Hereditary sensory neuropathy type I (HSN-I) is an autosomal dominant peripheral neuropathy affecting sensory and motor neurons. The disease involves distal sensory loss, distal muscle wasting and weakness, and variable neural deafness. The HSNI locus has been mapped to a genetic interval of 3-4 cM on chromosome 9q22.1-q22.3 and is flanked by markers D9S1781 and FB19B7. This interval contains the gene NFIL3, a transcription factor that is regulated by the cytokine IL-3. Northern blot analysis of NFIL3 showed a ubiquitously expressed 2.2-kb mRNA. Expression was highest in the lung, with lower levels of expression in the brain and spinal cord. Mutation analysis by direct sequencing of reverse transcription/polymerase chain reaction products from HSN-I patients excluded the coding region of the NFIL3 from being involved in the pathogenesis of HSN-I.