Exon 6 was replaced with a modified one in which an A-to-T point mutation results in the amino acid substitution of tyrosine with phenylalanine at position 147 (p.Y147F). A loxP site flanked neomycin resistance gene cassette was inserted into intron 6. Quantitative real-time PCR analysis revealed normal mRNA levels in the cortex of P12-P17 homozygous mutant mice.