The TKD encoded by exons 13 to 17 is required for signal transduction.18 Sequence annotation in the UniProt database shows that natural NTRK1 variations associated with CIPA are mainly located in the TKD domain (http://www.uniprot.org/uniprot/P04629#P04629). The gene discussed is NTRK1; the disease is hereditary sensory and autonomic neuropathy type 4.