Exons 3 through 6 that encode the first three Ig domains of the protein were replaced with a neomycin resistance cassette. Aberrant splicing of exon 2, which encodes the ATG start site and the leader sequence, to exon 7 or 9 produces a minor protein product lacking the first two Ig domains and a major protein product lacking the first three Ig domains. The level of protein expression for the mutant allele was about half that of the wild-type allele. Despite the truncation, mutant protein was expressed on the cell surface of sensory neurons. It was predicted the truncation would interfere with cis binding to the L1 cell surface protein. This is a hypomorph allele.