Exon 2 was replaced with one in which coding nucleotide 330 (C), the third base of alanine codon 110 in the middle of the first poly-alanine stretch, was replaced with a G and had seven GCG alanine codons inserted after it (c.330C>GGCGGCGGCGGCGGCGGCGGCG). The resulting protein mutation (p.(A110_A111delinsAAAAAAAAA)) mimics a muation found in some X-linked mental retardation patients. A neomycin resistance gene cassette was inserted in to intron 1.