  As Gopnik noted, the pattern of inheritance in the KE family suggests that a single, dominant gene is responsible for the disorder. (See fig. 6) In the early 1990's, Fisher and colleagues began working to isolate the gene. First, it was localized to a region on chromosome 7q31 containing about 100 genes (Fisher et al. 1997, 1998; O'Brien et al. 2003). Later, it was identified (Lai et al. 2001; Fisher et al. 2003) as the gene FOXP2, which encodes a regulatory protein or ‘transcription factor’ (i.e., a protein that helps to regulate the rate of transcription of other genes in the genome — in the case of FOXP2, the protein acts to inhibit transcription of the downstream gene(s)). In affected family members, a single base-pair substitution in the gene coding for this regulatory protein leads to the insertion of the amino acid arginine (instead of the normal histamine) in an area of the protein (viz., the ‘forkhead binding domain’) that is critical for its ability to modulate the transcription of the downstream DNA. As a consequence, FOXP2 cannot perform its normal regulatory role in affected KE family members.