less prominent onion bulb change evident on sural nerve biopsy.