As the mouse nasal embryonic LHRH factor gene (Nelf) encodes a guidance molecule for the migration of the olfactory axon and gonadotropin-releasing hormone neurons, its human homolog, NELF, is a candidate gene for Kallmann syndrome, a disease of idiopathic hypogonadotropic hypogonadism (IHH) with anosmia or hyposmia. We report here characterization of NELF and results of mutation analysis in 65 IHH patients. Assembling EST clones, RACE, and sequencing showed that NELF mapped to 9q34.3 is composed of 16 exons and 15 introns with a 1,590-bp ORF encoding 530 amino acids. RT-PCR on a fetal brain cDNA library revealed five alternatively spliced variants. Among them, NELF-v1 has 93-94% identity at the amino acid level to mouse/rat Nelf, and four other transcripts are also highly conserved among the three species. A 3.0-kb transcript is expressed most highly in the adult and fetal brain, testis, and kidney, indicating that NELF plays a role in the function of these tissues. Mutation screening detected in a patient with IHH one novel heterozygous missense mutation (1438A>G, T480A) at the donor-splice site in exon 15 of NELF. As this mutation was not found in 100 normal control individuals, T480A may be associated with IHH. Four other novel SNPs (102C > T and 1029C > T within the coding region, and two IVS14+47C > T and IVS15+41G > A) were also identified in NELF.