Sequencing of Plp genomic and cDNAs showed a single nucleotide substitution, G-to-T, in exon 2 at coding nucleotide 115 which causes an alanine to serine substitution at position39 (p.Ala39Ser). Northern analysis showed that PLP mRNA was reduced by 90% in Plpjp-4J/Y compared to +/Y wild-type mice.